Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

2. Orthoptic treatment. The fusion is the factor that keeps the eyes in alignment in heterophoria. When the eye becomes decompensated, improvement of fusional divergence (relative negative convergence) is desired.

They consist of

(i) Divergence exercises on synoptophore (ii) Home stereogram exercise

(iii) Bar reading in case of convergence excess.

3.Prism may sometimes reduce symptoms. Children using glasses accept prisms better than those who do not use spectacles. Fresnel prism may be pasted over the spectacle glasses for temporary use.

4.Surgery is seldom required.

Exophoria

Here the eyes diverge on dissociation.

Types of exophoria

1.Convergence weakness—Here exophoria is greater for near than distance.

2.Divergence excess—Here exophoria is greater for distance than near.

3.In between the two—There is not much difference between near and distant deviation.

Exophoria should be differentiated from intermittent exotropia. Exophoria rarely measures more than 20 prism dioptres while in case of intermittent exotropia the measurement is more. Intermittent exotropia develop suppression hence they do not develop diplopia and become manifest.

Management

In children treatment is required only if the eye has tendency to become exotropic. Here also first step is to correct any error of refraction under cycloplegia followed by orthoptic treatment.

Hyperphoria

This is a vertical phoria, less common than horizontal phorias. However a combination of vertical phoria associated with horizontal phoria is common. As vertical fusional amplitude is relatively less, asthenopic symptoms are more in vertical phoria. Even a deviation of 2-4 prism diopters produces sufficient symptoms. The treatment is prescription of prism with base down in case of hyperphoria and base up in case of hypophoria. Strength of the prism is equally divided in two eyes. It is better only to neutralize one third to half of deviation by prism7. Surgery is indicated in large deviation with paretic element.

Dissociated vertical divergence (DVD) is also a type of hyper deviation and called double hyperphoria.

Cyclophoria

This is rarest form of latent squint with profound symptoms and is most missed type of phoria unless specifically looked for and eye is examined by Maddox wing, Maddox double rod,

and Maddox double prism. In this case the eyes have tendency to rotate along anterio-posterior axis. Excyclophoria is more common than incyclophoria. It is generally associated with vertical phoria.

Treatment is directed toward treatment of vertical phoria.

Manifest squint (Heterotropia)

Heterotropia is that state of muscle imbalance in which one of the eyes deviates in relation to the other eye. This can be :

1.Concomitant squint

2.Incominant (non comitant) squint

(a) Paralytic squint (b) Restrictive

(c) Kinetic8

Kinetic strabismus is a rare, often missed clinical condition, is due to irritative intracranial pathology resulting in unequal stimulation of nerves, nerve centres or muscles.

Concomitant squint

Characteristics of concomitant squint :

1.It is a visible diviation deviation.

2.The deviation is present most of the time.

3.The deviation may vary for distance and near.

4.The object is fixed by one eye at a time.

5.The fixation may alternate between two eyes.

6.The angle of squint remains constant in all directions of gaze.

7.The ocular movements are normal in all direction.

8.The squint may be mono-ocular or alternate.

Etiology of concomitant squint are the same as in latent except that there is a permanent break down of the fusion. Any eye can have concomitant squint -

1.As primary disorder—The deviation starts without being latent.

2.Latent squint getting so much decompensated that the eyes fail to revert to orthophoria.

Phoria → Intermittent tropia → Constant tropia

3.Spread of comitance in case of congenital squint.

Duane9 has divided squint into two basic types :

—Near dysfunction—Medial rectus dysfunction

—Distance dysfunction lateral rectus dysfunction.

This is based on the fact that medial recti are responsible for near and convergence and lateral recti are responsible for distance and divergence.

The etiological factors are :

1.Congenital—Mal-origin or insertion of one or more extra ocular muscles. There may be under development of muscle/muscles.

2.Defective vision in one eye due to any cause i.e. opacity in media, optic atrophy, macular lesion, ptosis, error of refraction.

3.Defective vision in both eyes—More in one than the other, the eye with less vision is more likely to squint.

4.Dissociation between accommodation and convergence - This is one of the most common causes of squint in children.

