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The Optic Nerve

Optic Nerve At the back of the eye is the retina. This is a layer of light sensitive cells that begin the process of interpreting the light that enters our eyes. The sensations the light causes on the retina are carried by the optic nerve to the brain, where they are interpreted into images we can understand.

To understand how it works, compare the optic nerve to the cable that brings TV programs into your living room. The satellite dish that receives the signals is like the retina - it has some inputs, but can't use them. The data is then sent down the cable (like the optic nerve) to your decoder (like the brain) which converts the data, into images we can understand.

The optic nerve is far more complex than the cable. It has approximately 1.1 million nerve cells. The optic nerves passes from the rear of each eye through the skull to a part of the brain called the visual cortex, which is located at the back of the brain, in an area called the occipital lobe. The visual cortex is that part of the brain that interprets the signals from the retina that the optic nerve has carried and converts them into images the rest of the brain can recognize.

While referring to a person's blind spot often means talking about an area where they have no knowledge or are weak (either physically or mentally), there is actually a real blind spot that we all have, or rather two of them - one for each eye. This is one specific area where our vision is blocked. It happens because the optic nerve head - the section of the optic nerve that connects to the retina does not have any photoreceptors (cells that respond to light). Because of this there is, in each eye, an area where vision is not possible.

Normally, we do not notice this because when both eyes are in use, the blind spot in one eye is covered by the seeing area of the other eye.

While the optic nerve is well protected inside the skull and is unlikely to suffer any physical damage, there are some medical conditions that can affect it and which should be guarded against.

  • Optic Atrophy. This is the degeneration of the nerve fibers that make up the optic nerve. It is normally hereditary, but may also be acquired either through some other eye infection or through toxic influence - consumption of tobacco, alcohol or other such substances in large quantities. This condition results in a gradual loss of vision in the eye with the affected optic nerve.

  • Optic Neuritis. This is an inflammation of the optic nerve. This may have many causes and is quite common. An occasional attack that could result in over sensitivity to light, itching and feelings of irritation within the eye and a blurring of vision are nothing to get worried about. However, if these symptoms do occur, it is best to have the condition checked by an eye specialist. If the attacks are frequent the condition must be considered as serious and could even lead to a loss of sight in the affected eye.

  • Papilledema. This is a condition that often affects both the eyes at the same time. The part of the optic nerve that connects to the retina becomes swollen. It is normally brought on by severe hypertension. While there are no immediate outward signs of this condition, if it is not spotted during a regular eye examination and treatment is not begun the damage can be permanent and may even result in a loss of vision in one or both eyes.

  • Ischemic Optic Neuropathy. This is caused when the blood supply to the optic nerve is disrupted or becomes inadequate. Any sickness or metabolic malfunction that disrupts the flow of blood in the body could cause the onset of this problem. This is another potential problem that should be spotted during an eye examination and treatment begun immediately. If it is allowed to persist the result could be loss of vision, either through a slow process or by a sudden onset.
  • Glaucoma. This is a disease that affects the optic nerve itself and slowly kills off the cells that make up the nerve, until it is left too weak to function.

The optic nerve is one of the most critical elements of the process of vision. The difficulty with any disorders that may arise is that there are few symptoms of the problem that can be perceived and understood by the layman. That is why regular eye checkups are so important. Most problems are treatable, if caught in time.

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