Hemispheric Asymmetry of Outer Retinal Structure and Function in Retinitis Pigmentosa.

OBJECTIVE: To investigate vertical hemispheric asymmetry of the outer retinal structure using structural and functional parameters in patients with retinitis pigmentosa (RP) and assess its association with genotype and age. DESIGN: A retrospective observational study. PARTICIPANTS: We analyzed 928 eyes from 496 patients with advanced RP at a single tertiary center. METHODS: We measured hemispheric asymmetry of the outer retinal structure using a fully automated deep learning pipeline for segmenting the ellipsoid zone (EZ) from volume scan images obtained by spectral-domain OCT. Additionally, we evaluated the visual field asymmetry with a custom algorithm to quantify field angles assessed using Goldmann perimetry across 24 meridians. We assessed hemispheric asymmetries using linear mixed-effects models and performed subgroup analyses to determine whether the asymmetry was associated with genotype and age. Further, we modeled longitudinal changes in EZ area using exponential decline. MAIN OUTCOME MEASURES: Superior and inferior hemispheric preservation of the EZ area (mm2) and Goldmann perimetry angle (°), as well as their respective superior-to-inferior (sup/inf) ratios. RESULTS: At the initial presentation, the superior EZ area was significantly larger than the inferior area (3.47 ± 0.11 mm2, mean ± standard error of mean, 95% confidence interval [CI]: 3.26 mm2-3.68 mm2 vs. 2.86 ± 0.09 mm2, 95% CI: 2.69 mm2-3.03 mm2; P < 0.001), yielding a mean superior-to-inferior ratio of 1.33 ± 0.03 (95% CI: 1.26-1.40). We observed the most pronounced asymmetry in eyes with EYS variants (1.93 ± 0.21, 95% CI: 1.51-2.34). Visual field analysis demonstrated an average inferior-to-superior visual field ratio of 1.23 ± 0.02 (95% CI: 1.19-1.27), indicating inferior hemifield dominance (P < 0.001). Age-stratified analysis revealed significantly greater relative preservation of the superior EZ area in older age groups (P = 0.040). The rate of annual loss of EZ area was 11.13 ± 0.58% (95% CI: 9.99%-12.27%) in a longitudinal subset of 725 eyes. CONCLUSIONS: Patients with RP consistently exhibited vertical hemispheric asymmetry of the outer retinal structure, with superior dominant structural and inferior dominant visual field preservation. This spatially polarized pattern represents a novel characteristic of RP and provides new insights into the regional vulnerability of photoreceptors. FINANCIAL DISCLOSURES: The authors have no proprietary or commercial interest in any materials discussed in this article.