The effect of perioperative embolisation on visual function in patients undergoing carotid endarterectomy

Objectives: To investigate the effect of carotid artery embolisation detected by transcranial Doppler (TCD) monitoring during carotid endarterectomy (CEA) on visual function. Design: A prospective study. Visual function was assessed by an independent ophthalmalogist. Materials: One hundred consecutive patients undergoing carotid endarterectomy. Methods: All patients underwent pre- and postoperative retinal fundoscopy and automated visual field analysis. Intraoperative emboli were detected by continuous TCD monitoring of the middle cerebral artery. Results: Preoperatively, six patients had fundoscopic evidence of silent retinal embolisation, five patients had visible emboli associated with amaurosis fugax. Visual field analysis found no significant difference between ipsi- and contralateral eye scores. Only patients with occlusions of major retinal vessels had clinically reduced visual function. Intraoperatively TCD identified embolisation in 83/91 of monitored operations. Postoperatively, ipsilateral visual field scores deteriorated while contralateral eye scores remained unchanged, however only one new retinal embolus was detected. The incidence of TCD detected embolisation was not associated with a corresponding deterioration in postoperative visual function. Conclusions: (1) A group of patients can be identified who experience "silent" retinal embolisation prior to CEA. (2) Clinically significant retinal embolisation resulting from CEA is uncommon. (3) CEA is associated with a deterioration in the visual field scores for the ipsilateral eye compared with the contralateral eye but the mechanism for this small but significant deterioration remains unclear.