Fig. 14.7 Diagnostic positions of gaze: primary position (E); secondary positions (B, D, F, H); tertiary positions (A, C, G, I); cardinal positions (A, C, D, F, G, I)


2. Sherrington’s law of reciprocal innervation. According to it, during ocular motility increased flow of innervation to the contracting muscle is accompanied by decreased flow of innervation to the relaxing antagonist muscle. For example, during dextroversion, an increased innervation flow to the right LR and left MR is accompanied by decreased flow to the right MR and left LR muscles.
Diagnostic positions of gaze
There are nine diagnostic positions of gaze (Fig. 14.7). These include one primary, four secondary and four tertiary positions.
1. Primary position of gaze. It is the position assumed by the eyes when fixating a distant object (straight ahead) with the erect position of head (Fig. 14.7E). 2. Secondary positionsof gaze. These are the positions assumed by the eyes while looking straight up, straight down, to the right and to the left (Figs. 14.7B, D, F and H).
3. Tertiary positions of gaze. These describe the positions assumed by the eyes when combination of vertical and horizontal movements occur. These include position of eyes in dextroelevation,

dextrodepression, levoelevation and levodepression (Figs. 14.7A, C, G and I).
4. Cardinal positions of gaze. These are the positions which allow examination of each of the 12extraocular muscles in their main field of action. There are six cardinal positions of gaze, viz, dextroversion, levoversion, dextroelevation, levoelevation, dextrodepression and levodepression (Figs. 14.7 A, C, D, F, G and I).
SUPRANUCLEAR CONTROL OF EYE MOVEMENTS
There exists a highly accurate, still not fully elucidated, supranuclear control of eye movements which keeps the two eyes yoked together so that the image of the object of interest is simultaneously held on both fovea despite movement of the perceived object or the observer’s head and/or body.
Supranuclear eye movement systems include: 1. Saccadic system
2. Smooth pursuit system 3. Vergence system
4. Vestibular system
Chapter 14	Disorders of Ocular Motility	341


5. Optokinetic system
6. Position maintenance system
All these systems perform specific functions and each one is controlled by a different neural system but share the same final common path the motor neurons that supply the extraocular muscles. 1.Saccadic system.Saccades are sudden, jerky conjugate eye movements, that occur as the gaze shifts from one object to another. Thus, they are performed to bring the image of an object quickly on the fovea. Though normally voluntary, saccades may be involuntarily aroused by peripheral, visual or auditory stimuli.
2. Smooth pursuit eye movement system. Smooth pursuit movements are tracking movements of the eye as they follow moving objects. These occur voluntarily when the eyes track moving objects but take place involuntarily if a repetitive visual pattern is displayed continuously. When the velocity of the moving object is more, the smooth pursuit movement is replaced by small saccades (catchup saccades), voluntary saccades serve to bring new objects of interest on the fovea centralis.
3. Vergence movement system. Vergence movements allow focussing of an object which moves away from or towards the observer or when visual fixation shifts from one object to another at a different distance. Vergence movements are very slow disconjugate movements. 4. Vestibular eye movement system. Vestibular movements are usually effective in compensating for the effects of head movements in disturbing visual fixation. These movements operate through the vestibular system and constitute the vestibulo ocular reflex (VOR).
5. Optokinetic system. The system helps to hold the images of the seen world steady on the retinae during sustained head rotation. This system becomes operative, when the vestibulo-ocular reflex (VOR) gets fatigued after 30 seconds. It consists of a smooth pur suit movement following the moving scene, succeeded by a rapid saccade in the opposite direction (Optokinetic nystagmus).
6. Position maintenance system. This system helps to maintain a specific gaze position by means of rapid micromovements called ‘flicks’ and slow micromovements called ‘drifts’. This system co-ordinates with other systems. Neural pathway for this system is believed to be the same as for saccades and smooth pursuits.

BINOCULAR SINGLE VISION

DEFINITION
When a normal individual fixes his visual attention on an object of regard, the image is formed on the

fovea of both the eyes separately; but the individual perceives a single image. This state is called binocular single vision. In other words, binocular single vision is the coordinated use of both eyes so as to produce a single mental impression.
DEVELOPMENT OF BINOCULAR SINGLE VISION
Binocular single vision is a conditioned reflex which is not present since birth but is acquired during first 6 months and is completed during first few years.
The process of its development is complex and partially understood.
Important milestones in the visual development are: • At birth there is no central fixation and the eyes
move randomly.
• By the first month of life fixation reflex starts developing and becomes established by 6 months.
• By6 months,the macular stereopsis and accommo-dation reflex is fully developed.
• By 6 years of age full visual acuity (6/6) is attained and binocular single vision is well developed.
Prerequisites for development of binocular single vision
1. Straight eyes starting from the neonatal period, with precise coordination for all directions of gaze (motor mechanism).
2. Reasonably clear visionin both eyes so that similar images are presented to each retina (sensory mechanism).
3. Ability of visual cortexto promote binocular single vision (mental process).
Therefore, pathologic states disturbing any of the above mechanisms during the first few years of life will hinder the development of binocular single vision and may cause squint.

GRADES OF BINOCULAR SINGLE VISION Worth has described three grades of binocular single vision, which are best tested with the help of a synoptophore.
Grade I—Simultaneous perception. It is the power to see two dissimilar objects simultaneously. It is tested by projecting two dissimilar objects (which can be joined or superimposed to form a complete picture) in front of the two eyes. For example, when a picture of a bird is projected onto the right eye and that of a cage on to the left eye, an individual with presence of simultaneous perception will see the bird in the cage (Fig. 14.8A).
Grade II—Fusion. It consists of the power to superimpose two incomplete but similar images to form one complete image (Fig. 14.8B).
342	Section III   Diseases of Eye
















Fig. 14.8 Slides for testing three grades of binocular vision : A, simultaneous perception; B, fusion; C, stereopsis



The ability of the subject to continue to see one complete picture when his eyes are made to converge or diverge a few degrees, gives the positive and negative fusion range, respectively.
Grade III—Stereopsis. It consists of the ability to perceive the third dimension (depth perception). It can be tested with stereopsis slides in synoptophore (Fig. 14.8C).
ANOMALIES OF BINOCULAR VISION Anomalies of binocular vision include suppression, amblyopia, abnormal retinal correspondence (ARC), confusion and diplopia.
Suppression
It is a temporary active cortical inhibition of the image of an object formed on the retina of the squinting eye. This phenomenon occurs only during binocular vision (with both eyes open). However, when the fixating eye is covered, the squinting eye fixes (i.e., suppression disappears).
Tests to detect suppression include Worth’s 4-dot test, four dioptre base out prism test, red glass test and synoptophore test (see page 352).
Amblyopia
Definition.Amblyopia, by definition, refers to a partial reversible loss of vision in one or both eyes, for which no cause can be found by physical examination of the eye, i.e., there is absence of any organic disease of ocular media, retina and visual pathway. Pathogenesis. Amblyopia is produced by certain amblyogenic factors operating during the critical period of visual development (birth to 6-7 years of age). During this period, the visual pathway continues to develop and brain learns to interpret the signals that come from the eye. If, for any reason, a young child

cannot use one or both eyes normally, then the vision is not developed completely and the condition is called amblyopia. The most sensitive period for development of amblyopia is first six months of life and it usually does not develop after the age of 6-7 years.
Amblyogenic factors include:
• Visual (form sense) deprivation as occurs in anisometropia,
• Light deprivation e.g., due to congenital cataract, and
• Abnormal binocular interaction e.g., in strabismus. Types. Depending upon the cause, amblyopia is of following types:
1. Strabismic amblyopia results from prolonged uniocular suppression in children with unilateral constant squint who fixate with normal eye. Squint is the most common cause of amblyopia.
2. Stimulus deprivation amblyopia (old term: amblyopia ex anopsia) develops when one eye is totally excluded from seeing early in life as, in congenital or traumatic cataract, complete ptosis and dense central corneal opacity.
3. Anisometropic amblyopia occurs in an eye having higher degree of refractive error than the fellow eye. It is more common in anisohypermetropic than the anisomyopic children. Even 1-2 D hypermetropic anisometropia may cause amblyopia while upto 3 D myopic anisometropia usually does not cause amblyopia.
4. Isoametropic amblyopia is bilateral amblyopia occurring in children with bilateral uncorrected high refractive error.
5. Meridional amblyopia occurs in children with uncorrected astigmatic refractive error. It is a selective amblyopia for a specific visual meridian.
Chapter 14	Disorders of Ocular Motility	343


Clinical characteristics of an amblyopic eye are:
1. Visual acuity is reduced. Recognition acuity is more affected than resolution acuity.
2. Effect of neutral density filter. Visual acuity when tested through neutral density filter improves by one or two lines in amblyopia and decreases in patients with organic lesions.
3. Crowding phenomenon is present in amblyopics i.e., visual acuity is less when tested with multiple letter charts (e.g., Snellen’s chart) than when tested with single charts (optotype).
4. Fixation pattern may be central or eccentric. Degree of amblyopia in eccentric fixation is proportionate to the distance of the eccentric point from the fovea.
5. Colour vision is usually normal, may be affected in deep amblyopia with vision below 6/36.
Treatment of amblyopia should be started as early as possible (younger the child, better the prognosis). Amblyopia therapy works best when initiated in young children under 3 years of age.
1. Occlusion therapy i.e., occlusion of the sound (normal) eye to force use of amblyopic eye is the main stay in the treatment of amblyopia. However, before the occlusion therapy is started, it should be ensured that:
• Opacity in the media (e.g., cataract), if any, should be removed first, and
• Refractive error, if any, should be fully corrected. Simplified schedule for occlusion therapy depending on the age is as below:
• Upto 2 years, the occlusion should be done in 2:1, i.e., 2 days in sound eye and one day in amblyopic eye.
• At the age of 3 years, 3:1, • At the age of 4 years, 4:1,
• At the age of 5 years, 5:1, and • After the age of 6 years, 6:1.
Duration of occlusion should be until the visual acuity develops fully, or there is no further improvement of vision for 3 months.
2.Penalization, i.e., blurring of vision of normal eye either by using atropine (atropine penalization) or by using over plus lenses in spectacles (optical penalization) can be used as alternative when occlusion is not possible. 3. Pleoptic exercises were recommended in the past to re-establish foveal fixation especially in young children.
4. Pharmacologic manipulation using levodopa/ carbidopa has been studied as an adjunct to occlusion therapy.
5. Perceptual learning is also suggested as an adjunct to occlusion therapy.

6. Computerized vision therapy using specially designed software has come into vogue for the treatment of amblyopia with controversial results. Vision therapy works on the concept of operant conditioning (a form of psychological learning). Computerized Home Vision Therapy (CHVT) can be prescribed as supplementary treatment to  the occlusion therapy.
Abnormal retinal correspondence (ARC)
In a state of normal binocular single vision, there exists a precise physiological relationship between the corresponding points of the two retinae. Thus, the foveae of two eyes act as corresponding points and have the same visual direction. This adjustment is called normal retinal correspondence (NRC). When squint develops, patient may experience either diplopia or confusion. To avoid these, sometimes (especially in children with small degree of esotropia), there occurs an active cortical adjustment in the directional values of the two retinae. In this state fovea of the normal eye and an extrafoveal point on the retina of the squinting eye acquire a common visual direction i.e., become corresponding points. This condition is called abnormal retinal correspondence (ARC) and the child gets a crude type of binocular single vision.
Tests to detect abnormal retinal correspondence include Worth’s four-dot test, litmus stereo test, Bagolini striated glass tests, after image tests and synoptophore tests (see pages 351-352).

