Pressure Changes in the Ophthalmic Artery After Carotid Occlusion: An Experimental Study in the Rabbit

IN recent years ophthalmologists have become increasingly aware of the syndrome of carotid occlusion, as many patients with this condition present themselves complaining of ocular symptoms.Indeed, these may be the only symptoms, and the responsibility of the ophthalmologist is considerable when he alone has the chance of detecting the condition.The two commonest ocular symptoms associated with this syndrome are homolateral blindness and crossed hemianopic field defects.The latter have been ascribed with some certainty to lesions of the middle cerebral artery (Walsh and Smith, 1952), and are unlikely to be present without associated systemic symptoms; but homo- lateral blindness, whether transient or permanent, may be the patient's only complaint.This second group of cases, originally the sole responsibility of the ophthal- mologist, has been the subject of considerable study.Reasonable though not wholly satisfactory explanations have been advanced for the development of optic atrophy, but the mechanism of the transient attacks of blindness is still unknown and further investigation is required.Although it is known that grave alterations in the blood pressure occur distal to stenosis or occlusion of a carotid artery (Sweet and Bennett, 1948; Sweet, Sarnoff, and Bakay, 1950; Bakay and Sweet, 1952, 1953), the fact that not all patients with carotid occlusion suffer from transient attacks of blindness or permanent optic atrophy (Johnson and Walker, 1951) suggests that further knowledge of the blood pressure between the central retinal artery and the carotid block would be desirable.-Elder (1926) has shown that, in the normal anaesthetized cat, there is a 25 per cent.fall in pressure from the ophthalmic artery to the central retinal artery; correspondingly any fall in pressure in the ophthalmic artery is likely to give rise to an even lower pressure in the retinal vessels. DukeThe studies of Sweet and his collaborators on pressure changes in the carotid artery and its branches distal to an occlusion have not been performed in the case of the ophthalmic artery.These workers were well aware of the value of such a reading, but the inaccessibility of the vessel made the introduction of a cannula technically impossible.