The Impacts of Episcleral Plaque Brachytherapy on Ocular Motility

Background: To investigate the effect of various factors on ocular motility disturbance after episcleral plaque brachytherapy with Ruthenium 106 (¹⁰⁶Ru).Methods: Twenty consecutive patients who underwent plaque brachytherapy for all types of intraocular tumors were included in this interventional prospective case series. Ruthenium-106 was used with a mean total dose of 93.2 ± 21.2 Gy toward the tumor apex. Full orthoptic examinations were performed before and after the surgery.Results: The average follow-up time was 6 months (range: 4-9 months). Two (10%) out of 20 patients developed exotropia. The mean age of patients without strabismus was higher than the patients with strabismus (49.8 ± 10.7 years compared to 23 ± 4.2 years, respectively) (p = .011). Strabismus was observed in the patients who had tumors with larger apical diameters (7.6 ± 2 mm compared to 4.1 ± 0.9 mm, respectively) (p = .021). The mean radiation dose to the tumor base in the group with strabismus was higher than the group without motility disturbance (1046.5 ± 604.1 Gy compared to 384.3 ± 175.3, respectively) (p = .021). Most tumors were located in the inferotemporal fundus (30%), followed by supratemporal location (25%), supranasal (10%), and macular region (10%). A higher percentage of patients with postoperative strabismus underwent muscle manipulation compared to the patients who did not develop this complication (100% compared to 38.9%).Conclusion: Manipulation of the extraocular muscles, high doses of radiation, and low vision could cause strabismus after episcleral plaque brachytherapy.