eMedicine Specialties > Ophthalmology > Optic Nerve

Optic Neuropathy, Compressive

Author: Talmadge (Ted) Cooper, MD, Adjunct Clinical Associate Professor, Department of Ophthalmology, Stanford Medical School
Contributor Information and Disclosures

Updated: Sep 10, 2007

Introduction

Background

The optic nerve extends from the back of the eye, traverses through the orbit and the optic canal, to the optic chiasm. The intraocular optic nerve is about 1 mm in length, the intraorbital segment is 25 mm in length, the intracanalicular segment is about 9 mm in length, and the intracranial component is about 16 mm in length. The optic nerve is most vulnerable to compression where it is adjacent to or surrounded by bone and is relatively immobile.

The hallmark of compressive optic neuropathy is a slowly progressive visual loss accompanied by a relative afferent pupillary defect and typically a central scotoma. Delay in diagnosis of compressive optic neuropathy is not uncommon because patients may not note early symptoms, or the visual loss may be misinterpreted as optic neuritis. Consider compressive optic neuropathy in the differential diagnosis of all corticosteroid responsive optic neuropathies. A workup of incidentally discovered optic atrophy should be completed to exclude a compressive lesion. Management of compressive optic neuropathy is difficult. Many of the conditions causing the compression are resistant to current treatment. Even well-performed surgery can worsen vision.

Pathophysiology

Optic nerve compression may result in ischemia or disruption of axonal transport.

Frequency

United States

This condition is relatively rare. Incidence in a large health maintenance organization was found to be about 4 cases per 100,000 per year. Most of these cases were due to thyroid ophthalmopathy.

Mortality/Morbidity

• Lesions that cause compression of the optic nerve are quite rare, but, when they occur, blindness is not uncommon.
• A small number of lesions that cause optic nerve compression are primary malignancies or metastases, which may result in death.
• Optic nerve tumors may occasionally extend intracranially and be life threatening.
• Optic nerve gliomas in adults are rare but very aggressive, lethal lesions. Optic nerve gliomas are much more common in children, have a much better prognosis, and are frequently associated with neurofibromatosis.
• Optic nerve sheath meningiomas presenting in childhood are rare but are considered more aggressive lesions. Optic nerve sheath meningioma presents more commonly in adulthood and generally has a slowly progressive course.

Sex

Thyroid ophthalmopathy and meningiomas are more common in women than in men and may cause compressive optic neuropathy.

Age

• This condition may occur at any age.
• It rarely is seen in children, with the exception of optic nerve glioma.
• It is most commonly encountered in patients aged 30-50 years.

Clinical

History

• Patients with compressive optic neuropathy typically present with slowly progressive visual loss.
• Visual complaints may be somewhat vague and nonspecific. The chronicity of the lesion may be indeterminate since patients may incidentally discover their visual loss when one eye becomes blind.
• Rarely, patients with compressive optic neuropathy will have sudden visual loss (eg, pituitary apoplexy, bleeding optic nerve glioma).
• Compressive optic neuropathy may be found during routine eye examination or refraction.
• It may be discovered following cataract surgery when the expected improvement in visual acuity does not occur.
• Observant patients may complain of ipsilateral dyschromatopsia (ie, objects seem less bright and colors are subdued in the affected eye compared with the uninvolved side).
• Patients sometimes present with complaints of visual field loss.
• It is not uncommon in cases of compressive optic neuropathy for a friend or relative to note the appearance of proptosis (ie, affected eye appears larger or more protuberant).

Physical

Compressive optic neuropathy may affect visual acuity, brightness perception, color vision and desaturation of hue, visual fields, pupils, relative position of the eyes, resistance to retropulsion of the globe, extraocular motility, and the fundus.

