10-Diopter fixation test for amblyopia.

Fixation-preference testing has been useful in detecting amblyopia in children unable to give reliable visual acuities, except for children with small-angle tropias and those without manifest deviations. This study introduces a method of fixation testing that includes all children, regardless of the presence or size of the deviation. By placing a 10-diopter vertical prism over one eye, we induce a vertical deviation. Once the eyes are dissociated, fixation preference is evaluated and used to predict the presence of amblyopia. We prospectively studied fixation patterns in 98 children with either small-angle tropia or essentially straight eyes. All children with amblyopia of two lines or more showed abnormal fixation patterns, and those without amblyopia showed normal patterns. We were able to obtain fixation patterns on all children studied, including 13 infants less than 24 months of age. This test proved to be a reliable, objective method for detecting amblyopia in children with straight eyes or in children with microstrabismus of almost any age.