Long-term reduction in infrared autofluorescence caused by infrared light below the maximum permissible exposure.
OBJECTIVE
Many retinal imaging instruments use infrared wavelengths to reduce the risk of light damage. However, we have discovered that exposure to infrared illumination causes a long-lasting reduction in infrared autofluorescence (IRAF). We have characterized the dependence of this effect on radiant exposure and investigated its origin.


METHODS
A scanning laser ophthalmoscope was used to obtain IRAF images from two macaques before and after exposure to 790-nm light (15-450 J/cm(2)). Exposures were performed with either raster-scanning or uniform illumination. Infrared autofluorescence images also were obtained in two humans exposed to 790-nm light in a separate study. Humans were assessed with direct ophthalmoscopy, Goldmann visual fields, multifocal ERG, and photopic microperimetry to determine whether these measures revealed any effects in the exposed locations.


RESULTS
A significant decrease in IRAF after exposure to infrared light was seen in both monkeys and humans. In monkeys, the magnitude of this reduction increased with retinal radiant exposure. Partial recovery was seen at 1 month, with full recovery within 21 months. Consistent with a photochemical origin, IRAF decreases caused by either raster-scanning or uniform illumination were not significantly different. We were unable to detect any effect of the light exposure with any measure other than IRAF imaging. We cannot exclude the possibility that changes could be detected with more sensitive tests or longer follow-up.


CONCLUSIONS
This long-lasting effect of infrared illumination in both humans and monkeys occurs at exposure levels four to five times below current safety limits. The photochemical basis for this phenomenon remains unknown.
The Institute of Optics, University of Rochester, Rochester, New York, United States Center for Visual Science, University of Rochester, Rochester, New York, United States.
Benjamin D
BD
Masella
The Institute of Optics, University of Rochester, Rochester, New York, United States.
David R
DR
Williams
Flaum Eye Institute, University of Rochester, Rochester, New York, United States.
William S
WS
Fischer
Center for Visual Science, University of Rochester, Rochester, New York, United States.
Ethan A
EA
Rossi
Center for Visual Science, University of Rochester, Rochester, New York, United States Flaum Eye Institute, University of Rochester, Rochester, New York, United States.
Jennifer J
JJ
Hunter
D000818:Animals; D004596:Electroretinography; D005260:Female; D005451:Fluorescein Angiography; D007259:Infrared Rays / Q000009:adverse effects*; D008062:Lipofuscin / Q000378:metabolism; D008252:Macaca fascicularis; D008253:Macaca mulatta; D008297:Male; D008452:Maximum Allowable Concentration; D009887:Ophthalmoscopy; D061848:Optical Imaging; D011833:Radiation Injuries, Experimental / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D012160:Retina / Q000528:radiation effects*; D012164:Retinal Diseases / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism; D058609:Visual Field Tests; D014794:Visual Fields
D008062:Lipofuscin
light damage; radiation damage; retina; retinal pigment epithelium; scanning laser ophthalmoscopy