In our cohort, no patient in the current study had RON diagnosed. One of 72 irradiated patients had spiraling isopters on Goldmann perimetry without visual acuity loss as late as 11 years after radiation therapy. Because of her unusual visual fields, Goldmann peri-metry was repeated five times over a time period of 17 months with consistent spira-ling. Fundoscopic examination of both eyes revealed normal optic discs. Gadolinium-enhanced magnetic resonance imaging showed no pertinent abnormalities, such as high signal in the optic nerves or chiasm21. Visual-evoked potentials showed no amplitude reduction or latency increase with pattern stimulation. Two years later, the spiraling had disappeared and visual acuity remained normal. Although she was initially considered to have atypical RON22, this diagnosis was rejected when visual field defects normalized.
As shown in Table 1, we found 27 pertinent series of patients in whom the develop-ment of RON was considered. From these series, we calculated that 11 of 2,063 patients had RON, yielding an incidence of 0.53% (95% CI, 0.26%-0.96%). We found an addi-tional 14 RON single-case reports in the literature, making a total of 25 cases.
In 16 of these cases, visual acuity loss was reported (Table 2). It was bilateral in nine patients (56%) and unilateral in seven patients (44%). Of the 25 eyes affected, 13 eyes (52%) had no light perception; two eyes (8%) had light perception; two eyes (8%) had hand movements; four eyes (16%) had a visual acuity between 20/800 and 20/100, and four eyes (16%) had a visual acuity better than 20/100.
In the 23 RON cases in which data were available, the peak latency between radiation therapy and the development of RON was between 12 and 18 months18 (Table 2). The median latency time was 11 months (range, 2-54 months). Four patients (16%) had a latency period longer than 18 months.
In the 21 RON cases in which total radiation dose and radiation fraction size data were available, 14 patients (67%) received a total dose of more than 50 Gy and/or a daily fraction size more than 2 Gy. Of note, seven patients (33%) who had visual loss caused by RON were treated with a supposedly safe daily radiation fraction size and total radiation dose. Information was not available in most reports with respect to the ICRU 50/62 recom-mended minimum (95% of the prescribed dose) and maximum radiation doses (107% of the prescribed dose) to the optic system20.
In the 20 RON cases in which patient age or gender was reported, the median patient age was 54 years (with 12 patients being older than 50 years), and 12 (60%) were women (95%CI,36%-81%).

Table 1 (click to view)

Table 2 (click to view)