In Vivo Retinal Phototoxicity Study

Establishing safety limits for light exposure in ophthalmic instruments

We have discovered two new and unexpected effects on the primate retina caused by prolonged exposure to bright visible light (Morgan et al, 2008). The observed effects are autofluorescence (AF) photobleaching and, at higher light levels, retinal pigment epithelium (RPE) disruption (Fig. 1). These effects raise interesting questions about how light interacts with the retina and if they are ultimately deleterious for the eye (Hunter et al, 2012).

Autofluorescence (AF) Photobleaching

Exposures to 568 nm light at irradiances > 5 J/cm2 produce an immediate reduction in lipofuscin AF. This is a transient effect that recovers within several hours. These light levels are up to 2 orders of magnitude below the photochemical maximum exposure (MPE) specified by the ANSI standard for the safe use of lasers (ANSI Z136.1, 2007).

RPE Disruption/Photodamage

Higher exposures (irradiances > 247 J/cm2) to 568 nm light the AF photobleaching effect is followed by a disruption of RPE cell mosaic, seen in RPE fluorescence images in vivo. This RPE disruption occurs at light levels at or slightly below the MPE, which is alarming because the MPE is typically about 10 times below the damage threshold (ANSI Z136.1, 2007). The delay in the appearance of this RPE disruption or photodamage implies that the mechanism of damage is photochemical and not thermal in origin.

Publications

Center for Visual Science University of Rochester