Fundus autofluoresence (AF) is a rapid noncontact, noninvasive way to evaluate RPE function. Autofluorescence is the intrinsic fluorescence emitted by a substance after being stimulated by excitation energy. Ocular structures that autofluoresce include the corneal epithelium and endothelium, lens, macular and RPE pigments, optic nerve drusen, and RPE deposits in Best disease. The clinical use of fundus AF relies on the fact that the predominant source of autofluorescence in the macula is lipofuscin. When the RPE phagocytoses photoreceptor outer segments, which consist of retinoids, fatty acids, and proteins, lipofuscin accumulates as an oxidative by-product within the RPE cells. The pigment within lipofuscin that causes autofluorescence is A2E, named for its derivation from 2 molecules of vitamin A aldehyde and 1 molecule of ethanolamine. A loss of RPE cells has been shown to be accompanied by substantial loss of autofluorescent content.
Fundus AF can be imaged using an SLO that uses blue laser excitation (488 nm) and a 500-nm barrier filter to isolate light from other ocular autofluorescent structures. By examining fundus AF images and thus lipofuscin accumulation, clinicians can evaluate problems with the RPE. For example, with the loss of RPE containing lipofuscin, areas of geographic atrophy appear dark under AF. Surrounding this dark area is a ring of elevated autofluorescence due to lipofuscin. Some evidence suggests that this increased autofluorescence, especially at the edge of this dark area, may predict geographic atrophy formation and expansion. Autofluorescence has also been helpful in assessing RPE health in exudative AMD and can consistently visualize serous pigment epithelium detachment. It is important to remember, however, that reports on the use of AF in the diagnosis and management of AMD are preliminary at best and sometimes conflicting. There also remains a need for further data to clarify the relationship of AF patterns in the formation and expansion of geographic atrophy.
. Fundus autofluorescence and age-related macular degeneration.2003;110:392–399.