glaucoma and blindness

Millions of peoples in the world have glaucoma. Sadly, over half of the persons with glaucoma do not know they have it, underscoring the aptness of 17th Century poet John Milton’s phrase “the sneak thief of sight” to describe his own experience with glaucoma. But blindness is not inevitable in glaucoma. With early diagnosis and treatment, most patients do not have significant vision loss. A common reaction of patients when they first learn they have glaucoma is to assume they will eventually go blind. The reality is that when glaucoma is diagnosed early and under treatment, patients usually do very well. With treatment, most patients with glaucoma are able to keep their vision and have a normal life. It’s important for patients to continue lifelong treatment and follow their doctor’s directions.


The Anatomy of the Eye and Glaucoma
Glaucoma is actually a group of eye diseases that have in common damage to the optic nerve.Located in the back of the eye, the optic nerve is composed of over 1 million cells. Each cell is several inches long and about 1/20,000th of an inch in diameter. The optic nerve can be damaged in glaucoma as a result of elevated intraocular pressure (IOP). Normal IOP ranges from 10 to 21 mm Hg. Increased IOP can compress the optic nerve, causing nerve cells to die little by little. Elevated IOP is the most common cause of glaucoma.


The IOP is increased in glaucoma because of a buildup of fluid inside the eye. This fluid is called aqueous humor. It is a watery fluid produced by the ciliary body, located behind the iris. Aqueous fluid helps keep the cornea and lens healthy. When the fluid leaves the cornea and lens area, it flows through a tiny spongy structure called the trabecular meshwork.


The trabecular meshwork is1/50th of an inch wide and is situated in the angle where the iris and cornea meet. The trabecular meshwork functions as the eye’s drain, allowing the aqueous fluid to drain from the eye and go into the bloodstream. Glaucoma can occur when the correct amount of fluid cannot flow from inside the eye and through the trabecular meshwork.


IOP elevation is not the only cause of glaucoma. In some patients, glaucoma occurs even though the IOP is normal. This form of glaucoma is believed to be related, at least in part, to poor blood flow to the optic nerve. Also, IOP elevation does not always result in glaucoma. Some people can tolerate an elevated pressure for their entire lives without having damage to the optic nerve. Yet some people can have a normal pressure but the optic nerve is sensitive to that pressure. It’s very difficult to pinpoint exactly when glaucoma comes on. Everybody is different.


Risk Factors for Glaucoma
Everyone over the age of 45 is at risk of glaucoma, and the risk rises as people age. The strongest risk factor is IOP elevation. Approximately 5 to 10 million Americans have elevated IOP. African-Americans are at increased risk of glaucoma. It is six to eight times more common in African-Americans than in whites.


The risk of glaucoma is also increased in patients who have taken steroid drugs for a long time or have had a previous eye injury. A blow to the eye, a chemical burn or penetrating injury can lead to glaucoma if the trabecular meshwork is damaged by the injury. Glaucoma can develop soon after the injury or a long time after the injury. Anyone who has had eye trauma should have regular eye exams.


Types of Glaucoma
The most common type of glaucoma is primary open-angle glaucoma. It affects approximately 1% of all Americans, usually after age 50. Primary open-angle glaucoma is usually accompanied by an IOP of over 22 mm Hg. This form of glaucoma is termed “open-angle glaucoma” because the angle where the cornea and iris meet is of normal size. It causes no symptoms until vision loss has occurred.


Normal-tension glaucoma is another type of open-angle glaucoma. It may account for as many as one third of the cases of primary open-angle glaucoma. With normal-tension glaucoma, the IOP remains in the normal range, but for some reason, the optic nerve is susceptible to damage even when the IOP is normal. This type of glaucoma may stem, at least in part, from inadequate blood flow to the optic nerve. It is diagnosed by the abnormal appearance of the optic nerve and changes in the peripheral vision.


Angle-closure glaucoma is another form of glaucoma. It affects approximately 500,000 persons in the United States. It tends to be inherited, with several members of a family having the disease. Angle-closure glaucoma is most common in persons of Asian descent. The anatomy of the eyes plays a key role in the development of this type of glaucoma. It is called “angle-closure glaucoma” because the angle where the cornea and iris meet is small, interfering with the passage of aqueous fluid between the iris and lens and causing a buildup of fluid and increased IOP. Some patients with angle-closure glaucoma develop acute glaucoma.


