The role of full-field stimulus threshold in evaluating Bietti crystalline dystrophy

Visual functional testing methods are limited and cannot be well applied in all kinds of ocular diseases, especially those with low-vision. To determine whether full-field stimulus threshold (FST) is an effective method in evaluating Bietti crystalline dystrophy (BCD), with the capability in replacing other traditional visual functional methods, we designed the study.

This study was a prospective cross-sectional observational study, conducted from September 2022 to March 2023. It was a sub-study of Beijing Tongren Eye Disease Clinical Database Biobank. The study was conducted in Beijing Tongren Hospital, Capital Medical University. BCD patients who were diagnosed based on clinical features, validated by whole-exome sequencing were included. The normal volunteers were included as control group. All BCD patients underwent comprehensive evaluations, including FST, best-corrected visual acuity (BCVA), color vision, microperimetry, full-field electroretinography (ffERG), optical coherence tomography (OCT), multimodal imaging system and 4 self-reported questionnaires. The normal control group subjects only conducted FST examination. The correlation between FST and BCVA, and the differences of FST values between disease severity groups, were evaluated. The BCVA logistic regression model, FST model and hybrid model's performance (area under the curve [AUC]) were tested in predicting disease severity.

43 BCD patients (40.60 ± 8.57 years, 22 female [51%]) and 36 normal volunteers (38.56 ± 12.42 years, 21 female [58%]) were included. FST showed a moderate correlation with BCVA scores. Stage 2 group exhibited notably lower FST values than the stage 3 group, while the severely diminished group showed remarkable lower FST values than the extinguished group. The hybrid model showed better performance (AUC = 0.9221 and 0.9496) than FST model (AUC = 0.9026 and 0.9429), better than BCVA model (AUC = 0.8549 and 0.8487) in predicting disease severity.

The FST serves as a useful indicator for evaluating visual function and predicting the severity of disease in patients with BCD. The clinical implementation of FST value will serve as an important assay in various ocular diseases, necessitating further validation studies prior to its application.