What is The Glaucoma Optic Nerve?
The glaucoma optic nerve is a paired cranial nerve (CNII) and is part of the central nervous system. The optic nerve carries sight impulses from the eye retina to the visual cortex in the brain. The nerve contains millions of fibers which are connected to the back of the eye.
The nerve is divided into four sections which are:
- The optic head
- The orbital part
- The intracanalicular part
- The cranial part.
The optic head leaves the optic disc at the back of the eye and the nerve travels up into the brain.
The optic nerve is covered in a lipid-rich substance called myelin which insulates and protects it. The myelin is essential for the optic nerve to function. Myelin helps the nerve to send electrical signals from the eye to the brain quickly.
The glaucoma optic nerve is responsible for transmitting color perception, contrast and brightness perception. The nerve controls the accommodation reflex and the light reflex.
The accommodation reflex is important when looking at near objects and the light reflex controls the constriction of the pupils.
Glaucoma Optic Nerve Injuries
The three most common cause of optic nerve damage are glaucoma, anterior ischemic optic neuropathy and optic neuritis. The nerve can get damaged due to trauma, compression, tumors, toxins and inflammation. Any damage to the optic nerve will result in visual problems and medical attention will be needed.
Glaucoma is a serious eye disease and is the leading cause of irreversible blindness leading cause of irreversible blindness in people around the world.
The eye gets nourished with a fluid called the aqueous humor which is constantly produced. If too much of the fluid is made it puts pressure on the eye which in turn, damages the optic nerve.
When pressure has damaged the optic nerve it often leads to partial or complete loss of sight. Glaucoma develops slowly and many patients do not know they have the disease until the damage is done. Regular checkups with an eye specialist are advisable to check fAdd or glaucoma and other eye conditions.
Anterior Ischemic Optic Neuropathy
Anterior ischemic optic neuropathy (AION) develops when the optic nerve does not get enough oxygenated blood. When blood vessels get damaged or diseased they will not deliver blood to nerves.
Anterior ischemic optic neuropathy results in impaired vision and in some cases total loss of sight in one or both eyes. Due to the optic nerve dying, the damage is permanent and sight will not return. The first symptom of the condition is a temporary darkening of vision.
Optic neuritis (ON) is inflammation of the optic nerve due to disease or infection. Infections such as meningitis, measles and mumps can cause optic neuritis which results in temporary visual problems.
Furthermore, optic neuritis is often one of the first symptoms of multiple sclerosis.
Optic neuritis usually heals by itself and does not need any medical treatment.
Blunt And Penetrating Trauma
Any kind of trauma to the eye or the surrounding area can cause glaucoma optic nerve damage. A direct blow to the eye causes bruising and blood vessels occasionally break. If the blood vessels are damaged the optic nerve could be affected.
Puncture wounds to the eye put the optic nerve at risk of injury. Penetrating trauma during surgery or as a result of an accident could damage the nerve as well as affect sight.
Wearing protective eyewear whenever possible helps to prevent eye wounds and is therefore preferable as penetrating trauma usually results in permanent damage to the optic nerve.
In rare cases, the glaucoma optic nerve is injured during a surgical procedure. The nerve may be severed and suffers penetrating trauma from the needle used for the anesthetic.
For instance, there have been several reported cases of optic nerve damage during cataract surgery.
Various things cause optic nerve compression which leads to visual problems. Any pressure in and around the glaucoma optic nerve will pinch or trap the nerve itself causing damage. When compressed, it will not send information to the brain and sight is therefore affected.
Tumors regularly cause damage to nerves due to the excess pressure they put on the optic nerve itself.
Blood vessels that swell around the area of the tumor cause further nerve injuries.
Toxins can lead to a condition called toxic optic neuropathy (TON) which causes visual impairment due to nerve damage.
Alcohol, tobacco and antibiotics all contain toxins that can damage the glaucoma optic nerve. Furthermore, cancer drugs such as tamoxifen have been known to cause irreversible optic nerve damage.
The symptoms associated with glaucoma optic nerve injuries include:
- Partial or total loss of sight
- Distorted vision
- Color blindness
- Eye pain
How Are Glaucoma Optic Nerve Injuries Diagnosed?
A basic eye test is not sufficient to check for optic nerve damage and more investigation is needed. Peripheral vision will be checked and the patient's eyes will be carefully examined. MRI scans of the brain are used to check for central nervous system lesions.
There are several tests eye specialists use to determine whether a patient has glaucoma. Tonometry is used to measure eye pressure and an ophthalmoscopy is used to examine the optic nerve to check for damage.
The optometrist will use drops to numb the patient’s eye before carrying out a tonometry test. Pressure is then applied to the eye by aiming a jet of warm air at the eye. The intraocular pressure reading gets picked up by the tonometer and the specialist will make a diagnosis.
The pressure is recorded in millimeters of mercury (mm Hg) and normal pressure is 12 - 22 mm HG. most glaucoma patients have a reading in excess of 20 mm Hg. It’s worth noting that all patients are different and a reading over 20 mm Hg does nt mean he patient has glaucoma.
An ophthalmoscopy is a diagnostic procedure which allows an eye specialist to see the optic nerve. Eye drops are put into the eye to dilate the pupils so that the shape and color of the optic nerve can be seen. A device is then used to magnify the optic nerve to check for any abnormalities.
Following these tests the eye specialist may also check the patients field of vision to determine whether sight has deteriorated. The angle between the iris and cornea can also be checked to determine how severe the glaucoma is.
How Are Glaucoma Optic Nerve Injuries Treated?
Damage to the glaucoma optic nerve is usually irreversible. The cable of fibers that make up the optic nerve are unable to regenerate unlike other nerves. The support cells for the optic nerve can also die following any damage.
The symptoms associated with glaucoma optic nerve damage can be managed. Pain can be managed with medication and anti-inflammatory drugs will also ease some of the symptoms.
Pressure on the eyes can also be managed in some cases. Eye drops are used to lower the pressure in the eye for patients with glaucoma. There are also eye drops that reduce the amount of aqueous humor that is made. Easing the pressure also slows down the progression of glaucoma.
Furthermore, laser surgery is used by specialists to relieve pressure that has built up in the eye. The laser helps the aqueous humor fluid to drain, which in turn reduces pressure. The laser is used in some cases to make a tiny hole in the iris which encourages fluid to siphon from the eye.
Incisional surgery is an option for some patients with glaucoma. During this procedure, a surgeon cuts a flap in the white part of the eye and creates a pocket in the conjunctiva. Aqueous humor is then reduced as it is absorbed by tissue around the eye. A surgeon may fit a drainage tube in the eye to further reduce pressure.
It is worth noting that although pain and other symptoms can be controlled, any loss of sight is permanent. Partially sighted patients will benefit from wearing prescription eyeglasses in order to see better.
After looking at all of the information it’s clear to see how important the glaucoma optic nerve is. A healthy functioning optic nerve is essential to maintain sight and quality of life. Although nerve optic damage is going to affect sight some of the symptoms can be monitored and controlled.