None — Glaucoma
Glaucoma is a condition characterized by damage to the optic nerve in the eye. This nerve sends information about images coming into the eye to the brain for processing.
The front part of the eye is filled with a continually produced fluid, called aqueous humor. To maintain the right amount of pressure, an equal amount of fluid drains out of the eye through the trabecular network, a collection of specialized cells and tissue. This network is located in an area of the eye where the iris and cornea meet (the drainage angle). If the drainage angle becomes narrowed or blocked, the fluid can't exit the eye as quickly as it should, and it accumulates. This causes increasing pressure and extra force on the delicate fibers in the optic nerve. Eventually, the higher pressure damages the nerve fibers.
There are several different kinds of glaucoma. The most common form is open-angle glaucoma. This occurs when the trabecular meshwork becomes less efficient in draining fluid, gradually raising intraocular pressure. In closed angle glaucoma, the drainage channel becomes suddenly blocked, causing intraocular pressure to increase rapidly. This is a medical emergency because optic nerve damage occurs very quickly and can lead to significant vision loss. Sometimes glaucoma can occur even when intraocular pressure is within a "normal" range. This is called, normal-tension glaucoma. Glaucoma that occurs in infants and young children is called, congenital glaucoma.
The American Optometric Association estimates about 2 million Americans have glaucoma. Risk for the condition increases with age (generally after 60). However, for an unknown reason, in African-Americans the risk for glaucoma increases after 40. Family history of glaucoma, previous eye injury, having certain eye conditions, low blood pressure and use of corticosteroids also increase the risk for glaucoma.
In the U.S., glaucoma is the second leading cause of blindness. The reason for the high incidence of vision loss is that the condition rarely causes any symptoms until the optic nerve has been significantly damaged. Over time, the patient loses side vision. Central vision remains, until eventually, like a shrinking hole of light, even central vision is lost. Health experts say early signs of glaucoma can be detected during a thorough eye examination.
Treating Glaucoma
Many patients with glaucoma can be managed effectively with medicated eye drops. These drugs either slow the production of aqueous humor or improve outflow through the drainage channel.
Glaucoma medication can sometimes cause significant unwanted side effects and doesn't work for everyone. In these cases, doctors may recommend some type of surgical intervention. Laser trabeculoplasty uses a laser to make tiny burns (not holes) in the trabecular meshwork. This stimulates the drainage function to work more efficiently.
In trabeculectomy, a drainage flap is made in the outer white part of the eye, creating a bleb, or fluid collection reservoir under the conjunctiva (the covering over the white of the eye). Fluid drains through the flap, collects in the bleb and is then absorbed into the blood vessels in the eye.
Another option for some patients is a drainage implant. A tiny tube or valve is surgically inserted into the eye. Excess fluid drains through the tube to an area beneath the conjunctiva, where it is absorbed into the blood vessels in the eye.
The Trabectome
Some eye surgeons are using a device, called the trabectome, to treat patients with open angle glaucoma. A small incision is made into the eye to access the drainage area. Then, pulses of electrosurgical energy are aimed at the tissue. The process destroys a small portion of the trabecular meshwork and a section of the inner wall of the vein in which the fluid drains from the eye (called the canal of Schlemm). This opens up a direct drainage channel into the vein to allow fluid to drain naturally from the eye.
Misha Syed, M.D., Ophthalmologist with UTMB Health Eye Center in Friendswood, TX, says the trabectome enables surgeons to treat patients using minimally invasive surgery. In some cases, the pressure is lowered enough that the patient no longer needs eye drop medication. Recovery time is short and most patients are back to normal activities in one to two weeks.
Syed adds the trabectome is just one tool in the treatment options for glaucoma. Patients should discuss the risks and benefits with their personal eye care professional. Experts say the trabectome may not be the best option for patients who have advanced stages of glaucoma or need to achieve very low intraocular pressure.
AUDIENCE INQUIRY
For information about the trabectome, or to locate a physician using the instrument, go to trabectome.com
For general information on glaucoma:
American Academy of Ophthalmology, public website, geteyesmart.org
American Optometric Association, aoa.org
Glaucoma Research Foundation, glaucoma.org
National Eye Institute, nei.nih.gov