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J. J. Hunter, J. I. W. Morgan, R. Wolfe, J. R. Sparrow, D. R. Williams; Ex vivo Changes in Retinal Pigment Epithelial Autofluorescence With Light Exposure. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1843.
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We previously described a reduction and subsequent recovery of macaque retinal pigment epithelial cell autofluorescence (AF) in vivo following exposure to visible light. To clarify whether these changes reflect the intrinsic properties of the fluorophores responsible for AF or are caused by other retinal changes (such as a light-induced migration of a screening pigment), we investigated whether similar AF changes could also be observed in two different ex vivo preparations.
Fixed tissue was imaged in the same adaptive optics scanning laser ophthalmoscope used in the in vivo studies. Flat-mounted human RPE slides (retina removed) or fixed cultured A2E-laden ARPE19 cells were placed in the retinal plane of a model eye and exposed to light of various powers, durations, and wavelengths from the visible to the infrared. Images were acquired before, immediately after, and up to 24 hours after the light exposure. AF changes were quantified by the normalized ratio of AF intensity inside the exposed area to control regions immediately outside the exposed area.
The in vivo and ex vivo experiments produced results that were similar in several respects. Both revealed a reduction in AF immediately following visible light exposure, but not with intense infrared exposure. Both showed reciprocity of power and duration, indicative of a photochemical rather than thermal origin for the effect. Both showed some recovery of AF subsequent to the reduction that immediately followed light exposure, though only partial recovery was observed in the ex vivo case. To produce the same AF reduction, roughly 10 times greater retinal irradiance was required in the in vivo case relative to the two ex vivo preparations.
The similarities between the in vivo and ex vivo results suggest that the metabolic activity of the living retina is not required to produce the immediate light-dependent reduction in AF and suggests that the effect reflects an intrinsic property of the fluorophores involved. One possible mechanism is the photooxidation of lipofuscin, which could have damaging consequences for the retina. If this is the mechanism, the fact that the living eye is 10 times less sensitive to AF changes and that it shows a complete, rather than a partial, recovery of AF intensity suggests that there may be metabolic mechanisms that actively protect against light-induced changes in lipofuscin.
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