Effects of pupil diameter on light detection and temporal modulation.

PURPOSE

This study compared the effects of pupil variation on light detection and temporal modulation across the central visual field.

METHODS

Light detection sensitivity (LDS) and low flickering frequency (6 Hz) temporal modulation sensitivity (TMS) of 20 young subjects were measured from the central visual field of the right eyes using an autumated perimeter (Medmont M600). The measurements were taken under 3 artificial pupils, i.e. 3 mm, 4.3 mm and 6 mm diameters. The sensitivities were grouped and averaged for different retinal eccentricities (3 degrees, 6 degrees, 10 degrees, and 15 degrees).

RESULTS

TMS and LDS were reduced with increasing retinal eccentricities (P < 0.001) and decreasing pupil diameters (P < 0.001). TMS collected from all pupil diameters were significantly different from each other (P < 0.001). Similarly, LDS under 3 mm pupil was statistically different from those of 4.3 mm and 6 mm (P < 0.003). Comparison of the hills of vision showed that pupil variation resulted in significantly different slopes (P = 0.001). The slopes were also found to be significantly different between TMS and LDS (P = 0.012).

CONCLUSIONS

The data showed that dilated pupil resulted in significantly higher sensitivities than those of smaller pupil for both visual functions. The difference in the slopes of hills of vision also suggested that the variation in retinal illumination affected the visual responses differently at various retinal eccentricities for TMS and LDS.