Optic Nerve Atrophy

Optic nerve atrophy (ONA) is an umbrella term used to describe a number of conditions, which result in vision loss. Optic nerve atrophy can be classified according to the cause of the atrophy, accordingly:

• Demyelinating
• Inflammatory
• Ischemic
• Traumatic

The cause of ONA is dependent upon the type of atrophy present:

• Demyelinating ONA, also known as optic neuritis, occurs in conditions such as multiple sclerosis and other demyelinating and inflammatory conditions. Patients often present with rapid loss of vision in one eye, which may be loss in part or all of the visual field.
• Ischemic ONA results from occlusion of blood vessels supplying the optic nerve and can occur in conditions such as vasculitis, giant cell arteritis, granulomatosis with polyangiitis, and rheumatoid arthritis. Patients with ischemic ONA develop rapidly progressing loss of vision, often in the superior aspect of their visual field.
• Traumatic ONA results from direct injury to the optic nerve, often from blunt force or accidents such as motor vehicle collisions.
• Inflammatory ONA, also known as infiltrative neuropathy, results in destruction of the optic nerve from locally invading tumors, infection and autoimmune processes such as sarcoidosis.

ONA is diagnosed by extensive ophthalmological investigation which may include:

1. Visual field testing: visual field defects in optic neuropathies can take several patterns including central, diffuse, arcuate, and altitudinal defect. The pattern of visual filed defect is not specific of any etiology and almost any type of field defect can occur with any optic neuropathy. However, altitudinal defects are more common in ischemic optic neuropathies and central, or cecocentral defects frequently accompany toxic/nutritional and hereditary optic neuropathies.
2. Electrophysiological testing: Visual evoked potential (VEP) are often abnormal in optic neuropathies. Although VEP is not necessary in the diagnosis of optic neuropathy, it can be useful in patients with early or sub-clinical optic neuropathy who may have normal pupillary responses and no discernible optic disc changes on clinical examination
3. Optical coherence tomography: a relatively new technique which uses low coherence light to penetrate tissue and a camera to analyze the reflected image. By performing circular scans around the optic nerve head, the peripapillary nerve fiber layer can be analyzed. This has been useful in the follow up of patients with optic neuritis, traumatic optic neuropathy, and Leber’s hereditary optic neuropathy

Symptoms of ONA often include tunnel vision (also known as scotoma), blurred vision, and loss of other visual fields. These defects are diagnosed on further investigation using the aforementioned techniques.

Currently, there are no effective conventional treatments for ONA. Following destruction of the optic nerve, regeneration of neurons using conventional medical treatment is not possible. Therefore, treatment with novel therapies, such as stem cells, offers a promising hope that regeneration of vision in ONA patients may be a possibility.

The mechanisms by which stem cells deliver their regenerative action are :

• Secretion of neurotrophic factors before or after differentiation. MSCs release certain neurotrophic growth factors including brain derived neurotrophic factor (BDNF) which may offer neuroprotection.
• Injection of MSC may result in anti-inflammatory effects, thereby increasing regeneration of neurons located within the optic nerve.