To elucidate the anatomical features which predispose artery over vein (AV) crossings to be the preferential sites for retinal branch vein occlusions (RBVO), 11 AV and six vein over artery (VA) crossings in 12 eyes from non-hypertensive donors who were aged 35 to 82 years, were studied by light and electron microscopy. At AV crossings the veins were often observed to abruptly alter direction to pass under the artery. Here focal stratification of the vein basement membrane opposite the point of contact with the artery was seen. A focal reduction in the vein lumen occurred at three of 11 AV crossings. In contrast, deviation of the vein, focal basement membrane stratification or focal narrowing was not seen at VA crossings. Both types of crossings had a common adventitial sheath when each vessel was of large calibre. This study demonstrated anatomical features which predispose AV crossings to be the preferential site for venous occlusion.Key words: Arteriovenous crossing, electron microscopy, light microscopy, pathogenesis, retinal branch vein occlusion.Venous obstruction in retinal branch vein occlusion (RBVO) is, with few exceptions, a focal event occurring at or in close proximity to the crossing of an artery and a vein, within a few disc diameters of the optic disc.',' The anatomical disposition of the artery and vein at crossings was recently found to play an important part in the pathogenesis of RBVO. Weinburg et in a retrospective clinical study, showed RBVOs have a definite predilection for artery over vein (AV; 97%) rather than vein over artery (VA; 3%) crossings. By comparison in normal eyes, 67% of crossings showed an AV pattern and 33% were of a VA configuration. Branch vein occlusion occurs more frequently in the superior retinal quadrant than the other three because it has more AV crossing^.^ This report describes anatomical features from light and electron microscopy which distinguish AV from VA crossings, predisposing the former to be the preferential site for venous obstruction. Materials and methodsTwelve eyes were obtained for corneal graft donation within six hours of death (Table l).Written informed consent for corneal donation and entry into this study was obtained in accordance with the ethical committee approval (File WJP/AQ). After the donor corneal buttons had been removed, the globes were immediately fixed in 2.5% glutaraldehyde buffered with Pipes.

Prompted by the concerns of the staff and patients, radiation hazards from Cobalt 60 (Co 60) plaque therapy for choroidal melanoma were recently assessed when two patients were concurrently treated at Christchurch Hospital. The risks from radiation to the attending medical staff, nursing personnel from the operating theatre and ward, and the patients' visitors were investigated.The radiation dose for all staff and visitors involved with the two patients was found to be well below the recommended weekly limits set by the International Commission on Radiological Protection. Our department code of practice to minimise radiation hazard during plaque therapy has been revised.

A 23-year-old woman who presented with blurred vision in her right eye from increasing astigmatism had a vascular ciliary body tumour. After slow growth was documented over a 15-month period the tumour was excised with an iridocyclectomy. Microscopically the tumour consisted of sheets of large polygonal cells with round nuclei and foamy cytoplasm, separated by numerous capillaries, findings consistent with a diagnosis of a haemangioblastoma. Haemangioblastomas occur in the retina in von Hippel's disease and this occurrence in the ciliary body is a rare event. Investigation of the patient with a CT of the head and an abdominal ultrasound revealed no systemic lesions suggestive of systemic angiomatosis or von Hippel-Lindau disease.