Retinal Damage Observed With Autofluorescence Imaging of Retinal Pigment Epithelium Cells in Vivo

Abstract

Purpose:: The American National Standards Institute (ANSI) provides a standard for the safe use of lasers from which maximum permissible exposures (MPE) of laser light can be calculated. This standard is used as a limit for exposures of light to the eye and to assess the safety of retinal imaging experiments. Here we detect retinal damage after light exposures by using adaptive optics (AO) scanning laser ophthalmoscopy to image the cones and retinal pigment epithelial (RPE) cells in the macaque retina in vivo.

Methods:: The macaque retina was simultaneously exposed to 153 µW of 830 nm, 39 µW of 904 nm, and 39.5 µW or 150 µW of 568 nm light for 15 minutes over a square ½ degree field using an AO scanning laser ophthalmoscope (SLO). Pre and post exposure images were taken of the cone photoreceptors and the RPE cells using AOSLO reflectance and autofluorescence imaging techniques, respectively. Follow up imaging of the cones and RPE cells was done 10 and 26 days after the exposures.

Results:: Both the 39.5 µW and 150 µW exposure caused an immediate darkening of the autofluorescence in the RPE cells. Two hours post exposure, the darkening of the RPE was still visible but relaxed. Ten days later, the area of retina exposed to the 150 µW light showed significant alterations. The RPE cells in this region appear to be missing, while RPE cells outside of the exposure remained visible. The cones in this region did not waveguide as expected and appeared cloudy. Conversely, the retinal area exposed to 39.5 µW appeared normal ten days post exposure. By 26 days, the retinal change observed from the 150 µW exposure had improved slightly. RPE cells appear to have migrated to fill in the exposed area. The cones still appeared abnormal.

Conclusions:: We have observed retinal damage in the macaque after exposure to light that is 2.67 times below the ANSI standard using AOSLO imaging of the cones and RPE cells. Whether the AOSLO provides a more sensitive measure of damage or the ANSI standard should not be applied for these exposure conditions remains to be determined. Meanwhile, researchers should use care when determining the safety of experiments with visible light exposures.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal pigment epithelium