François C. Delori

Light-Induced Retinal Changes Observed with High-Resolution Autofluorescence Imaging of the Retinal Pigment Epithelium

PURPOSEnAutofluorescence fundus imaging using an adaptive optics scanning laser ophthalmoscope (AOSLO) allows for imaging of individual retinal pigment epithelial (RPE) cells in vivo. In this study, the potential of retinal damage was investigated by using radiant exposure levels that are 2 to 150 times those used for routine imaging.nnnMETHODSnMacaque retinas were imaged in vivo with a fluorescence AOSLO. The retina was exposed to 568- or 830-nm light for 15 minutes at various intensities over a square (1/2) degrees per side. Pre- and immediate postexposure images of the photoreceptors and RPE cells were taken over a 2 degrees field. Long-term AOSLO imaging was performed intermittently from 5 to 165 days after exposure. Exposures delivered over a uniform field were also investigated.nnnRESULTSnExposures to 568-nm light caused an immediate decrease in autofluorescence of RPE cells. Follow-up imaging revealed either full recovery of autofluorescence or long-term damage in the RPE cells at the exposure. The outcomes of AOSLO exposures and uniform field exposures of equal average power were not significantly different. No effects from 830-nm exposures were observed.nnnCONCLUSIONSnThe study revealed a novel change in RPE autofluorescence induced by 568-nm light exposure. Retinal damage occurred as a direct result of total average power, independent of the light-deliverynnnMETHODnBecause the exposures were near or below permissible levels in laser safety standards, these results suggest that caution should be used with exposure of the retina to visible light and that the safety standards should be re-evaluated for these exposure conditions.

Anterior Optic Nerve Blood Flow Decreases in Clinical Neurogenic Optic Atrophy

Anterior optic nerve blood flow was studied in nine patients with unilateral neurogenic optic atrophy using noninvasive techniques. Disk reflectometry measurements from temporal sites demonstrated a significant reduction in the index of blood volume in atrophic optic nerves as compared with the contralateral optic nerves (P less than 0.00001). Laser Doppler measurements from the same temporal sites detected a significant reduction in the speed of blood (P less than 0.002). On average, blood volume was decreased by 49% +/- 11% and blood speed by 30% +/- 17%. Combining the results of these two techniques yielded a relative index of blood flow that showed a significant reduction in the atrophic nerves (P less than 0.0001), averaging 64% +/- 14% temporally. Nasally there was less reduction in blood flow. The results correlated well with clinical assessment of the degree of optic nerve damage (rho = 0.92, P less than 0.002). This study demonstrates that clinical neurogenic optic atrophy induces significant reductions in overall anterior optic nerve blood flow that are detected by these noninvasive techniques.