Vernier acuity in amblyopic and nonamblyopic children

We measured vernier acuity in normal and amblyopic children using a procedure that resembles a video game and is suitable for testing most children older than 4 years old. In this procedure, subjects align bars using two keys of a computer keypad. Following binocular practice trials, monocular vernier acuity was measured in 38 control children, 5 to 15 years old, and in 18 children with histories of amblyopia. Vernier acuity was defined as the standard deviation of adjusted position across a block of six trials. Vernier acuity improved as a function of age in the control subjects, indicating developmental improvement. Amblyopic subjects with strabismus (n = 5) and with both anisometropia and strabismus (n = 8) showed markedly impaired vernier acuity in their amblyopic eyes, with vernier acuitys four to five times larger than those of age-matched controls. However, the amblyopic subjects who were anisometropic (n = 5), without any history of strabismus, were not significantly different from control subjects in either eye. Testing with bars and gratings gave similar results. To our knowledge, this is the first study showing that vernier acuity deficits seen in adult amblyopes are also seen in child amblyopes.