Successful prism treatment for cyclic esotropia: A case report

To report a case of cyclic esotropia successfully treated with prismatic correction. A 9-year-old girl presented with intermittent esotropia and diplopia occurring over the previous 4 months. The patient had 30 prism diopters (PD) of esotropia at both distance and near. Ocular motility testing, other ophthalmic examinations, and brain magnetic resonance imaging revealed no abnormalities. At the third visit, the patient had 6 PD of intermittent esotropia without diplopia, and the eye position diary demonstrated esotropia every other day, which led to a diagnosis of cyclic esotropia with a 48-h cycle. The cyclic pattern persisted for 9 months following the initial visit. However, during a subsequent regular visit, the patient reported a newfound ability to self-adjust from "esotropic" days to "straight" days by tightly closing the eyes immediately after waking up in the morning, particularly when wishing to avoid strabismus. To address the condition, we affixed a Fresnel membrane prism on the glasses to compensate for the latent deviation on a "straight" day. During the subsequent 18 months, the esotropia completely resolved, and the patient was followed up with gradual decreases in prism power. Correcting latent deviation using a prism lens is a simple approach without potential side effects. The present findings suggest that this approach is a viable treatment option for cyclic esotropia during its early and periodic stages.