Effect of Fresnel prism in small-angle esotropia (≤ 20 prism diopters) with fixation preference

Abstract

Purpose We aimed to investigate the effects of Fresnel prism treatment for small-angle esotropia (≤ 20 prism diopters [PD]) with fixation preference. Methods We included 32 patients with remaining esotropia ≤ 20 PD measured using the simultaneous prism and cover test (SPCT) after full refractive error correction. Fresnel prism was applied to make patients orthotropic with glasses. Treatment was discontinued if remaining esotropia ≤ 4 PD was sustained during two consecutive follow-ups (2-month intervals) or if the angle continued to increase with prism adaptation. Patients were divided into treatment success and failure groups. Treatment success was defined by motor and visual acuity (VA) aspects. Criteria for motor success was residual esotropia ≤ 8 PD in patients with initial esotropia > 8 PD and a 30% decrease of esotropia in those with initial esotropia ≤ 8 PD. VA success was improvement of > 0.2 logMAR in the non-dominant eye. Results The initial esodeviation angle was 6.92 ± 4.66 PD at distance and 10.53 ± 5.58 at near. The logMAR VA was 0.10 ± 0.13 and 0.26 ± 0.20 in the dominant and non-dominant eye, respectively. Among the 32 patients, 14 showed motor success. Among 26 patients whose VA could be measured, 15 showed VA success. Factors influencing motor success were a small amount of maximum prescribed Fresnel prism, less frequent need for Fresnel prism adaptation, and high percentage of achieving orthotropia with Fresnel prism treatment. VA success was influenced by low frequency of anisometropia and the small amount of maximum prescribed Fresnel prism. Conclusion Fresnel prism could be a non-invasive treatment option for some patients with small-angle esotropia with fixation preference. Key messages What is known The optimal approach for addressing small-angle esotropia is a topic of debate. Not much research has been conducted on Fresnel prism treatment in patients with small-angle esotropia. What is new Motor success and visual acuity improvement were observed in some patients undergoing Fresnel prism treatment. Factors contributing to motor success were the small maximum angle of esodeviation, the less frequent necessity for Fresnel prism adaptation, and the achievement of orthotropia during Fresnel prism treatment. Visual acuity improvement was hindered by the presence of anisometropia and the large maximum prescribed amount of Fresnel prism. Fresnel prism treatment can be used as a treatment option for some patients with small-angle esotropia with fixation preference.