PurposeTo better understand the pathophysiology of geographic atrophy (GA), secondary to age-related macular degeneration, eyes affected by unilateral GA (and CNV in the fellow eye; U-GA group) or by bilateral GA (B-GA group) were evaluated using an integrated morpho-functional approach and quantifying biomarker of retinal macroglial activity.MethodsPatients with U-GA and B-GA and foveal-sparing were consecutively enrolled in a prospective study. All included eyes underwent fundus photography, fundus autofluorescence (FAF), foveal retinal and choroidal thicknesses (RT, CT), contrast sensitivity, best-corrected visual acuity (BCVA), low-luminance VA (LLVA) and low-luminance deficit (LLD), and mesopic and scotopic microperimetry and multifocal electroretinography (mfERG). Glial fibrillary acidic protein (GFAP), biomarker of Müller cell activation, was quantified in the aqueous humor (AH).ResultsForty eyes of 40 patients (18 in the U-GA group and 22 in the B-GA group) were studied. RT, GA area, BCVA, contrast sensitivity, mfERG, and microperimetry (at both background luminances) were not different between groups. CT was significantly thinner in U-GA compared to B-GA group (p = 0.020). Both LLVA and LLD were significantly worse in the B-GA vs U-GA group (p = 0.033 and p = 0.048, respectively). GFAP intraocular concentration was significantly higher in the B-GA group (p = 0.01).ConclusionsDifferent pathophysiologic mechanisms may be responsible for GA in unilateral (with CNV in the fellow eye) compared to bilateral GA cases. In unilateral cases, a thinner choroid seems to play a key role. Whereas, in bilateral cases, Müller cells and their supported photoreceptors may be primarily involved.