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W. H. Merigan, J. I. W. Morgan, J. J. Hunter, R. Wolfe, R. T. Libby, D. R. Williams; Histological Evidence of Retinal Damage in Macaque Caused by Exposure to 568 nm Light Below Previously Reported Damage Thresholds. Invest. Ophthalmol. Vis. Sci. 2009;50(13):345.
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We have previously shown that long exposure to 568 nm at levels near or below the American National Standards Institute (ANSI) Safe Use of Lasers maximum permissible exposure (MPE), produces alterations in in-vivo adaptive optics fluorescence retinal pigment epithelial (RPE) imaging. Light exposure over a wide range of intensities is followed by a transient reduction in RPE autofluorescence. Exposure to higher levels results in persistent derangement of the pattern of RPE autofluorescence. Here we report histological examination of light-exposed retina using confocal microscopy of wholemount retina as well as sectioning of some locations for detailed light microscopy.
Macaque retinas were given multiple localized prolonged laser light exposures during adaptive optics scanning laser ophthalmoscopy. The retina was exposed to 568 nm light over a square subtending 0.5° (126 µm) with energies ranging from 1 J/cm2 to 788 J/cm2. Pre-, immediately post-, and long-term post-exposure autofluorescence images of the RPE cells were taken over a 2° field. One macaque was subsequently sacrificed 12 days after 788 J/cm2 exposure, perfused with saline and 4% paraformadehyde, and the retinas removed and wholemounted. In-vivo images of the light exposed locations were then compared to ex-vivo confocal microscopy (Zeiss Meta 510 Laser Scanning Microscope). Finally, regions of two of the 788 J/cm2 exposure locations were dissected from the wholemount and sectioned.
Confocal microscopy found persistent morphological retinal changes for exposures of 247 J/cm2 and higher that correspond to the enduring changes observed in-vivo. At two sectioned locations, given 788 J/cm2 marked alterations of RPE cells and cone outer segments were observed, which confirmed and extended the findings from confocal microscopy.
Histological analysis confirms that previously observed RPE changes seen in in-vivo imaging correspond to morphological alterations in RPE cells and cone outer segments, produced using light levels that were previously thought to be safe. Future studies will examine the relative sensitivity of imaging and morphological methods for detecting light-induced alterations.
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