Management of patients with small-angle esotropia and subnormal stereopsis using Fresnel prism

Purpose: Monofixation syndrome (MFS) is a specific subnormal binocular vision status, either with or without a small deviation. Patients with MFS have a tendency to maintain stable ocular alignment. Correction of refractive errors and occlusion are considered as treatment option for amblyopia, and the status of MFS could be changed with long-term follow-up. The purpose of this study is to evaluate whether a Fresnel prism affected the visual acuity, angle of deviation, and sensory status in small-angle esotropia with subnormal stereopsis presenting with MFS features. Methods: Patients with small-angle esotropia within 8 prism diopters (PD) on the simultaneous prism and cover test from 2010 to 2019 were reviewed. Patients with subnormal stereopsis defined as more than 100 s of arc (arcsec) and with the central suppression with peripheral fusion were only included. A Fresnel prism was applied to the dominant eye, and the minimum follow-up period after Fresnel prism treatment was 24 months. We assessed patient clinical characteristics, course and response to therapy including visual acuity, angle of deviation, and stereopsis. Results: Twenty patients with a mean age of 5.5 ± 1.4 years were included. The mean duration of Fresnel prism treatment was 15.3 ± 10.3 months. After 50.7 ± 17.2 months of follow-up, VA of the non-dominant eye was changed from 0.26 ± 0.20 logMAR to 0.07 ± 0.17 logMAR (P <.001). The initial stereoacuities were 3.54 ± 0.27 log arcsec, ranged from 6000 to 400 arcsec. After the treatment with Fresnel prism, the final stereoacuities were 3.09 ± 0.58 log arcsec, ranged from 6000 to 100 arcsec (P =.001); nine patients (45%) improved stereoacuity more than two octaves. No changes in the angle of deviation or a change of fixation were observed. Conclusions: After use of Fresnel prism, there was some improvement in visual acuity and stereopsis in patients with MFS features. Following occlusion and refractive correction, management using Fresnel prism could be attempted in small-angle esotropic patients with amblyopia or subnormal stereopsis.[Figure not available: see fulltext.].