Glaucoma is a progressive degeneration of the optic nerve in the back of the eye. The optic nerve acts like a “telephone line,” sending vision information from the eye to the brain. Glaucoma causes blind spots develop in the vision, usually starting from the outside periphery and extending toward the center. If glaucoma is not treated, blindness will result.
Glaucoma is a leading cause of vision loss. Loss of vision from glaucoma can often be prevented. Early detection and treatment are key to preventing blindness from glaucoma. Fortunately, effective treatments are available for the vast majority of people with glaucoma.
What causes glaucoma?
Usually the cause of glaucoma is high eye pressure. High eye pressure pushes on the optic nerve in the back of eye, causing it to slowly degenerate. Why this happens is not fully understood.
The fluid circulating in the eye (the aqueous humor) is being produced by the ciliary body and drained by the trabecular meshwork. In glaucoma, the pressure is too high because fluid isn’t being drained as fast as it is being produced. About 10% of people with glaucoma have normal pressures, meaning an elevated pressure is never measured.
What are the different types of glaucoma?
There are many different kinds of glaucoma. The most basic division is between closed angle and open angle. In order for fluid to drain out of the eye, it passes through the angle created by the cornea and iris, then into the trabecular meshwork. If the angle is narrow or closed, outflow is blocked, and pressure rises. In open angle glaucoma, the problem is a blockage in the trabecular meshwork itself. Common types of open angle glaucoma include:
• Primary: the most common, due to microscopic blockage in the trabecular meshwork.
• Pseudoexfoliation: excessive connective tissue (elastosis) produced in the eye is deposited over the trabecular meshwork, plugging it.
• Pigment Dispersion: the dark melanin pigment on the iris comes off and plugs the trabecular meshwork
• After trauma: the trabecular meshwork is damaged.
What tests may be performed?
• A dilated examination of the optic nerve is the most important test since glaucoma is an optic nerve disease.
• Intraocular pressure
• A visual field test, to measure your side vision, where glaucoma usually causes damage first. This is a computer game that takes about 5-10 minutes per eye.
• Pachymetry, to measure central corneal thickness. People with thin corneas are at higher risk for for developing glaucoma, and people with thicker corneas are at less risk.
• Gonioscopy. This is a contact lens with mirrors attached, which allows the examiner to look at the angle and trabecular meshwork, which aren’t visible from a straight-on view. This helps determine if the angle is open or closed, and which glaucoma subtype you have.
• Nerve fiber layer analysis. A detailed view of the nerves around the optic nerve. Possibly more sensitive than a visual field in detecting damage from glaucoma.
• Color optic nerve photographs. These are potentially very import as baseline documentation. At future examinations, these photographs will be helpful in determining if the optic nerves are suffering more damage.
What are the symptoms of glaucoma?
Usually there are no symptoms, which makes screening for glaucoma a top public health priority. Symptoms, usually some sort of vision loss, only develop very late in the disease process, after most of the optic nerve has already been damaged. A rare type of glaucoma, called “acute narrow angle,” can cause pain, headache, nausea, vomiting, haloes, and vision loss.
How will I know if I have glaucoma?
The triad of high pressures, optic nerve damage, and side vision loss is the most common way to diagnose glaucoma. This triad is not true for everyone, though. For example, it is possible to have glaucoma and never have a high eye pressure. For this reason, a glaucoma test consists of more than a pressure check, but also an examination of the optic nerve.
At a screening examination, optic nerves and intraocular pressure will be checked. If abnormalities are found, visual fields and other baseline testing will be performed. If some but not all criteria for diagnosing glaucoma are present, the diagnosis of “glaucoma suspect” is made, and follow-up examinations are scheduled. If during follow-up as a glaucoma suspect, progressive changes are discovered typical of glaucoma (optic nerve damage, or visual field loss for example), glaucoma will be diagnosed. When glaucoma is diagnosed, treatment will be recommended.
How is glaucoma treated?
Glaucoma is treated by lowering eye pressure with eyedrops, lasers, or surgery. The type and severity of glaucoma guide the treatment. The more advanced the glaucoma, the lower the eye pressure should be for long term control.
In open angle glaucoma, first treatments are usually eyedrops used once or twice a day. Eyedrops work for most people. If eyedrops don’t lower the eye pressure enough, laser trabeculoplasty may be performed. The laser, which is administered in a few minutes as an outpatient, allows the fluid in the eye to filter faster through the trabecular meshwork, which lowers pressure. Finally, surgery can lower eye pressure if eyedrops and laser do not. The most common surgery for glaucoma is trabeculectomy using a medicine called mitomycin to limit healing. During trabeculectomy, a filtering path is created for fluid to leak out of the eye under the upper lid. Trabeculectomy is effective, but risks of very low pressure and infection have lead to the development of safer, but perhaps not as effective, alternatives.
If the angles are narrow or closed, laser peripheral iridotomy (LPI) will be performed to create a bypass for aqueous to flow through the angle, where it then filters out of the eye. Many patients with narrow angle glaucoma will still need to use eyedrops to lower pressure, and may need traditional surgery like trabeculectomy with mitomycin.
More information on this condition can be found at the National Eye Institute’s website.