Fundus autofluorescence and Photobleaching : Definitions

Fundus autofluorescence (AF) imaging is a non-invasivemethod for detection of fundus fluorophores. The 488 nm blue (short wavelength: SW) or the 787 nm near-infrared (NIR) wavelenght are usually used to induce AF of fluorophores located in the retinal pigment epithelium (RPE). In case of excitation with SW light, the resulting AF comes predominantly from A2E located in the lipofuscin granules of the RPE. On the other hand, excitation with NIR light seems to highlight the melanin. Regardless of the type of fluorophore in the RPE, the exciting light has to pass first through the retina and especially through the photoreceptor layer. The photopigment absorbs a part of the light, which will not be transmitted to the RPE. Therefore, RPE fluorophores will be less AF. In the same time, photo-isomerization of the 11-cis-retinal to 11-trans-retinal by the photon absorbance will be the beginning of the visual signal. Thereby, retinal photopigment loose its absorption property and the light will be easily distributed to the RPE fluorophores. This photoreceptor bleaching phenomenon could be used to better understand the origin of the hyper-AF pattern: hyper-AF of the RPE or lack of absorbance of signal due to photopigment loss