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J. J. Hunter, J. I. W. Morgan, J. L. Norris, D. R. Williams; Multiple Lipofuscin Fluorophores Are Involved in Photochemically-Induced Autofluorescence Reduction. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5168.
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© ARVO (1962-2015); The Authors (2016-present)
Using in vivo adaptive optics scanning laser ophthalmoscopy (AOSLO) equipped with fluorescence imaging capabilities, we previously reported an immediate reduction in macaque RPE autofluorescence (AF) intensity in response to 568 nm light, followed by either full recovery (≤ 210 J/cm2) or permanent retinal damage (≥ 247 J/cm2). These exposures were expected to be safe (ANSI Z136.1-2007). To determine if only one or if multiple lipofuscin fluorophores are responsible for this AF reduction, we explore the AF response to different wavelengths of light.
In vivo macaque RPE and cone mosaics were imaged before and after exposure to either 488 nm or 568 nm light over a square ½° field using fluorescence-AOSLO. AF images with excitation wavelengths at 488 nm and at 568 nm were taken of a 2° field centered on the exposure location both before and after the exposure. AF emission was detected over a 40 nm bandwidth centered at 624 nm. For each excitation wavelength, the change in AF intensity between the pre- and post-exposure images was quantified.
Considerably more AF reduction was observed when the wavelengths of the exposure and the AF excitation were the same than when they were different, which is not consistent with a single underlying molecular species. There appears to be similar susceptibility to AF reduction by the AF molecules excited with 488 nm and 568 nm light, suggesting that the molecular species at each wavelength have similar AF reduction efficiency. Long-term disruption of the RPE was observed within 2 weeks after exposure to 488 nm light of 79 J/cm2 or greater.
Because the shape of the action spectrum for AF reduction changes depending on the wavelength of the light exposure, more than one lipofuscin fluorophore is involved. Future work is needed to identify the molecular mechanisms involved and to determine their potential toxic properties and role in light damage. In addition to the previously reported safety hazards of 568 nm light, long-term damage was observed following exposures to 488 nm light that were 2x below previously reported photochemical damage thresholds. Thus, photochemical light safety standards do not provide the order of magnitude safety margin that many assume.
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