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. Cohort study PARTICIPANTS: Four hundred and forty-five eyes of 224 patients with clinical diagnosis of RP. AF 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 for 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 dependant variable for linear regression by evaluating R2 values. Linear mixed-effects modelling was utilized to account for inter-eye correlation. AF ring size characteristics at baseline and ring progression rates. A total of 439 eyes had SWAF imaging at baseline with the AF ring observed in 206 (46.9%) eyes. Mean (95% CI) 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 analysed as the dependant variable, mean progression was -0.07 ln(mm2)/year which equates to 6.80% decrease in ring area per year. Similar rates were found in NIRAF (area: -0.59 mm2/year, horizontal extent: -0.12mm/year and ln(Area): -0.08 ln(mm2)/year equating 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. Our data suggests 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 RP clinical trials.