Diplopia
Diplopia refers to simultaneous perception of two images of a single object. Diplopia may be binocular or uniocular.
Binocular diplopia
Occurs due to formation of image on dissimilar points of the two retinae (see page 354, Fig. 14.24). Causes of binocular diplopia are:
■Paralysis or paresis of the extraocular muscles (commonest cause)
■Displacement of one eyeball as occurs in space occupying lesion in the orbit, and fractures of the orbital wall,
■Mechanical restriction of ocular movements as caused by thick pterygium, symblepharon and thyroid ophthalmopathy
■Deviation of ray of light in one eye as caused by decentred spectacles
■Anisometropia i.e., disparity of image size between two eyes as occurs in acquired high anisometropia (e.g., uniocular aphakia with spectacle correction).
344	Section III   Diseases of Eye


Types. Binocular diplopia may be crossed or uncrossed.
■Uncrossed diplopia. In uncrossed (harmonious) diplopia the false image is on the same side as deviation. It occurs in convergent squint as in lateral rectus paralysis.
■Crossed diplopia. In crossed (unharmonious) diplopia the false image is seen on the opposite side. It occurs in divergent squint as in medial rectus paralysis.
Uniocular diplopia
Though not an anomaly of binocular vision, but it will not be out of place to describe uniocular diplopia along with binocular diplopia. In uniocular diplopia an object appears double from the affected eye even when the normal eye is closed.
Causes of uniocular diplopia are:
• Subluxated clear lens (pupillary area is partially phakic and partially aphakic).
• Subluxated intraocular lens (pupillary area is partially aphakic and partially pseudophakic).
• Double pupil due to congenital anomaly, or large peripheral iridectomy or iridodialysis.
• Incipient cataract.Usually polyopia i.e., multiple images may be seen due to multiple water clefts within the lens.
• Keratoconus.Diplopia occurs due to changed refractive power of the cornea in different parts.
Treatment of diplopia
Treat the causative disease. Temporary relief from annoying diplopia can be obtained by occluding the affected eye.

STRABISMUS

DEFINITION AND CLASSIFICATION
Definition
Normally, visual axis of the two eyes are parallel to each other in the ‘primary position of gaze’ and this alignment is maintained in all positions of gaze.
A misalignment of the visual axes of the two eyes is called squint or strabismus.
Classification of strabismus
Broadly, strabismus can be classified as below: i.  Apparent squint or pseudostrabismus.
ii. Latent squint (Heterophoria) iii.Manifest squint (Heterotropia)
1.  Concomitant squint 2.  Incomitant squint.
PSEUDOSTRABISMUS
In pseudostrabismus (apparent squint), the visual axes are in fact parallel, but the eyes seem to have a squint:

1. Pseudoesotropia or apparent convergent squint may be associated with:
• Prominent epicanthal fold (which covers the normally visible nasal aspect of the globe and gives a false impression of esotropia).
• Negative angle kappa.
2. Pseudoexotropiaor apparent divergent squint may be associated with:
• Hypertelorism, a condition of wide separation of the two eyes (i.e., wide IPD), and
• Positive angle kappa.

HETEROPHORIA

Heterophoria also known as ‘latent strabismus’, is a condition in which the tendency of the eyes to deviate is kept latent by fusion. Therefore, when the influence of fusion is removed the visual axis of one eye deviates away. Orthophoria is a condition of perfect alignment of the two eyes which is maintained even after the removal of influence of fusion. However, orthophoria is a theoretical ideal. Practically, a small amount of heterophoria is of universal occurrence and is known as ‘physiological heterophoria’.
Types of heterophoria
1. Esophoria or latent convergent squint refers to tendency of the eyeballs to deviate inward.
It may be:
i.  Convergence excess type (esophoria greater for near than distance).
ii. Divergence weakness type (esophoria greater for distance than near).
iii.Non-specific type (esophoria which does not vary significantly in degree for any distance).
2. Exophoria or latent divergent squint refers to tendency of the eyeballs to deviate outwards.It may be: i.  Convergence weakness type (exophoria greater for
near than distance).
ii. Divergence excess type (exophoria greater on distant fixation than the near).
iii.Non-specific type (exophoria which does not vary significantly in degree for any distance).
3. Hyperphoria is a tendency of the eyeball to deviate upwards, while hypophoria is a tendency to deviate downwards. However, in practice it is customary to use the term right or left hyperphoria depending on the eye which remains up as compared to the other.
4. Cyclophoria or torsional deviation is a tendency of the eyeball to rotate around the anteroposterior axis. When the 12 O’clock meridian of cornea rotates nasally, it is called incyclophoria and when it rotates temporally it is called encyclophoria.
Chapter 14	Disorders of Ocular Motility	345


Etiology
A. Anatomical factors
Anatomical factors responsible for development of heterophoria include:
1. Orbital asymmetry.
2. Abnormal interpupillary distance (IPD). A wide IPD is associated with exophoria and small with esophoria.
3. Faulty insertion of extraocular muscle.
4. A mild degree of extraocular muscle weakness. 5. Anomalous central distribution of the tonic
innervation of the two eyes.
6. Anatomical variation in the position of the macula in relation to the optical axis of the eye.
B. Physiological factors
1. Age. Esophoria is more common in younger age group as compared to exophoria which is more often seen in elderly.
2. Role of accommodation. Increased accom-modation is associated with esophoria (as seen in hypermetropes and individuals doing excessive near work) and decreased accommodation with exophoria (as seen in simple myopes).
3. Role of convergence. Excessive use of convergence may cause esophoria (as occurs in bilateral congenital myopes) while decreased use of convergence is often associated with exophoria (as seen in presbyopes).
4. Dissociation factor such as prolonged constant use of one eye may result in exophoria (as occurs in individuals using uniocular microscope and watch makers using uniocular magnifying glass).

Factors predisposing to decompensation
• Inadequacy of fusional reserve,
• General debility and lowered vitality,
• Psychosis, neurosis, and mental stress, • Precision of job, and
• Advancing age.

Symptoms
Depending upon the symptoms heterophoria can be divided into compensated and decompensated. Compensated heterophoria. It is associated with no subjective symptoms. Compensation of heterophoria depends upon the reserve neuro-muscular power to overcome the muscular imbalance and individual’s desire for maintenance of binocular vision.
Decompensated heterophoria. It is associated with multiple symptoms which may be grouped as under:


1. Symptoms of muscular fatigue. These result due to continuous use of the reserve neuromuscular power. These include:
• Headache and eyeacheafter prolonged use of eyes, which is relieved when the eyes are closed.
• Difficulty in changing the focus from near to distant objects of fixation or vice versa.
• Photophobia due to muscular fatigue is not relieved by using dark glasses, but relieved by closing one eye.
2. Symptoms of failure to maintain binocular single vision are:
• Blurring or crowding of words while reading,
• Intermittent diplopia due to temporary manifest deviation under conditions of fatigue, and
• Intermittent squint (without diplopia) which is usually noticed by the patient’s close relations or friends.
3. Symptoms of defective postural sensations cause problems in judging distances and positions especially of the moving objects. This difficulty may be experienced by cricketers, tennis players and pilots during landing.
Examination of a case of heterophoria
1. Testing for vision and refractive error. It is most important, because a refractive error may be responsible for the symptoms of the patient or for the deviation itself. Preferably, refraction should be performed under full cycloplegia, especially in children.
2. Cover-uncover test. It tells about the presence and type of heterophoria. To perform it, one eye is covered with an occluder and the other is made to fix an object. In the presence of heterophoria, the eye under cover will deviate. After a few seconds, the cover is quickly removed and the movement of the eye (which was under cover) is observed. Direction of movement of the eyeball tells the type of heterophoria (e.g., the eye will move outward in the presence of esophoria) and the speed of movement tells whether recovery is slow or rapid.
3. Prism cover test. (see page 351).
4. Maddox rod test. Patient is asked to fix on a point light in the centre of Maddox tangent scale (Fig. 14.9) at a distance of 6 metres. A Maddox rod (which consists of many glass rods of red colour set together in a metallic disc) (Fig. 14.10) is placed in front of one eye with axis of the rod parallel to the axis of deviation (Fig. 14.11).
The Maddox rod converts the point light image into a line. Thus, the patient will see a point light with one eye and a red line with the other. Due to
346	Section III   Diseases of Eye













Fig. 14.9 Maddox tangent scale

















Fig. 14.10 Maddox rod





















A

dissimilar images of the two eyes, fusion is broken and heterophoria becomes manifest. The number on Maddox tangent scale where the red line falls will be the amount of heterophoria in degrees. In the absence of Maddox tangent scale, the dissociation between the point light and red line is measured by the superimposition of the two images by means of prisms placed in front of one eye with apex towards the phoria.
5. Maddox wing test. Maddox wing is an instrument (Fig. 14.12) by which the amount of phoria for near (at a distance of 33 cm) can be measured. It is also based on the basic principle of dissociation of fusion by dissimilar objects.
The instrument is designed in such a way that, through its two slits, right eye sees a vertical white arrow and a horizontal red arrow and the left eye sees a vertical and a horizontal line of numbers. The patient is asked to tell the number on the horizontal line which the vertical white arrow is pointing (this will give amount of horizontal phoria) and the number on the vertical line at which the red arrow is pointing (this will measure the vertical phoria). The cyclophoria is measured by asking the patient to align the red arrow with the horizontal line of numbers (Fig. 14.13).
6. Measurement of convergence and accommodation is important in planning the management of heterophorias.
• Near point of convergence (NPC) can be measured with the help of a RAF rule or the Livingstone




















B


Fig. 14.11 Maddox rod test for horizontal (A) and vertical (B) heterophorias
Chapter 14	Disorders of Ocular Motility	347

1.Correction of refractive error when detected, is most important. It may correct the phoria and/or relieve the symptoms.
2. Orthoptic treatment. It is indicated in patients with heterophoria without refractive error and in those where heterophoria and/or symptoms are not corrected by glasses. Aim of orthoptic treatment is to improve convergence insufficiency and the fusional reserve. Orthoptic exercises can be done with synoptophore. Simple exercises to be carried out at home should also be taught to the patient.
3. Prescription of prism in glasses. It may be tried in selected cases of hyperphoria and in troublesome cases of esophoria and exophoria. Prism is prescribed
Fig. 14.12 Maddox wing	with apex towards the direction of phoria to correct only half or at the most two-thirds of heterophoria. 4. Surgical treatment. It is undertaken in patients with marked symptoms which are not relieved by other measures. Aim of the surgical management is to strengthen the weak muscle or weaken the strong muscle.

CONCOMITANT STRABISMUS











Fig. 14.13 Maddox wing test

binocular gauge. The normal NPC is considered to be around 70 mm.
• Near point of accommodation (NPA) should be measured after the NPC. NPA can be measured with the help of a RAF or Prince’srule. Normal NPA varies with the age of patient (see page 47).
7.Measurement of fusional reserve. It can be done with the help of a synoptophore or prism bar. The normal values of fusional reserve are as follows:
• Vertical fusional reserve: 1.5°–2.5°
• Horizontal negative fusional reserve (abduction range): 3°–5 °
• Horizontal positive fusional reserve (adduction range) : 20°–40°.
Treatment
Treatment described below, is indicated mainly in patients with decompensated heterophoria (i.e., symptomatic cases).

