Last Updated on Sunday, 08 January 2012 14:46
Glaucoma is characterised by damage to the optic nerve â€“ the bundle of nerve fibres that connects the eye to the brain. This damage occurs as a result of the increase in pressure in the fluid within the eye. At first there may be no noticeable symptoms, but as the condition progresses it causes a loss of peripheral vision, blurriness, the appearance of halos around lights and other vision problems.
Glaucoma Symptoms and Causes
There are five types of glaucoma, each with different causes. In open angle types, the drainage channel, or angle, between the iris and the cornea is open ( as it should be to allow fluid to drain), but for some reason it is blocked. With closed angle glaucoma the angle between the iris and cornea closes preventing normal fluid from draining.
Primary Open Angle Glaucoma
This is the most common form of glaucoma. There are typically no early warning signs or symptoms of open angle glaucoma. It is a chronic condition that occurs when the vessels that drain fluid away from the eye become partially blocked. The fluid called the aqueous humour, cannot drain properly and builds up in these vessels, increasing pressure within the eye. This pressure squeezes the optic nerve and the retina, restricting blood flow. Deprived of adequate blood supply the cells in the optic nerve gradually die. Natural aging appears to cause most of the primary open angle glaucoma in adults.
Closed Angle Glaucoma
This rare condition is also called acute glaucoma or narrow angle glaucoma. Eye pressure rises suddenly, in a matter of hours, when the drainage structures between the iris and the cornea become clogged.
The problem often affects people born with and unusually narrow drainage structure. Symptoms include pain, nausea and rapid vision loss. This is a medical emergency and must be treated immediately to avoid blindness.
Normal Tension Glaucoma
This is a type of open angle glaucoma, pressure within the eye is normal. It is unclear why the optic nerve becomes damaged, but one theory is that the blood supply is reduced because of another medical condition, such as coronary artery disease. Though rare, normal tension glaucoma is most likely to affect people with a family history of heart disease.
This is a complication of an eye injury or disease that increases eye pressure, such as cataracts, diabetes or a tumour. Secondary glaucoma can also be a side-effect of steroids, which may interfere with eyeâ€™s drainage systems.
This birth defect is an abnormality in the drainage channels of the eye. It is usually diagnosed in the first year of life. Most cases are caused by a genetic mutation.
Glaucoma Risk Factors
Risk factors for glaucoma include:
- Being over the age of 40
- Family history of glaucoma
- Mutation of the myocilin gene
- Eye injury
- Eye tomours
- Heart Disease
Glaucoma can be diagnosed during a routine eye examination. An ophthalmoscope is used to examine the optic nerve. The front of the eyes are examined with a slitlamp, an instrument that uses a powerful microscope and a narrow light and a narrow beam of light to view the cornea, lens, fluids, and anterior chamber of the eye.
A key test is tonometry which measures intraocular pressure. Normal pressure within the eye is 10-22 mm (1/4-3/4) of mercury. Higher pressure is often a sign of glaucoma. Other possible diagnostics are symptoms of vision loss.