Interocular Symmetry and Repeatability of Foveal Outer Nuclear Layer Thickness in Congenital Achromatopsia

ABSTRACT Purpose To examine the intraobserver repeatability of foveal outer nuclear layer (ONL) thickness measurements and evaluate interocular symmetry for patients with achromatopsia (ACHM) and controls. Design Cross-sectional study. Subjects Sixty-four patients with CNGA3 - or CNGB3 -associated ACHM and 38 patients with normal vision were recruited for analysis. Methods Horizontal line scans through the fovea of each eye were acquired using optical coherence tomography. Three foveal ONL thickness measurements were made by a single observer using custom software to analyze repeatability. Interocular symmetry was assessed using the average of the three measurements for each eye. Main Outcome Measures The main parameter being measured is foveal ONL thickness. Results Mean (± SD) foveal ONL thickness for ACHM patients was 74.86 ± 17.82μm (OD) and 75.30 ± 15.68μm (OS) compared to 110.60 ± 15.67μm (OD) and 110.53 ± 13.91μm (OS) for controls. Foveal ONL thickness did not differ between eyes for ACHM (p = 0.821) or control patients (p = 0.961). Intraobserver repeatability was high for foveal ONL measurements in ACHM patients (ICC = 0.939, OD and 0.915, OS) and controls (ICC = 0.991, OD and 0.984, OS). Conclusions Foveal ONL thickness can be measured with excellent repeatability. While foveal ONL thickness is reduced in ACHM compared to controls, the high interocular symmetry indicates that contralateral ONL measurements could be used as a negative control in early-phase monocular treatment trials.