Natural History Study of Retinal Structure, Progression, and Symmetry Using Ellipzoid Zone Metrics in RPGR-Associated Retinopathy.

PURPOSE:This is a quantitative study of retinal structure, progression rates, and interocular symmetry in retinitis pigmentosa GTPase regulator gene (RPGR)-associated retinopathy using spectral-domain optical coherence tomography (OCT). DESIGN:Prospective, observational cohort study. METHODS:Thirty-eight subjects at Moorfields Eye Hospital in London were assessed with 2 spectral-domain OCT-derived ellipzoid zone (EZ) metrics with repeatability assessments. EZ width (EZW) measurements were made on transfoveal line scans. En face images of the EZ area (EZA) were generated from high-density macular volume scans and were quantified. Baseline size, progression rate, symmetry, associations with age and genotype, and baseline structure-function correlation were investigated. RESULTS:Baseline EZW and EZA measurements were 1963.6 μm and 3.70 mm², respectively. The mean EZW progression rate was 233.6 μm per year, and the mean EZA rate was 0.67 mm² per year. Relative interocular difference as an index of symmetry was 3% for both metrics, indicating good baseline symmetry in general-although significant variation existed across the cohort. Analysis of variance found a significant effect of age but not genotype on EZ dimension and progression rates. Larger EZ dimension and greater progression were seen in younger subjects. A positive correlation between EZ dimension and progression was evident. Overall exponential decline rates of 8.2% with EZW and 15.5% with EZA were obtained. Good functional correlation was found with EZW demonstrating stronger correlation; however, EZA correlation with function was also significant. CONCLUSIONS:EZ metrics are sensitive structural biomarkers for measuring residual extent and progression in RPGR-associated retinopathy. Our elucidation of the natural history will provide clinicians and patients with more knowledge about the condition and inform the design and interpretation of interventional trials.

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