I have just examined a 5-year-old boy. It was his first eye examination and he had a history of a suspected right convergent strabismus. Visual acuity is right 6/24 and left 6/9. Refractive error after cycloplegia is right +4.50DS and left +1.50DS and there is no movement on cover test with refractive correction in place. Ophthalmoscopy indicates no eye disease. What should I do?
This sounds like a right, fully accommodative esotropia. When accommodating one of the eyes, usually the one with the greater hyperopia because of the accommodative, convergence, pupil constriction triad. The over-convergence associated with the extra accommodation required to overcome the hyperopic refractive error can precipitate a loss of binocular control and lead to the development of esotropia.
The chances of an esotropia developing depends on the amount of hyperopia. Where the hyperopia is small, the child will be able to maintain binocular control because the amount of over-accommodation required to produce clear vision is small. The child learns to accommodate without over converging.
Where the hyperopia is large, the child may not be able to produce clear near vision no matter how much extra-accommodation is exerted and therefore there is no need to over-accommodate and over-converge and there is no esotropia. However, where the hyperopia is small enough to allow the child to generate clear vision by over-accommodation but large enough to disrupt their binocular control, over-convergence will cause an esotropia.
Only about 20% of children with hyperopia greater than +3.5 diopters develop strabismus.
Where the esotropia is solely a consequence of uncorrected hyperopic refractive error, providing the child with the correct glasses and ensuring that these are worn all waking hours, is often enough to control the deviation. The esotropia will only be seen when the child removes their glasses. It is important to explain this to the parents as some may be disappointed to learn that the esotropia will persist when the glasses aren’t worn. In order to avoid amblyopia, it is imperative that the parents ensure that the child wears the glasses all waking hours. When the patient is older contact lenses can be used as these will aid participation in sports.