Relationship Between Fixation Stability and Visual Function in Fellow and Amblyopic Eyes in Anisometropic Amblyopia

Abstract

Purpose : Anisometropic amblyopia, typically characterized as unilateral amblyopia, significantly affects both monocular and binocular vision. Contrary to traditional understanding, emerging studies indicate that the non-amblyopic or fellow eye (FE) might also experience subtle deficiencies. This research, employing psychophysical testing methodologies on subjects with anisometropic amblyopia, is designed to assess the fixation stability (FS) in both the amblyopic eye (AE) and the fellow eye (FE), offering insights into the broader impacts of this condition.

Methods : The study enrolled 36 patients with anisometropic amblyopia (mean age = 15.86 ± 7.49 years). Comprehensive assessments were conducted for each participant, encompassing best-corrected visual acuity (BCVA) using the ETDRS chart after complete refractive correction, contrast sensitivity function (CSF) using the qCSF approach, and fixation stability (FS) of both the FE and the AE. FS was quantified by measuring the bivariate contour ellipse area (BCEA) and calculating the percentage of fixation points within 1° and 2° from the fovea (P1 and P2). The FS categories—stable (P1 ≥ 75%), relatively unstable (P1< 75% <P2), and unstable (P1 & P2 < 75%)—were determined based on the criteria established by Fuji et al., using microperimetry.

Results : In this study, the FEs and AEs of patients exhibited significant differences in several key visual parameters. The BCVA comparison showed -0.02 ± 0.07 for FEs vs 0.73 ± 0.33 logMAR for AEs, the area under the log CSF was 1.72 ± 0.25 vs 0.76 ± 0.37, and the BCEA at 68.2% was 0.58 ± 0.32 vs 1.0 ± 0.38 log deg^2, indicating poorer visual performance in AEs (p < 0.001 for all). Based on Fuji's classification, unstable or relatively unstable fixation was observed in 17 of the 36 FEs and in 34 of the 36 AEs. A significant correlation in AEs was noted between BCEA at 68.2% and both BCVA (r = 0.39, p < 0.001) and the area under the log CSF at low spatial frequencies (r = 0.40, p < 0.001), a relationship not found in FEs.

Conclusions : Our study reveals fixation stability defects in both the FE and the AE in anisometropic amblyopia, indicating a wider impact than previously understood. These insights are critical for developing more comprehensive treatment strategies that address the visual deficiencies in both eyes of amblyopic patients.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.