Open-angle glaucoma: tips for earlier detection and treatment selection

Journal of Family Practice, Feb, 2005 by Ahmad A. Aref, Brian P. Schmitt

Setting a target pressure. Before beginning therapy, an ophthalmologist sets a target pressure that should halt further optic nerve damage. The initial target pressure is usually 20% to 30% lower than the pretreatment pressure. If damage to the optic nerve is already substantial, the target pressure may be set even lower. (2)

Stepwise therapy. Topical medications are usually given first, as eye drops. A comparison of these medications is outlined in Table 2. If IOP cannot be lowered pharmacologically, argon laser trabeculoplasty (ALT) is the next step. If the pressure still cannot be lowered, filtering surgery is the final alternative (SOR: C). (2)

Pharmacologic options

Medical agents work in 1 of 2 ways to lower IOP: by decreasing production of aqueous humor, or by increasing drainage of aqueous humor out of the eye. Though most glaucoma medications are given topically, severe systemic side effects can occur. (2) Because the consulting ophthalmologist may not be aware of a patient's other medical conditions, inquire about the topical ocular drops being recommended to make certain they are not contraindicated and to be alert to the potential for adverse effects (SOR: C). (13)

Beta-adrenergic antagonists can lower IOP by up to 31% (25) and are often used as first-line treatment (SOR: A). (21) However, nonselective beta-blockers (timolol, carteolol, levobunolol, metipranolol) are associated with a number of adverse effects including bronchospasm, (33) bradycardia, and hypotension. (34)

Betaxolol is a selective beta-blocker with less tendency to cause pulmonary side effects, (34) but it may still do so in patients with severe pulmonary disease. (35) Selective beta-blockers lower IOP to a lesser degree than nonselective drugs (36) and can cause the same cardiac effects of bradycardia and hypotension. (38)

Prostaglandin analogs (latanoprost, travoprost, unoprostone) increase drainage of the aqueous humor. Prostaglandins are clinically and statistically superior to beta-blockers, having lowered I0P by up to 40% in randomized controlled trials. (37) Side effects include increased eyelash growth and iris pigmentation, (26) and muscle and joint pain. (38)

Alpha-adrenergic drugs (apraclonidine, brimonidine) lower aqueous humor production. Apraclonidine administered topically does not cross the blood-brain barrier, effectively lowering IOP without causing cardiovascular side effects. (28) The most common side effects are dry nose, dry mouth, (28) and follicular conjunctivitis. (29) Unlike apraclonidine, brimonidine crosses the bloodbrain barrier and can cause mild hypotension. (30) One randomized controlled trial found no statistical difference in efficacy between brimonidine and apraclonidine, both lowering I0P by up to 23%. (39)

Carbonic anhydrase inhibitors block water flow into the eye, preventing aqueous humor formation. Until recently, carbonic anhydrase inhibitors such as acetazolamide were administered only orally and adverse effects were therefore common. (27) Topical carbonic anhydrase inhibitors (brinzolamide, dorzolamide), recently introduced, lower IOP by up to 26% and with few side effects. (31)