Objective visual acuity testing by optokinetic nystagmus suppression.

The features of optokinetic nystagmus (OKN) suppression were investigated in various kinds of visual disturbances including those of optical, retinal, higher cortical and psychogenic etiologies. A new OKN suppression device was developed, modifying the principle of Ohm. Objective visual acuities were calculated using the visual angle of OKN suppression dots which were arranged in 12 steps corresponding to the visual acuity from 0.03 to 1.0 as determined by Landolt's method. A total of 286 cases were tested. Results were classified into four types of coincidence between objective and subjective visual acuities. The first group showed equivalent acuities. Normal subjects, cases of corneal opacity, aphakia with intraocular lens implantation and functional amblyopia belonged to this category. In the second group, objective acuity could not be determined because of fixation disturbance due to cortical lesion. The subjective acuity better than the objective acuity was obtained in the third group which consisted of cases with macular hole, central serous retinopathy and optic neuritis with central scotoma. Disturbance of foveal fixation to the OKN suppression dot seemed to be the reason for this difference in the acuities. In the fourth group, the objective acuity was better than the subjective acuity. This occurred in cases of psychogenic visual disturbance and malingerer.