Longitudinal Natural History Study of Visual Function in Bietti Crystalline Dystrophy: Implications for Early...

To delineate the natural history of visual function parameters over time in individuals with Bietti crystalline dystrophy.

This was a single-center retrospective longitudinal cohort study. Participants (n = 29) with a clinical diagnosis of Bietti crystalline dystrophy who harbored two alleles of disease-causing variants of the cytochrome P450 family 4 subfamily V member 2 gene (CYP4V2) were enrolled. Best-corrected visual acuity (BCVA), visual field (VF), and full-field ERG (ffERG) at baseline and their changes during the follow-up period were evaluated. Annual progression rates were calculated using three methods.

The mean age at the initial visit was 34.2 ± 7.5 years, with 5.9 ± 3.1 years follow-up. The annual progression rate from the longitudinal analysis using averaged individual progression rates was 0.079 logMAR units for BCVA, 1.14 dB for mean defect (MD) value of VF, and -18.06 µV and -5.45 µV for the b-wave amplitudes of scotopic 3.0 ERG and photopic 3.0 ERG, respectively. Mixed-model linear regression revealed annual progression rates of 0.068 logMAR units, 0.86 dB, -13.29 µV, and -3.75 µV, respectively. Cross-sectional progression rates from visual function versus age at baseline were 0.011 logMAR units, 0.47 dB, -1.85 µV, and -1.07 µV, respectively, which were significantly slower than those from the longitudinal data. Interocular symmetries for the MD values of VF and ffERG were good.

Annual BCVA, VF, and ffERG progression rates were rapid, emphasizing the need for regular follow-up and early intervention. The progression rate cannot be inferred accurately from cross-sectional data from patients of different ages.