It is a type of manifest squint in which the amount of deviation in the squinting eye remains constant (unaltered) in all the directions of gaze; and there is no associated limitation of ocular movements.

Etiology
It is not clearly defined. The causative factors differ in individual cases. As we know, the binocular vision and coordination of ocular movements are not present since birth but are acquired in the early childhood. The process starts by the age of 3–6 months and is completed up to 5–6 years. Therefore, any obstacle to the development of these processes may result in concomitant squint. These obstacles can be arranged into three groups, namely: sensory, motor and central.
1. Sensory obstacles. These are the factors which hinder the formation of a clear image in one eye. These include:
• Refractive errors,
• Prolonged use of incorrect spectacles, • Anisometropia,
• Corneal opacities,
• Lenticular opacities,
• Diseases of macula (e.g., central chorioretinitis), • Optic atrophy, and
• Obstruction in the pupillary area due to congenital ptosis.
348	Section III   Diseases of Eye


2. Motor obstacles.  These factors hinder the maintenance of the two eyes in the correct positional relationship in primary gaze and/or during different ocular movements. A few such factors are:
• Congenital abnormalities of the shape and size of the orbit,
• Abnormalities of extraocular muscles such as faulty insertion, faulty innervation and mild paresis,
• Abnormalities of accommodation, convergence and AC/A ratio.
3. Central obstacles. These may be in the form of: • Deficient development of fusion faculty, or
• Abnormalities of cortical control of ocular movements as occurs in mental trauma, and hyperexcitability of the central nervous system during teething.
Clinical features of concomitant strabismus (in general)
The cardinal features of different clinico-etiological types of concomitant strabismus are described separately. However, the clinical features of con-comitant strabismus (in general) are as below: 1.Ocular deviation.Characteristics of ocular deviation are:
• Unilateral (monocular squint) or alternating (alternate squint).
• Inward deviation (esotropia) or outward deviation (exotropia) or vertical deviation (hypertropia).
• Primary deviation (of squinting eye) is equal to secondary deviation (deviation of normal eye under cover when patient fixes with squinting eye).
• Ocular deviation is equal in all the directions of gaze.
2. Ocular movements are not limited in any direction. 3. Refractive error may or may not be associated.
4. Suppression and amblyopia may develop as sensory adaptation to strabismus. Suppression may be monocular (in monocular squint) and alternating (in alternating strabismus). Amblyopia develops in monocular strabismus only and is responsible for poor visual acuity.
5. A-V patterns may be observed in horizontal strabismus. When A-V patterns are associated, the horizontal concomitant strabismus becomes vertically incomitant (see page 357).
Types of concomitant squint
Three common types of concomitant squint are: 1. Convergent squint (esotropia),
2. Divergent squint (exotropia), and 3. Vertical squint (hypertropia).


CONVERGENT SQUINT
Concomitant convergent squint or esotropia denotes inward deviation of one eye (Fig. 14.14) and is the most common type of squint in children. It can be unilateral (the same eye always deviates inwards and the second normal eye takes fixation) or alternating (either of the eyes deviates inwards and the other eye takes up fixation, alternately).
Clinico-etiological types
Depending upon the clinico-etiological features convergent concomitant squint can be further classified into following types:
1. Infantile esotropia
Clinical features.Infantile esotropia, previously called as congenital esotropia, is characterised by following features (Fig. 14.14):
• Age of onset, is usually 1–2 months of age, but may occur any time in first 6 months of life.
• Angle of deviation is usually constant and fairly large (>30°).
• Fixation pattern. Binocular vision does not develop and there is alternate fixation in primary gaze and cross fixation in the lateral gaze.
• Amblyopia develops in 25–40% cases.
• Associations include inferior oblique overaction (usually developing after 1 year of age),dissociated vertical deviation (DVD) in about 70–90% cases, and latent horizontal nystagmus.
Treatment. Surgery is the treatment of choice.
• Amblyopia treatment by patching the normal eye should always be done before performing  the surgery.
• Recession of both medial recti is preferred over unilateral recess-resect procedure.
• Time of surgery. Surgery should be done between 6 months to 2 years (preferably before 1 year of age).













Fig. 14.14 Concomitant convergent squint (infantile esotropia)
Chapter 14	Disorders of Ocular Motility	349


2. Accommodative esotropia
It occurs due to overaction of convergence associated with accommodation reflex. Accommodative esotropia is the most common type of squint in children (previously it was believed that congenital esotropia was most common). When esotropia develops around 2–3 years of age, it is most likely accommodative. It is of three types: refractive, nonrefractive and mixed.
i. Refractive accommodative esotropia: It usually develops at the age of 2 to 3 years and is associated with high hypermetropia (+4 to +7 D). Mostly it is for near and distance (marginally more for near) and fully correctable by use of spectacles (Fig. 14.15).
ii. Non-refractive accommodative esotropia: It is caused by abnormal AC/A (accommodative convergence/accommodation)  ratio.  This may occur even in patients with no refractive error. Esotropia is greater for near than that for distance (minimal or no deviation for distance). It is fully corrected by bifocal glasses with  add +3 DS for near vision. Miotics may be useful in younger children not suitable for bifocals. Miotics facilitate accommodation and thus reduce the accommodative convergence.
iii. Mixed accommodative esotropia: It is caused by combination of hypermetropia and high AC/A ratio. Esotropia for distance is corrected by correction of hypermetropia; and the residual esotropia for near is corrected by an addition of +3 DS lens.










A

3. Acquired Non-accommodative esotropias
This group includes all those acquired primary esodeviations in which amount of deviation is not affected by the state of accommodation. It includes: i. Essential acquired or late onset esotropia, acute concomitant esotropia, cyclic esotropia, nystagmus blockage syndrome, esotropia in myopia and microtropia.
ii. Essential acquired or late onset esotropia. It is a common variety of concomitant convergent squint. It typically occurs during first few years of life any time after six months of age. It is of three types:
• Basic type. In it the deviation is usually equal at distance and near.
• Convergence excess type. In it the deviation is large for near and small or no deviation for distance.
• Divergence insufficiency type. It is characterised by a greater deviation for distance than near.
Treatment includes early surgery after correction of the associated refractive error and amblyopia.
4. Sensory esotropia
It results from monocular lesions (in childhood) which either prevent the development of normal binocular vision or interfere with its maintenance. Examples of such lesions are: cataract, severe congenital ptosis, aphakia, anisometropia, optic atrophy, retinoblastoma, central chorioretinits, and so on.
5. Consecutive esotropia
It results from surgical overcorrection of exotropia.
DIVERGENT SQUINT
Concomitant divergent squint (exotropia) is characterised by outward deviation of one eye while the other eye fixates.
Clinico-etiological types
It can be classified into following clinico-etiological types:
1. Congenital exotropia
It is rare and almost always present at birth. It is characterised by a fairly large angle of squint, usually alternate with homonymous fixation in lateral gaze, and no amblyopia.









B
Fig. 14.15 (A) Accommodative esotropia, (B) fully corrected by spectacles

2. Primary exotropia
It may be unilateral or alternating and may present as intermittent or constant exotropia.
Intermittent exotropia. It is the most common type of exodeviation with following features:
• Age of onset is usually early between 2 to 5 years. • Deviation becomes manifest at times and latent at
others. Precipitating factors include bright light, fatigue, ill health and day dreaming.
350	Section III   Diseases of Eye


• Sensory testing usually reveals good fusion, stereopsis and no amblyopia.
Constant exotropia. If not treated in time the intermittent exotropia may decompensate to become constant exotropia (Fig. 14.16).
Types. Primary exotropia may be of following three types:
• Convergence insufficiency type of exotropia is greater for near than distance,
• Divergence excess type of exotropia is greater for distance than near, or
• Basic non-specific type exotropia is equal for near and distance.
3. Secondary (sensory deprivation) exotropia
It is a constant unilateral deviation which results from long-standing monocular lesions (in adults), associated with low vision in the affected eye. Common causes include: traumatic cataract, corneal opacity, optic atrophy, anisometropic amblyopia, retinal detachment and organic macular lesions.
4. Consecutive exotropia
It is a constant unilateral exotropia which results either due to surgical overcorrection of esotropia, or spontaneous conversion of small degree esotropia with amblyopia into exotropia.
EVALUATION OF A CASE OF CONCOMITANT STRABISMUS
I. History
A meticulous history is very important. It should include: age of onset, duration, mode of onset (sudden or gradual), any illness preceding squint (fever, trauma, infections, etc.), intermittent or constant, unilateral or alternating, history of diplopia, family history of squint, history of head tilt or turn and so on.
II. Examination
1. Inspection. Large degree squint (convergent or divergent) is obvious on inspection.
2. Ocular movements. Both uniocular as well as binocular movements should be tested in all the cardinal positions of gaze.










Fig. 14.16 A patient with primary exotropia

3. Pupillary reactions. These may be abnormal in patients with secondary deviations due to diseases of retina and optic nerve.
4. Media and fundus examination. It may reveal associated disease of ocular media, retina or optic nerve.
5. Testing of vision and refractive error. It is most important, because a refractive error may be responsible for the symptoms of the patient or for the deviation itself. Preferably, refraction should be performed under full cycloplegia, especially in children.
6.  Cover tests
i. Direct cover test (Fig. 14.17). It confirms the presence of manifest squint. To perform it, the patient is asked to fixate on a point light. Then, the normal looking eye is covered while observing the movement of the uncovered eye. In the presence of squint, the uncovered eye will move in opposite direction to take fixation, while in apparent squint there will be no movement. This test should be performed for near fixation (i.e., at 33 cm) as well as distance fixation (i.e., at 6 metres).
ii. Alternate cover test. It reveals whether the squint is unilateral or alternate and also differentiates concomitant squint from paralytic squint (where secondary deviation is greater than primary).
7. Estimation of angle of deviation
i. Hirschberg corneal reflex test. It is a rough but handy method to estimate the angle of manifest squint. In it the patient is asked to fixate at point




















Fig. 14.17 Direct cover test depicting left exotropia
Chapter 14	Disorders of Ocular Motility	351


light held at a distance of 33 cm and the deviation of the corneal light reflex from the centre of pupil is noted in the squinting eye. Roughly, the angle of squint is 15° and 45° when the corneal light reflex falls on the border of pupil and limbus, respectively (Fig. 14.18).
ii. The prism and cover test (prism bar cover test i.e., PBCT). Prisms of increasing strength with apex towards the deviation are placed in front of one eye and the patient is asked to fixate an object with the other. The cover-uncover test is performed till there is no recovery movement of the eye under cover. This will tell the amount of deviation in prism dioptres. Both heterophoria as well as heterotropia can be measured by this test.
iii. Krimsky corneal reflex test.In this test, the patient is asked to fixate on a point light and prisms of increasing power (with apex towards the direction of manifest squint) are placed in front of the normal fixating eye till the corneal light reflex is centred in the squinting eye. The power of prism required to centre the light reflex in the squinting eye equals the amount of squint in prism dioptres.
iv. Measurement of deviation with synoptophore. All types of heterophorias and heterotropias (both objective and subjective angle of squint) can be measured accurately with it. In addition, many other tests can also be performed with this instrument (for details see page 352).
8.Tests for grade of binocular vision and sensory functions. Normal binocular single vision consists of three grades. Sensory anomalies include disturbances of binocular vision, eccentric fixation, suppression, amblyopia, abnormal retinal correspondence and diplopia. A few common tests for sensory functions are as follows:
i. Worth’s four-dot test. For this test, patient wears goggles with red lens in front of the right and green lens in front of the left eye and views a box with four lights—one red, two green and one white (Fig. 14.19).












