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Optic Nerve Atrophy
Optic Nerve Atrophy (ONA) also known as Second
cranial nerve atrophy is a permanent visual impairment
caused by damage to the optic nerve. The optic nerve
which is comprised of over a million nerve fibers (axions)
and functions like a cable carrying information from the
eye to be processed by the brain. When some of these
nerve fibers are damaged the brain doesn't receive
complete vision information and sight becomes blurred.
Atrophy (wasting away) ranges from partial where some
axons are damaged to profound where the majority are
damaged. The ability to see clearly (visual acuity) is
affected due to nerve damage that occurs in the central
part of the retina and is responsible for detail and color
vision (macula). These areas of the eye are more
vulnerable to the effects of atrophy. ONA resulting from
damage to the optic nerve can affect one or both eyes
and may also be progressive, depending on the cause.
Glossary
Axon: single projection from a nerve cell that under
normal conditions, carries nerve impulses away from the
cell body.
Optic Nerve Hypoplasia: refers to underdevelopment of
the optic nerve during pregnancy.
Causes of the Eye Condition
The causes of optic atrophy vary from acquired
problems such as; tumors of the visual pathways,
inadequate blood flow, called ischemic optic neuropathy
(most often affects the elderly) or oxygen supply
(hypoxia ischemia) before or shortly after birth, trauma,
hydrocephalus, heredity, and rare degenerative diseases
have been identified as causes of ONA. There are also
several rare forms of hereditary optic nerve atrophy that
affect children and young adults, which are usually
hereditary. The autosomal dominant is the milder form
and has a gradual onset of deterioration in childhood but
little progression thereafter; the autosomal recessive is
more severe and is present at birth or within 2 years and
is accompanied by nystagmus. Leber's Disease is
suspected of being X-linked and occurs most commonly
in 20 to 30 year old males where some vision is retained
with varying degrees of visual impairment. The
hereditary pattern is dominant and the gene is passed to
50% of the offspring. If a tumor is causing the ONA
progression may be halted by removal of the tumor. The
optic nerve can also be damaged by shock, various toxic
substances, radiation, and trauma. Various eye
diseases, such as glaucoma, can also cause optic nerve
atrophy. Additionally, the condition can be caused by
diseases of the brain and central nervous system, such
as cranial arteritis (sometimes called temporal arteritis),
multiple sclerosis, brain tumor, and stroke.
Treatments
Unfortunately, there is no effective treatment for optic
atrophy and the damaged axon cannot be regenerated.
Early diagnosis is the best defense because if the cause
can be found and corrected, further damage can be
prevented.
References:
Texas School for the Blind and Visually Impaired
(October 31, 2005). Optic Nerve Atrophy Pediatric Visual
Diagnosis Fact Sheet™. Retrieved July 3, 2011, from
http://www.tsbvi.edu/seehear/spring99/ona.htm
University of Michigan Kellogg Eye Center. (2010),
Optic Atrophy. Retrieved July 3, 2011, from
http://www.kellogg.umich.edu/patientcare/conditions/opti
c.atrophy.html
New York Times. (July 3, 2011) Optic Nerve Atrophy.
Retrieved July 3, 2011,
http://health.nytimes.com/health/guides/disease/opticnerve-atrophy/overview.html
Special Education Exchange. (1996 - 2011). OPTIC
ATROPHY. Retrieved July 3, 2011, from
http://www.spedex.com/resource/documents/veb/optic_a
trophy.html
University of Maryland Medical Center. (1997- 2011),
Optic nerve atrophy – Overview. Retrieved July 3, 2011,
from http://www.umm.edu/ency/article/001622.htm
Developed by Stephen Atwood