Beta-adrenergic antagonists act against, or block, adrenalin-like substances. These drops work in the treatment of glaucoma by reducing the production of the aqueous humor. For years, they have been the gold standard (to which other agents are compared) for treating glaucoma. These medications include timolol (Timoptic), levobunolol (Betagan).
Used once or twice daily, these drops are very effective. However, side effects, such as the worsening of asthma or emphysema , bradycardia (slow heart rate), low blood pressure , fatigue, and impotence prohibit their use in some patients.
Betaxolol (Betoptic) is a beta-adrenergic antagonist that is more selective in working just on the eye and, therefore, carries less risk of heart (cardiac) or lung (pulmonary) side effects than other drops of this type.
Prostaglandin analogs are similar in chemical structure to the body's prostaglandins. Prostaglandins are hormone-like substances that are involved in a wide range of functions throughout the body. These drops work in glaucoma by increasing the outflow (drainage) of fluid from the eye.
The prostaglandin analogs have replaced timolol as the most commonly prescribed drops for glaucoma. They can be used just once a day. This class of medications has fewer systemic (involving the rest of the body) side effects than timolol, but can change the color of the iris as well as thicken and darken the eyelashes. These drops are also more likely to cause redness of the eyes than other classes of eye drops. In some patients, they may also cause inflammation inside the eye. These medications include latanoprost (Xalatan), travoprost (Travatan), and brimatoprost (Lumigan).
Adrenergic agonists are a type of drops that act like adrenalin. They work in glaucoma by both reducing the production of fluid by the eye and increasing its outflow (drainage). The most popular adrenergic agonist is brimonidine (Alphagan). This agent seems to protect the optic nerve from damage beyond just lowering the intraocular pressure. However, there is up to a 12% risk of local (eye) allergic reactions.
Carbonic anhydrase inhibitors work in glaucoma by reducing the production of fluid in the eye. Eye-drop forms of this type of medication include dorzolamide (Trusopt) and brinzolamide (Azopt). They are used two or three times daily.
Carbonic anhydrase inhibitors are otherwise used as pills (systemically) to remove fluid from the body in patients with swelling (edema) that is caused by fluid retention. Oral forms of these medications used for glaucoma include acetazolomide (Diamox) and methazolamide (Neptazane). Their use in this condition, however, is limited due to their systemic (throughout the body) side effects, including reduction of body potassium, kidney stones, numbness or tingling sensations in the arms and legs, fatigue, and nausea.
Parasympathomimetic agents, which are also called miotics because they narrow (constrict) the pupils, act by opposing adrenalin-like substances. They work in glaucoma by increasing the aqueous outflow from the eye. These drops include pilocarpine , demecarium (Humorsol), echothiophate (Phospholine Iodide), and isoflurophate (Floropryl).
Currently, pilocarpine is the only one of these medications being used for glaucoma. It is used primarily to keep the pupil small in patients with a particular iris configuration (plateau iris) or in patients with a narrow angle prior to laser iridotomy. (See the section above on closed-angle glaucoma.)
Osmotic agents are an additional class of medications used to treat sudden (acute) forms of glaucoma where the eye pressure remains extremely high despite other treatments. These medications include Isosorbide (given by mouth) and Mannitol (given through the veins). These medications must be used cautiously as they have significant side effects including nausea, fluid accumulation in the heart and/or lungs (congestive heart failure and/or pulmonary edema), bleeding in the brain, and kidney problems. Their use is prohibited in patients with uncontrolled diabetes, heart, kidney, or liver problems.
Several new classes of glaucoma drops are currently under development or awaiting FDA approval.