Ординатура / Офтальмология / Английские материалы / Manual of Practical Cataract Surgery_Sundararajan_2009

Understanding the Basics of Strabismus 109

4.Congenital Paresis:

Due to some unknown reasons, there may be some paralysis or paresis of one or two ocular muscles of eye producing squint. As the macular fixation develops 2-3 months after birth, it is either noticed or not. The same paresis or palsy may also occur as a result of serious illness to the child at this age. The palsy may be in horizontal, vertical or oblique muscles.

5.Dissociation of the eye as a result of uncorrected refractive errors producing hazy unacceptable visioneven if corrected. The corrected power may be under or insufficient. Sometime the astigmatic correction could be incorrect. Extended patching of one eye. Due to congenital aquired macular defect leading to defective fixation.

6.If visual pathways are defective due to some lesion.

7.General ill-health conditions.

Divergent Squint: (concomitant) Exotropia

1.Due to Neuro-muscular inco-ordination of unknown reasons at the age of 3 - 5 years divergent squint occurs as intermittant first, ending as constant in the following types:

a.Divergent excess types -for distance.

b.Convergence insufficiency type for near (maddox wing)

2.Unilateral myopia-uncorrected, producing divergent squint of the myopic eye. In bilateral myopia, if untreated - produce alternating type of divergent squint.

3.As a result of some serious pathology in the eye producing loss of eye presents as divergent squint.

4.Overcorrection in convergent squint.

5.Medial rectus paralysis in 3rd nerve palsy.

6.General ill-health, etc.

110 Manual of Practical Cataract Surgery

Points to remember in Esotropia

a.High hypermetropia ->overaction of ciliary muscles-> overaction of convergence for near first->Squint.

b.Uncorrected high hypermetropia (due to inco-ordination between accommodation and convergence)->deviation intermittant first, below 3 years.

c.Myopia from birth->in infants -> esotropia persists.

d.in infants ->paralysis or paresis ->tropia of all types.

e.uncorrected and under corrected refractive errors -> unequal vision and clarity.

f.Macular pathology in infancy-or anywhere in visual pathology.

g.Defective general health.

Points to remember in Exotropia

a.Neuromuscular inco-ordination->after 3 years - >intermittant->constant-primary-not appear to be related to refractive errors.

b.Unilateral myopia or myopic astigmatism -> one eye- >divergent.

c.Bilateral myopia-> alternating squint.

d.Eye with no vision->Exotropia.

Symptoms

1.In early cases there will be diplopia, subsequently followed by absence of diplopia ->supression.

2.Cosmetically defective appearance.-deviation of one or both eyes as noticd by parents or relatives.

3.In school children it is noticed.

4.In children, if is noticed along with yellow or white reflex of pupils (one should exclude the various causes of pseudoglioma mainly retinoblastoma in children).

Understanding the Basics of Strabismus 111

Eye Examination--routine

1.Inspection:

•To find out whether convergent or divergent squint.

•To find out small degree, moderate or severe degree pseudosquint or true squint.

•Sudden onset or gradual onset.

•Intermittant or constant type (an observer can notice) family history.

2.Visionaquity.

3.Ocular motility:

•To find out whether it is a paralytic or non-paralytic each eye should be tested separately.

4.Pupillary reflexes:

•To rule out the other causes of peudoglioma especially retinoblastoma.

5.Cycloplegic refraction to find out the refractive errors.

6.Cover test -in children, using a torch light one can find out approximatively the angle of deviation in degrees.

•Cover one eye and look for recovery movements. Though this tests is not much useful in obvious squint, it is an important test to find out whether the child is fixing uniocularly or bilaterally. The co-operation of the child is difficult.

7.To find out the angle of deviation:

a. Corneal reflex test -useful in children as mentioned. b. Perimeter test -The number of degrees on the arc will

give a clue to the angle of deviation.

c.Prism and cover test – By changing the increasing strength of prisms (base-in or base out for convergent or divergent squint) till the recovery movement is abolished one can find out the correct amount of deviation.

Understanding the Basics of Strabismus 113

8.Binocular Function test:

a.Simultaneus perception test: In synaptophore, by using slides of two dissimilar objects the patient may be asked to see slides like -lion and cage and asking them to put the lion in the cage.

b.Fusion: In this, there will be two slides of dissimilar pictures but incomplete, like cat or rabbit holding flowers. By asking the patients to fuse both into one complete picture (super-imposed) the patient has the ability to fuse. In case it does not, but simply comes and goes -it may be taken as suppresion.

c.Stereopsis(depth perception): In this, there are slides of two dissimilar objects. The patient is asked to appreciate the depth by superimposeing both.

