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M. E. Schneck, G. Haegerstrom-Portnoy, L. A. Lott, J. A. Brabyn; Binocular Summation and Inhibition for Low Contrast Among Elders. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5496.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the frequency and degree of binocular summation and inhibition for low contrast vision measures in an older population.
Participants were 95 older volunteers (mean age 80.5 years, range 71.8 to 93.5) selected on the basis of having best corrected high contrast acuity of 20/40 or better in at least one eye. Low contrast acuity (LCA) at 10% and 20% contrast), low contrast acuity in glare, low contrast low luminance acuity and contrast sensitivity were measured with best correction binocularly and monocularly. Binocular summation was defined as binocular performance >=0.10 better than that of the better eye; inhibition as binocular performance >= 0.10 log unit worse than the better eye monocular measure.
Depending on the measure, between 27% and 50% of this older group show differences between binocular and better monocular vision. Summation and inhibition are fairly similar in frequency for all the low contrast acuity measures; however, for contrast sensitivity summation occurs nearly 4 times as often as inhibition. For each measure, the difference between binocular and better monocular performance is significantly (though not strongly) related to the interocular difference in performance (correlation coefficients 0.2 - 0.4). The same is true when age is taken into account. Interestingly, in cases of small interocular differences, summation and inhibition both occur. When interocular differences are large, binocular summation does not occur.
Binocular inhibition in older observers for low contrast measures is more common than has been reported for high contrast acuity. For example, the Latino Eye Study reported inhibition in 2% (and summation in 21%) of elders for high contrast acuity. The high frequency of binocular summation for some measures suggests that monocular measurement of vision in this age group does not necessarily reflect function under everyday viewing conditions. On the other hand, the high frequency of inhibition suggests that some elders may function better when the poorer eye is covered.
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