In patients who are unable to read an acuity chart, measurements of VEP amplitude in response to different check or bar sizes can be used to estimate visual acuity. The pattern size is "swept" from large to small while measuring VEP amplitude. The check or bar size at which the extrapolated VEP amplitude equals zero is a completely objective measure of visual acuity. This procedure is fast (less than two minutes, excluding the time to prepare the patient), accurate, and useful in diagnosing a variety of visual disorders in children and adults.