Structure-Function Relationships in Geographic Atrophy Based on Mesopic Microperimetry, Fundus Autofluorescence, and...

To examine relationships between retinal structure and visual function in geographic atrophy (GA) by analyzing spatial agreement between absolute scotomas and macular structure, focusing on (1) choroidal hypertransmission, a key feature of complete retinal pigment epithelium and outer retinal atrophy (cRORA), and (2) fundus autofluorescence (FAF)-defined GA.

Mesopic microperimetry (using a novel T-shaped pattern) and multimodal imaging were recorded longitudinally in a phase II GA trial. Horizontal and vertical optical coherence tomography (OCT) line scans (corresponding to the T axes) were graded for choroidal hypertransmission; FAF images were graded for GA. Spatial concordance between zones of absolute scotoma and atrophy was quantified by the Dice similarity coefficient (DSC).

The analysis population comprised 24 participants (mean follow-up 26.8 months). For concordance between absolute scotoma and choroidal hypertransmission, estimated mean DSC was 0.70 (95% confidence interval [CI], 0.64-0.77). This was significantly higher than for FAF-defined GA (0.67; 95% CI, 0.61-0.74; estimated mean difference = 0.03, 95% CI, 0.02-0.05, P < 0.001). Mean OCT choroidal reflectivity was strongly associated with likelihood and severity of scotoma.

Spatial concordance between absolute scotomas and GA structural features is moderately high and slightly higher for choroidal hypertransmission than FAF-defined GA. This supports choroidal hypertransmission, a key cRORA feature, as an outcome measure in interventional trials. OCT provides more information to explain visual function than FAF alone. However, given some discordance for both structural features, performing microperimetry alongside imaging remains important.

These findings provide insights into the complex relationship between retinal structure and visual function and contribute to a nuanced understanding of outcome measures.