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AE Lindsey, RK Chawla, E Townes-Anderson; Spatial Sensitivity Decreases With Age in the Adult Tiger Salamander . Invest. Ophthalmol. Vis. Sci. 2002;43(13):729.
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Purpose: We have proposed that the tiger salamander (Ambystoma tigrinum) could serve as a model for age-related retinal degeneration (Townes-Anderson, Colantonio, and St. Jules, 1998), and have demonstrated that histological degeneration as well as a decrease in the optomotor response occurs in large (old) compared to small (young) salamanders. The purpose of this study was to quantify differences in spatial sensitivity between young and old animals. Methods: Optomotor responses of small (≤20cm; n = 4) and large (≥22cm; n = 9) salamanders were measured under both photopic (250W) and scotopic (9W) luminance levels using a series of rotating square wave gratings (7 rotations/min; 0.02 - 0.30 cycles/deg visual angle) presented in random order. Threshold was defined as the stimulus value at which the probability of responding (turning in the direction of rotation) was 0.5. Results: Small and large salamanders had similar peak spatial frequency sensitivity under photopic conditions; the peak sensitivity for both was 0.08 cycles/deg visual angle. However, larger salamanders had higher mean photopic luminance threshold values, on average, for all spatial frequencies tested. Under scotopic luminance levels, a shift in peak sensitivity to a lower spatial frequency (0.04 cycles/deg) was observed in large but not small animals. In addition, mean scotopic luminance contrast threshold values increased for spatial frequencies between 0.05 and 0.20 cycles/deg compared to photopic conditions for both small and large animals with larger animals consistently higher than smaller animals. Conclusion: (1) Larger (presumably older) salamanders may have lower contrast sensitivity under photopic light levels, and lower contrast sensitivity as well as reduced acuity under scotopic light levels compared to smaller animals. If so, this would be consistent with the known progression of retinal degeneration with age in this species. (2) A quantitative optomotor technique can be used to assess visual function in salamanders of different ages. Thus, the tiger salamander is not only a good model to study the cell biology of age-related retinal degeneration, but a useful model to study the visual changes that occur during aging.
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