Fig. 14.18 Hirschberg corneal reflex test


Interpretation
• In normal binocular single vision, the patient sees all the four lights in the absence of manifest squint (Fig. 14.19A).
• Inabnormal retinal correspondence (ARC) patient sees four lights even in the presence of a manifest squint (Fig. 14.19B).
• In left suppression the patient sees only two red lights, (Fig. 14.19C).
• In right suppression the patient sees only three green lights, (Fig. 14.19D).
• In alternating suppression the patient sees three green lights and two red lights, alternately.
• In diplopia the patient sees five lights (2 red and 3 green) (Fig. 14.19E).
ii. Tests for fixation. It can be tested with the help of a visuoscope or fixation star of the ophthalmoscope. Patient is asked to cover one eye and fix the star with the other eye. Fixation may be centric (normal on the fovea) or eccentric (which may be unsteady, parafoveal, macular, paramacular, or peripheral (Fig. 14.20).
iii. After-image test. In this test the right fovea is stimulated with a vertical and left with a horizontal bright light and the patient is asked to draw the position of after-images.
Interpretation
• A patient with normal retinal correspondence will draw a cross (Fig. 14.21A).
• An esotropic patient with abnormal retinal correspondence (ARC) will draw vertical image to the left of horizontal (Fig. 14.21B).






















Fig. 14.19 Worth’s four-dot test
352	Section III   Diseases of Eye















Fig. 14.20 Types of fixation	Fig. 14.22 Synoptophore








Fig. 14.21 After-image test: A, normal retinal corres-pondence; B, esotropia with ARC; C, exotropia with ARC


• An exotropic patient with ARC will draw vertical image to the right of horizontal (Fig. 14.21C).
iv. Sensory function tests with synoptophore. Synoptophore (major amblyoscope) consists of two tubes, having a right-angled bend, mounted on a base (Fig. 14.22). Each tube contains a light source for illumination of slides and a slide carrier at the outer end, a reflecting mirror at the right-angled bend and an eyepiece of +6.5 D at the inner end (Fig. 14.23). The two tubes can be moved separately or together by means of knobs around a semicircular scale. Synoptophore is used for many diagnostic and therapeutic indications in orthoptics. Synoptophore tests for sensory functions include: ■Estimation of grades of binocular vision (see page 341). ■Detection of normal/abnormal retinal corres-pondence (ARC).It is done by determining the subjective and objective angles of the squint. In normal retinal correspondence, these two angles are equal. In ARC, objective angle is greater than the subjective angle and the difference between these is called the angle of anomaly. When the angle of anomaly is equal to the objective angle, the ARC is harmonious. In unharmonious ARC angle of anomaly is smaller than the objective angle.
v. Neutral density filter test. In this test, visual acuity is measured without and with neutral density filter placed in front of the eye. In cases with functional








Fig. 14.23 Optical principle of synoptophore



amblyopia visual acuity slightly improves while in organic amblyopia it is markedly reduced when seen through the filter.
TREATMENT OF CONCOMITANT STRABISMUS Goals of treatment are:
• To achieve good cosmetic correction, • To improve visual acuity, and
• To maintain binocular single vision.
However, many time it is not possible to achieve all the goals in every case.

Treatment modalities. These include the following:
1. Spectacles with full correction of refractive error should be prescribed in every case. It will improve the visual acuity and at times may correct the squint partially or completely (as in accommodative squint).
Chapter 14	Disorders of Ocular Motility	353


2. Occlusion therapy. It is indicated in the presence of amblyopia. After correcting the refractive error, the normal eye is occluded and the patient is advised to use the squinting eye. Regular follow-ups are done in squint clinic. Occlusion helps to improve the vision in children below the age of 10 years. (For occlusion regimen see page 343).
3. Preoperative orthoptic exercises. These are given after the correction of amblyopia to overcome suppression.
4. Squint surgery. It is required in most of the cases to correct the deviation. However, it should always be instituted after the correction of refractive error, treatment of amblyopia and orthoptic exercises. ■Basic principles of squint surgery.These are to weaken the strong muscle by recession (shifting the insertion posteriorly) or to strengthen the weak muscle by resection (shortening the muscle). ■Type and amount of muscle surgery. It depends upon the type and angle of squint, age of patient, duration of the squint and the visual status. Therefore, degree of correction versus amount of extraocular muscle manipulation required cannot be mathematically determined. However, roughly 1 mm resection of medial rectus (MR) will correct about 1°–1.5° and 1 mm recession will correct about 2°–2.5°. While l mm resection and recession of lateral rectus (LR) muscle will correct 1°–2°. The maximum limit allowed for MR resection is 8 mm and recession is 5.5 mm. The corresponding figures for LR muscle are 10 mm and 8 mm, respectively.
5. Postoperative orthoptic exercises. These are required to improve fusional range and maintain binocular single vision.

INCOMITANT SQUINT

It is a type of heterotropia (manifest squint) in which the amount of deviation varies in different directions of gaze. It includes following conditions:
1. Paralytic squint,
2. ‘A’ and ‘V’ pattern heterotropias, and 3. Restrictive squint.
PARALYTIC STRABISMUS
It refers to ocular deviation resulting from complete or incomplete paralysis of one or more extraocular muscles.
Etiology
The lesions may be neurogenic, myogenic or at the level of neuromuscular junction.


I. Neurogenic lesions
Neurogenic lesions may occur at the level of nerve nucleus, nerve root, or any part of  the nerve in its course. Nuclear ophthalmoplegia refers to paralysis of extraocular muscles due to lesions of 3rd cranial nerve. They are more often bilateral.
Common causes of neurogenic lesions are:
1. Congenital. Hypoplasia or absence of nucleus is a known cause of third and sixth cranial nerve palsies. Birth injuries may mimic congenital lesions.
2. Inflammatory lesions. These may be in the form of encephalitis, meningitis, neurosyphilis or peripheral neuritis (commonly viral). Nerve trunks may also be involved in the infectious lesions of cavernous sinus and orbit.
3. Neoplastic lesions. These include brain tumours involving nuclei, nerve roots or intracranial part of the nerves; and intraorbital tumours involving peripheral parts of the nerves.
4. Vascular lesions. These are known in patients with hypertension, diabetes mellitus and athero-sclerosis.These may be in the form of haemorrhage, thrombosis, embolism, aneurysms or vascular occlusions. Cerebrovascular accidents are more common in elderly people. Ophthalmoplegic migraine or episodic ophthalmoplegia is a well known vascular condition characterized by recurrent attacks of headache associated with paralysis of 3rd (most common), 4th or 6th cranial nerve. The condition is often unilateral, persists for days or weeks and even tends to become permanent, in some cases.
5. Traumatic lesions. These include head injury and direct or indirect trauma to the nerve trunks. Head injury is common cause of 6th nerve palsy.
6. Toxic lesions. These include carbon monoxide poisoning, effects of diphtheria toxins (rarely), alcoholic and lead neuropathy.
7. Demyelinating lesions. Ocular palsy may occur in multiple sclerosis and diffuse sclerosis.
II. Myogenic lesions
1. Congenital lesions. These include absence, hypoplasia, malinsertion, weakness and musculo-facial anomalies.
2. Traumatic lesions. These may be in the form of laceration, disinsertion, haemorrhage into the muscle substance or sheath and incarceration of muscles in blow out fractures of the orbital walls (floor or medial wall).
354	Section III   Diseases of Eye


3. Inflammatory lesions. Myositis is usually viral in origin and may occur in influenza, measles and other viral fevers.
4. Myopathies. These include thyroid myopathy, carcinomatous myopathy and that associated with certain drugs. Chronic progressive ophth-almoplegia (CPO) is a bilateral myopathy of extraocular muscles; which may be sporadic or inherited as an autosomal dominant disorder. It is the most common (75% cases) type of mitochondrial myopathy. It is characterised by:
• Bilateral ptosis with slowly progressive ophth-almoplegia is typical presentation.
• Diplopia is usually not a complaint since all eye movements are reduced equally.
• Other associated symptoms of CPO include exercise intolerance, hearing loss, ataxia, sensory axonal neuropathy, parkinsonism, and clinical depression.

III. Neuromuscular junction lesion
It includes myasthenia gravis. The disease is characterised primarily by fatigue of muscle groups, usually starting with the small extraocular muscles, before involving other large muscles.
Clinical features
Symptoms
1. Diplopia. It is the main symptom of paralytic squint. It is more marked in  the field of action of paralysed muscle. It may be crossed (in divergent squint) or uncrossed (in convergent squint). It may be horizontal, vertical or oblique depending on the muscle paralysed. Diplopia occurs due to formation of image on dissimilar points of the two retinae (Fig. 14.24). The false image (seen by the squinting eye) is less distinct than the true image (seen by the other eye).
2. Confusion. It occurs due to formation of image of two different objects on the corresponding points of two retinae.
3. Nausea and vertigo. These result from diplopia and confusion and may cause vomiting also.
4.  Ocular deviation is typically a sudden onset.
Signs
1. Primary deviation. It is deviation of the affected eye and is away from the action of paralysed muscle, e.g., if lateral rectus is paralysed the eye is converged. Angle of deviation varies in different directions of gaze (incomitant).
2. Secondary deviation. It is deviation of the normal eye seen under cover, when the patient is made to fix with the squinting eye. It is greater than the primary deviation. This is due to the fact that the strong




















Fig. 14.24 Diplopia


impulse of innervation required to enable the eye with paralysed muscle to fix is also transmitted to the yoke muscle of the sound eye resulting in a greater amount of deviation. This is based on Hering’s law of equal innervation of yoke muscles.
3. Restriction of ocular movement. It occurs in the direction of the action of paralysed muscles.
4. Compensatory head posture. It is adopted to avoid diplopia and confusion. Head is turned towards the direction of action of the paralysed muscle, e.g., if the right lateral rectus is paralysed, patient will keep the head turned towards right. Ocular torticollis  refers to tilting of head and chin depression occurring to compensate for the vertical diplopia. It needs to be differentiated from the true torticollis occurring due to undue contracture of sternocleidomastoid muscle. 5. False projection or orientation. It is due to increased innervational impulse conveyed to the paralysed muscle. It can be demonstratedby asking the patient to close the sound eye and then to fix an object placed on the side of paralysed muscle. Patient will locate it further away in the same direction. For example, a patient with paralysis of right lateral rectus will point towards right more than the object actually is.
Note. Visual acuity is normal and there is no amblyopia as usually the paralytic squint develops in adults when visual acuity has already developed. However, if it occurs in children below 6 years than amblyopia can occur.
Pathological sequelae of an extraocular muscle palsy In all cases of extraocular muscle palsy, certain sequelae take place after some time. These occur
Chapter 14	Disorders of Ocular Motility	355


more in paralysis due to lesions of the nerves than the lesions of muscles. These include:
1. Overaction of the contralateral synergistic muscle. 2. Contracture of the direct antagonist muscle.
3. Secondary inhibitional palsy of the contralateral antagonist muscle.
For example, in paralysis of the right lateral rectus muscle there occurs (Fig 14.25):
■Overaction of the left medial rectus, ■Contracture of the right medial rectus and ■Inhibitional palsy of the left lateral rectus muscle.
Clinical varieties of ocular palsies
1. Isolated muscle paralysis. Lateral rectus and superior oblique are the most common muscles to be paralysed singly, as they have separate nerve supply. Isolated paralysis of the remaining four muscles is less common, except in congenital lesions.
2. Paralysis of the third cranial nerve. It is of common occurrence. It may be congenital or acquired. Clinical features of third nerve palsy (Figs. 14.26A and B) include:
• Ptosis due to paralysis of the LPS muscle.
• Deviation. Eyeball is turned down, out and slightly intorted due to actions of the lateral rectus and superior oblique muscles.
• Ocular movements are restricted in all the directions except outward.
• Pupil is fixed and dilated due to paralysis of the sphincter pupillae muscle.
• Accommodation is completely lost due to paralysis of the ciliary muscle.
• Crossed diplopia is elicited on raising the eyelid. • Head posture may be changed if pupillary area
remains uncovered.
3. Double elevator palsy, also known as monocular elevation deficiency is a congenital condition caused by third nerve nuclear lesion. It is characterised by paresis of the superior rectus and the inferior oblique muscle of the involved eye.











