From: “The Eye of A Surgeon”, by Dr Cynthia J MacKay
What is glaucoma?
You will damage your tire if the pressure is too high. The same is true of your eye. If your eye has a pressure that is too high, it will start to go blind. The higher the pressure, the faster you will lose your sight.
What determines the pressure inside my eye?
Your eye is like a tiny bathtub with a tap that is always on. Night and day, a clear fluid, called aqueous humor or, simply, aqueous, is produced by your ciliary body. This aqueous circulates constantly through the anterior chamber of your eye. Its task is to nourish your cornea and lens by bringing in sugar and oxygen, and taking away wastes.
Aqueous humor leaves your eye by going through a slot between the front of your iris and the back of your cornea, called your angle, into a tiny sieve, called your trabecular meshwork. This leads into a small drain, called Schlemm’s Canal, which finally empties into the small veins on the surface of your eye.
Why would the pressure in my eye go up?
Normally, inflow equals outflow, so that the pressure inside your eye, which is measured in millimeters of mercury, will be maintained between 8 and 22. (In some people, “normal” can be as high as 24 or 25).
Glaucoma is caused by a bad drain. If the aqueous humor does not drain out of your eye as fast as it is produced, your eye pressure will go up, and you will develop glaucoma.
What causes glaucoma?
Most glaucoma is hereditary.
If you have a close relative with glaucoma (a parent, or grandparent, a brother or sister) your risk of getting glaucoma doubles.
How common is glaucoma?
Glaucoma is the number two cause of blindness in the U.S. It is the number one cause for African-Americans, who tend to get the disease younger and more severely.
At least 2 million Americans have glaucoma. At least 80,000 have been blinded by it.
How does glaucoma make people go blind?
When your eye is struck by light, your optic nerve carries a signal from your eye up to your brain. This allows you to see. You can think of your optic nerve as an electric cord running to a lamp: the lamp could be working, but unless the cord is also functioning the lamp will not give out any light.
Your optic nerve is very sensitive to pressure. If the pressure inside the eye is too high, your nerve will begin to die. Like all nerves, once it is damaged it never completely recovers. As it dies, you will begin to go blind; first you will lose your peripheral vision, and, finally, your central vision will disappear.
How will I know if I have glaucoma?
You will not.
Glaucoma has been called the“sneak thief of sight”. If the pressure inside your eye goes up gradually, which is the case at least 95% of the time, you could have a pressure that is 2 or 3 times normal and not feel a thing.
Remember: peripheral vision is the first to go in glaucoma. By the time you begin to notice blank areas in your sight, 85 to 90 percent of your optic nerve will have been destroyed.
Only your ophthalmologist can tell you whether or not you have glaucoma. If you visit your ophthalmologist every 2 years when you are under the age of 40, and every year after you are 40, if you develop glaucoma it will be diagnosed at an early stage, and your sight will be saved.
What are the most common types of glaucoma?
70% of all adult glaucoma is PRIMARY OPEN ANGLE GLAUCOMA, or POAG. In POAG, the drain is open, and looks completely normal, but it does not work well.
We have recently discovered the abnormal protein that progressively clogs the drain in certain families with hereditary glaucoma.
There are two variants of open angle glaucoma where the drain does not look normal. In pseudoexfoliation glaucoma, common in Scandinavia, flakes of abnormal material shred off the lens and collect in the drain. In pigmentary glaucoma (which can occur in near-sighted people) the drain is blocked by pigment that rubs off the back surface of the iris.
In LOW, or NORMAL TENSION, GLAUCOMA (LTG or NTG), the pressure is consistently below 21, yet the optic nerve suffers damage, probably because it is unusually susceptible. In these patients, the pressure must be reduced drastically, to the low teens, to prevent further damage.
About 5% of glaucoma is ANGLE CLOSURE GLAUCOMA. This usually occurs in far-sighted people, who have small, short eyes and therefore shallow front chambers of their eyes.
In angle closure glaucoma, your angle is narrow, but open, at birth. As you get older, your lens gets bigger and bigger. Eventually, it pushes your iris so far forward that it blocks your trabecular meshwork, just like a washcloth might block the drain of a bathtub, causing your drainage angle to close.
The angle usually closes suddenly, so your eye pressure shoots up quickly. This high pressure causes acute, severe pain, so bad that you may vomit. Your vision gets cloudy, because your cornea fills with fluid. The eye gets red, especially right around the iris. This is a true eye emergency.
Ideally, a dangerously narrow angle should be detected on your routine exam, and laser iridotomy performed before your angle closes. This is yet another reason why you need to get regular eye check-ups.
Glaucoma which is non-hereditary, which develops because your drain has been damaged in some way so it no longer works well, is called SECONDARY GLAUCOMA.
One example of secondary glaucoma is ANGLE RECESSION GLAUCOMA. Here, severe blunt trauma to your eye rips the ciliary body away from the trabecular meshwork so that it no longer drains well. Angle recession is extremely common in boxers.
