Chronic (primary open-angle) glaucoma treatment

Glaucoma has long been recognised as a condition in which pressure of the fluid within the eye is higher than normal, specifically higher than 21 mmHg. The definition of glaucoma has changed recently given the knowledge that some people have glaucoma related damage at high pressures that are considered normal, i.e., less than 21 mmHg. This condition is called normal tension glaucoma. Therefore, the most accurate definition of glaucoma is the presence of characteristic damage to optic disc in the retina with or without elevated eye pressure.

Differences Between Glaucoma and Ocular Hypertension

People with ocular hypertension, chronic primary open angle glaucoma, and even normal tension glaucoma may be treated with eye drops that lower pressure within the eye.

Individualised Risk Factors

Currently, there is no consensus among ophthalmologists about when to start glaucoma eye drops. Ophthalmologists are more likely to initiate treatment with glaucoma eye drops when pressures go above 21 mmHg in patients depending on age, family history, and other measurements of the eye. Nevertheless, most ophthalmologists would treat patients with an intraocular pressure greater than 25 or those individuals with normal pressure who have evidence of glaucoma-related damage.

The decision to start treatment for glaucoma, therefore, depends on patient preferences, physician experience, and individualised factors. People who have obvious glaucoma such as greatly elevated eye pressure and/or damage to the optic disc in the retina will certainly be treated for the condition. However, people with moderately elevated pressures or not so obvious signs of damage may or may not be treated.

Certain risk factors make it more likely that an ophthalmologist will suggest treatment for glaucoma:

• People who have a large cup to optic disc ratio (a measurement taken of the retina) are more likely to receive treatment
• A person who has a first-degree relative with glaucoma is more likely to receive treatment
• Anyone who has bleeding in the optic disc is considered to be at high risk for visual field defects and is treated earlier rather than later. 

It is important to remember that glaucoma eye drops may have systemic side effects (effects on the rest of the body). In addition, some eye drops need to be administered up to four times a day, which can be challenging for even the most diligent of patients.

Glaucoma Eye Drops

The first line of therapy for treating glaucoma is eye drops. These eye drops either reduce the production of fluid within the eye or increase the rate that fluid is removed from the eye—both of which lower intraocular pressure. Sometimes one type of glaucoma eye drop will be enough to successfully treat a patient; however, it is more likely that two or more types of eye drops will be required. This can sometimes be achieved using products with 2 active ingredients. The main classes and names of glaucoma eye drops are:

• Prostaglandin agonists
  • Latanoprost
  • Bimatoprost
  • Tafluprost
  • Travoprost
  • Unoprostone
• Beta-blockers
  • Betaxolol
  • Carteolol
  • Levobunolol
  • Metipranolol
  • Timolol
• Carbonic anhydrase inhibitors
  • Acetazolamide (oral)
  • Brinzolamide
  • Dorzolamide
  • Methazolamide (oral)
• Alpha-adrenergic receptor agonists
  • Apraclonidine
  • Brimonidine
• Cholinergic agonists/Miotics
  • Pilocarpine

Prostaglandin agonists

Prostaglandin agonists have become the first choice of most ophthalmologists for treating open angle glaucoma. These eye drops tend to reduce intraocular pressure more than other eye drops, including beta-blockers. Prostaglandin agonists are effective, well tolerated, are only administered once a day, and cause few side effects. The most common side effects of prostaglandin agonists are redness (i.e. “bloodshot” eyes), eye irritation, and increased density and length of eyelashes. Unfortunately, prostaglandins can be quite expensive, though latanoprost recently became available as a generic forcing higher price competition.

Beta-blockers

Beta-blockers were formerly first choice eye drops for glaucoma because they are quite effective and only need to be administered once or twice a day. They are associated with eye irritation and dry eyes. The most serious adverse effect of using beta-blocker eye drops is that they can enter the bloodstream and cause heart and lung problems such as slow heart rate and asthma, respectively. Beta-blockers are generally less expensive than prostaglandins.

