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Simone Iwabe, Kendra McDaid, Gustavo Aguirre, William Beltran; ASSESSMENT OF RETINAL STRUCTURE FOLLOWING REPEATED LIGHT EXPOSURE IN THE LIGHT SENSITIVE T4R RHODOPSIN MUTANT DOG RETINA. Invest. Ophthalmol. Vis. Sci. 2013;54(15):296.
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© ARVO (1962-2015); The Authors (2016-present)
We previously reported that a 60 sec white light exposure to 0.1 mW/cm2 (170 lux) is a sub-threshold dose that does not cause retinal damage in T4R RHO dogs, while a corneal irradiance of 0.3 mw/cm2 (551 lux)-or supra-threshold dose-leads to mild ONL thinning 2 weeks post exposure. Here, we evaluated the effect of repeated exposures to sub and supra-threshold doses in the retinas of T4R/+ RHO mutant dogs.
Group A: T4R/+ dogs #1, #2 had the right eye exposed once at T0 and the left eye exposed 4 times at T0, T1, T2 and T3 with a 2 wk interval between exposures. Group B: T4R/+ dogs #3, #4 had the right eye shielded and the left eye exposed 4 times(T0, T1, T2 and T3). Within each group, one dog was exposed to sub-threshold doses (dogs #1, #3) while the other received supra-threshold doses (dogs # 2, #4). A non-mutant dog was used as a control (the right eye was shielded and the left eye was exposed 4 times at same time point to supra-threshold doses). ONL thickness was measured along the 4 cardinal meridians by non-invasive cSLO/sdOCT imaging before, and every 2 wks after each light exposure; as well as by histologic examination at termination.
No significant changes in ONL thickness were observed along any of the 4 meridians when comparing the shielded eye of dog #3 to the eyes of dogs #3 and # 1 that were exposed up to 4 times to a sub-threshold doses. Dog #2 that received a supra-threshold dose had a similar decrease in ONL thickness in the superior area 8 weeks after a one or 4 exposures (82,1 % and 86.2%, respectively). However, a difference was seen in the temporal meridian where a single exposure led to a 14.3% loss of ONL, while 4 exposures caused a more severe (63.4%) thinning. Dog #4 that also received a supra-threshold dose showed only a 16.1% decrease in ONL thickness in the superior meridian in the shielded eye vs. a 73.6% thinning in the eye exposed 4 times. No significant changes were observed in this dog in the temporal, nasal and inferior meridians.
Repeated light exposure to sub-threshold doses of light does not cause damage to T4R RHO retinas. However, repeated exposure to retinotoxic light intensities causes cumulative retinal damage that is worse than that achieved by a single exposure. These results may be relevant to the suggested cumulative light damage that occurs in human patients with some RHO mutations.
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