Geographic atrophy (GA) is a late stage of age-related macular degeneration (AMD) defined by progressive loss of retinal pigment epithelium (RPE), photoreceptors, and the underlying choriocapillaris. Because central visual acuity can remain relatively preserved until the fovea is involved, longitudinal imaging – especially lesion area and growth – has become the core objective measure for prognosis and therapeutic monitoring. In this article, Adam Hamilton summarises how modern imaging links metabolic stress signals, most notably fundus autofluorescence (FAF) as a surrogate of bisretinoid/lipofuscin-related RPE metabolism, coherence tomography (OCT), including photoreceptor band disruption, RPE attenuation, and hypertransmission into the choroid. modalities (FAF and OCT), practical quantification workflows including Heidelberg Engineering’s RegionFinder, segmentation, tracking, and growth prediction from OCT and FAF.

GA is a leading cause of irreversible central vision loss in older adults. Lesions usually begin parafoveally and expand over years, often coalescing and eventually involving the fovea. Progression rates vary widely between individuals; therefore, imaging is essential for defining phenotype, measuring growth, and providing patient-specific counselling.

Multimodal imaging is not redundant – it is complementary. FAF excels at outlining atrophic borders and perilesional ‘risk’ signatures by giving part of the ‘metabolic’ picture, while OCT provides cross-sectional structural biomarkers that confirm true RPE/photoreceptor loss and reveal early

Adam H amilton

WRITER

“FAF excels at outlining atrophic borders and perilesional ‘risk’ signatures by giving part of the ‘metabolic’ picture”

Finally, OCT enables structure–function conversations. Because visual acuity often underestimates functional impact until the fovea is affected, combining OCT with functional testing (e.g., microperimetry, low- luminance visual acuity) can better reflect patient experience.

OTHER IMAGING MODALITIES While this article focuses on OCT and FAF, as the most common imaging used in GA diagnosis and monitoring, it’s important to remember that other images can also be useful at times. These include:

OCT-A. Noninvasive choriocapillaris assessment; flow deficits around GA have been associated with progression and may add prognostic value.

Colour fundus photo. Baseline documentation of overall AMD phenotype; limited sensitivity for subtle atrophic borders compared with FAF/OCT.

In research settings, adaptive optics and fluorescence lifetime imaging add mechanistic insight, but these are not available to most clinicians.

REGIONFINDER AND MEASUREMENT WORKFLOWS Reliable lesion quantification requires more than a single good image: it depends on standardised acquisition, registration, and consistent editing rules. On the Heidelberg Spectralis platform, RegionFinder (Figure 3) provides semiautomated GA delineation on FAF by detecting areas of reduced autofluorescence and allowing clinician refinement. The RegionFinder guidance emphasises consistent acquisition and annotation practices to improve repeatability.

Evidence comparing manual and semiautomated approaches supports RegionFinder’s utility when quality control is applied. Mahmoudzadeh and colleagues found that semiautomated measurements can perform comparably to manual approaches, while reducing workload, provided that graders use consistent rules and review images to confirm that segmentation reflects true atrophy. For longitudinal reporting,