K Higgins¹, J White², R Asami², L Liu¹, B P Rosenthal3
¹Lighthouse International, Arlene R. Gordon Research Institute, New York, United States; ²VA New Jersey Healthcare System, Eye Clinic, East Orange, NJ, United States; 3Lighthouse International, Low Vision Services, New York, United States
Purpose: A transient adaptation factor (TAF) is incorporated into visual performance models used for lighting applications (e.g., tunnel lighting). It characterizes visibility loss by comparing threshold at each of several intervals following the onset of a transient change in light level to the threshold when the individual is fully adapted to the new light level. Since the TAF in many models (e.g., CIE Report 19/2.1) was based on studies using college-aged subjects, we evaluated the effect of age on transient adaptation. Methods: Thresholds were measured for a 20 msec. (642 nm) test probe in 7 young (mean age = 28.4 yrs) and 9 elderly individuals free of eye disease (mean age = 73.8 yrs) using a 2-alternative, spatial forced-choice procedure. Threshold were measured in the presence of a peripheral glare source (55 lux, 6 degrees left visual field) that was either exposed continuously (steady-state, or SS) or flashed for 1 sec. every 10 sec (transient). Transient thresholds were measured when test probe onset occurred 20, 50, 100, 200, 500, 700 and 900 msec. following the onset of the 1 sec. glare source. Results: For the young sample, mean threshold at 20 msec. was elevated by 1 log unit relative to their SS threshold; however their sensitivity recovered to a SS level within 200-500 msec. of glare onset. For the elderly sample, mean threshold at 20 msec. was elevated by 1.5 log units relative to their SS threshold level. Moreover, their sensitivity did not begin to approach their SS level of sensitivity until 900 msec. following glare onset. Further, the difference between samples could not be attributed to differences in dark-adapted threshold. In summary, these results suggest that a TAF derived from research using young subjects would likely underestimate the visibility loss experienced by the elderly individual when faced with the same transient change in light level (e.g., entering or exiting a tunnel).
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