In vivo fluorescence of the ocular fundus exhibits retinal pigment epithelium lipofuscin characteristics

Abstract

Purpose: To characterize the intrinsic fluorescence (autofluorescence) of the human ocular fundus with regard to its excitation and emission spectra, age relationship, retinal location, and topography, and to identify the dominant fluorophore among the fundus layers.

Methods: Using a novel fundus spectrophotometer, fluorescence measurements were made at 7 degrees temporal to the fovea and at the fovea in 30 normal subjects and in 3 selected patients. Topographic measurements were made in 3 subjects. Ex vivo measurements of fluorescence of human retinal pigment epithelium (RPE) were obtained and compared to in vivo data.

Results: Fundus fluorescence reveals a broad band of emission between 500 and 750 nm, a maximum of approximately 630 nm, and optimal excitation of approximately 510 nm. Exhibiting a significant increase with age, this fluorescence is highest at 7 degrees to 15 degrees from the fovea, shows a well-defined foveal minimum, and decreases toward the periphery. In vivo fluorescence spectra are consistent with those obtained ex vivo on human RPE. Measurements with short wavelength excitation are strongly influenced by ocular media absorption and reveal an additional minor fluorophore in the fovea.

Conclusions: Spectral characteristics, correlation with age, topographic distribution, and retinal location between the choriocapillaris and the photoreceptors suggest that the dominant fundus fluorophore is RPE lipofuscin. The minor fluorophore is probably in the neurosensory retina but has not been identified.