Abstract

Critical exposure duration for the test targets in measurement of visual function is sometimes very important, because even though patients demonstrate relatively high levels of visual acuity using conventional methods, they may for example occasionally require longer stimulus duration for proper reading of the acuity targets. In our previous study1) we reported that the critical duration of Landolt 'C' visual acuity was significantly prolonged in eyes with central serous retinochoroidopathy and macular edema. But the critical duration for the increment threshold was not prolonged in these diseased eyes, although the mean relative threshold energy of the diseased groups was significantly higher than that of the control group. We then measured the critical duration of achromatic2) and chromatic) grating visual acuity in a normal eye, with the purpose of clarifying the mechanisms behind these phenomenon. The critical duration of achromatic grating visual acuity in the normal subject was 73.0 and 140 msec under two different brightness conditions (Fig. 1), and these were significantly shorter than the results of the Landolt ‘C’ visual acuity test (0.62 sec., n=17 as shown in Fig. 2). The critical duration of red-green grating acuity under the 4 different conditions in the same subject was 129, 134, 136 and 129 msec (ARVO 1997, Fig. 3). These were similar to one result in the achromatic grating study (140 ms, white background=23.2 cd/sqm, contrast=73.1%).

© 1998 Optical Society of America