The preservation of ocular function despite occlusion of the ipsilateral internal carotid artery and ophthalmic artery was noted by Elschnig1 in 1892. He followed his observation of this now well-known circumstance by studies of collateral circulation to the eye. Injections of a gelatindye mixture were made into the external carotid system of several cadavers after ligation of the internal carotid artery and section of the ophthalmic artery. Not only did the dye discolor the face and conjunctivae but it stained the optic nerve and eye. Soon after injection had been started, the dye dripped from the distal cut end of the ophthalmic artery. He concluded that the collateral circulation so demonstrated was responsible for the preservation of ocular function when the internal carotid and/or ophthalmic arteries were occluded. From the observation that there was a rapid flow of the dye he postulated that the external carotid circulation might
VAN ALLEN MW, BLODI FC. Collateral Circulation to the Eye in Occlusion of the Internal Carotid Artery: Observations on the Influence of External Carotid Flow on Retinal Artery Pressure. AMA Arch Neurol. 1960;2(1):74–78. doi:10.1001/archneur.1960.03840070076008
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