 | Glaucoma: What Every Patient Should Know |  |
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Our nervous system has large unconscious components which are very useful. These unconscious components mean you don’t have to think about digesting lunch while reading this guide; the autonomic nerves do that for you on autopilot. These systems are controlled by chemicals that work like a lock and key. The chemical that activates the process is the key and the lock into which it fits is its “receptor”. When the key is in the lock, things happen. In addition, there are chemicals that fit the lock, but don’t activate the mechanism. These are called blockers or inhibitors. The unconscious nervous system has two main parts: the adrenergic and parasympathetic. Adrenergic receptors come in two flavors, given the Greek letters alpha and beta (A and B). Some 40 years ago, it was recognized that molecules that inhibit the beta adrenergic receptors strongly inhibit the making of aqueous humor at the ciliary body. Thus, they are called beta blockers. In the form of pills, millions of persons take this class of drug to lower blood pressure, decrease the chance of another heart attack, treat abnormal heart rhythm, and prevent migraine. Their generic names most often end in –olol (like propranolol).
The first beta blocker eyedrop approved by the FDA in 1978 was timolol (with the brand name Timoptic) which has long since gone generic, and there are now other forms of timolol (Betimol, Istalol, Timoptic XE) as well as related beta blockers like levobunolol (Betagan), betaxolol (Betoptic), and carteolol (Ocupress). The generic agents seem to lower eye pressure as well as the original brands of beta blockers. In some patients there is enough action from these agents that they can be used only once per day, but more frequently they need to be taken morning and night. Timolol’s ability to lower pressure has often been used as the gold standard for how good other drops need to be. There are different strengths (0.25%, 0.5%, and 1%) of some of the beta blockers available.
The possible side effects of beta blockers are both eye problems and general body issues. In the eye, there is tendency for eyes with poor tear function to make fewer tears. This is called dry eye syndrome or keratitis sicca. It is very common that the tears we make don’t keep the eye comfortable because they lack the oily components that keep tears from evaporating away too quickly. When little dry spots form, they hurt like needles or sand in the eye. In response, the eye tries to make more tears, but they’re as bad as they were before, so now there’s a sandy gritty feeling and the eye is tearing. The eye doctor will tell you to help dry, tearing eyes by putting artificial tears on the eye. This sounds wrong, since you've already got tears in your eyes. Think of it as fighting fire with fire: you're fighting tears with better tears. The non-prescription artificial tears have the oily component your own tears lack, so the tearing stops because a more effective, non-evaporating layer is formed by them. None of these tears we’re talking about has anything to do with the aqueous humor inside the eye, which never gets out onto the cornea. Tears come from a gland mostly up under the temple side of the upper eyelid. We don’t know why beta blocker drops make dry eyes worse, but if you are having symptoms like this, ask the doctor to stop the beta blocker to see if it helps. Allergy to the drug is uncommon with beta blockers, but it happens.
Now as a general rule, any time a patient thinks that a side effect is caused by a drop, consider stopping it immediately for a few days in one eye. That way you can compare the treated to the untreated eye. Often, the symptom isn’t helped, and we find out the drop isn’t the cause. When it is confirmed that the drop is the problem, we find a different one to take. This is the unilateral stop trial mentioned before.
The general body effects of beta blockers (or any drops) come through exposure of the drug to the surfaces inside the nose—the drops get there through the tear drainage system—hence, the description of how to block this with your fingers in the preceding section by nasolacrimal occlusion. All the reasons that beta blocker pills are given to treat disease can be bad side effects in people who are very sensitive to them: very slow heartbeat, lowered blood pressure, and intensification of wheezing in people with asthma or chronic lung disease. In fact, beta blocker eyedrops are almost never used in people with asthma. Some of the beta blockers actually raise the blood level of the bad kind of cholesterol. And, in some people there is a psychological depression and a loss of the appetite for sex in men. Naturally, any of these is significant enough that if they are happening due to drops, we change them.
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