Monocular vs. binocular measurement of spatial vision in elders

To evaluate the frequency and magnitude of binocular gain (and loss) for high-contrast acuity, various low-contrast spatial vision measures and contrast sensitivity in an elderly population.

Ninety-five individuals over the age of 70 (mean age 80.5 years, range, 71.8 to 93.5) with acuity of 20/40 (logMAR 0.3) or better in at least one eye participated. Each individual was tested binocularly and then monocularly on high-contrast acuity, various low-contrast acuity measures, and contrast sensitivity. Binocular gain for acuity measures was defined as better performance by one line or more under binocular conditions than with the better eye alone. Binocular loss was defined as poorer performance by one line or more binocularly than with the better eye alone. For contrast sensitivity, the criterion for binocular gain or loss was one letter triplet (0.15 log unit) or more difference. For each measure, the frequency of binocular gain and loss, as well as the mean gain or loss were determined.

The mean difference between binocular and better eye monocular acuity was <2 letters for all measures, suggesting little gain or loss. However, the percent of individuals showing a line or more of gain or loss ranged from approximately 20% for high-contrast acuity to 49.5% for low-contrast acuity at low luminance. This indicates that for 1/5 to (1/2) of individuals, binocular vision is not well represented by monocular vision measures. All low contrast measures and contrast sensitivity show more binocular gain/loss than standard acuity. As has been previously reported, in the presence of large interocular differences, binocular gain is not seen, but binocular loss does not necessarily occur.

For a significant portion of this elderly population, binocular performance is not well represented by better eye monocular measures. This indicates that to get a true sense of an individual';s vision function in daily life, one must measure vision binocularly.