Landolt C Recognition in Elderly Subjects is Affected by Scotopic Intensity of Surround Illuminants

In a previous study with young adults ages 20 to 40 years, we demonstrated that low contrast Landolt C recognition was better with smaller pupils than with larger pupils even though task retinal illuminance was higher for larger pupils. Pupil size in these studies was controlled by the spectrum of the far surround illumination which was prevented from affecting task luminance.

The present study used the same procedures as our previous study with 7 healthy elderly adult subjects between the ages of 61 and 66. Because senile miosis is a characteristic of the aging eye, spectral changes in the surround might be expected to produce relatively smaller changes in pupil size and hence performance. Surprisingly, although the scotopically enhanced surround lighting produced relatively smaller pupil size changes than in young adults, the performance enhancements were comparable to those of young adults.

As in the previous study the task was recognition of the orientation of the gap in the C that was presented on a CRT with contrasts varying from 18% to 80%. Two surround illuminants were compared, both provided a luminance of 53 cd/m² on the front wall at visual angles larger than 30. Subjects had at least 20/20 vision and perform the task with their spectacles if normally used.