Objective techniques of visual acuity assessment in infancy.

Three primary techniques for objective assessment of visual acuity in the preverbal infant are variations of optokinetic nystagmus, forced preferential looking and visual evoked potentials. Although these tests are useful, the clinician must be aware of their shortcomings. Failure to evoke optokinetic nystagmus may reflect the infant's lack of interest in the stimulus, an inherently uninteresting stimulus, or a defect in the motor system generating the nystagmus, other than failure to see the stimulus. Forced choice preferential looking has provided useful information about visual development in preverbal infants. The need for more complex stimuli to yield more precise estimates of acuity than the standard grafting stimuli, especially in cases of amblyopia, is discussed. Visual evoked potentials, like forced preferential looking, may grossly overestimate the acuity of the amblyopic patient. Of the techniques discussed, it holds the most promise.