Infantile esotropia

Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic features, and treatment.

Name and Features
Historically the term 'Congenital strabismus' was used to describe constant esotropias with onset between birth and six months of age. However, this term was felt to be an inadequate classification as it covered a variety of esotropias with different causes, features and prognoses.

In 1988, American ophthalmologist Gunter K. Von Noorden discuussed what he described as 'Essential Infantile Esotropia'. He described the condition as: ''early acquired, not... congenital ..., although congenital factors may favor it's development between the ages of 3 and 6 months'' and identified this squint sub-type as having the following features:

1. Onset between birth and six months of age.

2. Large size (greater than 30 dioptres).

3. Stable size.

4. Not associated with abnormalities of the central nervous system.

5. Often associated with defective abduction (outward movement) and excessive adduction (inward movement) of the eyes.

6. Also associated with oblique muscle dysfunction and Dissociated Vertical Deviation.

7. Initial alternation of the squint present with crossed fixation - i.e. the affected individual uses the left eye to look right and the right eye to look left.

8. Limited potential for binocular vision.

The same condition had also previously been described by other ophthalmologists, notably Cianca (1962) who named it Cianca's Syndrome and noted the presence of manifest latent nystagmus, and Lang (1968) who called it Congenital Esotropia Syndrome and noted the presence of abnormal head postures. In both cases, however, the essential characteristics were the same, but with emphasis placed on different elements of the condition.

Helveston (1993) further clarified and expanded upon von Noorden's work, and incorporated the work of both Lang and Cianca into his summary of the characteristics of the condition:

1. Esotropia between 10 and 90 dioptres in size 2. Either alternation or fixation preference may be present (if the latter then amblyopia may result. 3. neurologically normal. 4. Hyperopic correction does not eliminate or significantly reduce the squint size. 5. Frequent nystagmus (latent or manifest latent). 6. The patient may or may not have any or all of the following associated conditions: Oblique muscle dysfunction, vertical incomitance, dissociated vertical deviation, asymmetric optokinetic nystagmus, torticollis. 7. Presence will be 'confirmed' by 6 months. 8. Best treatment results in subnormal binocular vision.

Cause
This remains undetermined at the present time. A recent study by Major et al reports that:

Prematurity, family history or secondary ocular history, perinatal or gestational complications, systemic disorders, use of supplemental oxygen as a neonate, use of systemic medications, and male sex were found to be significant risk factors for infantile esotropia.

Differential Diagnosis
Clinically Infantile esotropia must be distinguished from:

1. VIth Cranial nerve or abducens palsy 2. Nystagmus Blockage Syndrome 3. Esotropia arising secondary to central nervous system abnormalities (in cerebral palsy for example). 4. Primary Constant esotropia. 5. Duane's Syndrome

Initial Treatment
The aims of treatment are as follows:

1. The elimination of any amblyopa 2. A cosmetically acceptable ocular alignment 3. long term stability of eye position 4. binocular cooperation.

The patient will have a full eye examination to identify any associated pathology, and any glasses required to optimise acuity will be prescribed - although infantile esotropia is not typically associated with refractive error. Amblyopia will be treated via patching of the non-squinting eye with the aim of achieving full alternation of fixation. Management thereafter will be surgical.

Surgery
Controversy has arisen regarding the selection and planning of surgical procedures, the timing of surgery and about what constitutes a favourable outcome.

1. Selection and planning

Some ophthalmologists, notably Ing and Helveston, favour a prescribed approach often involving multiple surgical episodes whereas others prefer to aim for full alignment of the eyes in one procedure and let the number of muscles operated upon during this procedure be determined by the size of the squint.

2. Timing and outcome

This debate relates to the technical anatomical difficulties of operating on the very young versus the possibility of an increased potential for binocularity associated with early surgery. Advocates of early surgery believe that those who have their surgery before the age of one are more likely to be able to use both eyes together post-operatively.

A recent Dutch study (ELISSS) compared early with late surgery in a prospective, controlled, non-randomized, multicenter trial and reported that:

''Children operated early had better gross stereopsis at age six as compared to children operated late. They had been operated more frequently, however, and a substantial number of children in both groups had not been operated at all.''

Other studies also report better results with early surgery, notably Birch and Stager and Murray et al but do not comment on the number of operations undertaken.