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K.E. Higgins, J.M. White, L. Liu, V. Ciaccio, H. Gauthier; Effect of Age on Threshold Elevations Produced by Initial Onset of Directly and Indirectly Viewed Adapting Fields . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2774.
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Purpose: Boynton, Bush, and Enoch (1954) showed that the onset of an indirectly viewed glare source elevated a subject’s threshold by the same factor as a directly viewed (optically superimposed) adapting field of a certain luminance, provided that the glare source was sufficiently intense. This finding gave rise to the concept of equivalent veiling luminance as the mechanism for explaining the threshold elevating effects associated with disability glare sources. The objective of this experiment was to determine whether the threshold elevation produced by the initial onset of directly and indirectly viewed white light sources is the same in young and elderly subjects. Methods: All subjects were initially dark adapted for 10 minutes prior to testing. Each subject’s threshold was measured for a 20 msec (642 nm) test probe in young (N = 7, ages 20-40 yrs.) and elderly (N = 9, ages 60 – 80 yrs.) individuals free of eye disease using a 2-alternative, spatial forced choice procedure. Thresholds were measured when the test probe onset occurred 20 msec following the onset of either a peripheral glare source (55 lux white light, 6 degrees left visual field) or an optically superimposed 12 degree diameter adapting field (4.4 ftL) presented to the dark adapted eye for 1 sec during each 10 sec trial. Dark-adapted thresholds were also measured for each subject, and threshold elevation was expressed for each subject relative to his/her own dark-adapted threshold. Results: The magnitude of threshold elevation was virtually identical for both young and elderly subjects (2.7 log units) and for both light sources tested (2.7 log units). Conclusions: Neglecting differences in absolute sensitivity, the results suggest that the mechanisms underlying the visual system’s response to the initial onset of direct and indirectly viewed adapting fields is similar in young and elderly subjects. The results are also consistent with those of Boynton, Bush & Enoch.
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