Exploration and Application of Multiluminance Mobility Test in Bietti Crystalline Dystrophy.

Purpose: This study evaluated the multiluminance mobility test (MLMT) as a functional vision assessment tool for Bietti crystalline dystrophy (BCD) and explored its relationship with structural and visual function parameters. Methods: A retrospective study of 34 BCD patients (67 eyes) incorporated 2 additional low light levels (0.1 and 0.5 lux) into the MLMT. Visual function assessments included best-corrected visual acuity, visual field (VF), and microperimetry (MP). Macular structure was evaluated via spectral-domain optical coherence tomography. MLMT performance was correlated with these parameters using Spearman's rank correlation tests. Results: Despite severe global photoreceptor dysfunction, a notable proportion of participants (38.8%) passed the MLMT at 1 lux or less, with 23.9% reaching the lowest luminance (0.1 lux). MLMT lux scores correlated significantly with best-corrected visual acuity (ρ = -0.5322; P = 0.0012), mean defect of VF (ρ = -0.5919; P = 0.0005), and mean macular sensitivity of MP (MS-MP; ρ = 0.7175; P < 0.0001). Subgroup analysis revealed that subjects with preserved foveal ellipsoid zone had significantly higher MLMT lux scores and better MS-MP (both P < 0.05) than those with ellipsoid zone atrophy. Although visual function parameters were markedly impaired in certain patients, their MLMT performance remained relatively favorable. Conclusions: The standardized MLMT has a limited range for assessing advanced BCD. Preservation of central macular structure, rather than visual acuity alone, appears to be critical for mobility performance in BCD patients. Disease-specific adaptations of functional end points are needed for BCD clinical trials. Translational Relevance: To assess functional vision for BCD, the MLMT requires adaptation, and clinical trials should incorporate macular structural parameters.