Beta-blockers: how are they used to treat glaucoma?

There are a variety of treatment options available for glaucoma, including eye drops, laser procedures and surgery. All of these treatments are aimed at balancing and controlling eye fluid pressure, called the intraocular pressure (IOP), and protect the optic nerve as a result.

Eye drops are often the first choice of treatment for glaucoma and, used regularly, can help to keep the IOP at the correct level, reducing the risk of optic nerve damage.

One of the reasons eye drops can be so effective is an active ingredient in them called beta-blockers. Here, we’ll take a closer look at what beta-blockers are, and how they work to control intraocular pressure.

What are beta-blockers?

Used in a variety of glaucoma eye drops, topical (medication applied to a specific part of the body) beta-blockers are agents that reduce IOP by blocking specific nerve endings in the part of the eye that produces aqueous humour (eye fluid), causing the amount of fluid to be reduced.

Reducing pressure in the eyes helps slow optic nerve damage, decreasing the rate of vision loss. Studies have shown that beta-blockers may typically help lower the IOP inside the eyes by about 25%.1

How do beta-blockers treat glaucoma?

Beta-blockers lower the amount of aqueous humour produced by blocking the receptor sites (adrenoceptors) for stress hormones.

A receptor is the part of a cell where hormones bind to inform the cell what to do. In this case, by blocking the adrenoreceptors, beta-blockers can prevent the cell from sending the signal to create more aqueous humour, ultimately lowering IOP.

Two classes of topical beta-blockers are currently available — non-selective and selective. Depending on various co-existing or underlying medical conditions, a patient may be prescribed a non-selective or cardioselective beta-blocker.2

What are the different types of beta-blockers for glaucoma treatment?

There are a number of different beta-blockers for glaucoma treatment, however Timolol is the most prescribed beta-blocker for glaucoma treatment due to its efficacy, cost-effectiveness and the fact it’s a preservative-free formulation.10

Timolol

Timolol is a topical beta-blocker that can reduce both elevated and normal intraocular pressure by inhibiting the production of aqueous humour.

In fact, when used twice daily, it’s been shown to decrease in the production of aqueous humour, inducing a significant fall in lOP, by 13-48%3.

What are the side effects of Timolol?

Like all medicines, Timolol can cause side effects, although not everybody gets them. Unless the effects are serious, use of Timolol should not be stopped before consulting your doctor.

Common side effects of Timolol may include:

  • Generalised allergic reactions
  • Low blood glucose levels
  • Insomnia
  • Eye irritation
  • Slow heart rate
  • Abnormal changes in taste function
  • Muscle weakness

Rarer side effects may include a reduced libido and depression.

Should you feel any of these side effects, always discuss them with your eye doctor before anything else.

How should you store Timolol?

Timolol eye drops should be stored at temperatures below 25°C and protected from light. This should preserve the quality of the formula. However, opened bottles are strongly advised to be discarded four weeks after opening, even if there is solution remaining.

How do I know if Timolol is right for me?

In cases of chronic open angle glaucoma, and you fail to respond adequately to Timolol alone, Timolol is often prescribed along with other local and oral glaucoma treatment options. You can discuss these options openly with your ophthalmologist.

The use of Timolol is also not recommended alongside respiratory disorders such as asthma and bronchitis, or certain heart irregularities and conditions such as diabetes.

Timolol may also show inadequate or adverse effects due to certain medications you might be taking, especially for lowering blood pressure, treating heart ailments, managing diabetes, other eye drops for the treatment of glaucoma and any medicines obtained without a prescription.

In all these cases, use of Timolol eye drops is recommended only after due consultation with your ophthalmologist. They will go through your medical history to ensure the correct glaucoma eye drops, or other treatment option, are prescribed.

Levobunolol

Levobunolol was introduced as an alternative to Timolol because of its long duration of action. This means that it can be administered once-daily, with the possibility of fewer adverse effects.4 Levobunolol has an IOP lowering effect roughly equivalent to that of Timolol.

Use of Levobunolol may present side effects similar to those of Timolol in people who have respiratory difficulties. If you have any problems with your breathing or respiratory system, your doctor may not recommend Timolol or Levobunolol, and it’s important that the doctor knows of any previous breathing-related conditions, such as asthma.5

Carteolol

Carteolol is a nonselective beta-blocker that has been shown to produce a significant reduction in lOP in glaucoma patients.

