Measurement and analysis of glare recovery

Abstract

Glare recovery is defined as the visual phenomenon associated with the return of retinal sensitivity to the pre-glare level after a short duration exposure to intense light. Experimentation with an existing glare recovery testing device and a TV pupillometer resulted in the development of a new test apparatus which is described in this dissertation. The device utilizes psycho-physical responses by the test subject before and after a glare exposure to measure the relative visual degradation occurring before glare recovery is complete. The testing method employed with this apparatus is suitable for determining the glare recovery of large numbers of subjects without the requirement of a complicated experimental set-up or the need to instrument the subject. Tests conducted on more than 50 subjects, producing over 8200 data elements, verified the ability of the test device to measure glare recovery. Analysis of these data provides the basis for the following description of the glare recovery phenomenon. Immediately after glare stimulation, a period of extensive visual degradation occurs due to extreme photopigment bleach. A second phase, which the author calls the latent phase, shows visual sensitivity at, or above, the pre-glare level. This latent period is probably the result of the combination of the photochemical reaction and lateral inhibition in the retina. A third phase, characterized by oscillation of visual sensitivity caused by pupillary unrest, is the direct result of an afterimage. This phase, in many individuals, continues for several minutes after the glare exposure before the pre-glare visual stability is again attained. Comparison of data collected on subjects with slight visual abnormalities (color blindness, myopia, and hyperopia) and corrected vision to that collected on normal subjects showed marked differences. Most subjects with visual defects maintained a considerably longer period of visual instability during the third phase of recovery and a longer duration initial phase. The physiological causes for this cannot be determined without more research.