Purpose: The determine whether significant compression of the optic nerve by the internal carotid artery (ICA) can produce a glaucomatous optic neuropathy in patients without elevated intraocular pressure (IOP).

Study Design: Retrospective case series.

Subjects: Patients with an optic neuropathy referred to neuro-ophthalmologists for a question of glaucomatous versus non-glaucomatous optic neuropathy. 

Methods: Patients were included in the study if they had preserved visual acuity, color vision, a visual field defect consistent with glaucoma, optic nerve cupping without obvious pallor of the neuroretinal rim, intraocular pressure (IOP) less than 21mmHg on all clinical visits, open angles on gonioscopy and unequivocal radiological compression of the ipsilateral optic nerve by the ICA or other intracranial blood vessel.  

Main Outcome Measures: Visual acuity, visual field, and radiological findings.

Results: Three patients were included with a mean age of 56.3 (range 29 to 82) years. Patient 1 was a 58-year-old man incidentally noted to have left optic nerve cupping on a routine examination. He had an inferior arcuate defect and the left pre-chiasmatic optic nerve was elevated and compressed by a tortuous left ICA on magnetic resonance imaging (MRI). Patient 2 was a 29-year-old man with a 7-year history of normal tension glaucoma in the right eye treated with latanoprost. He had a superior greater than inferior arcuate defect and there was neurovascular conflict between the supraclinoid ICA and A1 segment of the anterior cerebral artery on MRI. Patient 3 was an 82-year-old woman with a 10-year history of normal tension glaucoma who had progression of her visual field defects despite low IOPs. MRI showed mass effect on the right optic nerve by a dolichoectatic right supraclinoid ICA. 

Conclusions: Significant radiological compression of the optic nerve by a normal, tortuous or dolichoectatic ICA can produce a glaucomatous optic neuropathy.

Glaucomatous-like optic neuropathy due to compression of the optic nerve by the internal carotid artery

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