TREATMENT

This consists of the following:

a.Correction of refractive errors by spectacles.

b.In case the patient has developed amblyopia - occlusion of the fixing eye should be done, followed by stimulation of the affected-amblyopic eye. If exccentric fixation has developed, the occlusion of the affected eye should be done. To make the unsteady fixation into steady fixation.Then follow the previous procedure.

c.Orthoptic procedures, if necessary to create binocular vision.

d.Surgery as a cosmatic correction in some patients.

CONVERGENCE

Convergence is a process by which the visual axis of both the eyes are directed towards the nose by synchronous adduction of both the medial recti muscles.

114 Manual of Practical Cataract Surgery

Types of Convergence: Convergence may be voluntary or reflexes. It is initiated in the visual cortex.

The reflex convergence is analysed in 4 components:

1.Tonic convergence.

2.Accommodative convergence.

3.Fusional convergence.

4.Proximal convergence.

Tonic Convergence

This depends on the tone of the muscles and occurs in the absence of any stimulation to accommodation. In cases of convergence-excess type, a non-accommodative esotropia is seen.

Treatment

By drugs

Accommodative Convergence

Normally when accommodation is exerted, an estimated amount of convergence is also exerted.

Treatment

This can be corrected by correcting refractive errors.

Fusional Convergence

Normally a certain amount of convergence is present for a normal accommodation. For finer adjustments necessary for binocular fixation -> this fusional convergence is required. This is involuntary.

Proximal Convergence:

An awareness of near object or subject creates an appropriate degree of convergence.

Understanding the Basics of Strabismus 115

Flow Chart: Treatment of concomitant squint in a child

Understanding the Basics of Strabismus 117

Amblyopia

Amblyopia can be discussed in the following types:

1.Stimulus deprivation amblyopia.

2.Strabismic amblyopia.

3.Anisometropic amblyopia.

4.Anisoconic amblyopia.

5.Ametropic amblyopia.

Treatment

1.Treatment of the cause of amblyopia.

2.Patching or occlusion of the normal eye so that the affected eye can be made to see and be stimulated by some methods.

Eccentric Fixation

The following are the types:

1.Fovial fixation.

2.Perifovial fixation.

3.Parafovial fixation.

Treatment

1.Occlusion or Patching of the affected eye so that the normal eye which is unsteady can be made to become steady.

2.Once the eye becomes steady, the regular treatment for amblyopia can be started. which is given above.

PARALYTIC SQUINT

Causes of paralysis of external ocular muscles

1.Any type of lesion in any one of the muscles or the nerve which supplies the same muscle starting from the nucleus of origin upto the place of insertion in the eye,

118 Manual of Practical Cataract Surgery

like congenital anomolies, infection, inflammation, benign or malignant conditions, trauma, toxins, vascular or spaceoccupying conditions can paralyse the function of the muscles producing the deviation of the eye-paralytic squint.

a.Superior rectus, inferior rectus.

b.Medial rectus, lateral rectus.

c.Superior oblique, inferior oblique muscles.

Lateral rectus muscle is supplied by 6th nerve (abducent nerve). Superior oblique muscle is supplied by 4th nerve (trochlear nerve) superior rectus, inferior rectus, medial rectus and inferior oblique --3rd nerve.

2.Sequelae of the affected muscles will be

a.Overaction of the contralateral synergist.

b.Contracture of the ipsilateral antagonist.

c.Secondary palsy of the contralateral antagonist.

The examples are:

a.For right lateral rectus palsy-the sequela are -overaction of left medial rectus, contracture of right medial rectus and secondary palsy of left lateral rectus.

b.For left superior oblique palsy-sequela are -overaction of right inferior rectus, contracure of the left inferior oblique and secondary palsy of right superior rectus.

3.Clinically the signs and symptoms are:

a.Diplopia(immediate) if the eye is having vision.

b.Due to this diplopia, the patient will have headache, nausea, vertigo, and other discomforts which gets cleared on closing the affected eye.

c.Defective movement of the affected eye.

d.Compensatory head posture and chin position.

Investigations

a.Diplopia chart to find out which specific side muscle is affected.