Optokinetic nystagmus as a measure of visual function in severely visually impaired patients

PURPOSE. To evaluate the efficacy of using optokinetic nystagmus (OKN) as an objective measurement of vision in severely visually impaired patients, in whom it is difficult to measure visual function reliably. Objective visual acuity (VA) measurements would be useful in the pre- and postoperative assessment of severely visually impaired patients who are potential candidates for visual rehabilitation strategies, such as retinal prostheses, neural and stem cell transplantation, and molecular approaches. METHODS. Full-field visual stimuli were used to evoke horizontal OKN responses in 17 subjects. Eye movements were recorded and analyzed to determine the maximum stimulus velocity (F_max) at which subjects could maintain an OKN response. This endpoint was compared to logMAR VA and Goldmann visual field (VF) test results. RESULTS. V_max was dependent on VA, VF, and the spatial frequency (SF) of the stimulus, yielding the equation V_max = 14.2·log(VA) - 6.20·log(SF) + 0.22·VF + 25.0. The findings suggest that V _max in the presence of full-field OKN stimuli may provide an objective measure of VA and peripheral vision. CONCLUSIONS. OKN testing may be useful as an additional, more objective means of assessing visual function in a select group of severely visually impaired patients who are being considered as candidates for new visual rehabilitative strategies.