A Study of Visual Performance Using Ophthalmic Filters

Merrill J. Allen

Jan 1962 · U.S. Air Force, Air Force Systems Command, Aeronautical Systems Division, Aerospace Medical Laboratory, Life Support Systems Laboratory

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"A study of the visual performance through five regularly available ophthalmic filter glasses, five identical filter glasses uniformly coated to 10 percent transmission, and five other identical filter glasses with a gradient density coating transmitting 10 percent in the center of the lens and about 0. 1 percent at the top of the lens was made using a 7- by 8- by 24-foot atmosphere chamber to simulate flight under adverse glare conditions. Controlled atmospheric conditions and chamber wall luminances of 7000 foot-lamberts and 400 foot-lamberts were provided. The far point test target was a threshold 1/2° white spot variable in brightness relative to the surround. The near target was a randomly presented number target set in a Link Trainer instrument panel. Panel luminances ranging from 0.1 to 0.43 percent of fog room wall luminances were provided and the subject's response time to adapt to the near target after adjusting the threshold spot at distance was the measure of visual performance through the specific filter being worn. Six subjects were used. Approximately 10, 000 judgments were recorded and analyzed for this study. The average time (under average experimental conditions using all subjects) required to identify a target on the instrument panel without sunglasses was 0.5994 sec.; with ordinary sunglasses, 0.6093 sec.; with uniform coating, 0.7603 sec.; and with gradient coating, 0.5057 sec. These include over 300 findings for the "no sunglasses" to 1800 findings for the gradient coating. Differences in performance could be accounted for on the basis of overall transmission effects without regard to filter color. All observers disliked the yellow filters. Threshold distant target recognition through gradient density filters was the poorest at low levels but the best at high levels by a narrow margin. Vision tended to be as good or better unaided than with most filters for a distant threshold target at about 490 foot-lamberts. However, at about 7000 foot-lamberts, the gradient density filter was again superior."--Abstract.