The IOP rises suddenly, to 40 to 70 mm Hg, causing intense pain and nausea and vomiting. The eye becomes very red, the cornea swells, and the vision becomes blurred with halos around lights. Another type of open-angle glaucoma is pigmentary glaucoma. An inherited disease, pigmentary glaucoma is more common in men than in women and often develops at a young age, when patients are in their 20s and 30s. With this form of glaucoma, pigment from the back surface of the iris rubs off and is deposited in the trabecular meshwork, causing the meshwork to clog and prevent the flow of aqueous fluid out of the eye.


While not a type of glaucoma, exfoliation syndrome can lead to glaucoma. Exfoliation syndrome is fairly common, occurring in about 10% of people over age 50. However, glaucoma does not always develop. With exfoliation syndrome, a whitish material builds up on the lens. The exfoliation material does not interfere with vision and is only visible with magnification during an eye examination. The material looks like dandruff flakes and can be rubbed off the lens by movement of the iris. The material may end up in the trabecular meshwork, clogging it, preventing aqueous fluid from leaving the eye and leading to IOP elevation and glaucoma. If exfoliation syndrome is present, the risk of developing glaucoma is about six times higher than the risk in persons without the syndrome.


How the Ophthalmologist Decides Glaucoma Is Present
Glaucoma is not usually diagnosed on the initial examination, unless it has gone undetected for a number of years in a patient who has not had regular eye examinations. The ophthalmologist may need to examine the eyes over a period of time to document any changes in the eye pressure, peripheral vision and optic nerve.



Elevated IOP by itself is not sufficient for the diagnosis of glaucoma. A patient with IOP elevation by itself is said to have ocular hypertension. Sometimes a patient with IOP elevation alone is considered to be a glaucoma suspect.


A glaucoma suspect is a patient with some of the findings seen in glaucoma but not enough findings to make a definite diagnosis of glaucoma. The patient may have an elevated pressure but totally normal visual field tests. Or the patient may have a normal pressure but an optic nerve that has the appearance of glaucoma. When a doctor tells a patient that glaucoma is suspected, the patient should ask, why is glaucoma suspected? Is it my optic nerve? My visual field? My eye pressure?. Similarly, if a diagnosis of glaucoma is made, patients should ask about their eye pressures, visual fields and the appearance of their optic nerves.


A combination of three tests performed during an eye examination provides information required for the diagnosis of glaucoma. Tonometry measures the IOP. The visual field test assesses the peripheral vision, an important measure of the health of the optic nerve. Ophthalmoscopy (also called funduscopy or fundus examination) lets the ophthalmologist look at the optic nerve to determine whether it is of normal shape and color. The pupil is dilated to obtain a good view of the optic nerve. On visual field testing, the patient looks straight ahead at a dark computer screen. Tiny dots of light are flashed on the screen, one at a time, in various areas of the peripheral vision. The patient indicates each time a flash of light is seen. Visual field testing provides a map of the peripheral vision, documenting any blind spots that may have developed as a result of glaucoma. Visual field testing can show whether glaucoma is stable or getting worse. Other tests may also be performed to evaluate glaucoma.


Treatment and Follow-up of Glaucoma
There are a variety of treatment options for glaucoma. Medications are typically the first line of treatment, but if medications don’t work, then surgical treatment is available. There are several basic kinds of eye drops for treating glaucoma. Those that help control glaucoma by decreasing the rate at which aqueous fluid flows into the eye and those that increase the rate it flows out of the eye. Sometimes a combination of eye drops is required to treat glaucoma. In some patients, a drug taken by mouth is needed to help reduce the flow of fluid into the eye.


Laser surgery, called trabeculoplasty, is another intervention for glaucoma. It is performed by using a laser beam to treat the trabecular meshwork, which permits the fluid to drain out of the eye more easily. Trabeculoplasty is about 80% successful at maintaining control of glaucoma at one year and 50% successful at 5 years.


Another surgical procedure is called trabeculectomy. In this procedure, the eye surgeon creates a new drainage channel in the eye to allow the fluid to drain more easily, reducing the pressure in the eye. Whether trabeculoplasty or trabeculectomy is done first depends on the individual patient. There are various factors to consider, such as the patient’s age, race and type of glaucoma.


The most common mistakes patients make after the diagnosis of glaucoma is not using their medicines correctly and not keeping follow-up appointments. Glaucoma is usually controllable but long-term follow-up and vigilance are required to prevent loss of vision. Regular eye examinations are crucial, both for early detection of glaucoma and for control of the disease. With as many as 50% of persons with glaucoma not knowing that they have it, perhaps the biggest challenge is finding ways to make regular eye examinations a part of everyone’s health care.