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Glaucoma (Primary Open Angle Glaucoma)
What is glaucoma?
Glaucoma is when the pressure inside of the eye damages the optic nerve. The optic nerve is the part of the eye that carries the images we see from the eye to the brain. The optic nerve is made up of many individual nerve fibers. Glaucoma damages nerve fibers, which can cause blind spots in our vision and vision loss to develop. In a nutshell, two factors combine to create glaucoma: 1) how high your eye pressure is and 2) how susceptible you are to that pressure.
Glaucoma is a very important and common disease. Millions of people in the United States suffer from glaucoma, and with the “graying of the population” millions more are expected to develop it over the next few decades.
What is intraocular pressure?
Glaucoma has to do with the pressure inside the eye, or intraocular pressure(IOP). The eye constantly makes a clear liquid called aqueous humor. This fluid production is important. If it were not produced the eye would shrivel up like a raisin instead of being plump like a grape. This fluid also serves a valuable role in nourishing the cornea and lens. To maintain a controlled pressure, the eye drains the aqueous humor through a drainage channel (the trabecular meshwork) present at the angle where the iris and cornea meet. The rate of production and drainage of aqueous humor need to be matched or else the pressure of the eye will be too high or too low. When the aqueous humor cannot drain properly, pressure builds up in the eye. The resulting increase in IOP can damage the optic nerve
The optic nerve damage of glaucoma results in blind spots. We can test for blind spots with a Visual Field Test. In this test each eye is tested in turn. As you look straight ahead a dim light is presented to the various points in your field of vision. You hit a button every time you see the light. The computer then generates a map of the seeing and non-seeing portions of your visual field.
The most useful way of distinguishing between a person with glaucoma, and someone who just has risk factors is regular examinations over time. The first tests that are performed serve as a baseline. If glaucoma damages your optic nerves, change will noticed on these tests.
What happens if you develop glaucoma?
The goal in treating glaucoma is to lower the pressure. Even in patients who develop glaucoma at normal IOPs, we know that lowering the IOP further can prevent further damage. Generally speaking we start off with drops to lower the pressure. The drops we have today are safer and more effective than the ones we used in the past.
Some people need additional treatments to supplement their drops. These can include laser surgeries in the office, or incisional surgeries in the operating room.
There are many different types of glaucoma, this discussion is about the most common type, Primary Open Angle Glaucoma.
What is the normal range for intraocular pressure?
The simple answer to this question is between 10 and 22 mmHg. However many people have pressures which are above this range but don’t develop damage. On the other hand, some people consistently have pressures that are in the normal range and do develop damage. Your individual susceptibility to eye pressure is important in the development of glaucoma.
Susceptibility to Glaucoma
Even people with "normal" IOP can experience vision loss from glaucoma. Unfortunately, the exact mechanisms that cause one person to be more susceptible than the next are not well understood. Each year volumes are written on glaucoma. Much is known about the complex biology involved, but there is still much to learn. Here are some demographic factors that play a role in one’s susceptibility:
*Age = The older you are the more common glaucoma becomes.
*Race = Glaucoma is common in the elderly of all races, but is especially common in African Americans.
*Family History = Having a blood relative with glaucoma is a risk factor for glaucoma, especially if they are your brother or sister.
The most important risk factors are the ones noted during routine eye exams such as an elevated IOP and an abnormal appearance of your optic nerve.
What does it mean to be a Glaucoma Suspect?
Your ophthalmologist may tell you that you are at risk for glaucoma if you have one or more risk factors. This is especially so for the risk factors that are noticed at the time of examination such as the IOP or appearance of the optic nerve.
Does Glaucoma have symptoms?
Most people who develop glaucoma notice no symptoms until late in the course of the disease when their vision is already seriously damaged. This is why it is important for all people older than 40 to get routine eye exams so that the risk factors for glaucoma can be identified early.
Some people mistakenly think that they can feel the pressure in their eye. A sensation of pressure in or around the eye is common, and is seldom related to the intraocular pressure. Only when the pressure is very high can one feel their pressure. In this case their eye is usually painful, red and sensitive to lights. When pressure is this high vision is usually hazy and halos are noted around lights.
You may have seen a picture or poster of “what glaucoma looks like.” In the picture you see a scene with a black blind spot. These pictures are factually incorrect, and lead people to think “How could I miss that, its so obvious?” You can’t “see” blind spots. In fact everyone has a normal blind spot in each eye that they are born with and never notice. The principle reason you can’t notice blind spots is that the brain automatically fills in this information with information from the other eye, and portions from the surrounding vision, and by quick scanning motions your eye makes many times each second. Eventually, however, glaucoma damage can become so severe that there isn’t enough surrounding vision to fill in the defects. By this time serious disability is present.
How does the doctor distinguish between someone with glaucoma and someone who just has risk factors for glaucoma?
Today we have many high-tech gadgets to help us diagnose and follow glaucoma. As mentioned above, the optic nerve gets damaged in glaucoma. We can test the optic nerve with a Spectralis Optical Coherence Tomographer (OCT.) This is a device that scans the optic nerve with a cold laser beam. It picks up the image with a digital camera and stores it in its memory. The computer then compares it to a database of hundreds of normal exams and also to your earlier exams.