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Causes of Optic Nerve Hypoplasia
Although there is no known cause of optic nerve hypoplasia, scientists understand the reason the disease develops in children. The origins stem from the second month of pregnancy when the primitive tissue known as the optic stalk begins to develop into nerve bundles. In certain fetuses, this process is either interrupted or altered in some way, through a process known as pruning.
As the bundles connect with the occipital lobe of the brain, overall and partial failure can occur. Otherwise, the nerves are streamlined by natural absorption of unneeded strands in a process called pruning. When pruning becomes overwhelming, the optic nerve is left not fully developed.
The reason this condition occurs to cause optic nerve hypoplasia is unknown. According to research, the disease is not genetic or hereditary. As such, there is no way to test for the condition while the fetus is developing.
Above right: Optic Nerve. (Supplied by Gray's Anatomy; Public Domain; http://upload.wikimedia.org/wikipedia/commons/f/f6/Gray773.png)
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Symptoms of de Morsier Syndrome
Optic nerve hypoplasia is identified in patients suffering from visual impairments of varying degrees. Some patients suffer from only slight vision disorder, while some have no light perception at all, making them completely blind. Others develop the condition known as esotropia, commonly known as “lazy eye.” Still others experience no symptoms whatsoever. The clarity of the vision is based primarily on the status of the optic nerve bundle rather than any other issues with the eyes.
Besides vision difficulties, children and adults who suffer from this disorder generally also experience various brain and pituitary problems. Many patients show abnormalities in the brain including the absence of important structures that link the hemispheres. The septum pellicidum, the tissue that connects the left and right ventricles of the brain, as well as the corpus callosum, nerve fibers connecting both lobes, may be missing. Pituitary problems include a lack of hormone production, impacting growth, metabolism, and overall sexual development.
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Diagnosing Septooptic Dysplasia
In order to diagnose optic nerve hypoplasia, doctors examine the back part of the eye known as the fundus using a process called opthalmoscopy. The exam includes analysis of the various parts of this section of the optic cavity including the optic disc, which can give doctors the best sign of optic nerve hypoplasia. When a person is suffering from this disease, they generally develop a condition commonly called “double-ring.” This has the visual appearing of a yellowish-white ring surrounding the optic disc.
The retina can also be examined. The blood vessels of this part of the eye normally descend from the nasal cavity. However, when a patient is suffering from septooptic dysplasia, they tend to come from a more centralized location. Additionally, the nerve fibers leading to this portion of the eye are thinner than normal.
Another sign can be identified in the fovea centralis, the center of the macula which helps sharpen vision. Normally, this section flexes as a person attempts to focus on an object. When this does not occur, it is generally a good sign that the person suffers from optic nerve hypoplasia.
Unfortunately, there is very little treatment for optic nerve hypoplasia. Most people who suffer from the disorder can lead normal lives depending on the level of visual, brain, and hormone problems. Scientists are currently researching treatment methods from stem cell technology, which may eventually be able to assist in the regrowth of the optic nerves and missing brain tissue.
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"Optic Nerve Hypoplasia Introduction" Magic Foundation: http://www.magicfoundation.org/www/docs/101.116/-optic-nerve-hypoplasia.html
"Optic Nerve Hypoplasia" National Federation of the Bling: http://nfb.org/legacy/fr/fr1/optic.htm