Association between fixation preference testing and strabismic pseudoamblyopia

Fixation preference testing is the mainstay of clinical diagnosis of strabismic amblyopia in preverbal children and infants. The purpose of this study is to evaluate the strength of the association between fixation preference and strabismic amblyopia.

Eighty patients (3 to 8.3 years) with manifest strabismus and the capability to cooperate with a Snellen acuity test were prospectively examined. Thirty patients were diagnosed as having partially accommodative esotropia, 15 as having congenital esotropia, 15 as having primary acquired esotropia, 15 as having congenital exotropia, and 5 as having hypertropia. Visual acuity levels were measured using a Snellen E-chart. Fixation preference was evaluated and graded from 0 (free alternation) to 3 (strong uniocular fixation). At the end, we compared visual acuity and the grade of fixation preference. Amblyopia was defined as a difference of two or more Snellen lines between the two eyes.

Sixty patients (75%) had strong uniocular fixation (grade 3). Of these patients, 50 (85%) had no amblyopia and only 10 had deep amblyopia. Ten patients (12.5%) had moderate fixation (grades 1 and 2). Of these patients, five (50%) had no amblyopia and five had moderate amblyopia. Ten patients (12.5%) had free alternation (grade 0). These patients had equal vision.

Treatment of strabismic amblyopia on the basis that the sound eye will show strong fixation preference can be hazardous. Fixation preference could be a severe form of eye dominance, and better methods for testing visual acuity in preverbal children are required.