The aim of our retrospective analysis in Chapter 4 was to describe the occurrence of radiation optic neuropathy (RON) in our cohort of patients treated with radiation therapy for a GH-secreting pituitary adenoma. RON is usually defined as a sudden and profound irreversible visual loss due to damage of the optic nerves or damage of the chiasm caused by radiation therapy. During the time period 1967-1998 63 patients with acromegaly were treated with external beam radiation therapy in our region. All visual field, visual acuity, fundoscopic examinations and imaging data from these patients were evaluated for diagnosing RON. Median follow-up time in this cohort was 84 months (range 18-250 months) between the first day of radiation therapy and last ophthalmological examination. The median total dose applied was 49.5 Gray and the median daily dose applied was 1.8 Gray. Two patients developed RON; one patient in one optic nerve 10 years after radiation therapy with visual acuity decreased to light perception only and another patient in both optic nerves 5 months after radiation therapy with vision loss to 1/60 in the left eye and 0.5 in the right eye. Most cases of RON occur within 18 months, but this series show, that late development can occur. RON is a rare but serious complication after external beam radiation therapy for acromegaly.
A clinician should be aware of this, also after a considerable latency time.