What is Glaucoma?
Primary open angle glaucoma (POAG) is the most common form of glaucoma, a disease where elevated pressures of intraocular fluid (referred to as aqueous humor or aqueous) in the eye slowly damage the optic nerve.
POAG is defined by a progressive reduction in the visual field of the affected patient, gradually narrowing vision from the periphery. It is generally associated with an elevation in intraocular pressure, to a level exceeding 21 mm Hg. While it is easily defined and diagnosed, it is an insidious disease with a slow but ongoing progression to eventual blindness. There are typically no symptoms of elevated intraocular pressure, e.g. pain, etc. If first diagnosed by a patient's measurable loss of visual field, the disease has already progressed to an irreversible stage.
Glaucoma is as yet incurable and vision loss is irreversible. Management of glaucoma typically aims at limiting and/or halting the potential loss of vision. It is estimated that up to 10% of patients that are diagnosed and receive treatment for their glaucoma will still experience irreversible loss of vision. Approximately 120,000 Americans are blind due to glaucoma, accounting for 9% - 12% of all blindness in the U.S.
Who is Vunerable?
- POAG is six to eight times more prevalent among African Americans than other ethnic group. In addition to this higher frequency, glaucoma often occurs earlier in life in African Americans - on average, about 10 years earlier than in other ethic populations. The reasons for this higher rate and subsequent blindness remain unknown.
- Patients over the age of 60 are six times more likely to have glaucoma when compared to patients under the age of 60.
Glaucoma Treatment
As the disease progresses the treatment for glaucoma increases in complexity and invasiveness.
- The first line therapy is pharmaceutical, typically eye drops that reduce intraocular pressure by either increasing aqueous outflow from the eye or reducing aqueous
production (inflow) into the eye. - When intraocular pressure can no longer be controlled by the use of pharmaceuticals, the physician may choose to first intervene by use of a laser in the office.
- If intraocular pressure can no longer be controlled by either pharmaceuticals and/or office laser procedures, the next step in patient management is surgery.
- If all of the above procedures have failed to control intraocular pressure, the final treatment is destruction of the ciliary body within the eye (cyclodestruction). This is
the structure in the eye responsible for aqueous production.
First Line Therapy: Pharmaceuticals
Beta blockers (Betimol®, Betoptic S®, Betagan®, Ocupress®, Timoptic®, etc.) are the most widely used of all glaucoma medications and are typically the first prescribed. Secondary medications include sympathomimetic alpha-adrenergic agonists (Alphagan® and Iopidine®); carbonic anhydrase inhibitors, both oral (Diamox® and Neptazane®) and topical (Trusopt® and Azopt®); miotics such as Ocusert®, Pilocar®, Pilopine®, etc; and, most recently, prostaglandin analogues (Xalatan®, Travatan®, Lumigan®, Rescula®).
All of these agents are widely used and all have minimal (but well understood) side effect profiles. Usage will depend on the progression of the disease, clinical evidence, or your physician's preference.
Second Line Therapy: Office Laser Procedures
The most commonly available laser procedures are:
- Selective Laser Trabeculoplasty (SLT): SLT uses a laser to target specific cells within the trabecular meshwork, the natural pathway for outflow of aqueous. Minimal damage to the surrounding trabecular tissue is sustained, while inducing a biological response that leads to reduction in intraocular pressure. SLT may be a repeatable procedure - up to twice each year -- but the data establishing this as fact are still being accumulated.
- Argon Laser Trabeculoplasty (ALT): ALT uses an argon laser to open fluid pathways in the trabecular meshwork. Intraocular pressure is reduced, as aqueous outflow is increased. As it is inherently destructive, this procedure may be repeated only twice in a lifetime.
Third Line Therapy: Surgery
- Trabeculectomy: The first line surgical therapy, trabeculectomy, creates a 'filter,' allowing for outflow of aqueous through what is known as a bleb (a bubble of aqueous fluid that forms under the outer conjunctiva layer of the cornea that slowly allows the aqueous fluid to permeate out of the eye). A partial thickness flap is cut in the sclera (the white portion of the eye), exposing the trabecular meshwork. A punch is used to create perforations in the trabecular meshwork, allowing for the outflow of the aqueous into the bleb. The flap is then carefully put back in place with sutures to allow for fluid to exit the eye in a controlled fashion. The escaping aqueous captured in the bleb is then absorbed by the body and carried away by collateral circulation.
- The most common complication of trabeculectomy is premature closure due to the body's natural wound healing process. The body will attempt to heal the wound as well as the trabecular meshwork. Once the meshwork scars over, the outflow of aqueous will cease, requiring additional intervention, e.g. 'needling' of the bleb, surgical revision, etc. In order to prevent this complication, use of antifibrotic/antimetabolite agents (mitomycin-c, 5-fluorouracil) has become commonplace in trabeculectomy. These agents interrupt DNA synthesis, thereby diminishing the ability of the body to heal the site of aqueous outflow.
- Aqueous shunt surgery: In this procedure, a tube is implanted within the anterior chamber of the eye, shunting fluid to a valved reservoir. The reservoir is surgically implanted within the sclera. Here, the fluid accumulates and is released from the eye in a controlled fashion.
The Final Step: Cyclodestruction
Using an infrared laser, regions of the ciliary body are targeted and destroyed. With the means for producing aqueous humor irreversibly destroyed, intraocular pressure is controlled. Understandably, this treatment is generally regarded as a last and final option, typically employed on patients with little to no useful remaining vision. Performance of the procedure is designed not to preserve vision, but to reduce patient pain and/or discomfort.
Alternative Therapies
To find out information regarding alternative therapies visit - http://www.glaucoma.org/treating/update_on_alter.php