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Glaucoma is a disease of the optic nerve that involves the loss of ganglion cells which results in an optic neuropathy. Although raised intraocular pressure is an important risk factor for the development of glaucoma, damage to the optic nerve and visual field loss also need to be included in the diagnosis of glaucoma.
There are several types of glaucoma. The most common form is called primary open angle glaucoma (POAG), and it affects over 2 million people in the United States. There are no symptoms in POAG and it involves a slow, insidious loss of the peripheral visual field. It occurs in the presence of open anterior chamber angles where the aqueous humor drains. Other types of glaucomas include closed angle glaucoma, normal tension glaucoma, pigmentary glaucoma, juvenile glaucoma, and secondary glaucoma. In all types, the goal is to reduce the intraocular pressure (IOP). The normal range for IOP is 10-21mm Hg.
Generally, the first mode of treating glaucoma is to reduce the intraocular pressure with drugs, usually with eye drops. There are several classes of medications which help reduce intraocular pressure. Beta adrenergic receptor blockers, such as Timolol, help reduce IOP by decreasing aqueous humor production in the ciliary body. Prostaglandin analogs, such as Latanoprost have become very popular because of effectiveness and once a day dosing, and they decrease intraocular pressure by increasing uveoscleral outflow. Alpha-2-adrenergic agonists, such as Brimonidine, also decrease intraocular pressure by decreasing aqueous humor production. Carbonic anhydrase inhibitors, such as dorzolamide, are yet another class of drugs which decrease IOP by decreasing aqueous humor production.
Less commonly used agents include sympathomimetics, such as epinephrine, increase outflow through the trabecular meshwork. Miotic agents, such as Pilocarpine, also incrase outflow through the trabecular meshwork. There are also some combination drops on the market which combine different mechanisms and result in a greater reduction of IOP.
If medications fail to lower IOP sufficiently, the next step generally involves laser therapy. The SLT (selective laser trabeculoplasty) works by targeting melanin-containing cells in the pigmented trabecular meshwork without inducing any thermal damage to the adjacent non pigmented meshwork. The SLT induces a biologic response involving the release of cytokines that induce macrophage recruitment in order to reconstruct the trabecular meshwork, leading to a decrease in IOP. It can be repeated several times.
If medications and laser fail to decrease IOP sufficiently, the last option is surgery. The most common surgery performed to decrease IOP is a trabeculectomy. It involves making a partial thickness scleral flap which is connected to the anterior chamber, giving the fluid another area in which to drain, thereby reducing IOP. However, scarring of the surgery can result in decreased effectiveness. Another option is a glaucoma drainage implant, such as the Ahmed valve, the Baerveldt tube, or the Molteno implant. These are usually indicated for people who have failed maximal medical therapy and trabeculectomies. These implants all involve a tube which is places in the anterior chamber of the eye where the fluid circulates, and a plate is connected to the tube. The plate is inserted underneath the conjunctive and provides an area for the fluid to drain. Many glaucoma surgeries are done in conjunction with the use of anti-fibrotic agents such as Mitomycin-C and 5-Fluorouracil to decrease the risk of scarring and eventual failure.
There are several major studies in glaucoma which affect treatment as well. The Ocular Hypertensive Treatment Study (OHTS) helped place guidelines on who should be treated for ocular hypertension, that is, when the IOP is increased and the person is at risk for glaucoma, but there is no damage to the optic nerve or visual field deficits. It identified risk factors which made an ocular hypertensive more prone to having glaucoma. The Advanced Glaucoma Intervention Study (AGIS) reported that intervention differs in advanced glaucoma according to race. African-American patients did better with laser therapy initially, whereas Caucasian patients did better with trabeculectomy. The Collaborative Initial Glaucoma Treatment Study (CIGTS) studied the management of patients with medical therapy initially vs surgical therapy. Both groups showed a significant reduction in IOP.
Glaucoma is a common ocular disease that is expected to increase in prevalence over the next two decades. Its silent nature makes it difficult to detect, so it is important to screen people periodically, especially if they have a family history or other risk factors.
IF YOU WOULD LIKE YOUR QUESTIONS ANSWERED PERSONALLY
For more information on diagnosing and treating Glaucoma please call Dr. Robert Stewart's office at 713-668-6828 if you would like to schedule an appointment with Dr. Stewart please call 713-558-8711.
About Dr. Robert Stewart
Dr. Robert Stewart was born in Picayune, Mississippi in 1939. He graduated from Bellaire High School in Houston, TX and attended the University of Texas in Austin and the University of Texas Medical Branch in Galveston. He completed his internship and three year ophthalmology residency at Hermann Hospital now the University of Texas Medical Branch in Houston. Dr. Stewart was awarded the Heed Fellowship which allowed him to focus an additional year in glaucoma research at Barnes Hospital in St. Louis, MO.
In 1968 Dr. Stewart became the fourth member of the Houston Eye Associates. In 1970, through a relationship with Bill Conner the founder of Alcon Laboratories, he received a grant for the formation of the Conner Glaucoma Center at the University of Texas Medical School in Houston. He and his partner, Dr. Richard Kimbrough, continue to serve as co-directors of the Conner Glaucoma Center.
In 1972 Dr. Stewart created a glaucoma fellowship program which was approved by the American Board of Ophthalmology. This program was started to train ophthalmologists to become glaucoma specialists later in their career. He has over 20 previous fellows at this time practicing in different parts of this country and in the world.
In 1981, with the help of friends at the Baker Botts law firm, Dr. Stewart formed the Houston Eye Associates Foundation. This foundation provides eye care for indigent patients in and around the Houston area. Dr. Stewart has remained a director of this non-profit 501-C foundation since conception and is an integral part in charity driven projects such as the Houston Eye Associates Fun Run and the Marvin Zindler Golf Tournament.
Dr. Stewart has been the recipient of numerous awards, including the Distinguished Service Award from the Texas Society for the Prevention of Blindness and the American Academy of Ophthalmology certificate of award for distinguished service. This award is given to ophthalmologists who donate educational and instructional courses at the academy.
Dr. Stewart performs a considerable amount of clinical research studying medications used in cataract surgery and in the treatment of glaucoma. He has published over 75 articles in the ophthalmic literature, as well as several textbook chapters on glaucoma.
In 2005 he received the Ashbel Smith Distinguished Alumnus Award (ASDA) from the alumni association at the University of Texas Medical Branch (UTMB) at Galveston. He was cited for his contributions to the medical profession, support for the high standards of excellence within the profession and the prestige reflected upon his alma mater.
Dr. Stewart has been married to Edie Whitridge for 44 years and they have two sons, Dane & Colby. Colby practices ophthalmology at the Houston Eye Associates, and Dane runs a money management company. Dr. Stewart and his wife have five grandchildren all living in Houston.
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