Glaucoma

Glaucoma is a condition in which the pressure within the eye is elevated.  If untreated, it can damage the optic nerve and lead to blindness.  Since the optic nerve is relatively strong, it can often withstand years of elevated eye pressure before damage occurs.  However, once damage is done, it is irreversible.

There are two sorts of glaucoma: gradual onset (chronic) and sudden onset (acute).  Chronic glaucoma is the most common form and usually has no symptoms until an irreversible loss of vision has occurred.

Incidence; Causes and Development

Chronic glaucoma usually occurs after the age of 35 years but is sometimes seen in children.

The front of each eyeball is filled with a watery fluid called the aqueous humor, which is continually produced and drains from the front of the eye through a small channel.  An increase in pressure can result either from too much fluid being produced or from too little draining away: glaucoma is almost always due to the latter.

The cause of chronic glaucoma usually is unclear.

Other causes include blockage of a vein in the eye, tumors or pupil dilation.  When the pupil dilates, the drainage channel gets blocked: an attack of acute glaucoma can be brought on by anything that causes the pupil to dilate, such as dim lighting, certain eye drops and some medications such as various types of antidepressant medicine.

Signs and Symptoms

Loss of vision initially affects only the extreme edges of one's field of view; if the raised pressure is not treated, the impairment of vision spreads and can cause blindness.

Patients with chronic glaucoma experience a very gradual increase in eye pressure that slowly damages the optic nerve, resulting in a slow-but-progressive loss of vision.  Usually both eyes are affected and the visual loss may not be immediately apparent since it starts at the edges of the field of vision.  However, if it is not treated, it can eventually cause blindness.

In those with acute or 'closed-angle' glaucoma, symptoms start suddenly and usually affect only one eye.  Initially, there may be a slight decrease in vision, the appearance of colored halos around bright objects and pain in the eye and head.  After a few hours the symptoms become much more severe with rapid loss of vision and sudden, severe throbbing pain in the eye.  The eyelid swells and the eye becomes red and watery, with a dilated pupil that doesn't respond to light by closing, as it should.  There may be nausea and vomiting.  Although most symptoms disappear after treatment with medication, there may be some remaining loss of peripheral vision.  Attacks can re-occur, and if they do, each one tends to further reduce the field of vision.

Diagnosis and Tests

Glaucoma is diagnosed by measuring the pressure of the fluid in the eyeball: the intraocular pressure.  This is usually done with a tonometer, of which there are two basic types.  The simplest uses a puff of air blown against the surface of the eye.  More commonly, a Goldman tonometer is used, as this gives more accurate measurements.  To use this, the eye specialist will put some drops in the eyes.  These may sting slightly to start with but then the surface of the eye becomes numb.  Using a microscope, the tonometer is then brought in close so that it lightly touches the surface of the eye.  The procedure takes only a moment or two and is painless.  During an attack of acute glaucoma, the diagnosis is usually easily made.  However, in chronic glaucoma it is sometimes necessary to make a series of measurements over time to confirm the diagnosis.

There are some other tests that may be done.  Firstly, using an ophthalmoscope (an instrument with a bright light), the optic nerve at the back of the eye will be observed.  Secondly, a patient's visual fields may be examined by having them look straight ahead at a central point and say when they see a spot of light appear at the side.  Finally, the eye may be examined with a contact lens with a tiny mirror attached.  Eye drops are used to numb the surface of the eye first.  This examination may take 5 to 10 minutes.

Prognosis

Most people with glaucoma respond well to treatment.  Intraocular pressure can usually be controlled by the regular and sustained use of eye drops and medication, preventing any further loss of vision.