Glaucoma What is glaucoma?
If the drainage angle is blocked, excess
fluid cannot flow out of the eye, causing
the fluid pressure to increase.
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:
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
• 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.