Fig. 14.25 Pathological sequelae of the right lateral rectus muscle paralysis











A











B
Fig. 14.26 A patient with third cranial nerve paralysis showing: A, ptosis; B, divergent squint

4. Total ophthalmoplegia. In this condition, all extraocular muscles including LPS and intraocular muscles, viz., sphincter pupillae, and ciliary muscle are paralysed. It results from combined paralysis of third, fourth and sixth cranial nerves. It is a common feature of orbital apex syndrome and cavernous sinus thrombosis.
5. External ophthalmoplegia. In this condition, all extraocular muscles are paralysed, sparing the intraocular muscles. It results from lesions at the level of motor nuclei sparing the Edinger-Westphal nucleus.
6. Internuclear ophthalmoplegia. In this condition, there is lesion of the medial longitudinal fasciculus (MLF). It is the pathway by which various ocular motor nuclei are linked. Internuclear ophthalmoplegia is characterised by: defective action of medial rectus on the side of lesion, horizontal nystagmus of the opposite convergence is normal, as the pathway of convergence runs directly into the midbrain without involving the MLF.
Investigations of a case of paralytic squint
A. Evaluation for squint
Every case of squint should be evaluated utilising the tests described on page 350-352. Additional tests required for a case of paralytic squint are:
356	Section III   Diseases of Eye


1. Diplopia charting. It is indicated in patients complaining of confusion or double vision. In it patient is asked to wear red and green diplopia charting glasses. Red glass being in front of the right eye and green in front of the left. Then in a semi-dark room, he is shown a fine linear light from a distance of 4 ft. and asked to comment on the images in primary position and in other positions of gaze. Patient tells about the position and the separation of the two images in different fields. Fig. 14.27 shows diplopia charting in a patient with right lateral rectus palsy. 2. Hess screen test. Hess screen/Lees screen (Fig. 14.28) test tells about the paralysed muscles and


















Fig. 14.27 Diplopia chart of a patient with right lateral rectus palsy




















Fig. 14.28 Hess screen










Fig. 14.29 Hess chart in right lateral rectus palsy


the pathological sequelae of the paralysis, viz., overaction, contracture and secondary inhibitional palsy. The two charts are compared. The smaller chart belongs to the eye with paretic muscle and the larger to the eye with overacting muscle (Fig. 14.29). 3. Field of binocular fixation. It should be tested in patients with paralytic squint where applicable, i.e., if patient has some field of single vision. This test is performed on the perimeter using a central chin rest. 4. Forced duction test (FDT). It is performed to differentiate between the incomitant squint due to paralysis of extraocular muscle and that due to mechanical restriction of the ocular movements. FDT is positive (resistance encountered during passive rotation) in cases of incomitant squint due to mechanical restriction and negative in cases of extraocular muscle palsy.
B. Investigations to find out the cause of paralysis These include orbital ultrasonography, orbital and skull computerised tomography scanning and neurological investigations.
Paralytic vs. Non-paralytic squint
Differences between paralytic and non-paralytic squint are depicted in Table 14.2.
Management
1. Treatment of the cause. An exhaustive investigative work-up should be done to find out the cause and, if possible, treat it.
2. Conservative measures. These include: wait and watch for self-improvement to occur for a period of 6 months, vitamin B-complex as neurotonic; and systemic steroids for non-specific inflammations.
3. Treatment of annoying diplopia. It includes use of occluder on the affected eye, with intermittent use of both eyes with changed headposture to avoid suppression amblyopia.
4. Chemodenervation of the contralateral muscle with botulinum toxin may be useful during the recovery period.
Chapter 14	Disorders of Ocular Motility	357

Table 14.2: Differences between paralytic and non-paralytic squint


Features 1. Onset
2. Diplopia
3. Ocular movements 4. False projection


5. Head posture

6. Nausea and vertigo 7. Secondary deviation

8. In old cases pathological sequelae in the muscles

Paralytic squint Usually sudden Usually present
Limited in the direction of action of paralysed muscle
It is positive i.e., patient cannot correctly locate the object in space when asked to see in the direction of paralysed muscle in early stages.
A particular head posture depending upon the muscle paralysed may be present.
Present
More than the primary deviation

Present

Nonparalytic squint Usually slow
Usually absent Full
False projection is negative

Normal

Absent
Equal to primary deviation
Absent




5. Surgical treatment. It should be carried out in case the recovery does not occur in 6 months. Aim of treatment is to provide a comfortable field of binocular fixation, i.e., in central field and lower quadrants. The principles of surgical treatment involve strengthening of the paralysed muscle by resection; weakening of the overacting muscle by recession, and transplantation of normal muscle tendon at or near the insertion of paralysed muscle.
‘A’ AND‘V’ PATTERN HETEROTROPIA

Terminology
The terms ‘A’ or ‘V’ pattern squint are labeled when the amount of deviation in squinting eye varies by more than 10° and 15°, respectively, between upward and downward gaze.
‘A’ and ‘V’ esotropia. In ‘A’ esotropia the amount of deviation increases in upward gaze and decreases in downward gaze. The reverse occurs in ‘V’ esotropia. ‘A’ and ‘V’ exotropia. In ‘A’ exotropia the amount of deviation decreases in upward gaze and increases in downward gaze. The reverse occurs in ‘V’ exotropia.
Etiology
■Oblique muscle dysfunction is the commonest cause of AV pattern.
■Other causes include horizontal rectus muscle dysfunction, vertical muscle dysfunction and certain orbital factors.
Clinical presentations
A and V pattern heterotropia essentially refers to vertically incomitant horizontal strabismus. Thus, the horizontally comitant esotropias and exotropias

(described on page 347-350) may be associated with A or V patterns.
Treatment
Surgical treatment consists of correction of horizontal deviation along with:
• Weakening of overacting oblique muscle, inferior oblique for V pattern and superior oblique for A pattern.
• Transpositioning of horizontal rectus muscles is to be considered when there is no associated overaction of the oblique muscle. As shown in Fig. 14.29, Medial recti are transposed toward Apex of A or V (pattern) and Lateral recti toward Empty space (to remember mnemonic is MALE).
RESTRICTIVE SQUINT
In restrictive squint, the extraocular muscle is not paralysed but its movement is mechanically restricted.
Characteristic features of restrictive squints are:
• Smaller ocular deviation in primary position in proportion to the limitation of movement and
• Positive forced duction test (i.e., a restriction is encountered on passive rotation) (see page 356).
Common causes of restrictive squint are: • Duane’s retraction syndrome,
• Brown’s superior oblique tendon sheath syndrome, • Strabismus fixus,
• Dysthyroid ophthalmopathy (see page 414), and • Incarceration of extraocular muscle in blow-out
fracture of the orbit (see page 422).

1. Duane’s retraction syndrome
Duane’s retraction syndrome is a congenital ocular motility defect occurring due to paradoxical
358	Section III   Diseases of Eye


innervation of lateral or medial or both rectus muscles.
Characteristics features are:
• Limitation of abduction (type I DRS) or adduction (type II DRS) or both (type III DRS).
• Retraction of the globe and narrowing of the palpebral fissure on attempted adduction and widening of the palpebral fissure on attempted abduction.
• Eye in the primary position may be orthotropic, esotropic or exotropic.
2. Brown’s superior oblique tendon sheath syndrome
It is a congenital ocular motility defect due to fibrous tightening of the superior oblique tendon. It is characterized by limitation of elevation of the eye in adduction (normal elevation in abduction), usually straight eyes in primary position and positive forced duction test on attempts to elevate eye in adduction.
3. Strabismus fixus
It is a rare condition characterised by bilateral fixation of eyes in convergent position due to fibrous tightening of the medial recti.
STRABISMUS SURGERY
Surgical techniques
1. Muscle weakening procedures include recession, marginal myotomy and myectomy.
2. Muscle strengthening procedures are resection, tucking and advancement.
3. Procedures that change direction of muscle action. These include:
• Vertical transposition of horizontal recti to correct ‘A’ and ‘V’ patterns,
• Posterior fixation suture (Faden operation) to correct dissociated vertical deviation, and
• Transplantation of muscles in paralytic squints.

Steps of recession (Fig. 14.30)
1. Muscle is exposed by reflecting a flap of overlying conjunctiva and Tenon’s capsule.
2. Two vicryl sutures are passed through the outer quarters of the muscle tendon near the insertion.
3. The muscle tendon is disinserted from the sclera with the help of tenotomy scissors.
4. The amount of recession is measured with the callipers and marked on the sclera.
5. The muscle tendon is sutured with the sclera at the marked site posterior to original insertion.
6. Conjunctival flap is sutured back.


















Fig. 14.30 Technique of recession

Steps of resection (Fig. 14.31)
1. Muscle is exposed as for recession and the amount to be resected is measured with callipers and marked.
2. Two absorbable sutures are passed through the outer quarters of the muscles at the marked site.
3. The muscle tendon is disinserted from the sclera and the portion of the muscle anterior to sutures is excised.
4. The muscle stump is sutured with the sclera at the original insertion site.
5. Conjunctival flap is sutured back.

NYSTAGMUS

DEFINITION AND FEATURES
Nystagmus is defined as regular and rhythmic to-and-fro involuntary oscillatory movements of the

















Fig. 14.31 Technique of resection
Chapter 14	Disorders of Ocular Motility	359


eyes. It may be characterised by any of the following features:
1. It may be pendular or jerk nystagmus. In pendularnystagmus movements are of equal velocity in each direction. It may be horizontal, vertical or rotatory. In jerk nystagmus, the move-ments have a slow component in one direction and a fast component in the other direction. The direction of jerk nystagmus is defined by direction of the fast component (phase). It may be right, left, up, down or rotatory.
2. Nystagmus movements may be rapid or slow. 3. The movements may be fine or coarse.
4. Nystagmus may be latent or manifest.

PATHOGENESIS AND CLASSIFICATION Nystagmus occurs due to disturbance of the factors responsible for maintaining normal ocular posture. These include disorders of sensory visual pathway, vestibular apparatus, semicircular canals, midbrain and cerebellum.
Many classifications are in vogue for nystagmus. A simple classification modified from “Classification of Eye Movements Abnormalities and Strabismus (CEMAS)” is as below:
Physiological nystagmus • Optokinetic nystagmus • Endpoint nystagmus
• Physiological vestibular nystagmus.

