AAO 2026: New metrics for geographic atrophy progression account for lesion location and direction

Ophthalmology is now in “an era of GA therapeutics,” according to SriniVas Sadda, MD. That makes accurate measurement of geographic atrophy (GA) progression essential. At the American Academy of Ophthalmology (AAO) 2026 Retina Subspecialty Day in New Orleans, Sadda reviewed the limitations of existing growth metrics and introduced 2 new approaches. Sadda is a professor of ophthalmology at Doheny Eye Institute, UCLA.

Why progression measurement matters

Sadda said measuring GA progression serves 3 purposes:

• Identifying fast progressors in clinical practice
• Selecting patients for clinical trials
• “Even more critically,” measuring how patients respond to therapy

Limitations of existing metrics

Sadda reviewed the metrics used historically, starting with simple lesion area growth. Because GA expands at the lesion perimeter, larger lesions grow faster, which limits area-based comparisons.

Square root transformation was developed to correct for this imbalance. Sadda described it as a reasonable, simple approach. However, it becomes harder to apply to multifocal lesions, because lesions can merge or new foci can appear, altering the growth trajectory.

Perimeter-adjusted GA area generally works well, Sadda said, though it also carries caveats.

Accounting for foveal resiliency

Evidence suggests GA lesions may grow more slowly toward the fovea. This is one proposed reason the fovea can be spared.

At the recent Retina Society meeting, Sadda presented a mechanistic explanation for this apparent foveal resiliency. Cone density is greater in the fovea, and the correlation between photoreceptor density and atrophy progression may account for the slower foveal growth. In this model, the rate of photoreceptor death is relatively stable. Progression measures therefore need to account for both a lesion’s location and the direction in which it spreads.

Measuring the pace of border advancement

Sadda presented for the first time a recently published concept: measuring the pace at which the GA lesion border advances. This approach can be adjusted for lesion location and direction of spread, which evens out the growth rate.

According to Sadda, this matters most when evaluating therapies. Determining whether the pace of progression has changed after treatment requires controlling for all of these variables.

Weighting lesions by location

Sadda’s final point was that lesion location affects functional impact. “Sometimes when we treat every part of the macula as being equally important, we miss how impactful a GA lesion may be as it progresses into the fovea,” he said.

To address this, he introduced a GA severity score that weights a lesion based on its position. “I think that might be a better tool in the future for actually describing the full functional impact of a GA lesion,” Sadda said.

REFERENCE

1. Sadda S. New approaches for assessing the progression of geographic atrophy: implications for clinical trials and practice. Presented at: American Academy of Ophthalmology 2026 Retina Subspecialty Day; October 9-10, 2026; New Orleans, LA.