Evaluation of fixation in amblyopic patients with myopic anisometropia

This study aimed to evaluate amblyopic participants with myopic anisometropia who, despite not being initially diagnosed with strabismus, failed to improve their visual acuity (VA) after treatment. The hypothesis is that these individuals present with microtropia (MT) and sensory adaptations. Since they appear orthotropic on the unilateral cover test, the hypothesis was tested through an objective evaluation of fixation, the presence of eccentric fixation (EF) would indicate that these eyes are monocularly deviated.

Fourteen participants (16.07 ± 10.56 years) were recruited from the Vision Clinic at the University of Murcia. They were myopic, amblyopic, anisometropic, and initially classified as non-strabismic, with no improvement following treatment. They underwent refractive, motor, sensory, eye health and fixation assessments using visuoscopy.

A slight tendency towards esophoria was observed at distance (1.07Δ ± 2.67Δ) and near (2.50Δ ± 6.26Δ). Refraction in amblyopic eyes was 3D more myopic than in non-amblyopic eyes, showing a strong correlation (r=0.91, p<0.0001). A non-significant relationship was found between the degree of anisometropia and VA in the amblyopic eye (r = -0.27, p=0.3944), as well as between anisometropia and stereopsis (Spearman r_s = 0.22, p=0.439). Of the 14 amblyopic eyes evaluated, 10 presented with EF (indicating strabismus), 2 had unstable fixation, 1 could not be evaluated, and 1 presented central fixation.

The majority of the participants evaluated (71.4%) exhibited MT and EF. While this association is well-documented in hyperopic anisometropia, it has not been previously characterized in myopic anisometropia.