Pathological nystagmus Nystagmus of infancy
• Infantile nystagmus syndrome (INS)
• Fusion maldevelopment nystagmus syndrome (FMNS)
• Spasmus nutans syndrome (SNS) Acquired nystagmus
• Nystagmus due to disorders of visual fixation • Nystagmus caused by vestibular imbalance
• Acquired pendular nystagmus.

A. Physiological Nystagmus
Physiological nystagmus occurs normally in a variety of situations including optokinetic nystagmus (OKN), end gaze nystagmus (EGN) and physiological vestibular nystagmus (vestibulo-ocular reflex i.e., VOR)
1. Optokinetic nystagmus. It is a physiological jerk nystagmus induced by presenting to gaze the objects moving serially in one direction, such as strips of a spinning optokinetic drum. The eyes will follow a fixed strip momentarily and then jerk back to reposition centrally to fix up a new strip. Similar condition occurs while looking at outside things from a moving train.

2. End-gaze nystagmus. It is a fine jerk horizontal nystagmus seen in normal persons on extreme right or left gaze.
3. Physiological vestibular nystagmus(vestibulo-ocular reflex i.e., VOR). It is a jerk nystagmus which can be elicited by stimulating the tympanic membrane with hot or cold water. It forms the basis of caloric test. If cold water is poured into right ear the patient develops left jerk nystagmus (rapid phase towards left), while the reverse happens with warm water, i.e., patient develops right jerk nystagmus. It can be remembered by the mnemonic ‘COWS’ (Cold-Opposite, Warm-Same).

B. Pathological Nystagmus
I. Nystagmus of infancy
Three most common forms of nystagmus seen in childhood begin in infancy and therefore, are not congenital as believed earlier. These include:
• Infantile nystagmus syndrome,
• Fusion maldevelopment nystagmus syndrome, and • Spasmus nutans syndrome.
1. Infantile nystagmus syndrome is the new name given in the CEMAS system for the old congenital, motor and sensory nystagmus.
Etiology. It may be (I) Idiopathic or (II) Associated with sensory deprivation due to any of the following causes:
• Ocular albinism, • Aniridia, and
• Leber’s congenital amaurosis.
• Other causes include, bilateral congenital cataract, achromatopsia, congenital stationary night blindness, bilateral  optic nerve hypoplasia, bilateral congenital toxoplasmosis and bilateral macular hypoplasia.
Characteristic features. It is characterized by erratic waveform with or without roving eye movements associated with reduced visual acuity due to above mentioned conditions.
CEMAS criteria for INS includes: • Infantile onset,
• Ocular motor recordings show accelerating slow phases (diagnostic)
• Wave forms may change in early infancy,
• Head posture usually evident by 4 years of age.
• Vision prognosis dependent on integrity of sensory system.
Common associated findings:
• Progression from pendular to jerk, • Family history often positive,
• Null and neutral zones present, and
360	Section III   Diseases of Eye


• May decrease with induced convergence, increased fusion, extraocular muscle surgery, contact lenses, and sedation.
2. Fusion maldevelopment nystagmus syndrome (FMNS) is the new name for the old term-‘latent/ latent manifest nystagmus’ as described in CEMAS.
Characteristic features are: • Infantile onset
• Associated strabismus. May be associated with congenital esotropia and dissociated vertical deviation (DVD).
• Intensity decrease with age
• Nystagmus is not present, when both eyes are open. It appears when one eye is covered. Becomes manifest under monocular viewing conditions, i.e., in the presence of decreased vision in one eye as in anisometropic amblyopia, strabismic amblyopia, etc.
• It is a jerk nystagmus with rapid phase towards the uncovered eye. Low–amplitude pendular nystagmus (dual-jerk waveform), jerk in direction of fixing eye.
Note. While testing visual acuity in such patients, one eye should be fogged (by adding plus lenses in front) rather than occluding to minimize induction of latent nystagmus.
3. Spasmus Nutans syndrome (SNS) is the 3rd most common nystagmus seen in infancy.
Characteristic features include: • Infantile onset
• Abnormal head posture and head oscillation which improve (disappears) during childhood. Usually spontaneously remits clinically in 2 to 8 years, remains present with eye movement recordings.
• Normal MRI/CT scan of visual pathways.
• Ocular motility recordings-high-frequency (>10 Hz), asymmetric, variable conjugacy, pendular oscillations, small-frequency, low-amplitude oscillation.
II. Acquired nystagmus
Late onset or acquired nystagmus is usually characterized by oscillopsia, and is often associated with other neurological abnormalities. Acquired nystagmus includes:
i.  Nystagmus due to disorders of visual fixation. Also called as ‘Vision loss nystagmus’ may occur due to diseases affecting any part of the visual system from retina to visual cortex or conditions interrupting visual projection to the pons and cerebellum as below:
• Nystagmus in diseases of the retina.
• Nystagmus in diseases of the optic nerve.

• Nystagmus in diseases affecting the optic chiasma. • Nystagmus in diseases affecting the postchiasmal
visual system.
ii.  Nystagmus caused by vestibular imbalance

a. Peripheral vestibular nystagmus
Features. Conjugate horizontal jerk nystagmus with fast phase away from the side of lesion. Nystagmus improves with fixation and worsens with gaze towards fast phase.
Causes. It is associated with destructive lesions of vestibular system such as labyrinthitis and vestibular neuritis.
b. Central vestibular nystagmus It may be of the following types:
1. Up beat nystagmus. In primary position of gaze, the fast component is upward. It is usually seen in lesions of central tegmentum of brainstem.
2. Down beat nystagmus. In primary position of gaze the fast component is downward. It is usually associated with posterior fossa diseases and is typical of compression at the level of foramen magnum. It is a common feature of cerebellar lesions and Arnold Chiari syndrome.
Causes. It is usually associated with brainstem and cerebellar diseases.
3. See-saw nystagmus
Features. In it, one eye rises up and intorts, while other shifts down and extorts.
Causes.It is usually associated with upper brainstem lesions.
4. Periodic alternating nystagmus
Features. Conjugate, horizontal jerk nystagmus present in the primary gaze characterized by spontaneous direction changes every 60–90 seconds, with 10-15 second gap or null period, i.e., period of no nystagmus.
Causes. It occurs usually due to vestibulo-cerebellar diseases such as demyelination and Arnold Chiari malformation. It may also be associated with cervicomedullary junction lesions.
iii.  Nystagmus due to disorders of gaze holding
1. Gaze-evoked nystagmus
Features. Slow, conjugate horizontal jerk nystagmus in the direction of gaze (no nystagmus in primary gaze). It occurs at smaller angles than physiological end-gaze nystagmus, i.e., around 45° movement. Causes. It may occur due to:
• Neurological lesions of brainstem and posterior fossa, and
• CNS depression caused by certain drugs such as alcohol, anticonvulsants, and barbiturates.
Chapter 14	Disorders of Ocular Motility	361


2. Dissociated or disconjugate nystagmus (Ataxic nystagmus)
Features. It is special type of pathologic gaze evoked nystagmus which is unilateral or asymmetric nystagmus usually of the abducting and occasionally of the adducting eye.
Causes. It commonly occurs with internuclear ophthalmoplegia (INO)
3. Convergence retraction syndrome
Features. It is a jerk nystagmus with bilateral fast component towards the medial side. It is associated with retraction of the globe in convergence.
Causes. Classically associated with pinealoma, but may also occur with other neoplasms, stroke, trauma or multiple sclerosis.
4. Brun’s nystagmus.
Tumours in the cerebello-pontine angle, produce a low-frequency, large amplitude nystagmus, when the patient looks towards the side of the lesion, and a high-frequency, small-amplitude nystagmus, when the patient looks toward the side opposite to the lesion. The nystagmus that occurs on gaze towards the side of the lesion is gaze-evoked nystagmus caused by defective gaze holding, whereas the nystagmus that occurs during gaze towards the side opposite the lesion is caused by vestibular imbalance. This is called Brun’s nystagmus.
5. Centripetal and rebound nystagmus.
If a patient with gaze-evoked nystagmus attempts to look eccentrically for a sustained period, the nystagmus begins to decrease in amplitude and may even reverse the direction, this is called centripetal nystagmus. If the eyes are then returned to the central position, a short-lived nystagmus with slow drifts in

the direction of the prior eccentric gaze occurs. This is called rebound nystagmus. Both centripetal and rebound nystagmus reflect an attempt by brainstem or cerebellar mechanisms to correct for the drift of gaze-evoked nystagmus.
Causes of rebound nystagmus include: • Cerebellar diseases,
• Lateral medullary infarction, and
• Tumours confined to the flocculus.
iv. Acquired pendular nystagmus
• Usually disconjugate with horizontal, vertical and torsional components.
• May be associated with involuntary, repetitive movements  of  palate,  pharynx  and  face (oculopalatal myoclonus).

NYSTAGMOID MOVEMENTS
These are ocular movements which mimic nystagmus. These include:
1. Ocular flutter occurs due to interruption of cerebellar connection to brainstem. It is characterized by horizontal oscillation and inability to fixate after change of gaze.
2. Opsoclonus refers to combined horizontal, vertical and/or torsional oscillations associated with myoclonic movement of face, arms and legs. It is seen in patients with encephalitis.
3. Superior oblique myokymia is characterized by monocular, rapid, intermittent, torsional and vertical movements (which are best seen on slit-lamp examination).
4. Ocular bobbingrefers to rapid downward deviation of the eyes with slow updrift. It occurs due to pontine dysfunctions.
15

Disorders of Eyelids



CHAPTER OUTLINE

APPLIED ANATOMY Gross anatomy Structure
Glands of eyelids Blood supply Nerve supply
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CONGENITAL ANOMALIES OEDEMA OF EYELIDS
INFLAMMATORY DISORDERS OF EYELIDS Blepharitis
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External hordeolum (stye) Chalazion
Internal hordeolum Molluscum contagiosum
EYELASH DISORDERS Trichiasis
•



APPLIED ANATOMY
GROSS ANATOMY
The eyelids are mobile tissue curtains placed in front of the eyeballs (Fig. 15.1). These act as shutters protecting the eyes from injuries and excessive light. These also perform an important function of spreading the tear film over the cornea and conjunctiva and also help in drainage of tears by lacrimal pump system.
Parts of eyelid. Each eyelid is divided by a horizontal furrow (sulcus) into an orbital and tarsal part. Position of lids. When the eye is open, the upper lid covers about one-sixth of the cornea and the lower lid just touches the limbus.
Canthi. The two lids meet each other at medial and lateral angles (or outer and inner canthi). In Caucasians with the lids open, the lateral canthus is about 2 mm higher than the medial canthus. Palpebral aperture. It is the elliptical space between the upper and the lower lid. When the eyes are open it measures about 10–11 mm vertically in the centre and about 28–30 mm horizontally.

