In a prospective study of neurological complications of coronary bypass surgery, detailed pre- and post-operative bedside ophthalmological evaluation was undertaken in 312 patients. Post-operative neuro-ophthalmological complications developed in 80/312 (25.6%) patients and included: areas of retinal infarction (17.3%); retinal emboli (2.6%); visual field defects (2.6%); reduction of visual acuity (4.5%) and Horner's syndrome (1.3%). Neuro-ophthalmological complications were not observed in a control group of 50 patients undergoing major peripheral vascular surgery. Ten of 75 patients reviewed at 6 months still had detectable neuro-ophthalmological abnormalities, but functional disability occurred only in those with persistent visual field defects. Multivariate analysis revealed that extra-coronary vascular disease, severe and prolonged duration of heart disease prior to operation, and large drop in haemoglobin level during surgery may predispose to neuro-ophthalmological complications.