During the period 1967-1998, 80 patients with acromegaly were diagnosed at the University Hospital Groningen, The Netherlands. The diagnosis of acromegaly was based on the typical clinical features of acral enlargement and soft tissue swelling and was confirmed by appropriate laboratory tests. In all operated patients histological evaluation of the specimen confirmed the presence of a GH-producing pituitary adenoma.
In 1999 and 2000, a retrospective investigation was performed. The ophthalmological, surgical and radiation therapy data were reviewed. The time period 1967-1998 was chosen because data before 1967 were frequently incomplete. To be included in the present survey, time of follow-up had to be at least 18 months. The ophthalmological data obtained before treatment were available in all but two patients and after radiation therapy from all patients.
Of these 80 cases, 63 patients, who were treated with external beam radiation therapy, were included in our survey. External radiation therapy was mostly performed at the University Hospital Groningen (n = 56), but also in 2 other regional institutions (n = 7), where equivalent radiation therapy schedules were applied.
Before 1977 the neurosurgical procedures were craniotomies only. Since 1978 the transsphenoidal approach was the preferred method.
Visual acuity was measured with a Snellen acuity chart. A visual acuity less than 0.8 was defined as impaired. Visual fields were obtained with Goldmann kinetic perimetry. The visual field data (n = 1195) of all patients at diagnosis, after neurosurgery and/or radiation therapy were retrospectively reviewed by one neuro-ophthalmologist.

We diagnosed RON using the criteria by Kline et al. and Parsons et al.7,9 :
• Irreversible visual loss with visual field defects, indicating optic nerve or chiasmal dysfunction.
· Absence of visual pathway compression due to recurrence or progression of tumour,
radiation-induced neoplasm, arachnoidal adhesions around the chiasm, radiation retino-pathy or any other apparent ophthalmological disease.
· Absence of optic disc edema.
· Optic atrophy within 6 – 8 weeks after onset of symptoms.
Evaluation of RON was performed by review of visual field, visual acuity and fundoscopic examinations in combination with imaging of the sellar region.
The time span of follow-up was defined by the period between the first day of radiation therapy and the last ophthalmologic examination.