• Distichiasis Madarosis
ANOMALIES IN THE POSITION OF LID MARGINS Entropion
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Ectropion Symblepharon Ankyloblepharon Blepharophimosis Lagophthalmos Blepharospasm Ptosis
Lid retraction TUMOURS OF EYELIDS
•
•
•
Benign tumours Premalignant tumours
Malignant tumours














Fig. 15.1 Gross anatomy of the eyelid


Lid margin. It is about 2 mm broad and is divided into two parts by the punctum. The medial, lacrimal portion is rounded and devoid of lashes or glands.
The lateral, ciliary portion consists of a rounded anterior border, a sharp posterior border (placed against the globe) and an intermarginal strip (between the two borders). The grey line (which marks junction of skin and conjunctiva) divides the intermarginal strip into an anterior strip bearing
Chapter 15	Disorders of Eyelids	363


2–3 rows of lashes and a posterior strip on which openings of meibomian glands are arranged in a row. The splitting of the eyelids when required in operations is done at the level of grey line.
STRUCTURE
Each eyelid consists (from anterior to posterior) of the following layers (Fig. 15.2):
1. Skin. It is elastic having a fine texture and is the thinnest in the body.
2. Subcutaneous areolar tissue. It is very loose and contains no fat. It is thus readily distended by oedema or blood.
3. Layer of striated muscle. It consists of orbicularis muscle which forms an oval sheet across the eyelids. It comprises three portions: the orbital, palpebral (pretarsal and preseptal parts) and lacrimal. It closes the eyelids and is supplied by zygomatic branch of the facial nerve. Therefore, in paralysis of facial nerve there occurs lagophthalmos which may be complicated by exposure keratitis.
In addition, the upper lid also contains levator palpebrae superioris muscle (LPS). It arises from the apex of the orbit and is inserted by three parts on the skin of lid, anterior surface of the tarsal plate and conjunctiva of superior fornix. It raises the upper lid. It is supplied by a branch of oculomotor nerve. 4. Submuscular areolar tissue. It is a layer of loose connective tissue. The nerves and vessels lie in this layer. Therefore, to anaesthetise lids, injection is given in this plane.
5. Fibrous layer. It is the framework of the lids and consists of two parts: the central tarsal plate and the peripheral septum orbitale (Fig. 15.3).
i. Tarsal plate. There are two plates of dense connective tissue, one for each lid, which give shape

















Fig. 15.2 Structure of the upper eyelid












Fig. 15.3 Tarsal plates and septum orbitale

and firmness to the lids. The upper and lower tarsal plates join with each other at medial and lateral canthi; and are attached to the orbital margins through medial and lateral palpebral ligaments. In the substance of the tarsal plates lie meibomian glands in parallel rows.
ii. Septum orbitale (palpebral fascia). It is a thin membrane of connective tissue attached centrally to the tarsal plates and peripherally to periosteum of the orbital margin. It is perforated by nerves, vessels and levator palpebrae superioris (LPS) muscle, which enter the lids from the orbit.
6. Layer of non-striated muscle fibres. It consists of the palpebral muscle of Muller which lies deep to the septum orbitale in both the lids. In the upper lid it arises from the fibres of LPS muscle and in the lower lid from prolongation of the inferior rectus muscle; and is inserted on the peripheral margins of the tarsal plate. It is supplied by sympathetic fibres.
7. Conjunctiva. The part which lines the lids is called palpebral conjunctiva. It consists of three parts: marginal, tarsal and orbital. (For structures of conjunctiva see page 60).
GLANDS OF EYELIDS (FIG. 15.4)
1. Meibomian glands. These are also known as tarsal glands and are present in the stroma of tarsal plate arranged vertically. They are about 30–40 in the upper lid and about 20–30 in the lower lid. They are modified sebaceous glands. Their ducts open at the lid margin. Their secretion constitutes the oily layer of tear film.
2. Glands of Zeis. These are also sebaceous glands which open into the follicles of eyelashes.
3. Glands of Moll. These are modified sweat glands situated near the hair follicle. They open into the hair follicles or into the ducts of Zeis glands. They do not open directly onto the skin surface as elsewhere. 4. Accessory lacrimal glands of Wolfring. These are present near the upper border of the tarsal plate.
364	Section II   Diseases of Eye



















Fig. 15.4 Glands of eyelids

BLOOD SUPPLY
Arteries of the lids (medial and lateral palpebral) form marginal arterial arcades which lie in the submuscular plane in front of the tarsal plate, 2 mm away from the lid margin, in the upper lid and about 4 mm away in the lower lid. In the upper lid another arcade (superior arterial arcade) is formed which lies near the upper border of the tarsal plate. Branches go forward and backward from these arches to supply various structures.
Veins. These are arranged in two plexuses: a post-tarsal which drains into ophthalmic veins and a pre-tarsal opening into subcutaneous veins. Lymphatics. These are also arranged in two sets: the pre-tarsal and the post-tarsal. Those from lateral half of the lids drain into preauricular lymph nodes and those from the medial half of the eyelids drain into submandibular lymph nodes.
NERVE SUPPLY
Motor nerves are facial (which supplies orbicularis muscle), oculomotor (which supplies LPS muscle) and sympathetic fibres (which supply the Muller’s muscle).
Sensory nerve supply is derived from branches of the trigeminal nerve such as lacrimal, supraorbital and supratrochlear nerves for upper lid; and the infraorbital nerve with infratrochlear branch for lower lid.

CONGENITAL ANOMALIES

1. Congenital ptosis. It is a common congenital anomaly. It is described in detail in the section of ptosis on page 379.

2. Congenital coloboma. It is a rare condition characterised by a full thickness triangular gap in the tissues of the lids (Fig. 15.5). The anomaly usually occurs near the nasal side and involves the upper lid more frequently than the lower lid. Treatment consists of plastic repair of the defect.
3. Epicanthus. It is a semicircular fold of skin which covers the medial canthus. It is a bilateral condition and may disappear with the development of nose. It is a normal facial feature in Mongolian races. It is the most common congenital anomaly of the lids. Treatment consists of plastic repair of the deformity. 4. Distichiasis. (see page 371)
5.Cryptophthalmos. It is a very rare anomaly in which lids fail to develop and the skin passes continuously from the eyebrow to the cheek hiding the eyeball (Fig. 15.6).
6. Microblepharon. In this condition, eyelids are abnormally small. It is usually associated with microphthalmos or anophthalmos. Occasionally, the lids may be very small or virtually absent and the condition is called ablepharon.
7. Epiblepharon refers to a congenital anomaly in which a horizontal fold of tissue rides above the lower eyelid margin. It usually disappears with the growth of face and needs no surgical correction.
8. Euryblepharon refers to unilateral or bilateral horizontal widening of palpebral fissure. It is usually associated with lateral canthal malposition and lateral ectropion. Congenital euryblepharon usually involves the lateral portion of lower eyelids.

OEDEMA OF EYELIDS

Owing to the looseness of the tissues, oedema of the lids is of common occurrence. It may be classified as inflammatory, solid and passive oedema.















Fig. 15.5 Congenital coloboma upper eyelid
Chapter 15	Disorders of Eyelids	365

















Fig. 15.6 Cryptophthalmos

I. Inflammatory oedema. It is seen in the following conditions.
1. Inflammations of the lid itself, which include dermatitis, stye, hordeolum internum, insect bites, cellulitis and lid abscess.
2. Inflammations of the conjunctiva, such as acute purulent, membranous and pseudomembranous conjunctivitis.
3. Inflammations of the lacrimal sac, i.e., acute dacryocystitis and lacrimal abscess.
4. Inflammations of the lacrimal gland, i.e., acute dacryoadenitis.
5. Inflammations of the eyeball, such as acute irido-cyclitis, endophthalmitis and panophthalmitis.
6. Inflammations of the orbit, which include orbital cellulitis, orbital abscess and pseudotumour.
7. Inflammations of the paranasal sinuses, e.g., maxillary sinusitis.
II. Solid oedema of the lids. It is chronic thickening of the lids, which usually follows recurrent attacks of erysipelas. It resembles inflammatory oedema of the lids but is harder in consistency.
III. Passive oedema of the lids. It may occur due to local or general causes.
1. Local causes are: cavernous sinus thrombosis, head injury and angioneurotic oedema.
2. General causes are congestive heart failure, renal failure, hypoproteinaemia and severe anaemia.

INFLAMMATORY DISORDERS OF EYELIDS
BLEPHARITIS
Blepharitis is a subacute or chronic inflammation of the lid margins. It is an extremely common disease which can be divided into following clinical types:

• Bacterial blepharitis,
• Seborrhoeic or squamous blepharitis,
• Mixed staphylococcal with seborrhoeic blepharitis, • Posterior blepharitis or meibomitis, and
• Parasitic blepharitis.

Bacterial Blepharitis
Bacterial blepharitis, also known as chronic anterior blepharitis, or staphylococcal blepharitis or ulcerative blepharitis, is a chronic infection of the anterior part of the lid margin. It is a common cause of ocular discomfort and irritation. The disorder usually starts in childhood and may continue throughout life.
Etiology
Causative organisms, most commonly involved are coagulase positive Staphylococci. Rarely, Streptococci, Propionibacterium acnes, and Moraxella may be involved.
Predisposing factors, usually none, may rarely include chronic conjunctivitis and dacryocystitis.
Clinical features
Symptoms include chronic irritation, itching, mild lacrimation, gluing of cilia, and mild photophobia. The symptoms are characteristically worse in the morning. Remissions and exacerbations in symptoms are quite common.
Signs (Fig. 15.7) are as below:
• Yellow crusts are seen at the root of cilia which glue them together.
• Small ulcers, which bleed easily, are seen on removing the crusts.
• Red, thickened lid margins are seen with dilated blood vessels (rosettes).
• Mild papillary conjunctivitis and conjunctival hyperemia are common associations.
Complications and sequelae of long standing bacterial blepharitis include:
• Lash abnormalities such as madarosis (sparseness or absence of cilia), trichiasis (misdirected cilia), and poliosis (graying of lashes).












Fig. 15.7 Bacterial blepharitis
366	Section II   Diseases of Eye


• Tylosis, i.e., thickening and scarring of lid margin. • Eversion of punctum leading to epiphora.
• Eczema of skin and ectropion may develop due to prolonged watering.
• Recurrent styes (external hordeola) are a common complication.
• Marginal keratitis, and occasionally phlyctenulosis may develop.
• Tear film instability, and dry eye may result.
• Secondary inflammatory and mechanical changes in the conjunctiva and cornea are common because of intimate relationship between the lid margins and ocular surface.
Treatment
Bacterial blepharitis should be treated promptly, as below, to avoid complications and sequelae:
1. Lid hygiene is essential at least twice daily and should include:
• Warm compresses for 5–10 minutes to soften the crusts,
• Crust removal and lid margin cleaning with the help of cotton buds dipped in the dilute baby shampoo or solution of 3% sodium bicarbonate.
• Avoid rubbing of the eyes or fingering of the lids. 2. Antibiotic should be used as below:
• Eye ointment should be applied at the lid margin, immediately after removal of the crusts.
• Antibiotic eye dropsshould be used 3–4 times a day. • Oral antibiotics such as erythromycin or doxycycline may be useful in unresponsive patients and those complicated by external hordeola and abscess of
lash follicle.
3. Topial steroids (weak) such as fluoromethalon may be required in patients with papillary conjunctivitis, marginal keratitis and phlyctenulosis.
4. Ocular lubricants, i.e., artificial tear drops, are required for associated tear film instability and dry eye.

Seborrhoeic or Squamous Blepharitis Seborrhoeic blepharitis is primarily anterior blepharitis with some spill over posteriorly. It is of common occurrence.
Etiology. It is usually associated with seborrhoea of scalp (dandruff). Some constitutional and metabolic factors play a part in its etiology. In it, glands of Zeis secrete abnormal excessive neutral lipids which are split by Corynebacterium acne into irritating free fatty acids.
Symptoms. Patients usually complain of deposition of whitish material (soft scales) at the lid margin associated with mild discomfort, irritation, occasional watering and a history of falling of eyelashes.

