Retinal embolization during carotid angioplasty and stenting: Mechanisms and role of cerebral protection systems

Carotid stenting has become an accepted alternative to endarterectomy, but fear of embolic stroke has impeded its generalized application. The retina provides a unique observatory for the study of emboli, which may occur either directly or indirectly via collaterals to the ophthalmic artery. Systems under development for cerebral protection differ in their capacity to trap small emboli and in their protection of the collateral circulation. We evaluated 118 sequential patients undergoing carotid stenting using fundoscopy, fluorescein retinal angiography, and visual field examination. The site and size of emboli was assessed, and degree of edema estimated. All patients were treated using distal protection during carotid stent implantation: 38 patients with the Theron system (using routine flushing toward the external carotid) and 80 patients with the Percusurge(R) system (aspiration only). Retinal embolization occurred in 6 of the 118 patients (4%), of whom 2 were symptomatic (1.7%). Using the Theron system, 5 of 38 patients (13.2%) had emboli while 1 of 80 (1.25%) had emboli using the Percusurge system (P = 0.019). Symptoms occurred only with emboli >20 mum. Symptomatic retinal embolization is uncommon during carotid stenting, but is more likely when external to internal carotid collaterals are not protected. Cerebral protection system designs should take into consideration the existence of collaterals and the need to protect against smaller sized emboli, which may cause blindness in the retinal circulation.