Glaucoma: What you should know?
Author: Sherman Winston Reeves, M.D., M.P.H.
Definition:
Glaucoma is a form of eye disease in which the optic nerve of the eye is damaged, causing loss of vision. While many forms of glaucoma exist, glaucoma can be broadly divided into two categories, open angle glaucoma and angle closure glaucoma.
The most common form of glaucoma, called open angle glaucoma, is a so-called “silent disease” in its early stages. It is painless, and the vision loss that occurs is typically not noticeable until after significant damage has already been done. For this reason, everyone should have regular eye exams, and people with a family history or personal risk factors for glaucoma should undergo even more frequent screenings for the disease. Another form of glaucoma is called angle closure glaucoma. Though far less common than open angle glaucoma, it can also cause damage to the optic nerve, though sometimes much more rapidly and in a painful fashion that is noticeable to the patient.
Both categories of glaucoma, however, result in the same, characteristic damage to the optic nerve of the eye. As the eye is damaged from glaucoma, optic nerve fibers are destroyed, causing the optic nerve to look increasingly “cupped,” as if a larger and larger ice cream scooper is used to remove a pit from its center. As this loss of tissue progresses, it becomes visible to the doctor examining the eye, helping make the diagnosis of glaucoma. The progressive loss of optic nerve tissue causes loss of vision as well. The peripheral vision is usually affected at first. Then, as the disease progresses, central vision or even total blindness can occur.
Causes of glaucoma:
Though glaucoma is a very well know disease and many treatments are available for it, doctors don’t fully understand how it occurs or why it occurs some eyes and not in others.
The cause of open angle glaucoma, in particular, is vexing for doctors. A prevailing belief among doctors and scientists that study glaucoma is that the disease may be caused by an abnormality of the drainage system of the eye, called the trabecular meshwork. This structure is located in the front of the eye where the iris and cornea meet. In open angle glaucoma, though the trabecular meshwork looks normal when it is microscopically examined, doctors believe that some form of intrinsic dysfunction, which is not visible on examination, develops, causing it to become less capable of draining eye fluid, the aqueaous humor. However, the aqueous fluid is constantly being produced by the eye. As such, if the trabecular meshwork drain fails to allow the fluid to leave the eye, the eye pressure can increase, much like an over inflated basketball.
In angle closure glaucoma, the trabecular meshwork drain may become physically occluded by the iris, abnormal blood vessels or scar tissue, which can also cause dramatic and sometimes rapid rises in the eye pressure.
The increase of eye pressure may be one of the ways in which the optic nerve may become damaged in glaucoma. In fact, many people who suffer from open angle glaucoma have abnormally high eye pressures, suggesting that eye pressure is related to the mechanism of glaucoma damage. However, some eyes can tolerate abnormally high eye pressures without suffering damage at all, whereas others begin to lose vision if chronically high pressures continue over time. Even more perplexing is that some eyes can also suffer glaucomatous damage when the eye pressure is normal, which is called normal tension glaucoma. In short, doctors believe that while eye pressure plays a role in glaucoma, and that lowering the eye pressure is helpful for treating glaucoma, other unknown structural abnormalities in the eye or optic nerve are also at play in the disease.
While more than 40 types of glaucoma can occur, the following are the most common forms of open angle and angle closure glaucoma:
Open angle glaucomas: These glaucomas are diagnosed by the presence of characteristic glaucomatous optic nerve changes on exam by the doctor and/or visual field loss typical of glaucoma, but with a normal appearing trabecular meshwork drainage system of the eye.
Primary open angle glaucoma: The most common form of glaucoma. As it occurs in absence of other eye conditions which could cause glaucoma, it is called “primary.”
Pseudoexfoliation glaucoma: A form of open angle glaucoma in which dandruff-like material collects inside the eye, and can cause dysfunction of the trabecular drain.
Pigmentary glaucoma: A form of open angle glaucoma in which pigment from the iris becomes abnormally mobile in the eye and may cause dysfunction in the trabecular drain.
Angle closure glaucomas: These glaucomas are diagnosed by the presence of iris tissue, abnormal blood vessels or scar tissues physically closing off the trabecular drainage system. With the trabecular drain closed, the eye pressure can increase greatly which, if allowed to persist, results in the characteristic optic nerve and/or visual field loss typical of glaucoma.
Primary angle closure glaucoma: Occurs due to an anatomical abnormality of the eye in which the iris may periodically come in contact with the lens of the eye. This may occur when the iris is partially dilated, which happens in lower light situations like a movie theater. The lens-iris contact, called pupillary block, may result in abnormal flow of aqueous fluid within the eye, and cause the iris to compress against the cornea over the trabecular drain, closing off the outflow path for the aqueous fluid. As a result, the eye pressure can increase dramatically, often in a rapid fashion, resulting in pain and acutely decreased vision.
Neovascular glaucoma: Several forms of eye disease, such as diabetes and vascular problems of the eye, can result in the growth of new blood vessels over the trabecular meshwork. With the new blood vessels also comes scar tissue, which can close off the trabecular drain directly or by pulling iris over it as the scarring progresses. As a result, the eye pressure can increase greatly and glaucomatous damage to the optic nerve can occur.
Angle recession glaucoma: When an eye suffers from a blunt injury, such as being hit with a softball, the trabecular drainage system of the eye can become damaged. If enough of the drain is damaged, malfunction of the drainage of aqueous eye fluid can occur, leading to a rise in eye pressure and subsequent glaucomatous damage to the optic nerve. The rise in eye pressure with angle recession glaucoma often occurs many years after the eye was injured.
