January is Glaucoma Awareness Month.
Glaucoma, The Silent Thief of Sight
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.
Will I go blind from glaucoma?
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.
How is glaucoma detected?
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 and additional imaging machines to examine the optic nerve and retinal layers.
Who Gets Glaucoma? – Risk Factors
- Age – People over the age of 60 are at increased risk for the disease with the risk of developing glaucoma increasing slightly with each year.
- Family history – Having a family history of glaucoma increases the risk of developing glaucoma.
- Medical conditions – Some studies indicate that diabetes may increases the risk of developing glaucoma, as does variations in blood pressure (high and low) and heart disease.
- Physical injuries to the eye—Severe trauma, such as being hit in the eye, can result in immediate increased eye pressure and future increases in pressure due to internal damage. Injury can also dislocate the lens, closing the drainage angle, and increasing pressure.
- Other eye-related risk factors—Eye anatomy, namely corneal thickness and optic nerve appearance indicate risk for development of glaucoma. Conditions such as retinal detachment, eye tumors, and eye inflammations may also induce glaucoma. Some studies suggest that high amounts of nearsightedness may also be a risk factor for the development of glaucoma.
- Corticosteroid use – Using corticosteroids for prolonged periods of time appears to put some people at risk of getting secondary glaucoma.
How is glaucoma treated?
- 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.
- Laser surgery – Laser trabeculoplasty helps to drain fluid out of the eye. A laser beam is used to stimulate the trabecular meshwork (an area of tissue in the eye located around the base of the cornea, near the ciliary body. It is responsible for draining the eye) to help it to work more efficiently at fluid drainage. The results may be somewhat temporary, and the procedure may need to be repeated.
- Conventional surgery – If medication and laser surgery aren’t effective in controlling eye pressure, a filtering procedure called a trabeculectomy may be required. Filtering microsurgery involves creating a drainage flap, allowing fluid to percolate into and later drain into the vascular system.
- Drainage implants – Another type of surgery, called drainage valve implant surgery, may be appropriate for people with uncontrolled glaucoma, secondary glaucoma or for children with glaucoma. A small silicone tube is inserted in the eye to help drain aqueous fluid.
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.