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

PURPOSE: Quantitative study of retinal structure, progression rates and interocular symmetry in RPGR-associated retinopathy using spectral domain optical coherence tomography (SD-OCT).

DESIGN: Prospective, observational cohort study.

METHODS: SETTING: Moorfields Eye Hospital, London, UK SUBJECTS: 38 subjects MAIN OUTCOME MEASURE: Two SD-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 quantified. Baseline size, progression rate, symmetry, associations with age and genotype, and baseline structure-function correlation were investigated.

RESULTS: Baseline EZW and EZA were 1963.6 μm and 3.70 mm2 respectively. Mean EZW progression rate was 233.6 μm/year and mean EZA rate was 0.67 mm2 /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. ANOVA results demonstrated 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 signficant.

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.