Optic Atrophy
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Disease Entity
Optic atrophy refers to the death of the retinal ganglion cell axons that comprise the optic nerve with the resulting picture of a pale optic nerve on fundoscopy. Optic atrophy is an end stage that arises from myriad causes of optic nerve damage anywhere along the path from the retina to the lateral 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 thus optic nerve damage is better termed optic neuropathy.
Etiology
Anything that can compromise ganglion cell function can cause (over time) optic atrophy (and more broadly optic neuropathy). Optic atrophy can occur due to damage within the eye (glaucoma, optic neuritis, papilledema, etc.), along the path of the optic nerve to the brain (tumor, neurodegenerative disorder, trauma, etc.), or it can be congenital (Leber’s hereditary optic atrophy, autosomal dominant optic atrophy).
Risk Factors
Risk factors run the gamut from increased intraocular pressure (glaucoma), ischemia, compression (tumors), inflammation, infection, etc. See differential diagnosis below.
General Pathology
The optic nerve is a bundle of 1.2 million axons of retinal ganglion cells that carries visual information from the retina to the brain. The optic nerve is myelinated by oligodendrocytes that do not regenerate after damage. In optic nerve atrophy there is loss of axons and shrinkage of myelin leading to gliosis and widening of the optic cup.
Primary prevention
Optic atrophy is the end stage of a process causing damage to the optic nerve. 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 (removal of the process causing the damage) 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. Occasionally if the process causing damage is removed before apoptosis occurs (as for instance removal of a pituitary tumor compressing the chiasm or reducing inflammation in sarcoid) some improvement in visual function may be noted. A complete diagnosis is based on optic nerve appearance, tests of visual function (visual field, contrast, color, acuity), identifying the causative factor of the damage, 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 suggestive of glaucoma.
Optical Coherence Tomography has become a valuable tool to verify the status of the nerve fiber layer/ganglion axons. Quantification of the nerve fiber layer height and 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 needs to know how the eye arrived at this juncture. A careful history with attention to past medical history including all medications, time course of vision loss, associated symptoms etc is critical for arriving at a correct diagnosis.
Physical examination
A complete eye exam including visual field, assessing color and contrast vision, intraocular pressures, looking for afferent pupil defect, and fundoscopy should be done.
Signs
Optic atrophy is a sign and typically is noted as optic nerve pallor. This is the end stage of a process resulting in optic nerve damage. Because the optic nerve fiber layer is thinned or absent the disc margins appear sharp and the disc is pale, probably reflecting absence of small vessels in the disc head.
EXAMPLES OF OPTIC ATROPHY (NEUROPATHY):
Symptoms
The main symptom of optic atrophy is vision loss. Any other symptoms are attributable to the underlying process that caused the disc damage (such as pain with angle closure glaucoma).
Clinical diagnosis
Optic atrophy is usually not difficult to diagnose (characteristic pale optic disc) but the cause for the optic atrophy may be 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) and OCT to assess the thickness of the nerve fiber layer may be helpful in such cases.
Characteristic visual field patterns include papillomacular defect (cecocentral scotoma), arcuate defect (include altitudinal) or temporal wedge defect (nasal fibers) for prechiasmal, bitemporal (superior) field defects for chiasmal lesions, and hemianopsia for post-chiasmal lesions.
The following work up should be considered for patients presenting with unexplained optic atrophy:
- Check for afferent pupil
- Visual fields 30-2,color vision
- MRI of brain and orbit with contrast
- CT with contrast (check bony disease, sinuses)
- Blood pressure and check of cardiovascular health (carotids, etc.), Glucose
Screen for these if history or examination are suggestive:heavy metals, B12, folate, FTA ABS, VDRL, ANA, homocysteine, ACE, Antiphospholipid antibodies, TORCH panel [1]
Diagnostic procedures
- Visual Field Testing (Humphrey 30-2, Tangent Screen) - to help localize the location of the lesion.
- Optical Coherence Tomography (OCT) - to assess the thickness of peripapillary retinal nerve fiber layer and/or ganglion cell layer.
- ERG, mERG - to rule out retinal disease.
- Neuro-imaging (MRI, CT) – to asses for tumors, bone growth, sinusitis, fractures, multiple sclerosis, and infections.
Laboratory test
As stated above, if history or examination are suggestive, it may be useful to screen for: heavy metals, B12, folate, VDRL, ANA, homocysteine, ACE, Antiphospholipid antibodies, TORCH panel.
Differential diagnosis
Optic atrophy is not usually difficult to diagnose but might be confused with optic nerve hypoplasia, myelinated nerve fibers, myopic or scleral crescent, or tilted disc.
The causes for optic atrophy include:
- Compressive – secondary to papilledema, tumor, bony growth (fibrous dysplasia, osteopetrosis), thyroid eye disease, chiasmal (pituitary etc), optic nerve sheath meningioma, disc drusen, increased intraocular pressure (glaucoma)
- Vascular – arteritic and non-arteritic ischemic optic neuropathy, diabetes,
- Inflammatory – sarcoid, systemic lupus, Behcet’s, demyelination (MS), etc.
- Infectious – viral, bacterial, fungal infections - herpes, TB, bartonella, etc.
- Toxic & nutritional – many medications such as ethambutol, amiodarone, methanol, vitamin deficiency etc.
- Metabolic – diabetes
- Neoplastic – lymphoma, leukemia, tumor, glioma
- Genetic – Autosomal dominant optic atrophy (OPA1), Leber’s hereditary optic atrophy, Leber's hereditary optic neuropathy, as a late complication of retinal degeneration.
- Radiation optic neuropathy
- Traumatic optic neuropathy
Management
The management goal is to intervene before optic atrophy 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.
Prognosis
Studies in glaucoma (based on OCT nerve fiber layer measurements and other methods) have shown that the optic nerve has some reserve (axons) before vision loss is appreciated. After that reserve is depleted small changes in nerve fiber loss lead to significant decrease in vision. Early detection is key since we cannot 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
- ↑ Lee AG, Chau FY, Golnik KC, Kardon RH, Wall M. The diagnostic yield of the evaluation for isolated unexplained optic atrophy. Ophthalmology 2005; 112(5):757-759
