Why does Geographic Atrophy appear densely hypoautofluorescent on FAF?

Geographic Atrophy (GA) appears densely hypoautofluorescent on fundus autofluorescence (FAF) primarily because it is associated with the loss of the Retinal Pigment Epithelium (RPE) and consequently a reduction in the accumulation of lipofuscin, a pigment that is normally present in healthy retinal tissue. The RPE cells play a crucial role in visual function, including the recycling of photoreceptor outer segment components, and they store lipofuscin as a byproduct of this metabolic activity.

In areas of geographic atrophy, the RPE is atrophied or absent, which leads to decreased levels of lipofuscin in those regions. Since lipofuscin is autofluorescent, its absence results in a lower autofluorescence signal, causing the affected areas to appear hypoautofluorescent on imaging. Thus, the hypoautofluorescence seen in geographic atrophy is directly related to the depletion of this pigment due to RPE cell loss.

This understanding clarifies the relationship between RPE health, lipofuscin presence, and the imaging characteristics observed in FAF.