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K.E. Higgins, J.M. White, D. Cades, V. Ciaccio, L. Liu; Early Dark Adaptation: Effect of Age . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5404.
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Sturr et al. (1991) reported that older, compared to younger, subjects (Ss) evidenced a slower recovery of sensitivity during the first second after the offset of a relatively intense pre–adapting field that would have produced appreciable bleaching of cone photopigment. In contrast, we (unpublished data) did not find any age difference when recovery was measured following exposure to a relatively moderate intensity, transient (1 sec. duration), peripheral, glare source Our objective was to determine if an age–dependent delay in early dark adaptation would occur at moderate light levels if the exposure was continuous instead of transient.
Twelve young (24.8±2.7 yrs) and 10 elderly (60.9±7.5 yrs) Ss in good ocular health with VA > 20/40 participated. Ss were initially pre–adapted for 7 minutes to a 12o diameter, 150 cd/m2 white adapting field (AF) with a small, dim, central fixation light. Subsequently, AF luminance was abruptly decreased to 1 cd/m2 for a duration of 2 seconds on each trail and then returned to 150 cd/m2 for the remainder of the trial. Over a series of trials, early dark adaptation thresholds were measured at several times (from 20 – 700 msec) after the AF decrement using a 2–alternative, spatial forced choice procedure. On each trial, a 45 arcmin, 20 msec test flash was presented either above or below the central fixation light. Also, steady–state (SS) thresholds were measured following 7 minutes of continuous adaptation to AF levels of 150 and 1 cd/m2.
A 2–way ANOVA showed a) the effect of age was significant, with thresholds being higher for the older Ss; b) the effect of time after AF luminance decrement was significant, with threshold decreasing with increased time in the dark for all subjects; c) the time by age interaction was also significant, indicating that recovery during early dark adaptation was significantly slower in the elderly sample.
Result "a" is consistent with earlier research. Result "b" is consistent with the work of Sturr et al., and, further, it suggests that our previous failure to observe an age–dependent difference in early dark adaptation, was due, at least in part, to the transient character of the pre–adapting field used in that study.
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