Effect of aging on stereoscopic interocular correlation.

PURPOSE This study was designed to evaluate the minimum interocular correlation (IOC) needed by the visual system to correctly perceive a static stereoscopic stimulus as a function of normal aging. It was also our goal to evaluate the feasibility of clinical charts testing this aspect of visual perception. METHODS Stereoscopic IOC threshold was determined in 100 normal observers (average age +/- standard deviation, 45.7 +/- 20.4 years) drawn from a clinical population between the ages of 10 and 85. We used partially correlated red-green random dot stereograms (RDS) displaying flat, square surfaces at 360 arcsec of either crossed or uncrossed disparity. RESULTS Older observers needed a higher binocular correlation to perceive the stereoscopic stimuli when compared with the younger groups. There is a slight increase in the threshold value of the individuals in the 45- to 64-year-old group and a further effect on the observers over 65 years of age. Data did not reveal any effects of gender, near point phoria, or fixation disparity on IOC thresholds. CONCLUSIONS Normal aging produces a statistically significant deficit in binocular correlation processing. This process is marginally correlated with stereo acuity measures even when stereoacuity floor effects are factored out. Although further experiments directly comparing stereoacuity and IOC are necessary and more refining is required to obtain optimum parameters, clinical stereoscopic IOC test charts appear feasible and may not assess the same processes as stereoacuity charts.