(a) Hypermetropia—In moderate degree of hypermetropia, the eye accommodates more to see clearly. This stimulates convergence as well as produces convergent squint.

(b) Myopia—An acquired myopic eye does not require accommodation for clear vision hence there is reduced convergence and the eye deviates out.

A child with congenital myopia has a very short far point, and can see only near object. To see near things he has to converge more than an emmetrope of same age, this results in convergent squint.

5.Deficient fusional power

6.Secondary change in paretic muscle

A child born with paralysis of one of the muscles, may recover over a period of time, but its direct antagonist develops contracture and under action of muscle that was limited to one gaze only, spreading to all directions of gaze.

7.Heredity—About 10% of squint have family history.

Types of heterotropia

Heterotropia can be unilateral (monocular) or alternate. Unilateral heterotropia is more common than alternate. A squint is said to be unilateral when one the eyes squints constantly and the other eye fixes. If the fixing eye is covered, the squinting eye takes up the fixation and the fixing eye deviates under cover. In both eyes the angle of squint is equal. As soon as the cover is removed the previously covered eye takes up fixation and the other eye squints.

In alternate squint when the fixing eye is covered, the squinting eye deviates under cover and remains deviated when the cover is removed. The angle of deviation is equal in both eyes. The vision in both eyes is almost the same and loss of vision is not much. Generally both the eyes are emmetropic. Even if there is any error of refraction present, it is of low grade. Alternate esotropia is more common than exotropia. The alternating eyes lack all the grade of vision.

According to direction of deviation, the eye can be esotropic, exotropic, hypertropic or rarely cyclotropic.

Diagnosis of heterotropia

Diagnosis of well established moderate manifest squint is simple. In fact the parents bring the child for complaints of squint. The child is generally unaware of squint. Once the child becomes aware especially the teenagers, they try to hide the cosmetic blemish keeping a downward gaze.

1.Examination of distant vision should get preference over all other examination and whenever there is diminished vision in any of the two eyes, the cause of the diminished vision should be determined by refraction, examination of anterior segment and fundus examination. Diminished vision in the squinting is common but the other eye too may have diminished vision due to same error of refraction or different errors of refraction may exist between the two eyes. There may be difference in vision in two eyes due to other causes.

2.The next step is to find out if the squint is real or pseudo squint.

3.Once pseudo squint has been ruled out, the next step is to exclude possibility of paralytic squint.

4.The above test leaves with only diagnosis i.e. concomitant squint that should be examined under following heads :

Cover test

This is most important but often neglected test. It differentiated between

(I) Pseudo and true squint, (II) Uniocular and alternate squint and (III) Paralytic and non paralytic squint.

It should be done for distance and near.

Measurement of angle of squint

(i) Hirschberg test (Corneal reflex test). The child keeps both eyes open and fixes a distant object with normal head posture.

A bright pin-point light is directed on the squinting eye from 33 cm distance and position of the image of the light is noted. In a normal eye, it should be centred over the pupil. In squinting eye, the image is formed opposite the direction of squint i.e. if the eye is deviated medially the reflex will form on temporal side of the pupil. Each 1 mm decentering denotes

7° or 14 PD of squint.

Besides manifest squint there are some causes of decentred corneal reflex. They are :

1.Angel kappa—A positive angle kappa may look like an exodeviation and a negative angle kappa may look like esodeviation.

2.In case of eccentric fixation in an amblyopic eye the light reflex remains decentred upon covering the second eye.

3.Ectopic macula

The corneal light reflex test is done for near also.

(ii) Krimsky test (Prism reflex test). This is a better test than Hirshberg test, but Hirshberg test is only the first part of this test. In this test prism of increasing power are placed before the eye until the light reflex is centred in the deviating eye. The child should be able to fix a light with the dominant eye. It is not influenced by eccentric fixation. However there may be a confusion in presence of large angle kappa. The observer should place himself exactly in front of the child to avoid parallax from the prism. The test is suitable even in children with poor vision in one eye.

