Background: A prospective study was conducted to determine if external ionizing radiation could favorably influence the orbital manifestations of Graves ophthalmopathy. Diabetes and untreated systemic hypertension were exclusion criteria. Radiation was directed to the orbits of 42 affected patients using 0.2 rad (20 Gy) delivered in 10 doses of 0.02 rad (2 Gy). Patients were periodically examined during a 3-year interval. Objective: To report retinal microvascular abnormalities observed in our study cohort. Methods: Fundus findings documented with ophthalmoscopy, stereoscopic color photography, and stereoscopic fluorescein angiography prior to radiation were compared with similarly documented findings approximately 3 years following radiation. Results: Prior to orbital radiation, retinal microvascular abnormalities were identified in 2 patients. The abnormalities were present bilaterally in one patient and unilaterally in the other. During the course of the study, microvascular abnormalities developed de novo in the unaffected retina of the latter patient while the retinopathy in the fellow eye progressed. Retinal microvascular abnormalities and their sequelae developed de novo in both eyes in 2 more patients. In addition to the radiation, other confounding factors known to be associated with microvascular retinopathy (uveitis, inadequately controlled systemic hypertension, and borderline blood glucose levels) were identified among the 3 patients whose eyes developed new retinal microvascular abnormalities. Conclusions: Whether the retinal microvascular abnormalities observed in these patients were caused or aggravated by external beam irradiation cannot be precisely ascertained. However, the observed progression and de novo development of retinal microvascular abnormalities within 3 years of orbital radiation raise concern that 0.2 rad (20 Gy) delivered to the orbit in 10 doses of 0.02 rad (2 Gy) may aggravate existing retinal microvascular abnormalities or cause radiation retinopathy in some patients with Graves disease. These findings and the failure of external beam radiation with 0.2 rad (2000 cGy) to favorably affect Graves ophthalmopathy, as demonstrated in a previous study, have led us to discourage further treatment of Graves ophthalmopathy with radiation.
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