Dark focus of accommodation in children with accommodative esotropia and hyperopic anisometropia

Abstract

We evaluated the dark focus of accommodation, referred to as tonic accommodation, in 60 young hyperopic subjects, 20 with and 20 without accommodative esotropia, and 20 with hyperopic anisometropia. We measured the distance, dark, and cycloplegic refractive errors by the Nidek Autorefractometer AR1600. The difference between dark and cycloplegic refractive errors was defined as the dark focus. The dark focus was significantly larger in esotropic eyes than in non-esotropic eyes, despite similar cycloplegic refractive errors in both types of eyes, suggesting that tonic accommodation may be associated with ocular position. The dark focus was similar in eyes of the same subjects with hyperopic anisometropia and also in normal and amblyopic eyes, suggesting that tonic accommodation is similar in both eyes in subjects with anisometropia and amblyopia.

Why Do Only Some Hyperopes Become Strabismic?

“…In the context of strabismus, when baseline tonic accommodation responses in fully optically corrected hyperopic children (mean age 9.6 years, range 5-15 years) with and without accommodative esotropia were compared, children with esotropia had a closer dark focus (2.7 D relative to their hyperopic far point) than those without (1.1 D) despite similar refractive errors. 137 This is inconsistent with the idea that increased tonic responses would be protective against strabismus in the simplest sense. If tonic responses were used, without driving the coupling, to overcome hyperopia in nonstrabismic patients, one would predict that these nonstrabismic patients would have higher tonic responses.…”

Accommodative anomalies in children

“…The accommodative system is complex; and comprises not only the amplitude but number of other functions known as Facets of accommodation. [ 17 18 19 20 ] Any of them can be underdeveloped and can give rise to ocular symptoms.…”