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Quan Lei, Brent Scott Carpenter, Robert Shakespeare, Daniel Kersten, Gordon E Legge; Simulating Reduced Acuity in Low Vision: Visibility of Steps and Ramps at Different Hours of the Day. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4700.
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People with low vision have difficulty navigating in indoor spaces when key mobility features, such as steps and ramps, have low visibility. Visibility can vary due to overall lighting levels or to changes in the pattern of lighting throughout the day. We hypothesize that the more severe the acuity reduction, the more vulnerable is vision to adverse effects of lighting. The purpose of the current study is to investigate the interacting effects of changing patterns of daylight and the level of acuity reduction on the visibility of steps and ramps.
An indoor space was simulated with one of five types of target- Step Up, Step Down, Ramp Up, Ramp Down and Flat Surface, illuminated by directional lighting through a window at different times of a day from 8AM to 6PM in hourly increments and viewed at two distances: 5 feet and 10 feet. The simulation was rendered using the Radiance software, producing a sequence of photometrically accurate HDR images. These images were then filtered using a linear model (Lei et al., IOVS 2016) to simulate different levels of acuity reduction, ranging from 20/20 (normal) to 20/1280. Normally sighted subjects were asked to identify the target in each image.
The overall responses of the subjects to the five targets closely resembled that of people with low vision making such judgments in a real space (Bochsler et al., IOVS 2013). Confusion between the targets increased with the severity of acuity loss and was most prevalent among Ramp Up, Ramp Down and Flat. Performance was better at the shorter viewing distance, particularly for more severe levels (20/640 and 20/1280) of acuity reduction. Moreover, performance varied as the pattern of daylight changed. A significant interaction (p<.001) was found between daylight hour and acuity level, so that the variation was more pronounced as acuity loss became more severe. The three-way interaction (p<.001) between these two factors and target type indicated that the combined effect of daylight pattern and acuity reduction was target-specific.
Our results suggest that variations of natural lighting throughout a day can significantly affect the visibility of key navigational features like steps and ramps, and the adverse effect of lighting gets worse with more severe acuity loss. This finding has important implications for low vision mobility training and architectural design of indoor spaces.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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