Nonlinear Reduction in Hyperautofluorescent Ring Area in Retinitis Pigmentosa

Purpose: To report baseline dimension of the autofluorescent (AF) ring in a large cohort of retinitis pigmentosa (RP) patients and to evaluate models of ring progression. Design: Cohort study. Participants: Four hundred and forty-five eyes of 224 patients with clinical diagnosis of RP. Methods: Autofluorescent rings from near-infrared AF (NIRAF) and short-wavelength AF (SWAF) imaging modalities in RP eyes were segmented with ring area and horizontal extent extracted from each image for cross-sectional and longitudinal analyses. In longitudinal analysis, for each eye, ring area, horizontal extent, and natural logarithm of the ring area were assessed as the best dependent variable for linear regression by evaluating R² values. Linear mixed-effects modeling was utilized to account for intereye correlation. Main Outcome Measures: Autofluorescent ring size characteristics at baseline and ring progression rates. Results: A total of 439 eyes had SWAF imaging at baseline with the AF ring observed in 206 (46.9%) eyes. Mean (95% confidence interval) of ring area and horizontal extent were 7.85 (6.60 to 9.11) mm² and 3.35 (3.10 to 3.60) mm, respectively. In NIRAF, the mean ring area and horizontal extent were 7.74 (6.60 to 8.89) mm² and 3.26 (3.02 to 3.50) mm, respectively in 251 out of 432 eyes. Longitudinal analysis showed mean progression rates of −0.57 mm²/year and −0.12 mm/year in SWAF using area and horizontal extent as the dependent variable, respectively. When ln(Area) was analyzed as the dependent variable, mean progression was −0.07 ln(mm²)/year, which equated to 6.80% decrease in ring area per year. Similar rates were found in NIRAF (area: −0.59 mm²/year, horizontal extent: −0.12 mm/year and ln(Area): −0.08 ln(mm²)/year, equated to 7.75% decrease in area per year). Analysis of R² showed that the dependent variable ln(Area) provided the best linear model for ring progression in both imaging modalities, especially in eyes with large overall area change. Conclusions: Our data suggest that using an exponential model to estimate progression of the AF ring area in RP is more appropriate than the models assuming linear decrease. Hence, the progression estimates provided in this study should provide more accurate reference points in designing clinical trials in RP patients. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.