If you have ever had a significant blow to your eye, for example from a squash or tennis ball or racquet, you should be checked for angle recession. If you have an angle recession, you are at high risk for developing glaucoma later in life. Make SURE to get your pressure checked regularly.
Another secondary glaucoma is STEROID-INDUCED GLAUCOMA.
Most people can take steroids, either by mouth or drops, without having their eye pressure go up, but certain susceptible people, who usually have a family history of glaucoma, can not. If they are given steroids, their eye pressure will rise.
If you have a family history of glaucoma, and you must take a significant amount of steroid for more than a few weeks, you should get your eye pressure checked.
NEO VASCULAR GLAUCOMA occurs when new abnormal blood vessels, caused by conditions such as diabetes and central vein occlusion, block your drain.
How will your ophthalmologist diagnose your glaucoma?
When your ophthalmologist dilates your pupil with those annoying drops that blur your vision and make you sensitive to light for an hour or two, one of the structures inside the eye that he or she will examine carefully is the head of the optic nerve.
Normally, this nerve has a healthy pink color, with a small shallow depression in its center called the cup. In glaucoma, your nerve becomes pale (called optic atrophy), and your cup gets wider and deeper (called excavation). Another important clue is the pressure in your eye, which is usually elevated if you have developed glaucoma. There may or may not be a small dash of blood at the margin of your nerve, called a flame hemorrhage.
If your pressure is high, and if your optic nerve has pallor and excavation, the diagnosis of glaucoma will be confirmed by further testing.
Your ophthalmologist will schedule a visual field test, to see if you have blank areas (scotomas) in your peripheral vision.
Since eye pressure in glaucoma notoriously fluctuates widely at different times of day, your ophthalmologist will probably tell you to come back to have your pressure taken every two hours over an entire day: 9:00, 11:00,1:00, 3:00, and 5:00.This is called a diurnal curve. This will tell your ophthalmologist how high your pressure goes, what time of day it runs the highest, and how much it varies. You should schedule all future visits at the time your pressure runs highest.
Your ophthalmologist may or may not order an ultrasound scan of your optic nerve, using Heidelberg Retinal Tomography, or HRT. HRT gives your ophthalmologist a 3 dimensional image of your optic nerve. This test can be repeated, and these images will show the smallest changes to the tissue of your nerve, allowing the ophthalmologist to detect even the slightest progression of your disease.
The accuracy of your pressure measurement will be checked by measuring the thickness of your cornea using a quick (1minute) painless technique called pachymetry.
How will my glaucoma be treated?
Glaucoma is treated by lowering eye pressure. This can be accomplished by drops, by pills, by laser surgery, and/or by knife surgery.
If you have narrow angle glaucoma, your ophthalmologist will use a YAG laser to create a tiny (1/4 of a millimeter) hole (IRIDOTOMY) in the periphery of your iris. This will open your angle by creating a “trap door” for your aqueous to flow into your trabecular meshwork.
This procedure takes about 5 minutes. You will experience a trivial amount of discomfort. You will need to take steroid drops for a short while afterwards.
If your laser iridotomy is done early enough, before your angle is scarred shut, there is an excellent chance that you will be cured by that procedure alone. If the diagnosis is made late, you will probably need to take drops to keep your pressure normal.
You should stop all blood thinners (Coumadin, aspirin, vitamin E, Echinacea, Ephedra, Ginkgo Biloba, Garlic, Ginseng, Kava, St. Johns Wort, Valerian) one week before your iridotomy, to minimize bleeding.
If you have open angle glaucoma, you will be treated by drops, and/or a laser procedure called selective laser trabeculoplasty(SLTP).
Glaucoma drops are of several different types. Some work by decreasing the production of aqueous humor; some work by increasing its outflow. You will probably have to experiment with several different types to find what works best for you. Each drop has its advantages and disadvantages. For example, betablockers cannot be used in people who have various lung diseases (asthma, smoking damage), or heart conditions (e.g., a slow heart rate).
If you cannot remember to take your drops, or if you are unable to manipulate the bottle properly, or if all drops have bad side effects for you, laser trabeculoplasty can be done.
In SLTP, a special laser is used to treat the trabecular meshwork so it will drain more freely. This is usually painless. SLTP is done on an outpatient basis. It will take about 10 minutes. You may resume normal activities immediately. It has a success rate of around 85%, and very few side effects, It will wear off with time, at a rate of about 10% each year, but it is repeatable.
If all else fails, various surgical procedures can be used to create an artificial passage from the inside of the eye to the outside.
Will I go blind if I have glaucoma?
Glaucoma is like any other chronic disease.
If you have diabetes, or high blood pressure, and you take your medication faithfully, your health will be just fine.
If you have glaucoma, and you take your drops every day as directed, and come back faithfully every 3 months to get your pressure checked, you will save your sight, drop by drop.
Just remind your siblings and children to get regular eye checks.