Session: Poster session A

The effect of Fresnel prism in small angle esotropia (?20 prism diopters) patients

Purpose: To investigate the effects of Fresnel prism in patients of small angles of esotropia with less than 20 prism diopters (PD).

Methods: This retrospective study included 32 patients with a residual esotropia of ≤ 20 PD measured by the simultaneous prism and cover test (SPCT) after full hypermetropic correction. Fresnel prism was applied to make the patients orthotropic with glasses. The treatment was discontinued if (1) orthotropia was sustained during two consecutive follow-ups at two-month intervals, (2) the angle continued to increase with prism adaptation. Patients were divided into two groups (treatment success and the treatment failure group). The criteria for treatment success was defined on both motor and sensory aspects, with remaining esotropia < 8PD and a visual acuity (VA) gained more than 0.2 logMAR, respectively. Our goal was to investigate the factors that influence the treatment outcomes.

Results: The initial angle of esodeviation was 6.92 ± 4.66 PD at distance, and 10.53 ± 5.58 at near. The logMAR VA was 0.10 ± 0.13 in the dominant eye, and 0.26 ± 0.19 in the non-dominant eye. Among 32 patients, 17 patients showed motor success. Among 26 patients, 15 patients showed sensory success. The factors influencing motor success were the maximum PD of prescribed Fresnel prism, maximum angle of esodeviation at distance and near, and the frequency of Fresnel prism adaptation. Sensory success was influenced by the presence of anisometropia and the maximum prescribed amount of Fresnel prism.

Conclusions: The factors influencing motor success suggest that a deep-seated monofixation status can hinder motor success following the removal of Fresnel prism. Considering the factors influencing sensory results, it can be inferred that challenges in visual improvement arise from a combination of abnormal binocular interaction due to strabismus and vision deprivation caused by anisometropia.