Controlling unwanted sources of threshold change in disability glare studies: a prototype apparatus and procedure.

One of the main purposes of cataract surgery is to reduce the debilitating effects of light scatter by the lens. An important effect of this intraocular forward scatter is to produce a veiling retinal illuminance from a glare source. The retinal contrast of the stimulus is thus reduced, and a quantifiable "disability glare" effect may be measured. A complication is introduced by the fact that intraocular scatter arises from other sources in addition to the lens. All present tests of glare disability fail to eliminate or control for these factors, nor do they control for the light adaptation effect of the glare source. The effects of lens removal may not be predicted accurately by such tests, and patients may report little improvement in visual function after surgery. The goal of this research is to provide the background for developing a method of measuring disability glare due only to light scatter in the lens. Thirty-seven patients with mild to moderate cortical cataracts served as subjects. A disability glare effect (DG) was measured with a Maxwellian-view system that eliminates or controls scatter from the iris, sclera, and retina, and which controls for light-adaptation effects from the glare source. DG with this method showed a significant correlation with objective measures of lens light back scatter. Suggestions were made for improvements in the apparatus and procedures for future clinical studies.