The Optokinetic Fusion Limit

Abstract

When examining optokinetic nystagmus the angular speed was gradually increased until the movements of the eyes ceased. This limit was called the “optokinetic fusion limit” (OFL). When the speed was decreased again a similar limit appeared when optokinetic nystagmus recurred. The investigations were performed with an apparatus where the variations in speed were controlled automatically and the movements of the eyes were recorded at the same time electronystagmographically.

Totally, 56 normal subjects were examined. Large variations in the interrelation between the two limits appeared; the most stable was in connection with the acceleration. The variation of limits was very close in one and the same subject. As a rule, the limits were distinct and easy to read, while in six subjects they were so diffuse that they could not be used when compiling the results.

The results showed that OFL appeared at angular speeds between 101-450%sec. (mean values 254-284°/sec.) at rotation to the right and the left.

The relation between OFL and the critical flicker-fusion frequency (CFF) was examined. It was found that the latter always appeared at considerably higher angular speeds, even at optimal conditions for the maximum speed limit of optokinetic nystagmus. Emphasis is put on the fact that CFF is a subjective method while OFL can be recorded objectively.

The influence of various factors such as attentions, accommodation and voluntary inhibition is discussed. The method is very objective and is suitable for continued studies with, for instance, load experiments with various pharmaceutics.