Glaucoma is permanent damage to the optic nerve often caused by an increase in intraocular eye pressure. This increased pressure is caused by a build up of aqueous humor, or fluid within the eye.
Normally the fluid, which the eye produces to nourish the eye, is produced behind the iris, in what is called the posterior chamber. It then drains away through narrow drainage channels in the angle between the iris and the cornea. If the fluid drains properly, pressure within the eye is kept normal. However, if a blockage occurs to prevent the outflow of aqueous humor, and it builds up to unhealthy levels, the resulting pressure on the optic nerve causes blindness.
There are several types of glaucoma depending on what has caused the blockage. More information can be found in the article covering the Causes of Glaucoma. The most common type is Open Angle Glaucoma. Now you know how important the angle within the eye is for draining aqueous humor, you will understand that if this angle becomes obstructed, fluid will build up, possibly resulting in glaucoma. This buildup may continue for months or even years and will go undetected. It is painless and gives no symptoms until sight is irreversibly lost. The only way to detect glaucoma and begin to prevent further deterioration of sight is to have regular eye checks with an ophthalmologist.
Glaucoma can only be detected by an eye doctor who will be able to detect early damage to the optic nerve using an ophthalmoscope. Other tests which a full eye test will include is the measuring of pressure inside the eye using a tonometer. The eye is numbed with eye drops and a plastic prism is moved towards the eye until it just touches the cornea. Intraocular pressure can then be measured, which may be the first indication of a possible risk of glaucoma.
As glaucoma develops in the eye, blind spots or patches of vision are lost. Gradually these spots become larger, where the optic nerve has been damaged. Eventually they merge. Usually it is the peripheral vision which is lost first. This may give the sufferer tunnel vision. They will have perfectly clear sight ahead of them, but will be blind at the sides. If treatment is not sought, the tunnel vision creeps over the eye causing permanent and total blindness.
The good news is that once glaucoma has been diagnosed, the patient can immediately begin treatment to avoid any further damage to their optic nerve. Unfortunately existing blindness caused by glaucoma cannot be reversed. There are many forms of treatment, outlined in the article Glaucoma Treatment in more detail. However, most doctors begin by prescribing eye drops to counter the problem.
Eye drops work in two ways on the open angle glaucoma. First they reduce the natural production of the aqueous humor. Secondly they open the angle again to allow drainage of the fluid out of the eye, releasing the pressure on the optic nerve. Some eye drops have a combination of components which will work on the eye simultaneously to reduce the production of fluid and increase the drainage. Alternatively eye drops for each patient, depending upon their medical history. Eye drops generally reduce the intraocular pressure by 30% which is usually sufficient to prevent any further damage to the ocular nerve.
The eye drops work by:
- Reducing the production of aqueous humor
- Relaxing the eye muscles to open the angle for drainage
- Causing the pupil to constrict, thereby opening the angle for drainage
- Reducing the intraocular pressure caused by the buildup of fluid
In 80% of Open Angle Glaucoma patients, eyedrops are successful in preventing further damage to the optic nerve. However, they are dependent upon the eye drops being administered fastidiously at the required time(s) each day; being administered properly into the eye effectively and usually they will need to be taken for the rest of the patient's life.
In the minority of cases, eye drops are unsuitable for the open angle glaucoma sufferer and other treatments have to be considered. Laser surgery may be required to open the clogged drainage channels in the trabecular meshwork. This is called Selective Laser Trabeculoplasty. Alternatively filtration surgery may be performed to remove a tiny portion of the trabecular meshwork to aid drainage, or an implant may be inserted for the same purpose. More details can be found in the article on Glaucoma Surgery.
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