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David P. Bissig, Robin Roberts, Bruce A. Berkowitz; Vison Loss in Healthy Aging: Isolating the Contributions of Eye Optics, and Central Retinal Structure and Function. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1885.
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To use a novel combination of objective, non-invasive metrics to identify the contributions of eye optics and central retinal structure and function to age-related declines in visual acuity and contrast sensitivity.
Young (2 mo.) and mid-aged (6.5 mo.) Long-Evans rats were studied with optokinetic tracking to evaluate visual performance and manganese-enhanced MRI (MEMRI, 44 mg MnCl2•4H20 / kg body weight, ip) to non-invasively measure eye and central retinal structure and retinal physiology (i.e., regulation of ions like calcium). One eye of each animal was patched to evaluate ion regulation of light- and dark-adapted retina of each rat. Depth of field and refractive state (i.e. optics) were estimated using MEMRI measures of eye morphology (lens thickness, radii of curvature, chamber depths, etc.) and Hughes’ schematic eye for the rat (Vision Research 19, 1979). After scanning, a subset of the mid-aged rats were retained for several months, when vision testing was repeated.
Relative to young rats, mid-aged rats have significantly lower visual acuity and contrast sensitivity (P < 0.05). Central intraretinal Mn2+ uptake was significantly higher in the mid-aged rats, and was correlated with worse acuity (P < 0.05). Optics also differed significantly between groups, and were correlated with acuity (P < 0.05). Sequential regression analyses revealed that, after accounting for animal age, significant (P < 0.05) relationships remained between visual acuity and both optics and Mn2+ uptake data. After 6.5 mo., contrast sensitivity, but not acuity, continued to decline (P < 0.05). Animals with higher retinal Mn2+ uptake showed greater declines in contrast sensitivity (P < 0.05).
These data raise the possibility that, in addition to the expected role of optics, changes in central intraretinal ion regulation also participate in declines in visual function. These data extend previous literature that links neuronal calcium regulation to age-related functional declines in other CNS structures.
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