Carbonic anhydrase inhibitors

Historically, carbonic anhydrase inhibitors were oral medications that had several undesirable side effects. Newer carbonic anhydrase inhibitors such as brinzolamide and dorzolamide are eye drops with many fewer systemic side effects. Unfortunately, this class of glaucoma treatments is not as effective as prostaglandins or beta blockers.7 Therefore, carbonic anhydrase inhibitors are usually second line medications.

Alpha-adrenergic receptor agonists

Alpha-adrenergic drugs are quite effective (on par with beta-blockers) but are associated with side effects such as itching, “watery” eyes, and “bloodshot” eyes. This class of drugs may be useful for treating normal tension glaucoma8 since they protect the eyes from glaucoma-related damage without necessarily reducing intraocular pressure.

Cholinergic agonists/Miotics

Pilocarpine eye drops are modestly effective and do not cause systemic side effects. However, they do cause a number of eye-related problems such as pinpoint pupils, vision disturbances, and can exacerbate symptoms related to cataracts.

Surgery for Glaucoma

Laser Surgery

A surgical laser can be used to improve the flow of fluid out of the eye. This procedure is called a laser trabeculoplasty. In people with chronic open angle glaucoma, laser trabeculoplasty can be quite effective with few side effects. While medical therapy (i.e. eye drops) is usually used before surgery, the safety and outcomes associate with laser surgery may make it more likely to be a first-line therapy in the near future.

Traditional Surgery

In mild to moderate glaucoma, eye surgeons may place a filter in the eye that helps fluid exit the eyeball. While this approach can be effective, scar tissue may form over the area and block fluid from exiting, which negates the effect of the surgery. In a separate type of surgery, small shunts or tubes that allow fluid exit the eye can be surgically implanted. While shunts are usually reserved for people who have advanced glaucoma, they may be used earlier in the progression of the disease for people with cataracts and certain other medical conditions.

Ongoing Glaucoma Monitoring

Regardless of whether treatment involves eye drops or traditional surgery, people with glaucoma must be monitored throughout life. This includes intraocular pressure testing, dilated eye exam, and visual field testing at a minimum. This testing may be as frequent as every 2 to 4 weeks in initial phases of treatment up to every few months until the ophthalmologist is convinced that the disease has stopped progressing. Monitoring may be less frequent for people who undergo laser surgery, but routine testing is still required throughout life.

References

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2. For which glaucoma suspects is it appropriate to initiate treatment? Ophthalmology. Apr 2009;116(4):710-716, 716 e711-782.
3. De Moraes CG, Demirel S, Gardiner SK, et al. Rate of visual field progression in eyes with optic disc hemorrhages in the ocular hypertension treatment study. Arch Ophthalmol. Dec 2012;130(12):1541-1546.
4. Care NCCfA. Glaucoma: diagnosis and management of chronic open angle glaucoma and ocular hypertension. National Collaborating Centre for Acute Care (UK); 2009.
5. Orme M, Collins S, Dakin H, Kelly S, Loftus J. Mixed treatment comparison and meta-regression of the efficacy and safety of prostaglandin analogues and comparators for primary open-angle glaucoma and ocular hypertension. Curr Med Res Opin. Mar 2010;26(3):511-528.
6. Garway-Heath DF, Crabb DP, Bunce C, et al. Latanoprost for open-angle glaucoma (UKGTS): a randomised, multicentre, placebo-controlled trial. Lancet. Dec 18 2014.
7. Vass C, Hirn C, Sycha T, Findl O, Bauer P, Schmetterer L. Medical interventions for primary open angle glaucoma and ocular hypertension. Cochrane Database Syst Rev. 2007(4):CD003167.
8. Krupin T, Liebmann JM, Greenfield DS, Ritch R, Gardiner S. A randomized trial of brimonidine versus timolol in preserving visual function: results from the Low-Pressure Glaucoma Treatment Study. Am J Ophthalmol. Apr 2011;151(4):671-681.
9. Rolim de Moura C, Paranhos A, Jr., Wormald R. Laser trabeculoplasty for open angle glaucoma. Cochrane Database Syst Rev. 2007(4):CD003919.
10. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. May 2012;153(5):789-803 e782.