Medical treatment in glaucoma management

The main aim of therapy in glaucoma management is reduction of IOP. There is now good evidence from multiple large randomised trials that reducing IOP is effective in preventing disease progression in ocular hypertension, primary open angle glaucoma, and even in so-called normal tension glaucoma. Target pressures in the low teens are associated with the lowest progression rates.

βblockers ( for example, timolol, levobunolol, carteolol, betaxolol, and metipranolol)

These reduce the secretion of aqueous and are still the most commonly prescribed topical treatment. Contraindications to their use include a history of lung or heart disease, as the drops may cause systemic β blockade. It is important to be aware that topical βblockers can unmask latent and previously undiagnosed chronic obstructive airway disease in elderly people. Systemic effects from eye drops can be reduced by occlusion of the punctum (finger pressed on the caruncle, which can be felt as a lump at the inner canthus of the eye) or shutting the eyes for several minutes after putting in the drops.
This reduces the lacrimal pumping mechanism and stops the eyedrops running down the lacrimal passages and being absorbed systemically via the nasal mucosa or by inhalation directly into the lungs. This may also enhance ocular absorption of the drugs. These drops are usually given twice a day, but long acting forms now available can be given once a day, either alone or in combination with other drops.

Prostaglandin analogues ( for example, latanoprost, travoprost, and bimatoprost)

These reduce the IOP by increasing aqueous outflow from the eye via an alternative drainage route called the uveoscleral pathway. It is possible to get reductions in IOP of up to 30–35% with these drugs. This ability to achieve larger reductions in IOP with improved systemic safety profiles has been a major therapeutic advance in glaucoma. Systemic side effects are minimal but an unusual side effect in a few patients with light irides is a gradual, permanent darkening of the iris. Patients often notice that their eyelashes increase in length and darken. For optimum effect, these drops are used once daily (at night).

Sympathomimetic agents

Topical adrenaline, once commonly prescribed, is now rarely used because of lack of efficacy compared with βblockers and adverse effects on the conjunctiva. A newer generation of agents that stimulate the  receptors of the sympathetic system is now used—for example, brimonidine (used twice a day) or apraclonidine. Contraindications include cardiovascular disease, because of the potential systemic sympathomimetic effects.

Parasympathomimetic agents ( for example, pilocarpine)

These constrict the pupil and “pull” on the trabecular meshwork, increasing the flow of the aqueous out of the eye. The small pupil may, however, cause visual problems if central lens opacities are present. Constriction of the ciliary body causes accommodation and blurred vision in young patients. Pilocarpine should not be used if there is inflammation in the eye, as the pupil may stick to the lens close to the visual axis (posterior synechiae) and affect vision. Pilocarpine is usually administered four times a day but can be used twice daily in a combined form with a βblocker, or once at night in a gel preparation, which reduces side effects. When patients first instill pilocarpine they often experience a marked brow ache, which tends to reduce with longer term use of the drug.

Pilocarpine therapy can increase the risk of retinal detachment. Carbonic anhydrase inhibitors These are available as topical (for example, dorzolamide, brinzolamide) or oral (for example, acetazolamide) agents. They reduce the secretion of aqueous, and the systemic form, administered orally, is the most powerful agent for reducing IOP, although unfortunately it may have side effects, including nausea, lassitude, paraesthesiae, electrolyte disturbances, and renal stones. The topical form has minimal systemic side effects. Carbonic anhydrase inhibitors should not be used in patients with sulphonamide allergy.

Neuroprotective agents

Experimental evidence exists that some neuroprotective agents may reduce intraocular pressure induced glaucomatous damage. However, at present there is no conclusive evidence that these agents are helpful in glaucoma, but large scale clinical trials are currently being carried out in this area.

Allergy to glaucoma drops

The main symptoms of drop allergy are intense itching and irritation of the eyes and eyelids, which are exacerbated by instillation of the drops. The characteristic signs of drop hypersensitivity include red injected eyes, red swollen eyelids, and ezcema like excoriation of the eyelids and periocular skin.

The patient may be hypersensitive to the active glaucoma drug or one of the preservative agents used to stabilise the preparation (usually benzalkonium chloride).

The diagnostic test for drop hypersensitivity is controlled cessation of therapy. Symptoms and signs should rapidly improve on withdrawal of the topical therapy. When patients are on multiple topical agents it can be difficult to isolate the agent responsible for the allergic reaction. In cases of allergy to the preservative agent in the drugs, some topical drugs used in glaucoma management are available in preservative free form.

Some frequently asked questions about glaucoma

• Q: What is childhood glaucoma and how can I prevent the disease from progressing?

A: Childhood glaucoma, also known as infantile or congenital glaucoma, is a disease of infants and is sometimes inherited. It involves a developmental abnormality of the trabecular meshwork, which is the drainage tissue of the eye. Treatment options include medications to lower intraocular pressure and/or anterior chamber angle surgery. Some patients may also need other types of glaucoma surgery. The goal of treatment is to lower the intraocular pressure to prevent permanent visual loss. It is also important to monitor the visual function and to treat any delay in the affected eye’s visual development.

• Q: I have been given a variety of eye drops in a failed attempt to control elevated eye pressure that was apparently caused by retinal vein occlusion in my left eye. I had many problems with the eye drops, including a terribly upset stomach, nausea, indigestion, heartburn and gas. My doctor changed my prescription to Xalatan and Timolol. I have noticed that the pupil in my left eye has become significantly larger than the pupil in my right eye, which is not being treated. Can Timolol cause this symptom and is it safe to continue to use it?

A: Timolol is a topical beta-blocker that acts to reduce intraocular pressure and is very commonly prescribed for the treatment of glaucoma. Timolol has not been shown to cause pupillary dilation. The size of your left pupil may be related to the prior retinal vein occlusion. Other causes of pupillary dilation include topical medications, iris neovascularization, prior intraocular surgery, and others. Your eye doctor should be able to determine the cause of your pupillary asymmetry.

• Q: Is it true that glaucoma patients cannot take medications like Actifed or Sudafed for relief of cold symptoms because they can cause a dangerous increase in eye pressure?

A: Cold medicines such as Actifed and Sudafed can cause mild pupil dilation, which can affect eye pressure. Patients with very narrow angles or untreated angle-closure should not take cold medications. Patients who have been treated for narrow-angle glaucoma or open-angle glaucoma can take cold medicines safely. Your eye care provider should be able to advise you as to the safety of this medication class in your particular case.

• Q: My husband is 36 years old and was just diagnosed with early-stage glaucoma in his left eye. There is no history in his family. Why did he develop this condition and will he be OK? He is now being treated with eye drops. Can you help me?

A: Primary open-angle glaucoma is a multifactorial disease that can affect patients in their 30s. Some patients have no family history of the disease. Glaucoma that affects only one eye may be related to other conditions such as trauma and pseudoexfoliation. Glaucoma that is detected in the early stages carries a better prognosis than glaucoma that is diagnosed at an advanced stage. Treatment involves reduction of the intraocular pressure and monitoring of the optic nerve function. With diligent treatment and follow-up, your husband should maintain vision throughout his lifetime.