Inverted optokinetic nystagmus (OKN) was observed by a method of examining the relationship between optokinetic nystagmus and target movement.
An Ohm type rotating cylinder was used to examine horizontal OKN. Twelve vertical stripes were drawn at equal intervals on its inner surface. The cylinder was rotated with an angular acceleration of 2°/sec2 for 90°sec. OKN, induced by the optokinetic stimulation, and signals indicating that stripes passed in front of the subjects, were simultaneously recorded by an electronystagmograph and a magnetic data recorder. Data on the tape were analyzed by a PDP-12 computer. The nystagmus wave and stripe movement were superimposed on a cathode ray tube. From the relationship between the two, the ocular ability to catch and follow the stripes was evaluated.
Inverted OKN was observed in 20 patients with congenital nystagmus.
In a representative examination, at a cylinder speed of 0-20°/sec, the eye followed the stripe movement with repeated saccadic movements of small amplitude. At a cylinder speed of 21° to 30°/sec, the moving stripe was followed by saccadic eye movements of large amplitude. When the cylinder speed surpassed 70°/sec, the amplitude and rhythm became uniform and developed into typical OKN. In this phase, the eye produced a saccadic eye movement in the direction of the stripe movement when the fovea registers a stripe.
These findings suggest that inverted OKN is due to stripe pursuit with saccadic eye movements.
