Ophthalmic artery pressure response to carotid occlusion

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Abstract
Experimental observations were made of the effects of cephalic vascular occlusions on ophthalmic artery pressure in the rhesus monkey. The primary channel of blood flow to the orbital vascular bed, the ipsilateral internal carotid, is the major contributor to arterial pressure in that bed. When this channel is patent, the effect of occlusion of alternate channels is insignificant. Common carotid occlusion has a greater damping effect on ophthalmic artery pressure than internal carotid occlusion alone because the former allows the external carotids to act as escape valves for retrograde internal carotid artery flow. Little contribution by the external carotid and its branches to orbital arterial pressure is found under these experimental conditions, contrary to both anatomic and clinical observations in the human being. Our work shows instead, the overwhelming importance of the opposite carotid and basilar vertebral contribution to orbital arterial pressure via the circle of Willis in the monkey. The systemic arterial pressure is an important determinant of the ophthalmic artery pressure, regardless of carotid occlusion. An independent increase of ophthalmic artery pressure over systemic femoral pressure occurs with bilateral carotid occlusion. It occurs between 15 and 45 minutes of occlusion, and its magnitude is between 20 and 30 mm. Hg. We have given indirect evidence to show that it is probably associated with enhanced cerebral blood flow. By the appropriate use of a pressure transducer or flow meter, the role of the external carotid artery subsequent to occlusion of the common carotid artery may be determined. Such predictable effects may help in deciding between common or internal carotid occlusion in the treatment of aneurysms.

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