Objective: The purpose of the study is to determine the amount of subarachnoid fluid of the optic nerve in normal adults using magnetic resonance (MR) imaging and to investigate whether the subarachnoid fluid is displaced in abduction as assumed by the 30°echographic test. Design: The design was a prospective observation study. Participants: Twenty-one healthy headache-free adults participated. Ten (48%) were men and 11 (52%) were women with a mean age of 34.3 ± 7.9 years. Intervention: Both optic nerves were examined in primary and 45°right and left gazes with T2 fast-spin echo fat- suppressed coronal MR imaging in quadrature head coil. Four MR images, 4 mm apart, starting from 4 mm posterior to the globe were obtained for both nerves simultaneously with an imaging time of 2 minutes and 24 seconds per gaze. Main Outcome Measures: Optic nerve and sheath diameters were measured. Results: Mean nerve diameters were 3.2 ± 0.4 mm anteriorly to 2.6 ± 0.4 mm posteriorly, and mean sheath diameters were 5.2 ± 0.9 mm anteriorly to 3.9 ± 0.4 mm posteriorly. Optic sheath diameters did not change significantly in abduction or adduction. Conclusions: Magnetic resonance imaging can be used effectively to determine the amount of subarachnoid fluid of the optic nerve. In normal adults, the amount of optic nerve subarachnoid fluid is variable and may be substantial. The authors' MR findings show that optic nerve subarachnoid fluid is not displaced significantly with abduction or adduction.
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