Natural history of central sparing in geographic atrophy secondary to non-exudative age-related macular degeneration.

Background: The macular central 1 mm diameter zone is crucial to patients' visual acuity, but the long-term natural history of central sparing in eyes with geographic atrophy (GA) is unknown.

Methods: We manually segmented GA in 210 eyes with GA involving central 1 mm diameter zone (mean follow-up=3.8 years) in the Age-Related Eye Disease Study. We measured the residual area in central 1 mm diameter zone and calculated central residual effective radius (CRER) as square root of (residual area/π). A linear mixed-effects model was used to model residual size over time. We added a horizontal translation factor to each data set to account for different durations of GA involving the central zone.

Results: The decline rate of central residual area was associated with baseline residual area (p=0.008), but a transformation from central residual area to CRER eliminated this relationship (p=0.51). After the introduction of horizontal translation factors to each data set, CRER declined linearly over approximately 13 years (r=0.80). The growth rate of total GA effective radius was 0.14 mm/year (95% CI 0.12 to 0.15), 3.7-fold higher than the decline rate of CRER (0.038 mm/year, 95% CI 0.034 to 0.042). The decline rate of CRER was 53.3% higher in eyes with than without advanced age-related macular degeneration in the fellow eyes at any visit (p=0.007).

Conclusions: CRER in eyes with GA declined linearly over approximately 13 years and may serve as an anatomic endpoint in future clinical trials aiming to preserve the central zone.