A prospective study of 80 patients with central retinal vein occlusion (CRVO) was performed to determine whether Doppler flow measurements can predict visual outcome. All patients at presentation, had full ophthalmological examination, fluorescein angiography, relative afferent pupillary defect test and electroretinography to distinguish between ischaemic and non-ischaemic occlusions. In addition, all patients were examined at presentation with colour Doppler ultrasound using a 7.5 MHz linear array probe. Both the clinical examinations and colour Doppler ultrasound were repeated at one year following initial presentation in a smaller group of 20 patients. A significant reduction in velocity within the central retinal vein was noted in the ischaemic compared with non-ischaemic CRVO affected eye at the time of the baseline scan. The minimum venous velocity within the central retinal vein was most severely affected. No velocity difference was present within the ophthalmic artery. Follow-up at one year with colour Doppler ultrasound showed an increase in blood velocity values within the central retinal vein in the CRVO affected eye but this was of no prognostic value and did not correlate with clinical outcome. Serial colour Doppler ultrasound examinations, therefore, have no clinical application in patients with CRVO and are of no prognostic value.