Glaucoma is defined as a progressive optic neuropathy causing damage to optic nerves that result in visual field defects.

The disorder is progressive in nature and is usually associated with increase in intraocular pressure (normal intraocular pressure ranges from 1020mmHg).

Therefore, management of glaucoma aims at decreasing the raised intraocular pressure which can be achieved either by reducing aqueous humour formation (formed by ciliary process) or improving the drainage (figure).

The aqueous humour is formed by ciliary process and drained mainly by trabecular meshwork.

Types of Glaucoma

Chronic Simple Glaucoma : It is a genetic disorder, characterised by a gradual increase in the intraocular pressure. In this condition, the potency of trabecular meshwork is affected.

Acute Congestive Glaucoma : It is generally seen in patients having a shallow anterior chamber and a narrow iridocorneal angle, who use mydriatics (eye drops bringing about dilation of the pupil). This condition is a medical emergency, which, if once under control is treated either surgically or by laser iridotomy.

Drugs

Following drugs are used for the treatment of glaucoma (table) :

Osmotic Agents : These agents reduce the intraocular pressure by drawing fluid from the eye into the circulation via osmotic effect. Mannitol (conc. of 20% ) administered by IV infusion with a dose of 1.5 g/kg body weight and glycerol (conc. 50% ) administered orally with a dose of 1.5 g/kg are the commonly used osmotic agents.

Carbonic Anhydrase Inhibitors : These agents include acetazolamide (oral, IV), dorzolamide (topical), and brinzolamide (topical). They act to reduce the intraocular pressure by decreasing the formation of aqueous humour. They inhibit the enzyme carbonic anhydrase non-competitively.

For treating patients with acute congestive glaucoma, acetazolamide is administered either IV or orally. However, for patients with chronic simple glaucoma, topical carbonic anhydrase inhibitors are preferred over systemic carbonic anhydrase inhibitors. This is because the topical agents have a considerably lesser risk of systemic side effects.

β-Adrenergic Blockers : These agents include timolol, betaxolol, levobunolol, carteolol, and metipranolol administered topically.

For treating patients with glaucoma, timolol is widely used because:

1. It lacks properties of a partial agonist or a local anaesthetic.
2. It has no effect on the size of the pupil or accommodation.
3. Its action lasts for a longer duration.
4. It is easily tolerable.
5. Its topical preparation is safe and very effective.

β-blockers should be used cautiously or contraindicated in bronchial asthma and heart failure.

An example of a selective β₁-blocker used for treating glaucoma is betaxolol. However, it is not as effective as the non-selective agents. It has a protective effect for retinal neurons. Levobunolol is an example of a long acting adrenergic β blocker.

Prostaglandins (PGs) : For the initial treatment of open-angle glaucoma, topical PGs like latanoprost and bimatoprost (PGF₂α analogues) are preferred. These agents have longer duration of action, high efficacy, and low incidence of systemic toxicity.

These agents are also used for treating acute congestive glaucoma. They facilitate uveoscleral outflow and thus reduce intraocular pressure. A combination of latanoprost and timolol is also available. Generally these agents do not produce systemic side effects; however they may result in ocular irritation and pigmentation of the iris.

Miotics : These are used to treat acute congestive and open angle glaucoma. Pilocarpine, a tertiary amine is used as a mitotic agent. It is administered topically and is absorbed well through the cornea. It decreases intraocular pressure by the drainage of aqueous humour.