Symptoms (What you may experience if you have a glaucoma):
With most forms of open angle glaucoma, often no symptoms are noticed by the patient when the disease is in its early stages. As the disease progresses to more advanced stages and increasing amounts of vision are lost, a person may notice a vague difficulty in seeing things at the edge of their vision. Often, the central vision remains quite good, though, and a person may not realize that treatment is needed until only a small tunnel of vision remains. For this reason, regular eye exams are important for screening for glaucoma.
Conversely, many forms of angle closure glaucoma do have symptoms. Typically, a person may experience episodes of pain, which may range from minimal discomfort to extreme aching pain of the eye and head. With these painful episodes, the vision may become very blurred. For this reason, people with angle closure often seek medical help sooner and are diagnosed with the disease before earlier than those with open angle glaucoma. Occasionally, though, angle closure symptoms are very mild and almost unnoticeable to the patient.
Examination for glaucoma:
Tests you may have at the doctor’s office:
To determine if you have glaucoma, your eye doctor will perform an eye evaluation. Your visual acuity will be measured. Additionally, your refraction, or best vision with glasses, may also be checked. Your eye pressure will also be measured carefully, and the thickness of your corneas may also be checked, as thinner corneas are a risk factor for glaucoma. Your pupils will also be tested, which help the doctor to determine if your optic nerves are working properly. Your peripheral vision will likely be checked by counting fingers with the edge of your vision. You may also have a computer check your peripheral vision during an automated visual field examination. Your doctor will perform a slit lamp examination to examine the eye and the lens. The trabecular drainage system of your eye may be examined with a special contact lens, called a gonioscopy lens. Your eyes may be dilated to help the doctor view the lens and the back part of the eye and examine the optic nerve carefully. A retinal exam may also be performed during the dilated examination. Photographs of your optic nerves or computer scans of the optic nerve shape may also be taken.
What your doctor sees in your eye if you have glaucoma:
As glaucoma progresses to moderate or advanced disease, optic nerve fibers are destroyed, causing the optic nerve to look increasingly “cupped,” as if a larger and larger ice cream scooper is used to remove a pit from its center. Your doctor may also be able to see the loss of small sections of retinal nerves around the optic nerve, or small areas of bleeding on the optic nerve. Additionally, if angle closure is present, your doctor may be able to see iris or scar tissue physically blocking the trabecular drain.
Treatment of Glaucoma:
Non-Surgical treatment:
The mainstay of glaucoma treatment in its early stages is the use of eye pressure lowering eye drops. These medications commonly work by decreasing the amount of aqueous humor fluid produced by the eye, effectively “turning off the tap” of eye fluid and thereby helping to lower the eye pressure. Other glaucoma eye drops work by causing more fluid to drain out of the eye. Most glaucoma can be slowed greatly or even halted with the use of eye drops alone.
Glaucoma Surgery:
Occasionally, eye drops alone are not enough to halt the progression of glaucoma. In these cases, doctors may turn to surgery to help lower the eye pressure. Several forms of eye surgery are available for glaucoma, including:
Laser treatment of the trabecular drain: By using special lasers focused onto the trabecular drain of the eye, your ophthalmologist may be able to cause a reduction in eye pressure. Laser surgery for glaucoma is typically painless, is performed in your doctor’s office, and usually takes only 10 to 15 minutes to complete.
Trabeculectomy: For more advanced glaucoma, or glaucoma that is unresponsive to eye drop or laser treatments, surgery in the operating room may be needed. In trabeculectomy surgery, a small drainage hole is surgically created in the eye to allow the aqueous humor eye fluid another route to drain out of the eye. This drainage site is referred to as a “bleb,” and looks like a small blister on the eye under the eyelid after the surgery has been performed. Trabeculectomy surgery usually takes one half to one hour to complete in the operating room and requires frequent postoperative visits with your doctor over the first few weeks after the surgery.
Tube shunt surgery: An alternative to trabeculectomy surgery is creating an alternate drain for the aqueous eye fluid by placing a small plastic tube inside the eye. The tube drains the eye fluid to a point under the eyelid in the eye socket. Tube shunt surgery is often used in situations where your surgeon thinks a trabeculectomy surgery may not accomplish the goal of lowering the eye pressure. Tube shunt surgery usually takes one half to one hour to complete in the operating room and requires frequent postoperative visits with your doctor over the first few weeks after the surgery.
Prognosis (How glaucoma will affect vision over the long-term):
Unfortunately, when vision is lost due to glaucoma, it cannot be restored. As such, it is very important to diagnose glaucoma early before substantial visual loss occurs. However, even after some visual loss occurs, the progression of glaucoma can usually be greatly slowed or even halted with medications and/or surgery. Fortunately, glaucoma also affects the peripheral vision first, damaging the central vision and causing severe disability only later in the disease process. Hence, with early diagnosis and treatment, most patients with glaucoma can maintain useful vision throughout their lives. Glaucoma is a lifetime disease, however, and drops and/or surgery, along with regular visits to the eye doctor, are required to keep it in check.
Prevention of glaucoma:
The best way to prevent vision loss from glaucoma is to diagnose and treat it before it can progress to significant visual loss. For this reason, everyone should have regular eye exams to screen for glaucoma. People who have a family member with glaucoma should undergo even more frequent screenings, as they may be at increased risk of developing the disease.
