Determining fixation accuracy with optical coherence tomography and its implication on visual acuity in amblyopia

Inaccurate fixation is a hallmark of strabismus and amblyopia. Recently, positional error of fixation in amblyopic children was assessed with Optical Coherence Tomography (OCT). This study extends the use of OCT to examine both positional error and stability of fixation in an adult population and investigates how lifelong impairment of fixation can impact visual acuity in amblyopia. Twenty macular cube scans per eye were acquired with the Cirrus HD-OCT in 30 amblyopes and 30 controls with normal binocular vision. The foveal location was identified with the instrument’s software as line scan coordinates to determine the distance between the fovea and the center of the scan. The average positional error and stability of fixation were calculated utilizing the foveal location measurements. Crowded monocular distance visual acuity (VA) was obtained from each eye. Amblyopic eyes demonstrated greater position error and fixation instability compared to fellow and control eyes. Simple linear regressions revealed a significant relationship between both position error and VA and fixation stability and VA. However, with multiple regression, position error alone was the significant predictor of VA. Fixation accuracy analysis from OCT imaging provides a quantitative assessment of fixation behavior, allowing for more comprehensive clinical management of amblyopia and predicting visual acuity.