Objective measurement of visual acuity by optokinetic response determination in patients with ocular diseases

To investigate the efficacy of optokinetic nystagmus (OKN) suppression and induction methods for the objective estimation of visual acuities in patients with various ocular diseases.

Prospective, descriptive study.

One hundred seventy-three eyes of 89 patients aged between 27 and 75 years who registered at our institution from January to December 2004 were prospectively enrolled onto this study. Ocular diseases included generalized retinal diseases (47 eyes), media opacity (32 eyes), refractive errors (31 eyes), glaucoma (27 eyes), maculopathies (26 eyes), and optic neuropathies (10 eyes). Horizontal optokinetic stimuli were presented on a 17-inch monitor screen at a distance of 40 cm from the subject in a dark room. Horizontal eye movements were recorded in each eye separately by infrared oculography. Objective visual acuities measured by using OKN suppression or induction methods were compared with subjective visual acuity assessments. The logarithm of minimal angle of resolution visual acuity was 1.03, and ranged from -0.08 to hand movement.

Linear regression identified minimum stripe stimuli required to induce OKN by using the OKN induction method, and the minimum dot size required to suppress OKN was found to be correlated with subjective visual acuity (P<.01). The induction method was useful in patients with visual acuities of 20/60 or worse, and the suppression method was useful in patients with visual acuities of 20/200 or better.

Combined use of the OKN induction and suppression methods provides a satisfactory means of determining objective visual acuity.