Aim: To determine whether compression of the optic nerve by the intracranial carotid artery (ICA) can be a causative factor of normal tension glaucoma (NTG). Methods: The medical records of 103 eyes of 54 Japanese patients with NTG and 104 eyes of 52 age matched control patients were reviewed. The neuroradiological findings of magnetic resonance images (MRI) were evaluated to determine the relation between the optic nerve and ICA. The clinical characteristics and general medical conditions, such as diabetes and systemic hypertension, were also compared between the two groups. Results: The prevalence of optic nerve compression by the ICA in patients with NTG was 49.5% , which was significantly higher than that in control group with 34.6% (P=0.035). Bilateral compression of the optic nerve was detected in 22 patients with NTG (40.7% ), and this was also significantly higher (P= 0.029) than that in the control group (11 patients, 21.2% ). In the NTG group, eyes with cup/disc ratio (C/D ratio) ≥ 0.7 showed a higher percentage of compression (52.6% ) compared with eyes with C/D ratio of < 0.7 (12.5% ; P=0.042). The presence of diabetes and hypertension did not affect the incidence of optic nerve compression by ICA significantly. Conclusions: The significantly higher percentage of NTG patients who had optic nerve compression by the ICA suggests that compression of the optic nerve by ICA may be a possible causative factor or a risk factor for optic nerve damage in some patients with NTG.
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