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Amblyopia and fixation eye movements

Published:August 03, 2022DOI:https://doi.org/10.1016/j.jns.2022.120373

      Highlights

      • Fixation abnormalities are seen in amblyopic and fellow eye of patients with and without nystagmus under monocular, binocular, and dichoptic viewing.
      • Fixation instability is greater in the amblyopic eye than fellow eye across all studies.
      • The varying results between fixation instability and extent of visual function deficits, particularly visual acuity of the amblyopic eye, could arise from different experimental conditions.
      • Eccentric (para-foveal) fixation, usually thought to be present in strabismic amblyopia patients, is also seen to a lesser extent in patients with anisometropic amblyopia.
      • The relationship between the extent of FEM abnormalities and eccentric fixation is unknown.
      • Evaluating and parsing the fast and slow FEMs and quantifying FEM metrics separately in patients with and without nystagmus can provide greater insights into the association between fixation instability and the extent of visual function deficits.
      • Characterization and quantification of FEM abnormalities can serve as a predictor of residual/recurrent amblyopia, and provide insights into variable treatment response.
      • There is limited evidence that FEM abnormalities or EF can improve with patching treatment.

      Abstract

      Amblyopia is a neurodevelopmental disorder caused by abnormal visual experience in early life that affects 3–5% of the population. Amblyopia results in a host of monocular and binocular visual afferent function deficits including reduced visual acuity, contrast sensitivity, depth perception, interocular suppression, and efferent function abnormalities such as unstable and inaccurate fixation. Conventional treatments such as patching therapy and newer dichoptic treatments are not always successful as 30–40% of patients experience recurrence/regression of amblyopia. There are numerous review articles focused on visual afferent function deficits and treatment modalities and outcomes in amblyopia. Recently, the advent of high spatial and temporal resolution eye trackers has spurred studies on fixation eye movements (FEMs) in healthy controls and neurologic and ophthalmic disorders. In this focused review, we will summarize studies evaluating FEM abnormalities in amblyopia. We will first describe the common devices and techniques used to quantify fixation abnormalities, and then highlight the importance of systematically evaluating the eye movements under different viewing conditions and describe the parameters crucial in assessing FEM abnormalities in amblyopia. We will summarize the evidence suggesting that FEM abnormalities are not limited to the amblyopic eye only but also affects the fellow eye and that FEM abnormalities can serve as biomarkers to predict the impact of amblyopia on visual functions. Beyond diagnosis, we will discuss the treatment and prognostic implications of the evaluation of FEM abnormalities in clinical practice.

      Keywords

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