Revision as of 11:54, July 6, 2010

Disease Entity

Optic atrophy refers to death of the retinal ganglion cell axons that comprise the optic nerve with the resulting picture of a pale optic nerve on funduscopy. Optic atrophy is an end stage that arises from myriad causes of optic nerve damage anywhere from the retina to the geniculate. Since the optic nerve transmits retinal information to the brain, optic atrophy is associated with vision loss. Optic atrophy is somewhat of a misnomer as atrophy implies disuse and optic nerve damage is better termed optic neuropathy.

Disease

Etiology

Anything that can compromise ganglion cell function can cause (over time) optic atrophy (and more broadly optic neuropathy).

Risk Factors

Risk factors run the gamut from increased intraocular pressure (glaucoma), ischemia, compression (tumors), inflammation, infection, etc. See differential diagnosis.

General Pathology

In optic atrophy there is loss of axons and shrinkage of myelin leading to gliosis and widening of the optic cup.

Pathophysiology

Primary prevention

Optic atrophy is the end stage of a process causing damage to the optic nerve. Current medical practice is currently unable to return function (regrow axons) to an atrophic optic nerve and at best is able to stabilize whatever function remains. Primary prevention is the goal to prevent loss of axons and optic atrophy (neuropathy).

Diagnosis

Since the optic nerve is the conduit for information from the retina to the brain, a damaged optic nerve will result in vision loss. Subtle damage might not affect acuity but may lead to a loss of contrast or color vision. Severe damage may lead from legal blindness to no light perception. Damage to a part of the optic nerve results in loss of vision in the corresponding visual field. A complete diagnosis is based on optic nerve appearance, tests of vision (visual field, contrast, color, acuity) and ruling out other causes for vision loss (such as retinal causes).

Certain disc appearances can help to determine the cause for the optic nerve damage. Sector disc pallor in an older individual could have been caused by NAION. Severe optic atrophy with gliosis again in an elderly person could have been due to giant cell arteritis. Damage from papilledema may leave retinal folds and sometimes glistening bodies in the optic nerve head. Cupping is always suggestive of glaucoma.

Optical Coherence Tomography has become a valuable tool to verify the status of the nerve fiber layer. Quantification of the nerve fiber layer height along with comparison with normative data can document axon loss and differentiate between optic nerve and retinal disease as a cause for vision loss.

History

History is critical in the diagnosis of optic atrophy since the physician wants to know how the eye arrived at this juncture. If this is not known then a careful history with attention to past medical history including all medications, time course of vision loss, associated symptoms etc. can be helpful.

Physical examination

A complete eye exam including visual field, assessing color and contrast vision, intraocular pressures, looking for afferent pupil defect, and funduscopy should be done.

Signs

Optic atrophy is a sign and typically is noted as optic nerve pallor which may be sectoral. This is the end stage of a process resulting in optic nerve damage.

Symptoms

The main symptom of optic atrophy is loss of vision. Any other symptoms are attributable to the underlying process that caused the atrophy (such as pain with angle closure glaucoma.

Clinical diagnosis

Optic atrophy is usually not difficult to diagnose but the cause for the optic atrophy may be very difficult to ascertain. Sometimes the cause of vision loss may be difficult to differentiate between subtle optic neuropathy and disease of the retina (or both). Electrophysiology can be helpful (ERG, mERG) in that case.Presented with unexplained optic atrophy the following work up should be considered:

Visual fields 30-2

MRI of brain and orbit with contrast

CT with contrast (check bony disease, sinuses)

Blood pressure and check of cardiovascular health (carotids, etc.)

Glucose, B12, VDRL, ANA, homocysteine, ACE, Antiphospholipid antibodies,

TORCH panel

Diagnostic procedures

Laboratory test

Differential diagnosis

Optic atrophy is not usually difficult to diagnose but might be confused with optic nerve hypoplaia, myelinated nerve fibers, myopic or scleral crescent, or tilted disc.

The causes for optic atrophy include:
Compressive – secondary to papilledema, tumor, bony growth, disc drusen, increased intraocular pressure (glaucoma)
Vascular – arteritic and non-arteritic ischemic optic neuropathy, diabetes,
Inflammatory – sarcoid, systemic lupus, Behcet’s, demyelination (MS),
Infectious – viral, bacterial, fungal infections
Toxic – many medications such as ethambutol, methanol, etc.
Metabolic – diabetes, vitamin deficiency,
Neoplastic – lymphoma, leukemia, tumor,
Genetic – Kjer’s (OPA1), Leber’s optic atrophy, Behr
Developmental/Congenital -
Radiation optic neuropathy
Traumatic optic neuropathy

Management

The primary management is to intervene before optic atophy is noted or to save remaining function. This will depend on the underlying cause for the optic nerve damage. For instance, intraocular pressure control in glaucoma, control of inflammation in sarcoid, etc.

General treatment

Medical therapy

Medical follow up

Surgery

Surgical follow up

Complications

Prognosis

Studies in glaucoma have shown that the optic nerve has some reserve before vision loss is noted but after that reserve is depleted small changes in nerve fiber loss lead to significant changes in vision loss. Early detection is key since we have not way to replace dead axons.

Additional Resources

The Neuro-Ophthalmology Virtual Education Library: library.med.utah.edu/NOVEL/
The North American Neuro-ophthalmolgy Society (NANOS):www.nanosweb.org

References

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