In addition, a theoretical benefit of Carteolol (but one that has not been proven clinically) is its ability to regulate the ocular pressure at which the blood enters the eye, which may help in more effective treatment of glaucoma.

Betaxolol

Betaxolol hydrochloride is a cardioselective beta blocker (targeting only one receptor) which reduces elevated as well as normal lOP, and reduces the production of aqueous humour without affecting the drainage of fluid from the eye.8

Followed as a twice daily regimen, Betaxolol offers some advantages over Timolol and the other beta blockers in terms of certain side effects. For example, Betaxolol might be considered the drug of choice in a patient with compromised respiratory or cardiac function if a beta-blocker must be used. Of course, every person is different and has different medical requirements so this does depend on individualities.

However, it is important to keep in mind that although Betaxolol may offer some advantages in terms of cardiovascular and respiratory effects, it may be less effective than Timolol and Levobunolol in reducing IOP.9

Can beta-blockers be combined with other drugs?

Beta-blockers are often employed in combination with other glaucoma eye drops. Timolol, the most common beta-blocker, for example, has been combined with almost all other topical drugs for convenience.

They are also often prescribed as a supplement to, or in combination with, another class of eye drops called prostaglandins.

There are various types of eye drops available to treat glaucoma, which can be prescribed individually or as combinations. The treatment type entirely depends on the unique circumstances of glaucoma, such as how far it has progressed, the glaucoma type, and how you react to certain medications. This is where your ophthalmologist will prescribe you with the most effective medication that meets your unique needs.

What are common general side effects of beta-blockers?

Common side effects of beta-blockers can include:

  • Low blood pressure
  • Reduced pulse rate
  • Fatigue

Beta-blockers can also cause shortness of breath in people who have a history of asthma or other respiratory disorders. Additionally, they can result in a change in cardiac activity such as a slowing down of the heart’s response rate during physical exercise. This is due to a decrease in the amount of blood the heart pumps out. Rare side effects may include reduced libido and depression.

Side effects that affect other parts of the body can be minimised by performing what’s called punctal occlusion after application of the eye drops. After you have taken your eye drops, press the bridge of your nose next to the eyes for about 20 seconds. This is a technique used to decrease the absorption of eye drop medications into the bloodstream through the tear duct.

If you want to find out more about the treatments for glaucoma, you can visit our dedicated glaucoma resources. Here, you can also learn more about the glaucoma causes and glaucoma diagnosis.

References

1. Abramowicz M (2010). Drugs for some common eye disorders. Treatment Guidelines From The Medical Letter, 9(99): 1–8.

2. Sambhara, D., & Aref, A. A. (2014). Glaucoma management: relative value and place in therapy of available drug treatments. Therapeutic Advances in Chronic Disease, 30–43.

3. Coakes RL, Brubaker RF. The mechanism oftimolol in lowering intraocular pressure. Archives of Ophthalmology 96: 2045-2048, 1978

4. Silverstone D, Zimmerman T, Choplin N, Mundorf T, Rose A, et al. Evaluation of once-daily levobunolol 0.25% and timolol 0.25% therapy for increased intraocular pressure. American Journal of Ophthalmology 112: 56-60, 1991

5. Berson FG, Cohen HB, Foerster RJ, Lass JH, Novack GO, et al. Levobunolol compared with timolol for the long-term control of elevated intraocular pressure. Archives of Ophthalmology 103: 379-382, 1985

6. Collignon-Brach J. Early visual field changes with beta-blocking agents. Summary. Survey of Ophthalmology 33 (Suppl.): 429- 430, 1989

7. Buckley MMT, Goa KL, Clissold SP. Ocular betaxolol. Drugs 1990; 40:75-90

8. Reiss GR, Brubaker RF. The mechanism of betaxolol, a new ocular hypotensive agent. Ophthalmology 90: 1369-1372, 1983

9. Buckley MMT, Goa KL, Clissold SP. Ocular betaxolol. Drugs 1990; 40:75-90

10. OpenPrescribing. (Sep ‘18 - Aug ‘19). https://openprescribing.net/analyse/#org=CCG&numIds=1106000Z0&denom=nothing&selectedTab=summary