title: An analysis of the incidence and risk factors of developing severe keratopathy in eyes after megavoltage external beam irradiation.
abstract: OBJECTIVE
  To investigate the incidence and risk factors of developing severe keratopathy in eyes exposed to megavoltage external beam irradiation.
  
  
  METHODS
  Retrospective noncomparative case series.
  
  
  METHODS
  The authors evaluated 88 eyes of 88 consecutive patients who had received irradiation of an entire orbit during radiation therapy for nasopharyngeal carcinoma. Mean follow-up was 40 months (range, 24-106 months).
  
  
  METHODS
  Slit-lamp biomicroscopic findings of the cornea after irradiation were categorized into four grades in accordance with a standard protocol. Grade 3 or above changes were defined as severe radiation keratopathy.
  
  
  METHODS
  The incidence of severe radiation keratopathy was evaluated along with patient's age, radiation dose, 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 from 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 lacrimal shield during radiation therapy (P < 0.01).
  
  
  CONCLUSIONS
  Radiation dose to the cornea is the most important factor in determining the outcome of radiation keratopathy. When the threshold dose is reached, visual prognosis is grave despite protection of the lacrimal gland. Clinical trials on newer strategies to treat ocular surfaces exposed to heavy irradiation are necessary.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Chinese University of Hong Kong.
authors.forename: S K
authors.initials: SK
authors.lastname: Kwok
authors.forename: P C
authors.initials: PC
authors.lastname: Ho
authors.forename: S F
authors.initials: SF
authors.lastname: Leung
authors.forename: S
authors.initials: S
authors.lastname: Gandhi
authors.forename: V W
authors.initials: VW
authors.lastname: Lee
authors.forename: D S
authors.initials: DS
authors.lastname: Lam
authors.forename: I C
authors.initials: IC
authors.lastname: Ngan
authors.forename: J L
authors.initials: JL
authors.lastname: Ming
mesh_terms: D000328:Adult; D000368:Aged; D003315:Cornea / Q000473:pathology / Q000528:radiation effects*; D003316:Corneal Diseases / Q000145:classification / Q000209:etiology* / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy; D009915:Orbit / Q000528:radiation effects; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000145:classification / Q000209:etiology* / Q000473:pathology; D011882:Radiotherapy, High-Energy / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors