THE EFFECT OF DIFFERENT FORMS OF MONOCULAR OCCLUSION ON MEASURES OF CENTRAL VISUAL FUNCTION

The purpose of this study was to determine whether clinically used mea sures of central visual function were influenced by the method of mono cular occlusion used. Twenty young visually normal subjects were teste d both monocularly and binocularly using an Australian Vision Chart No . 5 (which includes high and low contrast letters) and the Pelli-Robso n letter chart. During monocular assessments, the non-tested eye was o ccluded with either a translucent (frosted) diffuser, a +1.50 D (foggi ng) lens, or a white opaque occluder, A significant difference in mono cular sensitivity between the three occluder types was found for Pelli -Robson contrast sensitivity, and the high and low contrast letter acu ities, with poorest performance being recorded with the opaque occlude r in all cases. The same trend was evident in the derived binocular su mmation ratios which were found to vary with the type of occluder used before thp non-tested eye, as well as with the visual function measur ed. The data imply that binocular interactions occur during 'monocular ' testing of central visual function and that these interactions vary with the method of occlusion used. The clinical ramifications of these results are discussed. (C) 1998 The College of Optometrists. Publishe d by Elsevier Science Ltd. All rights reserved.