Biphasic Visual Temporal Impulse Response And Optokinetic Nystagmus

The conventional optokinetic nystagmus (OKN) is elicited by a large-field moving pattern. The study of OKN could contribute to the mechanism of oculomotor control and to the ophthalmological diagnosis. In the first part of this thesis, we applied time-domain analysis of "signals and systems" to motion perception experiments. Based on biphasic characteristic of the visual impulse response, we conjectured that the intermittent display of stationary gratings could induce sequential π-phase shift and result in motion perception, as well as elicit the corresponding alternating OKN. Experimental results confirmed this assumption: during the interstimulus interval (ISI) ranged from 33 to 83 ms, with the ISI luminance approximated to the mean luminance of the stimulus grating, a novel OKN elicited by the intermittent display of stationary gratings was observed and recorded. It can be labeled as "intermittent-display-grating induced OKN" (IDG-OKN). In the second part, considering that the biphasic visual impulse response is the feature of the magnocellular (M-cell) pathway, and the M-type ganglion cells are damaged in the primary open-angle glaucoma (POAG), we presumed that IDG-OKN of POAG could differ strikingly from that of normal subjects. In the present experiments, OKN has been compared among 11 POAG and 14 normal eyes with both the continuous and intermittent display of gratings. The results demonstrated that the conventional OKN has no significant differences between the two groups; on the contrary, for the intermittent display, the reverse OKN could be elicited from all normal subjects, but nearly none of glaucomatous eyes. Thus, this result provided an evidence for that the IDG-OKN is correlated to the function of M cells in the visual pathway, and suggested a possible approach for the diagnosis of POAG.