- Primary open angle glaucoma (POAG) is a chronic disease in which the internal pressure of the eye – intraocular pressure – is too high.
- POAG causes damage to the optic nerve and, if not treated, eventually blindness.
- People who are at risk for POAG include those who are over 35, diabetics, people with a family history of the condition, short-sighted people, black people, and people with heart and blood pressure problems.
- Because there are usually no symptoms until irreversible damage has occurred, regular pressure checks should be carried out on all people over age 35, especially those at increased risk of the disease.
- POAG is diagnosed by intraocular pressure assessment, examination of the optic disc and visual field measurement.
- It can be treated using eyedrops, tablets, and laser or conventional surgery, but lifestyle is also an important factor.
What is primary open angle glaucoma?Primary open angle glaucoma (POAG) is characterised by a gradual rise in the pressure inside the eye (the intraocular pressure). This causes slowly progressive loss of peripheral (side) vision, and if left untreated, late loss of central vision and ultimately blindness. This is a chronic disease that normally affects both eyes.
What causes primary open angle glaucoma?Changes occur in the outflow channels of the eye’s aqueous humor (the fluid inside the eye), resulting in increased pressure in the eye. This pressure causes slow destruction of the optic nerve, which normally transmits the “pictures” of everything we see to the brain. If the blood flow to the nerve is good, the nerve can be protected from the effects of the pressure, but if blood flow is poor, even normal pressure in the eye can damage the nerve.
As the optic nerve becomes increasingly damaged, the field of vision becomes progressively reduced, until eventually the whole field of vision is destroyed and the eye is blind.
Who gets primary open angle glaucoma and who is at risk?This is the most common form of glaucoma. It can affect any age person but is more common in people over the age of 40.
People who are particularly at risk for POAG include diabetics, people with a family history of the disease, short-sighted people, black people, and those who have a history of migraines or heart or blood pressure problems.
What are the symptoms and signs of primary open angle glaucoma?This disease shows no symptoms until very late in the disease when extensive damage has occurred. Slow loss of peripheral vision is often not picked up by the affected person.
Cupping of the optic disc, high intraocular pressure and visual field defects are symptoms that may show up during medical examination (see diagnosis below).
How is primary open angle glaucoma diagnosed?Because glaucoma may not cause any symptoms until irreversible damage has occurred, every routine eye examination – and ideally every physical examination – in all adult patients should include checking the pressure in the eye. This is called tonometry. A single normal reading does not rule out glaucoma since the eye pressure varies according to the time of day and the pressure rise in early glaucoma may be intermittent.
In addition to checking the intraocular pressure, the optometrist or doctor examines the optic disc (part of the optic nerve visible inside the eye) for characteristic changes. The optic disc may appear normal or show what is called "cupping", in which the centre is depressed, indicating glaucoma. The visual fields may also be checked, and may show characteristic defects in the periphery. If glaucoma is suspected, you should have a complete assessment and frequent follow-up examinations by a specialist eye doctor (ophthalmologist) and a detailed visual field examination.
Can primary open angle glaucoma be prevented?The disease itself cannot be prevented. However, damage to the eye from the disease can be prevented if it is diagnosed early and treated correctly. Therefore all people who are at increased risk for the disease require regular eye examinations.
How is primary open angle glaucoma treated?Most people can be treated with drugs administered as eye drops. Each patient must be carefully assessed to determine which drugs are appropriate.
Eyedrops in use include:
- Alpha agonists: e.g. Brimonidine, Ephedrine.
- Beta blockers: e.g. Betaxolol, Levobunalol, Carteolole, Metipranol, Timolol and others.
- Carbonic anhydrase inhibotors: e.g. Dorzolamide.
- Cholinergic agonists: e.g. Pilocarpine.
- Prostaglandin agonists: e.g. Latanoprost and others available soon in South Africa.
- Combinations of the above.
If eyedrops fail to stop the progression of the glaucoma, then laser or conventional surgery, or oral medication (acetazolamide) is used. Laser trabeculoplasty or filtering surgery improves aqueous drainage and acetazolamide reduces production of aqueous fluid. This reduces the pressure in the eye and prevents further damage to the optic nerve and vision.
Regular physical exercise reduces intraocular pressure and protects the optic nerve, and therefore this is an excellent way of treating the condition naturally. You will also derive other health benefits from the exercise. A low salt diet is potentially harmful to the glaucomatous eye. Therefore a normal amount of salt in your diet is important for the health of your eyes.
What is the outcome of primary open angle glaucoma?Untreated, the condition leads to blindness.
Treated, vision may be preserved as long as the treatment is continued for life.
When to call the doctorIf you have any of the risk factors for this disease you should see a doctor or an optometrist at least every year for a glaucoma check. If you have glaucoma, the condition must be managed by an ophthalmologist for the rest of your life.
Reviewed by Dr L.C. Boezaart, M.B.Ch.B, M.Prax.Med, M.Med (Ophth).
Last updated: 1/12/2004