[Determination of visual acuity using optokinetic nystagmus. A newly developed instrument based on Günther's principle]

Analysis of computerized optokinetic nystagmus induction and effect of contrast on ocular fatigue

Optokinetic nystagmus (OKN) is useful in evaluating visual function objectively, and the classical black-and-white-striped OKN drum is being replaced by video or computer monitor. However, the examinee may feel fatigue during test because of high contrast of luminous pattern from monitor. This paper suggests a plan to reduce eye fatigue of participant by decreasing contrast of patterns without reducing OKN response. Alternating black and white stripes are shown on flat-panel liquid-crystal display monitor and moved horizontally to evoke OKN of the examinee, and the OKN wasW observed through electrooculography (EOG). Eye fatigue was estimated from the number of eye blinking, along with dry eye questionnaire according to the contrast of the black and white stripes. White stripes are shown as 300cd/m², and gradual decrement in contrast by 75%, 50%, and 25% were given to investigate the effect of the contrast on the eye fatigue and the OKN. Blinking of the eye was recorded as a video clip and was analyzed by image processing to count the number of blinks while measuring OKN. Experimental results show that incidence of nystagmus does not substantially change with the change of contrast in stimulus pattern but the eye fatigue decreased by the reduction of the contrast. In conclusion, the examinee may choose the contrast option for the OKN test to reduce the stress onto their eye, without affecting the test result.

Measurement of distance objective visual acuity with the computerized optokinetic nystagmus test in patients with ocular diseases

BACKGROUNDS

To evaluate the efficacy of a computerized optokinetic nystagmus (OKN) test for determination of objective visual acuity (VA) at distance in patients with various ocular diseases.

METHODS

This is a prospective, non-interventional study that included 85 eyes of 71 patients with one or more ocular pathologies. Study patients were classified into group C (39 eyes of 30 patients with central visual damage), group P (24 eyes of 20 patients with peripheral visual defect) and group M (22 eyes of 21 patients with media opacity). Objective distance VA was measured with OKN induction and suppression methods, and the correlation between the objective and subjective VA at distance was evaluated using linear regression analysis. Mean subjective VAs were compared among each objective VA step and among the three groups.

RESULTS

Significant correlation was found between subjective distance VA and objective VA determined by both OKN induction and suppression methods in all three groups and in overall patients. In overall patients, the mean subjective VA was significantly different in several objective VA steps (Welch's ANOVA, p < 0.001 for induction and suppression methods). No significant difference in subjective VA among the three groups was found in any objective VA step.

CONCLUSIONS

Our objective VA test using OKN induction and suppression methods can be useful in estimating distance VA in patients with various ocular diseases.