Characterization of GA using SD-OCT. A. 2-D OCT of a healthy eye showing individual retinal layers. B. 2-D OCT of an eye with GA showing degradation of RPE and neural layers and enhancement of signal from the choroid. C. 2-D OCT for quantitation of GA progression. Highlighted green area corresponds to retina lost to atrophy from baseline to follow-up, allowing measurement of change in retinal thickness and GA lesion boundaries. RNFL, retina nerve fiber layer; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer (1 = external limiting membrane; 2 = inner photoreceptor layer; 3 = photoreceptor outer segment-RPE interdigitation; 4 = RPE-Bruch’s membrane complex; 5 = choriocapillaris and choroid).