The optic nerve is one of twelve cranial nerves, specifically cranial nerve II. Technically the optic nerve is not really a nerve, in that it is part of the central nervous system, and nerves are part of the peripheral nervous system, but it is still referred to that way.
The optic nerve is what transmits visual information from the retina to the brain. The photoreceptors of the retina sense light, and impulses are then sent through the optic nerve to where they can be interpreted as visual information by the brain. Damage to the optic nerve can mean partial or full blindness.
There are four major optic nerve diseases. They are:
* Glaucomatous Optic Nerve Disease (GOND) *
Glaucoma is a group of diseases of optic nerve blindness that develop progressively starting with loss of peripheral vision. Precisely what causes glaucoma is not fully known, though it has become increasingly understood that it is not a simple mechanical issue, but a neurodegenerative disease of the optic nerve. The lack of a continuous, sufficient blood flow results in neuronal cell death and loss of vision.
* Ischemic Optic Neuropathy (ION) *
Ischemic optic neuropathy is the more general condition of insufficient blood supply to the optic nerve. It is the most common cause of vision loss in older patients. Risk factors for ION include diabetes, hypertension, arteriosclerosis, and simply aging. Treatment is available for ION caused by the inflammatory blockage of arteries, and possible drug treatments are being investigated for the non-inflammatory variety.
* Leber Hereditary Optic Neuropathy (LHON)
As the name indicates, LHON is a hereditary condition. It is a mitochondrial (inherited only through the mother) disease stemming from a genetic mutation that renders nerve cells unable to produce energy and thus causes them to die. Though it can occur in men and women of all ages, the most common onset of LHON is in men in their twenties. From the onset of the disease, there is a loss of central vision within two to eight weeks, usually in both eyes. There is at present no treatment for LHON. There are tests for the genetic markers however-recommended for those with a family history of sudden blindness-and changes in lifestyle and diet appear to have some effect on when and if the disease will strike.
* Toxic Optic Nerve Disease *
Optic nerve damage and resulting blindness can be caused by drugs, nutritional (B1 and B12) deficiencies, metabolic disorders, radiation, and toxic substances, including smoking, alcohol, lead, DDT, digitalis, ergotamine, and many more.
“Optic Nerve Disorders.” Merck.com.
“Understanding Optic Nerve Disease.” International Foundation for Optic Nerve Disease.