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Simone Iwabe, Gui-Shuang Ying, Gustavo D. Aguirre, William A. Beltran; Visual Behavior and Retinal Structure Following Acute Light Exposure in Normal and T4R RHO Dogs. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1352.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of light exposure on visual behavior and retinal structure in rhodopsin (T4R RHO) mutant and normal dogs
Three T4R RHO dogs (age: 3 months) and 3 normal/control dogs (age: 4-5 months) that were housed under normal kennel cyclic (7 AM on - 7 PM off) light environment (~175-350 lux) were studied. Following overnight dark adaptation, acute light exposure to bright white light (corneal irradiance: 1 mW/cm2 for 1 min) was done in one eye, while the contralateral eye was shielded. Visual function prior to light exposure and at 24 hours and 2 weeks post exposure was assessed by running the dogs through a 3.6 m long obstacle course with 5 adjustable panels. Corneal shields were used to occlude vision from one eye, and test vision from the contralateral eye. Transit time was measured under 4 ambient light intensities to assess rod and cone visual function (0.2, 1, 10 and 65 lux). A total of 3 trials/eye were performed under each light intensity. Morphological retinal changes were also evaluated by non-invasive in vivo cSLO/OCT imaging before and 2 weeks after light exposure in both mutants and normals. At the end of study, histologic examination will be done
At the ages selected for this study, and when housed under standard kennel illumination, T4R RHO dogs maintain normal visual behavior, and retinal structure. Following acute bright light exposure to normal dogs, no statistically significant differences in mean transit times were noted between light exposed (L) and shielded (S) eyes at 24 hr [L: 4.56 sec (SE: ±0.08) vs S: 4.64 sec (± 0.11); P = 0.49], and at 2 week (L: 4.50 sec (±0.12) vs S: 4.47 sec (±0.11); P = 0.84] time points. OCT imaging and histology did not show any retinal thinning nor photoreceptor loss in control dogs. Visual behavior testing is ongoing in mutant dogs, and OCT imaging confirms outer retinal thinning
A short single exposure to bright white light that does not damage the retina of non-mutant dogs causes acute onset and rapid degeneration of rods in the T4R RHO dog. The use of a standardized obstacle to assess visual function in these animals will be a useful method for assessing the outcome of therapeutic intervention
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