Eye Diseases and Disorders Series
An LPR staff project - May 30, 2001
(This article is for information purposes only. Always consult your doctor for medical advice.)
Glaucoma is an insidious disease. It is often referred to as the sneak thief of sight, and rightly so. This is because people with glaucoma are often not aware that they have the disease until after they have already suffered some degree of permanent vision loss.
Types of Glaucoma
There are many types of glaucoma, and it is possible to have more than one type at the same time. The following is a list of a few of the various types of glaucoma.
Glaucoma and Vison Loss
- Open Angle (Chronic) Glaucoma: Open angle glaucoma occurs in eyes in which the anterior chamber is 'open', allowing the free movement of aqueous fluid. However, in this case, the Trabecular meshwork filter, part of the eye's drainage network, has become blocked. This blockage prevents the fluid from exiting the eyes via the Schlemm's canal. This blockage can occur due to a variety of causes, the result, however, is that the fluid cannot drain and the intraocular pressure (IOP) begins to rise. Open angle glaucoma is the most common form of glaucoma in the West.
- Closed Angle Glaucoma: In this case, the glaucoma arises when a blockage occurs that prevents the aqueous fluid from draining properly. The blockage often occurs due to a narrowing in the angle (where the iris and the cornea come together) of the anterior chamber, or because the anterior chamber is very shallow. In both cases, this is primarily due to an anatomical defect, rather than from any other cause.
- Pigmentary Glaucoma: This is another form of open-angle glaucoma. It is caused when tiny pieces of pigment are dislodged from the iris and becomes entangled in the trabecular meshwork, clogging up the filter.
- Low-Tension Glaucoma: Having an elevated IOP is commonly associated with the development of glaucoma. If your IOP is over 21 mm Hg, it is considered high. However, some people with normal eye pressure still develop glaucoma. Having glaucoma, and a low or normal IOP, is the hallmark of Low-Tension Glaucoma.
- Congenital Glaucoma: This occurs when a baby is born with glaucoma, and it results from developmental anomalies. Congenital glaucoma is very rare.
- Juvenile Glaucoma: If a child develops glaucoma, it is often called juvenile glaucoma, although the course of the disease is often very similar to that which occurs in adults.
Glaucoma, no matter the form it takes, is usually characterized by damage to the optic nerve, due to direct pressure on the nerve. It can also occur when the pressure cuts off, or diminishes the blood supply to the optic disc. This is where all the optic nerve fibers merge at the back of the eye.
Damage to the optic disc can often be seen during an eye exam. The optic disk can be deformed by the pressures exerted upon it, causing it to take on a cup like appearance. The optic disc is viewable upon examination, and the doctor can see the cupping, if any. The worse the damage, the deeper the cup. In a healthy eye the disc is flat. For individuals with low IOP's, or who have IOP's that fluctuate, this cupping can sometimes be the first indication that you have glaucoma. This is one of the many reasons why it is very important, especially if you are at risk of developing glaucoma, to regularly have a complete eye exam - even if you do not notice anything wrong with your eyes! Once the damage has occurred, it cannot be reversed.
How can you lose vision and not be aware of it?
Part of the insidious nature of glaucoma is that it is ordinarily a slowly progressing disease. When the rise in pressure is very slow, the eye adjusts to the increase without any outward display of symptoms. As the pressure rises and the optic nerve begins to atrophy, patients begin to experience vision loss. Usually, the peripheral vision is the first area of sight to be lost to glaucoma. When this loss is gradual, the brain automatically 'fills-in the blanks' so that you may not even notice the loss, even when it is severe. It is common for glaucoma sufferers to become aware of their vision loss only after having been given a complete eye exam. As well, many become aware that they may have a problem after being involved in a traffic accident, and they realize, after the fact, that they should have been able to see the other car.
Risk factors and the importance of regular eye exams
There is no single indicator available that will tell a person that he will, or will not, develop glaucoma. Therefore it is vital that everyone should have, on a regular basis, a comprehensive eye exam. This will allow your doctor to monitor changes in your eyes, over time. Seeing your doctor regularly allows for continual monitoring of any changes in your eyes, and should glaucoma develop, your doctor may be able to diagnosis it before it does any damage. This is especially important because glaucoma can be treated, but if left untreated it may result in blindness. As well, the earlier it is detected, and treatment begun, the less likely it is that it will result in significant vision loss. Sadly, despite being treatable, glaucoma is still the number one cause of blindness in the world. One reason for this staggering figure is that at least half the people with glaucoma are not even aware that they have it!
While it is impossible to say who will or will not develop glaucoma, there are some factors that have been shown to increase your risk of developing glaucoma. You are at greater risk of developing glaucoma if:
- You have a high IOP
- You are an African-American
- You are over 55-years-old
- You have a family history of glaucoma
- You've suffered an eye trauma
- You have severe myopia (nearsightedness)
- You have a history of long-term steroid or cortisone use
- You have diabetes
- Some studies also indicate that Native American's are also at a greater risk of developing glaucoma.
Most cases of glaucoma can be effectively treated with eye drops that work to lower the eye pressure or increase the drainage of the aqueous fluid. If the drops fail to work, glaucoma can be treated surgically, either with a laser or via conventional surgical methods. During the surgery, small holes are made in the eye. Two common procedures used to make these holes are called a peripheral iridectomy or a trabeculectomy. No matter what procedure is used, these holes act as drains, allowing more of the aqueous fluid to escape from the eye, thereby lowering the IOP.
If you have glaucoma - TAKE YOUR DROPS! It might be a pain having to take the drops, especially if you have to take them every few hours, but in the end it is well worth the bother. After all, once it is gone, you cannot get your eyesight back - at least not yet.
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