Zhengyang Liu, Lauren N. Ayton, Fleur O'Hare, Janan Arslan, Monica L. Hu, Jiang- Hui Wang, Doron G. Hickey, Myra B. McGuinness, Andrea L. Vincent, Fred K. Chen, Thomas L. Edwards

Purpose: Understanding between-eye symmetry in Bietti Crystalline Dystrophy (BCD) is important for prognosis counselling and to facilitate therapeutic clinical trials using the contralateral, untreated eye as an internal control. We evaluated the interocular symmetry of anatomical features and visual function among individuals with BCD, with a focus on the number, area and distribution of the unique retinal crystalline deposits.

Method: Thirteen Australian and New Zealand participants with confirmed biallelic CYP4V2 mutations and a characteristic BCD fundus appearance consented for the study. Crystals visible on colour fun- dus photography were manually counted. Spearman’s correlation coefficients (ρ), intra-class correlation coefficients (ICC) and Bland-Altman plots were used to assess anatomical and functional between-eye symmetry.

Results: Median participant age was 48 years, nine (69%) were female and five (38%) were of East Asian descent. Distance visual acuity ranged from 6/4.8 to light perception. Interocular correlation was high for fundus crystal area (ρ = 1.00; ICC = 0.97), fundus crystal count (ρ = 0.98; ICC = 0.97), and hypoautofluorescent area (ρ = 0.88; ICC = 0.98). Average foveal volume was moderately correlated between eyes (ρ = 0.73; ICC = 0.85). No significant correlation was found for foveal crystal count and area, average or central foveal thickness, best corrected visual acuity, and average macular or central foveal sensitivity.

Conclusion: Fundus crystal area, fundus crystal number and hypoautofluorescent area displayed strong interocular symmetry in this study. The anatomical symmetry shown in these data may influence the choice of outcome measures of future BCD trials, and provides valuable information for clinicians caring for patients with BCD.