Baseline Visual Field Findings in the RUSH2A Study: Associated Factors and Correlation With Other Measures of Disease Severity.

Purpose: To report baseline visual fields in the Rate of Progression in USH2A-related Retinal Degeneration (RUSH2A) study.
Design: Cross-sectional study within a natural history study.
Methods: Setting: multicenter, international.
Study Population: Usher syndrome type 2 (USH2) (n = 80) or autosomal recessive nonsyndromic retinitis pigmentosa (ARRP) (n = 47) associated with biallelic disease-causing sequence variants in USH2A.
Observation Procedures: Repeatability of full-field static perimetry (SP) and between-eye symmetry of kinetic perimetry (KP) were evaluated with intraclass correlation coefficients (ICCs). The association of demographic and clinical characteristics with total hill of vision (V _TOT ) was assessed with general linear models. Associations between V _TOT and other functional and morphologic measures were assessed using Spearman correlation coefficients and t tests.
Main Outcome Measures: V _TOT (SP) and III4e isopter area (KP).
Results: USH2 participants had more severe visual field loss than ARRP participants (P < .001, adjusting for disease duration, age of enrollment). Mean V _TOT measures among 3 repeat tests were 32.7 ± 24.1, 31.2 ± 23.4, and 31.7 ± 23.9 decibel-steradians (intraclass correlation coefficient [ICC] = 0.96). Better VA, greater photopic ERG 30-Hz flicker amplitudes, higher mean microperimetry sensitivity, higher central subfield thickness, absence of macular cysts, and higher III4e seeing area were associated with higher V _TOT (all r > .48; P < .05). Mean III4e isopter areas for left (4561 ± 4426 squared degrees) and right eyes (4215 ± 4300 squared degrees) were concordant (ICC = 0.94).
Conclusions: USH2 participants had more visual field loss than participants with USH2A-related ARRP, adjusting for duration of disease and age of enrollment. V _TOT was repeatable and correlated with other functional and structural metrics, suggesting it may be a good summary measure of disease severity in patients with USH2A-related retinal degeneration.
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