HEALTHNET

Vision Thief - Glaucoma

Glaucoma is not necessarily caused by elevated intraocular pressure, but in most cases, glaucoma is related to intraocular pressure.

(Posted on 9 November 2006)

Glaucoma is the collective term for a group of clinical conditions of the eye which can cause permanent damage to the retina and optic nerve. Initially, glaucoma affects visual field. If left untreated, the condition can lead to irreversible blindness. Nowadays, glaucoma is a leading cause of blindness.

Causes of Glaucoma

Glaucoma is not always associated with an elevation in intraocular pressure. However, elevated pressures are a risk factor for the development of glaucoma. Intraocular pressure is mainly regulated by the amount of fluid in the anterior chamber of the eye. Such fluid, known as aqueous humor, is generated by the ciliary body and passes through the pupil and into the anterior chamber angle and is drained from the bloodstream. If the outflow of aqueous humor is blocked and the aqueous humor is not properly drained, the pressure within the eye will increase and this may result in damage to the retina and optic nerve, affect vision and cause glaucoma.

Types of Glaucoma

Primary open-angle glaucoma

It is associated with a relative obstruction to aqueous humor outflow, which in turn causes the intraocular pressure to increase. This is the most common types of glaucoma. It is a chronic progressive disease of insidious onset and is usually asymptomatic until it has caused a significant loss of visual field.

Primary angle-closure glaucoma

This may be of acute or chronic type. There is a closure of the anterior chamber angle and the aqueous humor cannot be drained, leading to elevated intraocular pressure. The symptoms include painful eyes, nausea, vomiting, blurred vision, and appearance of haloes around lights. Redness of the eye and a cloudy cornea may occur too.

Normal tension glaucoma

In this type of glaucoma, the intraocular pressure is within the normal. However, there may be increased susceptibility to optical disc damage at normal intraocular pressure. The visual field may be affected.

Secondary glaucoma

This type of glaucoma result from other ocular conditions or disorders, such as severe cataracts, internal bleeding of the eyeball, and diabetes. In addition, improper use of steroids may cause glaucoma.

Congenital glaucoma

This occurs in babies and children. The inborn eye lacks a normal aqueous humor drainage system. Symptoms include larger than normal eyes, murky vision, photophobia and lacrimation.

Treatment of Glaucoma

There is no treatment for glaucoma but intraocular pressure can be reduced and vision may be preserved by the use of eye drops, oral drugs, laser surgery or aqueous humor shunt surgery. As regards medication treatment, drugs which reduce the production of aqueous humor include beta-blockers, carbonic anhydrase inhibitors and alpha adrenergic agents. Drugs which accelerate the drainage of aqueous humor include prostaglandin analogs and miotics. In case the intraocular pressure is too high and has to be reduced significantly, patients may have to use more than one type of eye drops.

Source: Hong Kong and Drug Education Resources Centre, The Society of Hospital Pharmacists of Hong Kong