GLAUCOMA

By Rachel Simpson, MD

WHAT IS GLAUCOMA?

Glaucoma is a potentially blinding eye disease in which there is gradual but progressive damage to the nerve fibers of the optic nerve. The optic nerve is the connection that carries the signals from the light-detecting cells in the eye to the part of the brain that interprets these images. Damage to the optic nerve results in reduced signals traveling from the eye to the brain, and since the brain cannot interpret information it does not receive, this missing information results in lost areas of vision (referred to clinically as visual field loss).

While we don’t fully understand all the factors that cause glaucoma, we do know that in many cases, the damage of glaucoma is strongly related to elevated pressure inside the eye. The best analogy is that of a kitchen sink. The faucet of the eye (called the ciliary body) is always on and produces a fluid called aqueous at a stable rate. In a normal eye, the drainage of fluid out of the eye (through a structure called the trabecular meshwork) occurs at the same rate as the production of fluid, keeping pressure in the eye stable. In glaucoma, the drain of the eye is slow (or sometimes completely clogged), and unlike a kitchen sink, which will overflow when the faucet is on but the drain is clogged, fluid cannot escape the eye any other way. This results in elevated pressure inside the eye. Chronically elevated pressure in the eye then causes damage to the optic nerve. It is important to note that people often confuse this internal aqueous drainage system with that of the external drainage system that drains tears out of the eye; however, the two systems are not related.

There are many different types of glaucoma. Primary open-angle glaucoma (POAG) is the most common form in the United States. It usually affects people over age 40, and the risk of developing glaucoma increases with increasing age; therefore, it can be considered an age-related disease. Because women live, on average, several years longer than men in industrialized countries like the U.S., the incidence of glaucoma is higher in women.

Glaucoma

 

WHO IS AT RISK FOR GLAUCOMA?

The answer depends in large part on the type of glaucoma. For the most common type of glaucoma (POAG), the risk factors are positive family history, certain races (particularly African Americans), and those with elevated pressure inside the eye. Less common types of glaucoma, such as angle-closure glaucoma, also tend to run in families, and patients with this type of glaucoma usually have a history of farsightedness. Patients with diabetes with severe diabetic eye disease are at risk for a type of glaucoma called neovascular glaucoma, and patients with extreme nearsightedness are at risk for a type of glaucoma called pigmentary glaucoma. Other factors that increase the risk of developing glaucoma include chronic eye inflammation (uveitis) or chronic steroid use (especially ocular steroid drops).

For all types of glaucoma, the greatest risk factor is age. The older you are, the more chance you have of developing glaucoma. This is the main reason why it is recommended that people over age 60, even apparently healthy ones, see an eye care professional at least every two years.

WHAT ARE THE SYMPTOMS OF GLAUCOMA?

Glaucoma is a silent disease; it has been called by some ‘The Silent Thief of Vision.’ Most of the common types of glaucoma have no symptoms; there is no pain, and vision changes can be very difficult for patients to detect until the disease is very advanced. Damage from glaucoma results in peripheral visual field loss; however, these losses are usually unnoticed by patients because the brain is able to compensate for missing areas of vision by filling in defects with what the brain thinks it should be seeing. Often it is only once severe visual field loss has occurred that patients will realize the extent of his or her loss of vision; unfortunately, once vision is lost it is irreversible. This is why there is a great need to diagnose glaucoma early before there is any loss of vision. Glaucoma is the best example of a serious eye disease for which early detection is crucial, because there are effective treatments that will prevent or slow vision loss.

CAN GLAUCOMA BE PREVENTED?

Glaucoma cannot be prevented, but like other chronic diseases, it can be managed. When untreated, glaucoma causes a steady loss of optic nerve cells over time. The aim of treatment is to stop (or severely slow) the loss of these nerve cells, thereby preserving vision. Awareness and vigilance are the keys to preventing blindness.

Everyone should have his or her intraocular pressure checked by an ophthalmologist or optometrist. The instrument the doctor uses to measure pressure is called a tonometer, and this is done either by a method called non-contact tonometry (the “air puff test”) or by applanation (using a prism and blue light). This test is a part of any routine eye exam. In addition, a dilated eye exam with careful evaluation of the optic nerve is critical, as there are some types of glaucoma where damage to the nerve occurs in the absence of elevated eye pressure. The best way to guard against vision loss from glaucoma is to have regular dilated eye exams from an eye care professional at least every two years starting at age 40. Your eye care professional will check eye pressure and also look for characteristic optic-nerve changes that may indicate early glaucoma. If anything looks abnormal, the doctor will measure the extent of your visual field by a painless method called perimetry.

If glaucoma runs in your family, you are at a significantly higher risk of developing glaucoma. Therefore, you should get complete eye examinations more frequently, starting at a younger age, to get treatment before permanent damage is done.

WHAT ARE THE TREATMENTS FOR GLAUCOMA?

It is important to emphasize that glaucoma is a chronic disease, and currently, there is no cure, but there are many methods for controlling it. It is also important to emphasize that once gone, the vision loss from glaucoma cannot be brought back. This is why early detection and careful surveillance are key to preserving vision and preventing blindness. Once diagnosed with glaucoma, your eye doctor will recommend initiating treatment designed to lower the pressure in your eye – usually by starting prescription eye drops. The drops work to lower the pressure in your eye by decreasing the production of aqueous fluid or by increasing the drainage of aqueous fluid. These eye drops are usually the first method of treatment used. There are multiple different types of drops, and sometimes two, three or even four different types of drops may be needed to lower the pressure to a safe level. If drops are not able to adequately lower eye pressure to a safe level, laser eye surgery is frequently the next step. Selective laser trabeculoplasty (SLT) is a painless, in-office laser procedure that increases drainage of aqueous fluid out of the eye. Finally, surgery may be considered if drops and laser are not enough.

Recent advances in minimally invasive glaucoma surgery (MIGS) allow some glaucoma surgical procedures to be done at the time of cataract surgery without adding additional risk or time to cataract surgery. These procedures are often considered for those who have mild or moderate glaucoma. Traditional glaucoma surgery options such as trabeculectomy or tube shunt surgery may also be considered if other methods fail or in those with advanced glaucoma.

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