Background
Open angle glaucoma (OAG) is a multifactorial optic neuropathy characterized by progressive retinal ganglion cell death and characteristic visual field pattern loss. Glaucoma is an increasingly important cause of blindness as the world’s population ages. Statistics gathered by the World Health Organization (WHO) in 2002 showed that glaucoma is the second leading cause of blindness worldwide, after cataracts. However, glaucoma presents a greater public health challenge because the blindness it causes is often progressive and irreversible.
In the United States alone, glaucoma has been diagnosed in more than 2 million people, who are at risk of becoming blind. Therefore, extensive research into the pathophysiology and understanding of glaucoma is underway to help guide pharmacologic and surgical interventions to slow this progressive optic neuropathy.
Elevated intraocular pressure (IOP) has been identified as a major risk factor for OAG, and current treatment aims focus on reducing and controlling IOP to limit disease progression.
Although additional risk factors for glaucoma have been identified, current treatments for decreasing IOP focus on either reducing the production of aqueous humor from the ciliary processes or on increasing the ability of the aqueous humor to drain from the eye.
Treatments include the use of topical and oral pharmacologic agents to inhibit the production of aqueous humor or to help with the outflow of aqueous humor along the uveoscleral pathway. In addition, laser trabeculoplasty procedures have been designed to help open the trabecular meshwork to aid the outflow of anterior chamber fluid. Other procedures have focused on destruction of the ciliary processes that produce aqueous humor.
However, use of daily topical medications creates a burden for patients, and studies have reported a very low compliance rate in patients using daily drops. Furthermore, patients often have variable responses to topical medications and laser treatments, and these treatment effects are often limited and ineffective at controlling IOP over many years. As a result of this, incisional surgical techniques have been designed to increase the drainage of aqueous humor in patients unresponsive to or noncompliant with topical therapy. These techniques include implanting artificial drainage valves (tube shunts) and surgically cutting additional passageways to drain the fluid (trabeculectomy/filter surgery). Risks associated with these surgical procedures include infection, cataracts, bleeding, hypotony, and filtration failure.
Traditional glaucoma-filtering surgery.