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Benjamin Masella, Jennifer J. Hunter, Lu Yin, Jennifer Strazzeri, Alfredo Dubra, William H. Merigan, David R. Williams; No Loss Of Photopigment Kinetics Or Contrast Sensitivity Seen After Photochemical Insult To The Retinal Pigment Epithelium. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3199.
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We have previously reported retinal pigment epithelium (RPE) disruption in primate retina exposed to visible irradiances near the maximum permissible exposure (MPE) defined by the American National Standards Institute (ANSI), but the functional consequences of this disruption are not known. This study combined high resolution retinal imaging with two functional measures: photopigment densitometry and microperimetry of contrast sensitivity. The former provides a noninvasive, objective measure of pigment recovery, while the latter measures the limits of sensitivity to luminance contrast. We used these measures to evaluate visual function in the presence of light induced RPE disruption.
Square regions in the living macaque retina were exposed to 568 nm light at 1.4 times the ANSI MPE, which produced photochemical disruption of the RPE.Densitometry - Six to eight weeks later, four retinal areas were fully bleached and photopigment density measurements were taken using an adaptive optics scanning laser ophthalmoscope (AOSLO). We simultaneously obtained two high resolution reflectance images (794 nm and 514 nm) of the photoreceptor layer at each exposed retinal location and the surrounding area. The high signal-to-noise ratio (SNR), 794 nm (no measurable effect on photopigment density) images were used for motion tracking to align the low SNR, 514 nm images, which provided a reflectance signal that varied with pigment density.Microperimetry - Contrast thresholds were measured 1 month after light exposure by having a trained macaque discriminate the orientation of minute patches of grating (gabor stimulus, σ = 0.15 deg) placed at the center of the light exposed area and at 9 locations around it.
We found no average difference in photopigment regeneration rate when compared to the immediately surrounding retinal area. Additionally, AOSLO images showed preserved cone structure within the area of RPE disruption. Microperimetry showed no measurable loss in contrast sensitivity.
Structural changes in RPE cells induced by bright light exposure do not necessarily compromise photopigment kinetics or contrast sensitivity. It is not known whether the disrupted RPE cells are still servicing their overlying photoreceptors or if an alternate pathway is involved.
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