Structural and functional phenotypic features and molecular analysis of Indian patients with Bietti crystalline dystrophy.

Purpose: Bietti crystalline dystrophy (BCD) is a rare retinal dystrophy, uncommon in Indians. This study describes the various phenotypic features seen in the Indian population. Methods: In this retrospective, descriptive case series, records of patients with either clinical or molecular diagnosis of BCD from 2009 to 2020 were perused. Phenotypic and genotype information was collected and analyzed. Results: This study included 58 patients of BCD (31 males) aged 21-79 years (mean: 47 ± 14 years). The age at onset ranged from 7 to 41 years (mean: 28.8 ± 5.1 years). Vision ranged from 20/20 to counting fingers. There were 18 (31%) patients with stage 1 with crystals and mild retinochoroidal atrophy, 22 (38%) with stage 2 with atrophy extending beyond arcades, and 18 (31%) with absent crystals and extensive atrophy of stage 3. Choroidal neovascular membrane was seen in four patients. The optical coherence tomography showed retinochoroidal thinning (84.6%), outer retinal tubulations (71.8%), and paradoxical foveal thickening with interlaminar bridges (7.7%). Electrophysiology and visual fields showed reduced responses in advanced retinochoroidal changes. Molecular confirmation was available in five patients; five mutations were seen in the CYP4V2. Conclusion: A wide variation is seen in the phenotypic picture of BCD. A molecular diagnosis is helpful in differentiating from other retinal dystrophies. The OCT shows the peculiar feature of the interlaminar bridge in early cases with photoreceptor loss. Further investigations into this OCT feature may provide insights into the pathogenesis of BCD. A genotype-phenotype correlation could not be done.