Signs include:
• Accumulation of white dandruff-like scales is seen on the lid margin, among the lashes (Fig. 15.8). On removing these scales underlying surface is found to be hyperaemic and greasy (no ulcers).
• The lashes fall out easily but are usually replaced quickly without distortion.
• Lid margin is thickened and the sharp posterior border tends to be rounded leading to epiphora, in long standing cases.
• Signs of bacterial blepharitis, as described above, may be superadded in patients with mixed seborrhoeic and bacterial blepharitis.
Complications are similar to bacterial blepharitis with comparatively lesser frequency (see page 365). Treatment includes:
• General measures include improvement of health and balanced diet.
• Associated seborrhoea of the scalp should be adequately treated.
• Local measures include removal of scales from the lid margin with the help of lukewarm solution of 3% soda bicarb or baby shampoo and frequent application of combined antibiotic and steroid eye ointment at the lid margin.
• Antibiotics, as described above in bacterial blepharitis, may be required in patients with mixed seborrhoeic and bacterial blepharitis.

Posterior Blepharitis (Meibomitis) Meibomitis, i.e., inflammation of Meibomian glands occurs in chronic and acute forms.
1. Chronic meibomitis
Chronic meibomitis is a commonly occurring meibomian gland dysfunction, seen more commonly in middle aged persons, especially those with acne rosacea and/or seborrhoeic dermatitis. Bacterial lipases are being blamed to play main role in the pathogenesis of chronic meibomitis.













Fig. 15.8 Seborrhoeic blepharitis
Chapter 15	Disorders of Eyelids	367


Clinical features
Symptoms include chronic irritation, burning, itching, grittiness, mild lacrimation with remissions and exacerbations intermittently. Symptoms are characteristically worse in the morning.
Signs include (Fig. 15.9):
• White frothy (foam like) secretions are frequently seen on the eyelid margins and canthi (meibomian seborrhoea).
• Opening of meibomian glands become prominent with thick secretions which can be expressed out by pressure on the lids giving toothpaste appearance. Meibomian gland orifices may also show capping with oil globules, pouting, recession, or plugging.
• Vertical yellowish streaks shining through conjunctiva can be seen on eversion of the lids. These represent the meibomian ducts filled with thick secretion.
• Hyperemia and telangiectasia of posterior lid margin around the orifices of meibomian glands can be seen frequently.
• Oily and foamy tear film with accumulation of froth on the lid margins or inner canthus.
• Secondary changes in the form of papillary conjunctivitis, and inferior corneal punctate epithelial erosions may be seen.
2. Acute meibomitis
Acute meibomitis occurs due to staphylococcal infection. It is characterized by painful swelling around the involved gland. Pressure on it results in expression of pus bead followed by serosanguinous discharge.
Treatment of meibomitis
1. Lid hygiene is essential at least once a day and should include:
• Warm compresses for several minutes.
• Expression of accumulated secretions by repeated vertical massage of lids in the form of milking.












Fig. 15.9 Chronic meibomitis

2. Topical antibiotics in the form of eye ointment should be rubbed at the lid margin immediately after massage, and
• Eye drops may be used 3–4 times a day.
3. Systemic tetracyclines, e.g., doxycycline 100 mg b.d. for 1 week and then o.d. for 6–12 weeks, remain the mainstay of treatment of posterior blepharitis because of their ability to block staphylococcal lipase production. Erythromycin may be used where tetracyclines are contraindicated.
4. Ocular lubricants i.e., artificial tear drops are required for associated tear film instability and dry eye disease.
5. Topical steroids(weak) such as fluoromethalon may be required in patients with papillary conjunctivitis.

Parasitic Blepharitis (Lash Infestation)
Etiology
Blepharitis associated with infestation of lashes by lice is not uncommon in persons living in poor hygienic conditions. The lice infestations include the following:
• Phthiriasis palpebrum refers to the infestation by phthirus pubis (crab louse). It is most commonly seen in adults in whom it is usually acquired as a sexually transmitted infection.
• Pediculosis refers to the infestation by pediculus humanus corporis or capitis(head louse). If heavily infested the lice may spread to involve lashes.
Clinical features
Infestation of lashes with lice causes chronic blepharitis and chronic follicular conjunctivitis. Symptoms includechronicirritation,itching,burning, and mild lacrimation.
Signs are as below (Fig. 15.10):
• Lid margins are red and inflamed.
• Lice anchoring the lashes with their claws may be seen on slit-lamp examination.
• Nits (eggs) may be seen as opalescent pearls adherent to the base of cilia.
• Conjunctival congestion and follicles may be seen in long standing cases.
Treatment
• Mechanical removal of the lices and nits with forceps.
• Application of antibiotic ointment and yellow mercuric oxide 1% to the lid margins and lashes.
• Delousing of the patient, family members, clothing and bedding is important to prevent recurrences.
EXTERNAL HORDEOLUM (STYE)
It is an acute suppurative inflammation of lash follicle and its associated glands of Zeis or Moll.
368	Section II   Diseases of Eye














Fig. 15.10 Phthiriasis palpebrum

Etiology
1. Predisposing factors are as below:
• Age. It is more common in children and young adults (though no age is bar) and in patients with eye strain due to muscle imbalance or refractive errors.
• Habitual rubbing of the eyes or fingering of the lids and nose, chronic blepharitis and diabetes mellitus are usually associated with recurrent styes.
• Metabolic factors, chronic debility, excessive intake of carbohydrates and alcohol also act as predisposing factors.
2. Causative organism commonly involved is staphylococcus aureus.
Clinical features
Symptoms include acute pain associated with swelling of lid, mild watering and photophobia. Signs are as follows:
• Stage of cellulitis is characterised by localised, firm, red, tender swelling at the lid margin associated with marked oedema (Fig. 15.11). Usually, there is one stye, but occasionally, these may be multiple.
• Stage of abscess formation is characterised by a visible pus point on the lid margin in relation to the affected cilia.
Treatment
• Hot compresses 2–3 times a day are very useful especially in cellulitis stage.
• Evacuation of the pus should be done by epilating the involved cilia, when the pus point is formed.
• Surgical incision is required rarely for a large abscess.
• Antibiotic eye drops (3–4 times a day) and eye ointment (at bed time) should be applied to control the infection.
• Systemic anti-inflammatory and analgesics relieve pain and reduce oedema.
• Systemic antibiotics should be used for early control of infection.

Fig. 15.11 Hordeolum externum (stye) upper eyelid

• In recurrent styes, try to find out and treat the associated predisposing condition.
CHALAZION
Chalazion, also called a tarsal or meibomian cyst, is a chronic non-infective (non-suppurative) lipogranulomatous inflammation of the meibomian gland. This is the commonest of all lid lumps.
Etiology
1. Predisposing factors are similar to hordeolum externum.
2. Pathogenesis. Usually, first there occurs mild grade infection of the meibomian gland by organisms of very low virulence. As a result, there occurs proliferation of the epithelium and infiltration of the wallsofthe ducts, which are blocked. Consequently, there occurs retention of secretions (sebum) in the gland, causing its enlargement. The pent-up and extravasated secretions (fatty in nature) act like an irritant and excite non-infective lipogranulomatous inflammation of the blocked meibomian glands and surrounding tissue.
Clinical features Symptoms include:
• Painless swelling in the eyelid, gradually increasing in size is the main presenting symptom.
• Mild heaviness in the lid may be felt with moderately large chalazion.
• Blurred vision may occur occasionally due to induced astigmatism by a very large chalazion pressing on the cornea.
• Watering (epiphora) may occur sometimes due to eversion of lower punctum caused by a large chalazion of the lower eyelid.
Signs include:
• Nodule is noted slightly away from the lid margin (Fig. 15.12) which is firm to hard and non-tender on palpation. Upper lid is involved more commonly than the lower lid probably because of
Chapter 15













Fig. 15.12 Chalazion upper eyelid

Disorders of Eyelids	369













Fig. 15.13 Incision and curettage of chalazion from the conjunctival side



the fact that upper lid contains more meibomian glands than the lower lid. Frequently multiple chalazia may be seen.
• Reddish purple area, where the chalazion usually points, is seen on the palpebral conjunctiva after eversion of the lid.
• Projection of the main bulk of the swelling on the skin side may be seen rarely instead of conjunctival side.
• Marginal chalazion, occurring occasionally, may present as small reddish grey nodule on the lid margin.
Clinical course and complications
• Complete spontaneous resolution may occur rarely. • Slow increase in size is often seen and eventually
it may become very large.
• Fungating mass of granulation tissue may be formed occasionally when the lesion bursts on the conjunctival side.
• Secondary infection may lead to formation of hordeolum internum.
• Calcification may occur, though very rarely.
• Malignant  change into meibomian gland adenocarcinoma (sebaceous cell carcinoma) may be seen occasionally in elderly people.
Treatment
1. Conservative treatment. In a small, soft and recent chalazion, self-resolution may be helped by conservative treatment in the form of hot fomentation, topical antibiotic eyedrops and oral anti-inflammatory drugs.
2. Intralesional injection of long-acting steroid (triamcinolone) is reported to cause resolution in about 50% cases, especially in small and soft chalazia of recent onset, located near the puncta, where incision and curettage may cause damage. 3.Incision and curettage(Fig. 15.13) is the conventional and effective treatment for chalazion.

• Surface anaesthesia is obtained by instillation of xylocaine drops in the eye and the lid in the region of the chalazion is infiltrated with 2% xylocaine solution.
• Incision is made with a sharp blade, which should be vertical on the conjunctival side (to avoid injury to other meibomian ducts) and horizontal on skin side (to have an invisible scar).
• Contents are curetted out with the help of a chalazion scoop.
• Carbolic acid cautery followed by neutralization with methylated spirit should be preformed in the cavity to avoid recurrence.
• Patching of eye should be done, after instilling antibiotic eye ointment, for about 6 to 12 hours.
• Postoperative treatment, to decrease discomfort and prevent infection, should be given in the form of hot fomentation, antibiotic eyedrops, oral anti-inflammatory, analgesics and oral antibiotics for 4-5 days.
4. Diathermy. A marginal chalazion is better treated by diathermy.
5. Oral tetracycline should be given as prophylaxis in recurrent chalazia, especially if associated with acne rosacea or seborrhoeic dermatitis.
Note. In recurrent chalazion malignancy should be ruled out.
INTERNAL HORDEOLUM
It is a suppurative inflammation of the meibomian gland associated with blockage of the duct.
Etiology
Predisposing factors are similar to hordeolum externum (see page 368).
Causative mechanism. Hordeolum internum may occur as:
• Primary Staphylococcal infectionof the meibomian gland or due to
370	Section II   Diseases of Eye


• Secondary infection in a chalazion (infected chalazion).
Clinical features
Symptoms include acute pain associated with swelling of the lid, mild watering and photophobia. Thus, the symptoms are similar to hordeolum externum, except that pain is more intense, due to the swelling being embedded deeply in the dense fibrous tissue.
Signs include a localized, firm, red, tender swelling of the lid associated with marked oedema. On examination,  hordeolum  internum  can  be differentiated from hordeolum externum by the fact that in it, the point of maximum tenderness and swelling is away from the lid margin and that pus usually points on the tarsal conjunctiva (seen as yellowish area on everting the lid) and not on the root of cilia (Fig. 15.14). Sometimes, pus point may be seen at the opening of involved meibomian gland or rarely on the skin.
Treatment
It is similar to hordeolum externum (see page 368), except that, when pus is formed, it should be drained by a vertical incision from the tarsal conjunctiva.
MOLLUSCUM CONTAGIOSUM