Glaucoma is one of the leading causes of blindness in Canada. Glaucoma is a group of eye diseases which lead to progressive degeneration of the optic nerve. This in turn can lead to loss of nerve tissue that results in gradual irreversible vision loss and potential blindness if not detected and treated early.
The most common form of glaucoma is primary open angle glaucoma. This form is associated with elevated pressure caused by a backup of fluid in the eye.
What causes glaucoma?
The precise cause is unknown. Glaucoma is generally associated with increased fluid pressure in the eye, however, damage can also occur when eye pressure is normal; this is called normal pressure or normal tension glaucoma. Some theories point to an inadequate blood supply or poor perfusion.
Primary open-angle glaucoma – This is the most common form of glaucoma. The human eye is constantly producing fluid inside the walls of the eye, called aqueous fluid. But if too much of this fluid is being produced within the eye, or if the fluid is not draining properly, it can put pressure on the optic nerve. One theory for how this might occur is that glaucoma is thought to develop when the eye’s drainage system becomes inefficient over time.
The optic nerve transmits all of the information the eye sees, and sends that information to the brain. When the optic nerve is damaged, the amount and quality of information sent to the brain decreases, and a loss of vision occurs. Usually peripheral vision is affected first, followed by central vision during the later stages of the disease.
Angle-closure glaucoma - This type of glaucoma, also known as, closed-angle glaucoma or narrow angle glaucoma, does not occur as often. It is considered a medical emergency that can cause vision loss within a day.
Angle-closure glaucoma happens when the drainage angle in the eye (formed by the cornea and the iris) closes or becomes blocked. With age, the lens in the eye becomes larger, pushing the iris forward and narrowing the space between the iris and the cornea. As this angle narrows, the aqueous fluid is blocked from exiting through the drainage system, resulting in a buildup of fluid and an increase in eye pressure.
Angle-closure glaucoma can be chronic (progressing gradually) or acute (appearing suddenly).
Secondary glaucoma - This type of glaucoma can occur as the result of an injury, infection or tumor in or around the eye that causes the pressure to rise. It may also be the result of a variety of medical conditions, medications and eye abnormalities. Infrequently, eye surgery can be associated with secondary glaucoma.
Normal-tension glaucoma - In this form, eye pressure stays within the “normal” range, but the optic nerve is still damaged. Why this happens is unknown.
It is possible that people with low-tension glaucoma may have an abnormally sensitive optic nerve or a reduced blood supply to the optic nerve caused by a condition such as atherosclerosis, a hardening of the arteries. In these circumstances even normal pressure on the optic nerve may be enough to cause damage.
If glaucoma is diagnosed at an early stage, treatment such as medication, eye drops and/or laser surgery can usually control or prevent further vision loss. If left untreated, some form of permanent vision loss is likely to occur.
The most common type of glaucoma is primary open-angle glaucoma. It develops painlessly and gradually and there are no early warning signs. Pressure in the eye slowly rises and unfortunately, the cornea adapts without swelling. If the cornea were to swell, which is usually a signal that something is wrong, there would be symptoms. Since this is not the case, this disease often goes undetected. It is painless, and the patient often does not realize that he or she is slowly losing vision until the later stages of the disease. However, by the time the vision is impaired, the damage is irreversible.
In other cases, glaucoma may appear suddenly and present warning signs and symptoms such as nausea, eye pain, red eyes, blurred vision and haloes around lights. This is called acute angle-closure glaucoma.
A comprehensive eye examination is often the only way to detect glaucoma. Your doctor of optometry will perform a simple and painless procedure called tonometry during your routine eye exam, which measures the internal pressure of your eye. Your optometrist will also look into your eye to observe the health of the optic nerve and retina, and inspect the drainage angle He or she may also use specialized equipment to measure your field of vision additional imaging machines to examine the optic nerve and retinal layers.
Medications - A number of medications are available to treat glaucoma. Usually, these medications are intended to reduce elevated intraocular pressure. A single medication may be prescribed or a combination of medications. The type of medication may change if it is not providing enough pressure reduction or if side-effects are being experienced.
Surgery - All procedures attempt to reduce the pressure inside the eye. Surgery may help lower pressure when medication is not enough, however it cannot reverse vision loss.
Treatment with daily eye drops and/or laser surgery is usually effective at maintaining your vision, but once vision is lost due to glaucoma, it cannot be restored. Patients with glaucoma must continue treatment for the rest of their lives. Since the disease can progress or change silently, compliance with treatment and eye examinations are essential. Treatment may need to be adjusted periodically.
Regular eye examinations with your optometrist are highly recommended to screen for and prevent glaucoma.
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