Incidence of Strabismus Post-Plaque Brachytherapy in Patients With Uveal Melanoma.

PURPOSE:To determine the incidence and type of strabismus in patients with uveal melanoma treated with plaque brachytherapy. DESIGN:Multicenter, retrospective incidence estimation study. METHODS:A total of 438 eyes of 438 patients with uveal melanoma treated with plaque brachytherapy between October 2011 and May 2021. Intervention was Iodine 125, and Palladium 103 plaque brachytherapy. The variables reviewed included incidence of nonresolving strabismus post-plaque brachytherapy, type of strabismus developed, extraocular muscles operated, and modality of treatment received. RESULTS:A total of 438 patients underwent plaque brachytherapy treatment for uveal melanoma. Eleven patients developed strabismus post-plaque brachytherapy (2.5%, n = 11/438). Of these patients, 5 (1.1%, n = 5/438) developed strabismus immediately postoperation. Specifically, 2 patients (0.5%, n = 2/438) developed strabismus immediately postoperation due to slipped muscles, 2 patients (0.5%, n = 2/438) due to decompensated phorias, and 1 patient (0.5%, n = 1/438) due to a fibrotic muscle. Six patients (1.4%, n = 6/438) developed late-onset sensory strabismus. A total of 355 patients (81.1%, n = 355/438) had their extraocular muscles disinserted during surgery, with the lateral rectus being the most common, accounting for 45.4% (n = 161/355), followed by the superior rectus at 26.8% (n = 95/355). Strabismus surgery was the most common treatment modality, comprising 72.7% (n = 8/11) of patients. CONCLUSIONS:The incidence of strabismus after plaque brachytherapy treatment for uveal melanoma was low and primarily classified as late-onset sensory strabismus. Previous studies may underestimate the long-term incidence of strabismus after plaque brachytherapy by focusing primarily on strabismus present immediately postoperatively.