Glaucoma
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What is glaucoma?
Glaucoma is a disease that damages the eye’s optic nerve. The optic nerve sends signals from your eye to your brain, where these signals are interpreted as the images you see.
If the drainage angle is blocked, excess fluid cannot flow out of the eye, causing the fluid pressure to increase.
In the healthy eye, a clear liquid called aqueous circulates inside the front portion of your eye. To maintain a constant eye pressure, your eye continually produces a small amount of aqueous fluid while an equal amount of this fluid flows out of your eye.
The fluid flows out through a very tiny drain called the trabecular meshwork via a channel called the drainage angle.
If you have glaucoma, the aqueous does not flow freely through the trabecular meshwork. Fluid pressure in the eye builds up and over time causes damage to the optic nerve.
Glaucoma can cause blindness if it is left untreated. When glaucoma develops, usually you don’t have any early symptoms and the disease progresses slowly. As a result glaucoma can steal your sight gradually. Thankfully, early diagnosis and treatment can help protect your vision.
Types of glaucoma:
Open-angle glaucoma
The most common form of glaucoma is called primary open-angle glaucoma. It occurs when the drainage angle /trabecular meshwork of the eye becomes less effective at removing fluid from the eye. As a result the pressure in the eye, called intraocular pressure (IOP), rises. Raised eye pressure leads to damage of the optic nerve.
Usually, open-angle glaucoma has no symptoms or visual symptoms in its early stages. As the optic nerve becomes more damaged, defects (blank areas) appear in your field of vision. You usually won’t notice these defects until the optic nerve is significantly damaged and the defects enlarge to encroach on your central vision. If all of the optic nerve is damaged blindness results.
Normal-tension glaucoma
Eye pressure is expressed in millimetres of mercury (mm Hg). 50% of patients with glaucoma do not have high eye pressure when first examined. This is because glaucoma can occur without raised intraocular pressure called normal tension glaucoma.
Although normal eye pressure is considered a measurement less than 21 mm Hg. Patients with normal tension glaucoma have eye pressures consistently below 21 mm Hg, but optic nerve damage and visual field loss still occur. People with normal-tension glaucoma have the same types of treatment used for open-angle glaucoma.
Conversely, ocular hypertension is a condition where someone has higher eye pressure than normal, but does not have other signs of glaucoma, such as optic nerve damage or visual field defects that show up in their peripheral vision (visual fields) when tested. Someone with ocular hypertension is considered a “glaucoma suspect” because he or she may be at risk for developing glaucoma later. Just like people with glaucoma, people with ocular hypertension need to be closely monitored by an ophthalmologist to ensure they receive appropriate treatment.
Closed-angle glaucoma
A less common form of glaucoma is closed-angle, or narrow-angle, glaucoma. Closed-angle glaucoma occurs when the drainage angle of the eye becomes blocked. Unlike open-angle glaucoma, eye pressure usually goes up very fast. The pressure rises because the iris — the coloured part of the eye — partially or completely blocks off the drainage angle. If the drainage angle becomes completely blocked, eye pressure rises quickly resulting in a closed-angle glaucoma attack. Symptoms of an attack include:
• Severe eye or brow pain;
• Redness of the eye;
• Blurred vision;
• Seeing coloured rainbows or halos;
An attack of closed-angle glaucoma attack is a medical emergency and must be treated immediately. Unfortunately, people at risk for developing closed-angle glaucoma often have few or no symptoms before the attack. Treatment of this type of glaucoma involves eye drops, oral medications to reduce intraocular pressure and sometimes laser surgery to the iris.