Edinburgh Napier University

  PURPOSE: To examine the effects of primary open-angle glaucoma and normal aging on visual sensitivity for targets known to bias responses from the magnocellular visual processing stream.

METHODS: Contrast sensitivity was measured for the detection and direction discrimination of low-spatial-frequency (0.5 cyc/deg), drifting (4-24 Hz) sinusoidal gratings in 15 patients with glaucoma (mean age, 58.7 years), 14 age-matched control subjects (mean age 55.8 years), and 10 young control subjects (mean age, 24.4 years). As a control, sensitivity was measured for the detection of stationary stimuli. Stimuli of 4.7 degrees square were presented at either 0 degrees eccentricity or at 20 degrees along the nasal horizontal meridian, under both photopic and scotopic levels of lighting.

RESULTS: Across a wide range of conditions, the ability to detect and discriminate visual motion declined significantly (P < 0.05) with increasing age, whereas the ability to detect stationary patterns was generally unaffected. The rate of decline was adequately described by a simple linear function. Control studies showed that the age-related motion sensitivity losses could not be attributed solely to decreases in retinal illuminance associated with increasing age. Of note, however, there were no significant differences in mean sensitivity between glaucoma and age-matched control groups for any of the conditions used.

CONCLUSIONS: Even under conditions believed to bias the response of the visual system to the magnocellular pathway, glaucoma subjects could not be reliably differentiated from control subjects on the basis of mean sensitivity to motion stimuli. The findings have two broad implications: first, that substantial neural loss specific for motion perception occurs during the processes of normal aging, and second, that sensitivity to motion targets per se may not be a useful indicator of neural integrity in the early stages of glaucoma