The Basics of Glaucoma
As the disease progresses if untreated patients can begin to lose their peripheral (side) vision or notice blind spots in their field of view.
GLAUCOMA. When most people hear or see this word they immediately think of the most horrifying end result: blindness. Though it’s true that glaucoma has blinded millions of people worldwide and continues to do so if caught early it can nearly always be controlled before it causes irreversible damage.
Here’s the scary part: Almost always when a diagnosis of glaucoma is made the patient has no idea that there is a problem. Typically they come to their appointment only for a routine eye exam or because they want new glasses or contact lenses.
You see in most forms of glaucoma nothing hurts and even the patient’s vision can be normal. Most newly diagnosed glaucoma patients scratch their heads in bewilderment because they thought things were just fine. But as the disease progresses if untreated patients can begin to lose their peripheral (side) vision or notice blind spots in their field of view. If it gets to this point it usually means that significant damage has already taken place. Until it gets to that advanced stage of disease patients have no clue that they have a problem. It’s for this reason glaucoma is commonly referred to as being insidious or sneaky. As a matter of fact glaucoma is appropriately referred to as the “sneak thief of vision”.
So what is glaucoma anyway?
There are several ways that glaucoma can manifest in the eye but common to all forms is the slow destruction of the optic nerve.
Think of the optic nerves (one in each eye) as thick cables that are plugged into the back of the eyes. These cables are connected to the brain which is located closely overhead. After entering the eyeball the components of the optic nerve - some 1.2 million tiny thread-like nerve fibers - spread throughout the retina. This is how we see; these fibers carry the electrical information from the light images of whatever enters our eyes back to the brain to be processed. It’s these tiny optic nerve fibers that are slowly destroyed in glaucoma.
So if we start out life with about 1.2 million of these optic nerve fibers how many can we afford to lose before our vision is severely compromised? The alarming thing is quite a few fibers - about 500000 - can be lost before we’ll pick it up with our diagnostic instruments. But things are improving fast. With newer more sophisticated instruments being developed we will should be able to catch things much earlier. Keep in mind once the nerve fibers are gone they’re gone; we currently have no way of restoring an optic nerve fiber that has been snuffed out by glaucoma.
FACT: About 300000 Canadians and 2.2 million Americans over the age of 40 are afflicted with glaucoma.
FACT: About 50% of these people have no idea they have the disease.
Visualize your bathroom sink
That’s right your sink. Water flows into the sink from the faucet and goes out through the drainage hole at the bottom. The eyeball has a similar yet unique plumbing system that’s located towards the front part of the eyeball.
Here a special fluid (known as ‘aqueous’ in eye doctor jargon) is being produced continuously (the faucet) throughout life. The aqueous circulates around inside the eye a bit and then drains out of the eye through a very elaborate drainage mechanism.
In our bathroom sink example if the drain were to become clogged up with hair or old toothpaste the water would not drain out fast enough to keep up with the faucet and would eventually flood over the sink’s edge if we didn’t regulate the faucet.
But the eye is unlike the open sink in the sense that it is a closed sealed sphere. This means that if the eye’s drainage mechanism is not working like it should and the aqueous fluid cannot exit the eye as fast as it’s being produced pressure builds up.
Elevated pressure. What’s at risk?
Remember the 1.2 million microscopic optic nerve fibers at the back of the eye? If the pressure gets too high it could spell danger for these very delicate fibers.
But what’s TOO high?
The search for the answer to this question has been at the center of most glaucoma research for the past two decades. We now know for sure that the higher the pressure inside the eye the greater the risk for developing glaucomatous damage (damage to the optic nerve fibers). But here’s where things get confusing. Not everybody who has glaucoma has high pressure. Researchers now recognize that there must be other factors at work beyond high eye pressure that can destroy the nerve fibers.
Who’s at risk?
First of all no one is immune to glaucoma. As eye doctors we are concerned about glaucoma in everyone from infants to senior citizens. Are there certain factors that place people at higher risk? The answer is definitely yes. Here are the main ones:
- Myopia (nearsightedness)
- Regular long-term Steroid/Cortisone use
- A previous eye injury
Eye pressure over 21mm If we were to randomly sample the eye pressure of 1000 people off the street about 950 would have pressure under 21mm (measured in millimeters of mercury). But just because the pressure is over 21 does not mean that they are destined for glaucoma. It s just a red flag a risk factor. As I said the higher the pressure the more likely it is that one will develop glaucomatous damage. Patients with pressure over 21 need to be closely monitored.
Family history of glaucoma. We’re learning about the hereditary characteristics of glaucoma at a very rapid pace. Scientists have already isolated several glaucoma genes and now with the completion of the human genome more discoveries will surely follow. Glaucoma definitely appears to `run´ in families. But once again just because someone in your family has glaucoma does not mean that you will necessarily develop the disease. Like elevated pressure it s another red flag and needs close monitoring.
Over the age of 45. While glaucoma can develop in younger patients it more frequently occurs as we get older. Age is another red flag though it s much more subtle. It’s what we call in this business a ‘soft sign’.
People of African descent. African-Americans have a significantly greater tendency for developing certain forms of glaucoma than do people of other races.
Other ‘soft’ signs People who have:
At this point in time treatment for glaucoma is focused on one thing: lowering the pressure. Whether it’s done with medication (eye drops and/or pills)laser surgery or conventional surgery the object is the same the lower the pressure the better.
Glaucoma medications may be applied topically in the form of eye drops or ointments or orally with pills or tablets. Topical medications reduce or control the pressure in one of two ways: (1) improves the drain or (2) turns down the faucet (reduces the production of aqueous).
On the horizon
A great deal of ongoing research is helping to develop alternative glaucoma therapies. For example some researchers feel that certain drugs can actually protect the optic nerve fibers from the ravages of increased pressure making them more resilient to damage. These “neuroprotective” drugs have thus far been shown to be beneficial only in laboratory animals. Other drug research is focused on an alternative theory of optic nerve damage i.e. poor blood flow to the optic nerve. These researchers feel that increasing the blood flow to the optic nerve will maintain a healthy supply of nutrients and oxygen thereby making the nerve fibers less vulnerable to damage.
Scientists are beginning to unravel the secrets of glaucoma. Particularly vexing is the group of patients with normal or even low eye pressure who will go on to develop glaucomatous damage of the optic nerve. For some reason the optic nerves of these folks succumb to pressure that is not very high. We’ve got much more to learn about this dreadful but highly preventable disease. Our quest is to find the earliest stages of damage and do something about it sooner rather than later.