Ophthalmology

OPHTHALMOLOGY: GLAUCOMA

It is estimated that over 200,000 Canadians have glaucoma1, but only half are aware that they have the disease. Unless one is tested for glaucoma by an eye care professional, they are usually unaware that they have this potentially blinding disease. Glaucoma commonly affects both eyes, however there are situations when only one eye may have glaucoma.

Risk Factors for Glaucoma.

People who are more likely to develop glaucoma include those who:

  • are over the age of 50
  • have abnormally high pressure within the eye
  • are related to someone who has glaucoma
  • are of African descent
  • are very near-sightedv
  • have diabetesv
  • are taking steroid medications
  • have high blood pressure
  • have had an eye injury or surgery

What is glaucoma? It is a symptomless condition usually associated with abnormally high pressure in the eye (above 21 mm Hg). There are situations when someone with a pressure less than 21mm Hg can have glaucoma, and situations when someone with a pressure above 21mm Hg does not have glaucoma. The most common form of glaucoma is primary open angle glaucoma. If the pressure in the eye is not reduced to normal levels, 12-21mm Hg , nerve damage can occur which can slowly lead to loss of vision.

What causes increased pressure in the eye? Inside the eye is a watery fluid called aqueous humor. This fluid is important because it bathes and nourishes different parts of the eye. Aqueous humor is made in the back (posterior) chamber of the eye and flows out through channels in the front (anterior) chamber of the eye (just as water runs from the faucet , into the sink, and down the drain). If these channels are clogged and the aqueous humor cannot leave the eye, the amount of fluid in the eye increases . This causes the pressure in the eye to rise. The amount of pressure in the eye is called the intraocular pressure (IOP).

What happens when intraocular pressure (IOP) is too high? When IOP is too high, it puts pressure on the optic nerve. This pressure is believed to cause damage to the nerve and slowly cause vision loss. Vision loss starts on the outside of the visual field, making things look fuzzy around the edge. If open-angle glaucoma goes untreated, the fuzzy edges slowly close-in until the entire visual field is black.

How is glaucoma treated? The aim of treatment is to reduce the intraocular pressure (IOP) to a level that will stop or reduce the damage to the optic nerve. (The optic nerve transmits visual signals to and from the brain and allows us to see).

Treatment Options:

(1) THERAPEUTIC- This is achieved by using eye drops or oral medications, prescribed by an ophthalmologist[eye care professional]. Oral medications are rarely used nowadays because most doctors prescribe eye drops. Some eye drops work by reducing the production of the watery fluid called aqueous humor. Others work by increasing the rate at which this watery fluid leaves the eye. There are some eye drops that work by both reducing the rate at which the fluid enters the eye and increasing the rate at which the fluid leaves the eye.

Depending on the chemical nature of the drug, it can be recommended for use by the glaucoma patient from once to four times daily.
(2) LASER– A laser beam is applied to the drainage portion of the eye, usually in one or two sessions, one or two months apart. It is painless and performed without the need for anaesthesia. In most cases this treatment will bring the eye pressure back under control by improving the drainage of fluid out of the eye.
(3) SURGERY – Filtration surgery creates a new drainage system from within the eye to under the lining membrane of the eye. The surgery is done under local anaesthesia and takes approximately 45 minutes to perform.

Other types of glaucoma. There are many types of glaucoma. The most common, primary open angle glaucoma, occurs at a rate of 0.4-0.7% in persons over the age of 40 and 2-3% in persons over the age of 702. Angle Closure Glaucoma , is less common and can cause loss of vision within 24-48 hours if not treated immediately. It is an emergency situation in which the individual experiences severe pain, redness in the eye, cloudy cornea, nausea and vomiting. This type of glaucoma develops when the outflow channels where the watery fluid leaves the eye, is completely or almost completely blocked.