Glaucoma

Types of Glaucoma

Primary Open Angle Glaucoma
Primary open angle glaucoma (POAG) is the most common of all types of glaucoma. The condition is diagnosed in the presence of an open angle, evidence of optic nerve damage, and peripheral vision loss consistent with glaucoma on a visual field test. Patients are usually treated with eye-drop and/or oral medications first, reserving laser and surgical procedures for "maximum medical therapy" failures, i.e., patients who have progression of glaucoma with a medical regimen. However, in many cases, an argument can also be made that laser therapy (argon laser trabeculoplasty) should be used initially, and medications secondarily. If eye-drop medication is chosen as the initial treatment, many ophthalmologists will recommend treatment of just one eye first, utilizing the second eye as a control, or "barometer", by which to gauge the effect of treatment. It is important for the patient to realize that eye-drop medications administered to only one eye may also lower pressure in the opposite eye due to a systemic effect. This is why baseline pressure measurements, prior to the initiation of treatment, are extremely important in assessing the efficacy of medications. 
Patients who have progression of glaucoma despite medical therapy and, perhaps, argon laser trabeculoplasty (ALT, or laser treatment) are usually recommended to have a glaucoma filtration procedure (trabeculectomy). Certain patients who have failed an initial glaucoma filtration procedure may be recommended for implantation of a glaucoma drainage device. These procedures are reviewed in the "Eye Procedures" section of this site.

Angle Closure Glaucoma 
Angle closure glaucoma may be subdivided into two basic types for the purposes of this discussion. These are known as primary angle closure glaucoma and acute angle closure glaucoma. 
Primary angle closure glaucoma accounts for 10% of glaucoma patients and two-thirds of these present asymptomatically (without symptoms). This condition is characterized by a narrow angle, i.e., the anatomy of the eye is such that aqueous fluid drainage via the trabecular meshwork (the primary fluid egress site) is relatively obstructed. In essence, the iris (colored part of the eye) is in close apposition to the cornea (front clear part of the eye) and physically obstructs the flow of fluid out of the eye. The treatment for this condition is a peripheral iridotomy (laser) or peripheral iridectomy (surgery). The effect of either procedure is the creation of a tiny opening in the iris. This allows aqueous fluid, made in the ciliary body (behind the iris), to flow directly through the iridotomy or iridectomy site, thereby leading to a falling backwards of the iris. This, in turn, clears the obstruction to the trabecular meshwork (drainage area). Treatment with glaucoma medications may be used before, and/or after, either procedure to further control glaucoma. The effect of a laser peripheral iridotomy (PI) is to convert a closed-angle into an open-angle, however, because of significant optic nerve damage, the patient may still require treatment for glaucoma. 
Acute angle closure glaucoma is one of the few types of glaucoma that presents with symptoms. Patients may present with blurred vision, colored halos, severe pain, red eye, and nausea or vomiting. On examination, the eye pressure is extraordinarily high, generally 40 to 70 mmHg (normal 10 to 21). The angle is noted to be closed in the affected eye except in cases in which the corneal edema (swelling) is so severe that it cannot be visualized. In this case, the ophthalmologist may examine the fellow eye and note a narrow angle or angle closure. The condition may require medical management to reduce the pressure, thereby allowing the corneal edema to resolve, and then a laser peripheral iridotomy (PI) is completed. If a laser PI cannot be completed due to severe corneal edema, a surgical peripheral iridectomy is completed.
 
Normal Pressure Glaucoma (Low-Tension Glaucoma) 
Normal pressure glaucoma, also known as low-tension glaucoma, occurs in approximately one-third of all patients afflicted with glaucoma. Patients with this condition have essentially the same findings as patients with primary open angle glaucoma (abnormal optic nerve findings and visual field loss), except that they are not demonstrated to have high intraocular pressures. As noted above, it is theorized that hypoperfusion (poor blood flow) of the optic nerve, mechanical factors in and around the nerve, and biochemical factors may play a role in the development of not only this type of glaucoma, but other types as well. The fact that migraines are more common in this form of glaucoma is further evidence to support the vascular (hypoperfusion) theory of normal pressure glaucoma. (Migraine is known to have a vasospastic (transient hypoperfusion) component, which leads to the headache.) 
Normal pressure glaucoma is often treated with eye-drop medications in attempt to further reduce pressure and stabilize the visual field. At this time, there appears to be more evidence to support the use of the eye-drop medication brimonidine than any other medicine in the treatment of normal pressure glaucoma. Some ophthalmologists also recommend argon laser trabeculoplasty (ALT) since this procedure may avoid the risks and expense of medications.