As shown in Table 1, the cohort was predominantly younger than 40 years (76%), and 47% of the study members were female. During the follow-up period, 51 cataract extractions were reported. One cataract extraction was reported in an eye with no radiation treatment for retinoblastoma compared with 36 cataract extractions in 312 eyes with a history of 1 course of radiotherapy treatment and 14 among 38 eyes with 2 or 3 courses of treatment. Compared with unirradiated eyes, the HR for cataract in eyes receiving 2 or more radiation treatments was 284 (95% CI, 37-2170). The significant (log rank, P < .001) differences in survival to cataract extraction according to number of external radiation treatments are depicted in Figure 2. The Kaplan-Meier curve shows that after 40 years of follow-up, 77% of the eyes with 2 or 3 radiotherapy treatments were operated on for cataract extraction, compared with 17% of eyes treated once and less than 1% of untreated eyes. The estimated average survival time to cataract extraction in unirradiated eyes was 71.7 years (95% CI, 71.2-72.2) compared with 50.8 years (95% CI, 47.6-54.0) and 31.6 years (95% CI, 26.6-36.7) in eyes treated with 1 or 2 to 3 radiotherapy treatments, respectively. The number of courses of external radiation treatments were significantly associated with cataract extraction in a multivariate model, with HRs of 57.3 (P < .001) and 332.7 (P < .001) for eyes treated with 1 or 2 to 3 treatments, respectively (Table 2). During the follow-up period, 30 cataract extractions were reported among the 318 eyes (78% with 1 treatment, 8% with 2 or 3 treatments) that were available for the dose-response analysis. In the multivariate model, children diagnosed with retinoblastoma after the first year of life were at higher risk (HR, 2.14; 95% CI, 1.06-4.33) of cataract extraction compared with children with retinoblastoma diagnosis at a younger age. In the dose-response analysis, eyes that were exposed to a therapeutic radiation dose of 5 to 22.0 Gy (mean, 8.1 Gy) had a 6-fold risk (95% CI, 1.33-27.15) for cataract extraction compared with eyes exposed to 2.5 Gy or less (mean, 1.0 Gy) (Table 3). Similar risk estimates were calculated when patients who were treated with brachytherapy alone were excluded from analysis.