(iii) Perimeter test. This is good only for grown up children. The child sits on a Lister’s perimeter with chin on the chin rest and fixes the central white dot. The other eye is allowed

to deviate. A torch light is moved on the arc of the perimeter from periphery to the centre until the light reflex is centred on the deviating eye. The position of the torch is read on the arc of the perimeter. This gives the angle of squint in degree, which is half of prism dioptre.

(iv) The synoptophore test. This is the most accurate method to measure angle of squint for distance and near in all direction of gaze, objective and subjective angle, angle of anomaly. The synoptophore also gives away presence of ARC and its type, grades of vision, measurement of range of fusion after image testing and AC/A.

It can be used for therapeutic use also in :

1.Amblyopia treatment with Haidinger brush.

2.Management of suppression

3.Treatment of ARC

4.Fusional exercises

In manifest squint, simultaneous macular perception is absent. There may be a suppression scotoma. The size and position of which varies according to type of squint. In esotropia, a small suppression scotoma is seen on nasal side of the disc, may involve macula. In exotropia, a large suppression scotoma is seen on temporal half of the retina including the fovea.

In uniocular squint, the scotoma is constant in the squinting eye, may lead to strabismic amblyopia. In alternate squint the scotoma alternates between the two eyes.

Binocular fusion may be absent in concomitant squint so is the stereopsis. The stereopsis can be tested on various types of stereoscopes.

Test for suppression :

(i) Worth four dot test (ii) Synoptophore

(iii) Four dioptre prism test (iv) Bagolini striated glass test (v) Red glass test

Test for abnormal retinal correspondence

1.Bagolini striated glass test

2.Synoptophore

3.After image test

Horizontal concomitant squint

Classically horizontal squints are divided in -

1.Simple horizontal squint (a) Esotropia

(b) Exotropia

2.Horizontal squint associated with vertical deviation

Clinically esotropia has also been classified according to its relation with accommodation, on the basis of this esotropia can be

Congenital (Essential infantile)12,13 esotropia

This is an important type of esotropia seen under six months of age. The importance lies in the fact that it causes permanent loss of binocular vision if not treated in time and the next important factor is that many a times early onset retinoblastoma may present as esotropia in an infant. Hence all children with real esotropia should be examined by ophthalmologist.

Characteristics of infantile esotropia14

1.It is rarely present at birth. It develops between two to six months.

2.It is not possible to predict which child will develop esotropia.

3.It can be hereditary.

4.It is uniocular, may show alternate fixation.

5.Angle of squint is always large i.e. 30-40 PD.

6.The deviation is equal for far and near.

7.The child has a tendency to cross fixate i.e. the child fixes the left field with right eye and right field with left eye. This sometimes gives an impression of bilateral lateral rectus palsy. In fact inspite of being non paralytic squint, adduction is stronger than abduction in infantile esotropia.

Abduction can be demonstrated by :

(i) The fixing eye is covered, an object of interest - a feeding bottle which is the most interesting object to an infant is moved in front of the squinting eye from medial to lateral. The chances are that the child will follow it to full abduction position.

(ii) If this fails the fixing eye is occluded for few hours. The child may develop abduction or it may take two to three days of occlusion of the fixing eye.

(iii) A feeding bottle is kept straight ahead of the child, both eyes are kept open. The child is allowed to fix it, then as the child fixes it, obviously with the fixing eye the head of the child is rotated quickly in the vertical axis i.e. to the right and then to the left. This will invariably demonstrate presence of abduction.

(iv) Stimulating oculo vestibular reflex - The child is held by the examiner at an arms length, face to face. The examiner rotates himself by 360° holding the child in the same position. The child will be observed to have conjugate deviation. The rotation is than repeated in the opposite direction.

8.Dissociated vertical squint is common. It generally develops by two years. It is a bilateral condition. The eyes deviates up and rotates outward under cover. As soon as the cover is removed the eye drift down and rotated medially. DVD may develop long after successful surgery as well.

9.Inferior oblique over action - There is decrease of convergence in up gaze showing V pattern (This is absent in DVD). The condition is unilateral to begin with but may become bilateral. It is also a common feature after successful surgery and the parents should be informed and forewarned about this. Fortunately most of the parents fail to notice it. When present it requires a separate surgery.

10.Unilateral superior oblique paresis15 may be present. The incidence is less than inferior oblique over action and DVD.

11.Nystagmus16 may be latent or manifest, resulting in abnormal head posture—To locate null point of nystagmus, to get better vision, convergence may be utilised to reduce nystagmus.

12.Vision is generally good. Amblyopia is common but may not develop in an alternator.

13.Refractive error—The child has low degree of hypermetropia. Refraction should always be tested under atropine.

14.There is no neurological defect.

Differential diagnosis

Differential diagnosis consists of accommodative squint, unilateral abducent palsy, Duane’s retraction syndrome, high AC/A ratio, nystagmus blocking syndrome, unilateral blind eye, incomplete Mobius syndrome, albinism, cerebral palsy.

Variants

1.Congenital esotropia syndrome consists of esotropia with other muscle malfunction i.e. SO over action, DVD, V syndrome etc.

2.Ciancia syndrome consists of (a) Esotropia

(b) Bilateral abduction defect

3.Manifest nystagmus that is latent.

4.Abnormal head posture

5.Lang’s syndrome. This consists of : (a) Torticollis

(b) DVD

(c) Nystagmus

(d) Excyclodeviation

(e) Early onset esotropia

Management

Management is essentially surgical. However before embarking upon surgery :

1.Any error of refraction should be corrected. Commonest error of refraction is low grade of hypermetropia. Refraction should always be done under atropine with usual precaution. If error of refraction turns out to be more than +3D, an accommodative factor should be considered. It is better to make the child slightly myopic.

2.Management of amblyopia by standard method.

I.Conventional—Full time complete occlusion by eye pad of the fixing eye. The duration should be 1 day for every year between two years to six years. Upto two years 2 days of occlusion is done.

II.Alternate occlusion—One day of occlusion of amblyopic eye i.e. in a three year child, the fixing eye is occluded for 3 days and on the fourth day the amblyopic eye is similarly occluded. In a four year child, it should be four to one and in a five year child, it should be five to one.

Occlusion should be continued :

(i) Until vision has been equalised in both eyes.

(ii) Optimal vision for the eye has been achieved. Sometimes an eye has to be occluded for three to six months.

(iii) There is no further improvement of vision in spite of sufficient occlusion.

Frequency of follow up depends upon age of the child. Younger the child more frequent

The visual acuity should be checked on every visit.

3.Miotics. Some children may respond to local miotics. Miotics should be used only when some binocularity has been reached. However children with non accommodative esotropia respond poorly with miotic. Commonly used miotic is phospholine iodide 0.03% to 0.125% once a day. If surgery is required, the anesthetist should be told about use of miotic during pre anaesthetic check up. The miotics are stopped for two three weeks17 before general anaesthesia is administered especially if succinyl choline is to be used to intubate the child, otherwise other muscle relaxtants that do not depend upon body choline esterase may be used.18

4.Surgery is the definitive treatment of congenital esotropia. Sooner it is done better are the results, but vision should be improved, alternation should be achieved and amblyopia should be managed before surgery.19 Chances of development of DVD and inferior oblique over action after 2 years are positive hindrances. The parents should be told about possibility of binocular surgery and repeat surgery before planning the surgery. Basically there are two groups of surgeries for congenital esotropia :

(1)Bilateral equal recession of medial rectus

(2)Recession one medial rectus with re-section of lateral rectus on the same eye.

5.Botulinum toxin (Botox) injection in the medial rectus - The injection is given under general anaesthesia under electromyographic control in the medial rectus. A common needle used to inject botox also acts as electrode for EMG. Effect of injection starts within twenty four to forty eight hours and lasts for two to three weeks after which the injection may be repeated. The injected muscle is paralysed and is said to be elongated, while its antagonist contracts. Drawbacks are cost of injection, its unpredictability and systemic toxicity. It should be given only by a person especially trained.

Other uses of botox in ophthalmology are :

1.Paralytic sqint (single muscle) injection is made in the direct antagonist

2.Cyclic esotropia

3.Thyroid ophthalmopathy

4.Ptosis