Visual Function Characteristics in STXBP1 Epileptic Encephalopathy Patients

<b>Background</b>: The goal of the study was to describe the visual function characteristics of children with developmental epileptic encephalopathy resulting from mutations in the <i>STXBP1</i> gene. <b>Methods</b>: The study included 26 consecutive patients from the Polish STXBP1 population (11 male and 16 female; mean age: 7 years and 4 months; SD 4.03; range: 2-16 years) evaluated at a single center for strabismus and binocular vision. Data were obtained from medical records, including ophthalmological, neurological, and genetic information, as well as orthoptic and ophthalmological examinations performed in the clinic. <b>Results</b>: No major eye disorders were identified during the ophthalmological evaluation. The average prevalence of hyperopia was 76.9% (mean for OD, OS), with hyperopia above 4.25 D occurring in 17.3% (<i>n</i> = 4) of participants. Astigmatism was present in 96.2% of patients, with values ≥ 2.75 D in 27% (<i>n</i> = 7) of the group. The mean disc-foveal angle across all subjects was 7.23° ± 6.85° (range: -10.34° to 19.77°). Convergence was absent in 53.8% (<i>n</i> = 14) of patients. Mean accommodation responses equal to or higher than +1.0 D in any eye were noted in 90.5% of subjects. The mean accommodative/convergence (AC/A) ratio was 1.16 (SD 1.05; range: 0-3.3). Fusion was diagnosed using the 20 base-out prism test in 77% (<i>n</i> = 20) of patients, of which 85% (<i>n</i> = 17) had a positive response. <b>Conclusions</b>: This is the first study to comprehensively assess visual function in children with STXBP1 synaptopathy. Binocular vision development in individuals with STXBP1 differs from that of the general population. Considering the high prevalence of refractive errors, deficits in accommodation, and a low AC/A ratio, early visual diagnostics and the use of corrective eyewear are recommended in these patients.