AN ANALYSIS OF THE INCIDENCE AND RISK-FACTORS OF DEVELOPING SEVERE KERATOPATHY IN EYES AFTER MEGAVOLTAGE EXTERNAL-BEAM IRRADIATION

Objective: To investigate the incidence and risk factors of developing severe keratopathy in eyes exposed to megavoltage external beam irrad iation, Design: Retrospective noncomparative case series. Participants : The authors evaluated 88 eyes of 88 consecutive patients who had rec eived irradiation of an entire orbit during radiation therapy for naso pharyngeal carcinoma. Mean follow-up was 40 months (range, 24-106 mont hs). Intervention: Slit-lamp biomicroscopic findings of the cornea aft er irradiation were categorized into four grades in accordance with a standard protocol. Grade 3 or above changes were defined as severe rad iation keratopathy. Main Outcome Measures: The incidence of severe rad iation keratopathy was evaluated along with patient's age, radiation d ose, lacrimal shielding, and tumor involvement of the trigeminal nerve . Results: Severe radiation keratopathy developed in 32 patients. Mean latency was 15 months (range, 4-36 months). Its incidence increased f rom 0% after doses less than 59 Gy to 100% after doses greater than 70 Gy. Between 59 Gy and 69 Gy, the adverse factor was omission of lacri mal shield during radiation therapy (P < 0.01). Conclusion: Radiation dose to the cornea is the most important factor in determining the out come of radiation keratopathy. When the threshold dose is reached, vis ual prognosis is grave despite protection of the lacrimal gland. Clini cal trials on newer strategies to treat ocular surfaces exposed to hea vy irradiation are necessary.