Understanding the Optic Nerve

 

Eyesight is one of the most essential senses that we possess. Our perception of the world around us is significantly diminished if our eyesight is compromised. Taking proper care of our eyes is imperative, and an awareness of how the optic system works within our bodies will help us do so effectively.

Most of us have a basic understanding of the visible structure of the eye and its function. This includes the cornea, iris, pupil, and also some parts that are not visible, which are the retina and the lens. To understand the inner workings of the entire optic system, we need to explore the function of one of its main components with which we may not be familiar, and that is the optic nerve.

What is the Optic Nerve?

The word “optic” is derived from the Greek word “optikos”, which means “related to sight.” The optic nerve is a pair, each connecting an eye to the brain. Simply put, its function is to transfer visual information from the eye to the brain. The eye receives visual information and the brain interprets it into images.
The optic nerve is the conduit for visual input, which is transferred in the form of electrical impulses, specifically from the retina at the back of the eye to the lateral geniculate nucleus (LGN) in the thalamus part of the brain. The LGN then transmits the information to the visual cortex of the brain, which processes the visual information and interprets it into images.

Where is the Optic Nerve Located?

The optic nerve is part of the central nervous system because of the nature of its development during the embryonic stage and its composition. There are twelve pairs of cranial nerves and the optic pair is the second, and this way it is grouped with the peripheral nervous system, of which it is technically not a part.  It is made up of nerve cells called ganglionic cells and is constructed from over a million nerve fibers. The only part of the brain or a direct extension of the brain, which is visible without surgery, is the head of this nerve. It can be observed through the eye by using an ophthalmoscope.

What are the symptoms of optic nerve damage?

Damage to the nerve may not always result in perceptible symptoms, which is why regular eye exams are necessary to ensure that the nerve is healthy or detect any early signs of damage. However, there are a few telltale signs that could alert you to possible nerve damage.  These are the most common symptoms of nerve damage. However, they could also be caused by less serious conditions, so the problematic eye will need to be tested further to pinpoint the cause.

– Pain in the eye with the movement of the eyeball.
– Pain in the brow or consistent pain in the eye even when still.
– Distorted vision such as blurring.
– Redness of the eye.
– Partial or total loss of vision.

A few other symptoms that could indicate optic nerve damage are:

– Abnormal size of the pupil, specifically dilation.
– Lack of reaction or abnormally decreased sensitivity to light.
– A visible bulging of the eye.
– Sudden inability to recognize finer details.
– Diminished color detection.
– Dim vision.
– Sudden appearance of blind spots.
– Appearance of extraneous visual elements like halos and rainbows.

A few symptoms of optic nerve damage may manifest in other parts of the body.

– Joint pain
– Fever
– Fatigue
– Loss of memory
– Nausea
– Neurological symptoms like forgetfulness and mental confusion
– Dizziness
– Weight loss

What are the common causes of optic nerve damage?

Glaucoma: Most common in adults over the age of 60, this affliction can lead to total blindness in its most severe form. The principal cause of glaucoma is abnormally high pressure in the eye. The fluid called aqueous humor in the eye drains out periodically. If too much fluid is being produced or the drainage system is not working as it should, pressure builds up in the eye and causes the optic nerve to gradually deteriorate.

Why Does the Optic Nerve Cause a Blind Spot?

Glaucoma is found to be genetic in many cases. Secondary conditions such as cardiac disease, hypertension and anemia can also cause it. The most common symptom is the appearance of blind spots. In several cases, the only symptom is vision loss that is so gradual as to be imperceptible.  The best prevention is periodic eye exams that include eye pressure measurements.

What Causes Optic Nerve Swelling?

Optic neuritis: Inflammation or swelling of the optic nerve causes optic neuritis. Adults between the ages of 20 and 40, women in particular are prone to this disorder. Its symptoms include pain in the eye especially with movement of the eyeball, diminished vision loss, peripheral vision loss, reduction in color perception and flashing lights.  Its main causes are multiple sclerosis and autoimmune diseases such as lupus. It can also be caused by bacterial infections and certain medications.

Stroke: A stroke blocks or reduces blood flow to certain vital parts of the body and causes damage. Optic nerve damage can be caused by a stroke or a specific type of stroke that affects the eye, called anterior ischemic optic neuropathy, where blood flow is restricted in the arteries that supply the optic nerve.

Trauma: Head and eye injuries can damage the nerve and so can certain types of vigorous exercises that can increase pressure in the eye.

Infections: Measles, chickenpox, herpes and Lyme disease.

Cancer: Tumors that develop in the region of the optic nerve, and other types of cancer as well, can cause it to deteriorate.

A deficiency of vitamin B12 is a condition that contributes to nerve damage.

In conclusion, the optic nerve is a vital element in the optic and neurological system of the human body and it directly influences the quality of your vision. It is susceptible to a variety of damage and disorders, which can be prevented by regular eye exams that include a focus on the optic nerve.  Any signs of vision impairment or eye irritation, however minor, could potentially be an indication of optic nerve damage and should be immediately examined by an ophthalmologist.  If you are afflicted by any such symptoms, schedule an appointment with a local eye doctor and they will conduct an examination and set you on your path to recovery.