What is glaucoma?
Glaucoma is a disease caused by elevated intraocular pressure (IOP). The elevated IOP damages and destroys the axons of the optic nerve, leading to progressive blindness. There are two types of Glaucoma - open-angle and angle-closure.
As a general rule, in the open-angle glaucomas, the eye is anatomically normal, but blockage or malfunction of the drain of the eye (the trabecular meshwork) leads to elevated IOP. In low-tension glaucoma, the abnormality is not in the meshwork but at the level of the optic disc. In the angle-closure glaucomas (yes, there are more than one), the trabecular meshwork is normal, but the iris is pushed against the meshwork, blocking the flow of fluid (aqueous humor) from the eye.
The analogy to a sink is a useful one. In a normal eye, the faucet is always on and the drain is always open. In open-angle glaucoma, the drain gets clogged. When this happens, aqueous can not leave the eye as fast as it produced, causing the fluid to back up. But since the eye is a closed compartment, the "sink" doesn't overflow; instead the backed up fluid causes increased pressure to build up within the eye. We need to use chemical drain-cleaner (eyedrops) to open the drain or turn down the faucet. If this is insufficient, we can snake the drain (laser trabeculoplasty), and if that doesn't work, we need to put in new plumbing (surgery).
In angle-closure glaucoma, the drain is normal, but it's covered by a stopper. We need to remove the stopper (laser iridotomy or laser iridoplasty) rather than treat with medications. Open-angle and angle-closure glaucomas are about as alike as a heart attack and a bullet wound to the heart. The disease mechanisms, the basic approach to treatment, and the prognosis all differ. And that is why the terminology is confusing.
Who is at risk for glaucoma?
Since glaucoma is produced by many different disorders, it occurs at all ages and in all races. However, some people are at greater risk than others:
- People over age 45. While glaucoma can develop in younger patients, it occurs more frequently with age.
- People with a family history of glaucoma.
- People with myopia are more prone to develop open-angle glaucoma. People with hyperopia are more prone to develop angle-closure glaucoma.
- There is no glaucoma exclusive to any race or ethnic group. However, there are some rough epidemiologic rules. Persons of African descent are more prone to develop POAG, by a ratio to about 4:1 compared to Caucasians. Pigmentary glaucoma occurs almost exclusively in Caucasians. Angle-closure is more common than open-angle glaucoma in Asians. Everyone can develop exfoliation syndrome, but it appears to be most common in those of European descent.
What is the treatment of glaucoma?
Glaucoma can be treated with eyedrops, pills, laser surgery, eye operations, or a combination of methods. The whole purpose of treatment is to prevent further loss of vision. Loss of vision in glaucoma is irreversible. Bringing the pressure under control will not restore lost vision, but only prevent further vision from being lost. Keeping the intraocular pressure under control is the key to preventing loss of vision from glaucoma. New approaches are being developed for the treatment of low-tension glaucoma.
Laser surgery has been used as treatment for a wide variety of glaucomas. The ability of light to penetrate the transparent structures of the eye (cornea and lens) allows it to have its desired affect on the targeted tissue. This is different from most other sites in the body, where penetration of light is blocked by the skin or thick outer tissues. Numerous different types of lasers are used in eye surgery for various purposes. These include argon, krypton, neodymium-YAG, diode, and excimer lasers.