[Studies on distortion of the optic nerve by the internal carotid artery].

The optic nerve (ON) is sometimes distorted by an atherosclerotic internal carotid artery (IC) which we observe during operations. However the distortion seldom causes visual dysfunction. In this paper, 102 nonoperative cases without severe visual disturbance or marked effect on the visual system were studied, using coronal section of MRI and IC angiography, to ascertion ON distortion by IC. The grading of the distortion was determined by coronal section of MRI. Grade (Gr) 0: No distortion of ON, Gr 1: Distortion of ON without chiasmal dislocation, Gr 2: Distortion of ON with chiasmal dislocation. The rate of Gr 0, Gr 1, and Gr 2 were 62.7, 21.6 and 15.7%, respectively. The age of Gr 0, Gr 1 and Gr 2 were 55.4 +/- 19.6, 63.5 +/- 14.7 and 68.9 +/- 5.0 years old, respectively (Gr 2 was different from Gr 0). The occupying rate was calculated by the following formula. The areas were measured by IC angiography of the optic canal: The area of IC in optic canal/The area of optic anal x 100%. The rate of Gr 0, Gr 1 and Gr 2 were 24.2 +/- 19.8, 76.3 +/- 13.2 and 62.0 +/- 28.2%, respectively (Gr 1 and 2 differed from Gr 0). With a rate of more than 70%, the patient had ON distortion by IC.(ABSTRACT TRUNCATED AT 250 WORDS)