Background
Compressive optic neuropathy (CON) is caused by injury to the optic nerve by an extrinsic lesion. [1]
The primary function of the optic nerve is to transmit visual information from the retina to the brain. The optic nerve contains the axons from the retinal ganglion cells and extends posteriorly from the globe, through the orbit and optic canal, to reach the optic chiasm. At the chiasm, contralateral nasal fibers decussate and join uncrossed temporal fibers to become the optic tracts. The optic nerve consists of more than a million nerve fibers. [2] The total length of the optic nerve averages 50 mm: 1 mm for the intraocular segment, 25 mm for the intraorbital segment, 9 mm for the intracanalicular segment, and 16 mm for the intracranial segment. [3] An injury to the optic nerve anywhere along this pathway by an extrinsic lesion is termed compressive optic neuropathy. [1]
Any lesion that produces associated mass effect can cause CON, including infectious (eg, aspergilloma), inflammatory (eg, inflammatory pseudotumor), vascular (eg, aneurysm), traumatic (eg, fracture, hematoma), and neoplastic (eg, meningioma, glioma) etiologies. [1] The optic nerve is particularly vulnerable to injury by a compressive force where it is adjacent to bone or in a small confined space (eg, orbital apex, optic canal). [4]
The clinical hallmarks of a compressive optic neuropathy include slowly progressive vision loss, reduced visual acuity and/or visual field, dyschromatopsia, a relative afferent pupillary defect, and eventual optic atrophy. Initially, the optic disc may be swollen or normal (retrobulbar optic neuropathy). Up to 75% of patients with intracranial tumors present with a headache. [4]
Clinicians should consider compressive optic neuropathy in the differential diagnoses of unexplained optic neuropathy. The initial evaluation should include a neuroimaging study, preferably MRI of the brain and orbits with and without contrast with fat suppression to evaluate for a compressive lesion.
The management of compressive optic neuropathy depends on the etiology. The surgical approach can be difficult, given the proximity of anterior visual pathway compressive lesions to critical neurovascular structures in the orbit and intracranial space.
Pathophysiology
Optic nerve compression by an extrinsic lesion has been postulated to cause atrophy of ganglion cell axons either through ischemia or mechanical disruption of axonal transport. Rarely, an intrinsic lesion of the optic nerve (ie, optic nerve glioma) can cause damage to the individual axons due to slow compression of the fascicles within the tumor.
Epidemiology
Compressive optic neuropathy can affect individuals of any age, sex, race, or ethnicity.
Frequency
United States
Compressive optic neuropathy (CON) is relatively rare, with an estimated incidence of about 4 cases per 100,000 individuals per year.
Mortality/Morbidity
Compressive optic neuropathy (CON) can lead to permanent vision loss, particularly if optic atrophy is evident at the time of diagnosis. However, with certain conditions such as Graves orbitopathy and pituitary adenomas, significant visual recovery may occur after surgical intervention. [5]
Tumors compressing the optic nerve in the intracranial space may cause additional neurologic morbidity (eg, endocrine dysfunction, cranial nerve palsies, papilledema, stroke).
Tumors within the orbit that cause CON may be associated with proptosis, ptosis, or diplopia. [6]
Trauma also can cause CON. Spheno-orbital or optic canal bone fractures and retrobulbar or optic nerve sheath blood within the orbit can compress the optic nerve and lead to acute vision loss. [7]
Prognosis
Prognosis depends on the type of lesion causing compression of the optic nerve.
Some tumors are relatively easy to excise, whereas others are likely to result in loss of vision.
Patient Education
Adequately inform the patient that vision may deteriorate despite surgery or radiation. Tumors can recur despite treatment.
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Axial MRI taken 3 weeks after the onset of distorted vision in the right eye; visual acuity is reduced to counting fingers at 1 ft. Evidence of optic nerve compression is not seen; disease in the sphenoid sinus is reported.
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MRI of same patient as in the image above taken 4 months later. Patient responded well to IV Solu-Medrol, but symptoms returned when steroids were reduced. Large mass compressing the right optic nerve is seen. Biopsy revealed lymphoma.
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A 72-year-old man with a moderate decrease in vision in the left eye (20/20 right, 20/25 left). Fundus examination revealed a normal right optic nerve.
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Same patient as in image above of a 72-year-old man with a moderate decrease in vision in the left eye (20/20 right, 20/25 left). Fundus examination revealed an atrophic left optic nerve.
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Neuroimaging study (MRI of brain and orbits) revealed an extensive meningioma involving the left orbital apex (arrow).