• Visual acuity
  • Visual acuity usually is reduced in the affected eye.
  • Refraction or at least pinhole acuity should be performed.
  • Compressive lesions causing axial proptosis may result in a hyperopic shift.
• Brightness perception usually is reduced in the affected eye.
• Color vision often is reduced in the affected eye. The Ishihara test plate is one of the most common methods of testing color vision in the office setting.
• Desaturation of hue: When a bright color, especially red, is viewed by each eye separately, the patient usually will describe the color to be less vivid or washed-out in the affected eye.
• Pupils
  • Examination of the pupils usually will reveal an ipsilateral relative afferent pupillary defect (Marcus Gunn pupil). This test is performed in a dimly lit room with the patient fixing his gaze on a distant object.
  • A bright focused light (eg, pen light, Finnoff transilluminator, indirect ophthalmoscope) is then shifted from one eye to the other about every 3 seconds.
  • The affected eye may appear to dilate, not constrict, or show increased pupillary escape when compared to the unaffected eye.
• Proptosis
  • It is best noted by viewing the globes from above the patient's forehead.
  • Formal measurement of the position of the anterior surface of the cornea in relation to the lateral wall of the orbit can be recorded with a Hertel exophthalmometer. This is a useful test in all cases of suspected optic nerve dysfunction. 
  • If more than 2 mm of proptosis exists, a space-occupying lesion of the orbit may be suspected, especially in the setting of decreased orbital retropulsion. 
  • Mild proptosis often is not noticed by patients and their physicians.
• Extraocular motility
  • The movement of the eye often is not affected by conditions causing compression of the optic nerve.
  • Disturbance of ocular motility or ptosis along with other signs of compressive optic neuropathy may suggest an infiltrative process, an inflammatory condition, or that the location of the lesion is at the apex of the orbit.
• Relative resistance to retropulsion of the globe
  • Pressing on the globes through the closed lids may reveal that more force is required to gently push one of the eyes into the orbit.
  • This suggests the presence of a space-occupying lesion in the orbit.
• Visual field examination
  • Because of the arrangement of nerve fibers as they course through the optic nerves and the chiasm, the site of compression produces specific visual field abnormalities.
  • The most common defects found with compression of the optic nerve anterior to the chiasm include enlarged blind spot, relative central scotoma, and constriction.
  • When compression of the optic chiasm occurs, a bitemporal hemianopia usually is found, although unilateral field loss or homonymous hemianopia may occur if the lesion is prefixed or postfixed.
  • Nearly all types of visual field abnormalities have been reported with compression of the optic nerve.
• Dilated fundus examination
  • A careful examination of the optic disc is important. Often, the optic disc may appear normal or pale.
  • With chronic compression of the optic nerve, optic atrophy results.
  • The triad of optic disc swelling followed by optic atrophy, optociliary shunt veins (optochoroidal collaterals), and progressive visual loss commonly is reported in compressive lesions of the orbital and intracanalicular optic nerve.
  • Optochoroidal collaterals are not pathognomonic of optic nerve sheath meningioma and can be seen with central retinal vein occlusion, chronic papilledema, and various compressive optic nerve lesions.
  • A finding of unilateral optic disc swelling may be the first sign of compressive optic neuropathy.
  • Even in the absence of visual and neurologic symptoms and an otherwise unremarkable complete ophthalmic examination, unilateral optic disc swelling should be investigated promptly with CT scan or MRI.
  • If no intracranial explanation is found, careful evaluation should be made to rule out an intraorbital or intracanalicular mass.
  • The presence of a swollen optic disc should raise the index of suspicion for a primary nerve sheath meningioma. However, a great variety of tumors have been reported with this finding.
  • Similarly, swollen discs have been reported more commonly in the presence of tumors within the orbit.
  • Less frequently, there have been reports of disc swelling with intracanalicular and intracranial tumors compressing the optic nerve.
  • Tumors causing proptosis may result in choroidal folds.

Causes

Causes of compressive optic neuropathy include the following:

• Primary malignancies or metastases
• Optic nerve tumors
  • Optic nerve gliomas
  • Optic nerve meningiomas
• Thyroid ophthalmopathy
• Cavernous hemangiomas
• Sarcoidosis
• Trauma
• Solid orbital tumors
  • Meningiomas
  • Hemangiomas
  • Schwannoma
• Cystic tumors
• Dermoid cysts
• Cholesterol granuloma
• Mucoceles
• Conjunctival orbital cysts
• Inflammatory and infiltrative processes

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