Development of a conceptual, HOV-inspired spatial weighting model for quantifying geographic atrophy severity

To develop a Hill of Vision (HOV)-inspired severity score for geographic atrophy (GA) and evaluate its ability to capture spatial characteristics of disease progression, including lesion location and proximity to the foveal center, compared with the conventional lesion area (ΔArea) metric.

This retrospective analysis included 103 untreated fellow eyes from the MAHALO study with fundus autofluorescence images available at all visits. GA lesions were delineated and binarized to generate mask images. A Gaussian weighting function based on the distance from the foveal center was applied to each lesion pixel to model the spatial distribution of retinal functional resolution, yielding a volumetric "severity score," that was kept unitless for the purpose of this exercise. For eyes with multifocal GA, total severity was defined as the sum of all lesion values. The correlation between ΔArea and ΔSeverity (0-18 months) was assessed using Pearson's coefficient. Lesion expansion direction was visualized using Euclidean distance maps.

Mean changes in ΔArea and ΔSeverity over 18 months were 1.02 ± 1.11 mm² and 5811 ± 4584, respectively. A weak but significant correlation was observed (r = 0.36, p < 0.01). Cases with peripheral enlargement showed modest severity increases, whereas parafoveal expansion caused steep severity rises despite relatively minimal area growth. Expansion maps revealed that the direction and expansion to the fovea strongly influenced severity progression.

The HOV-inspired severity score provides a spatially weighted framework for assessing GA progression and may complement conventional structural metrics by incorporating lesion location relative to the fovea.