Glaucoma Health Article

Definition

Glaucoma refers to a group of disorders that lead to damage to the optic nerve, the nerve that carries visual information from the eye to the brain. Damage to the optic nerve causes vision loss, which may progress to blindness. Most people with glaucoma have increased fluid pressure in the eye, a condition known as increased intraocular pressure.

Alternative Names

Open angle glaucoma; Chronic glaucoma; Closed angle glaucoma; Congenital glaucoma

Causes, incidence, and risk factors

Glaucoma is the second most common cause of blindness in the US. There are four major types of glaucoma:

• Open angle (chronic) glaucoma
• Angle closure (acute) glaucoma
• Congenital glaucoma
• Secondary glaucoma

All four types of glaucoma are characterized by increased pressure within the eyeball, and therefore all can cause progressive damage to the optic nerve. Open angle (chronic) glaucoma is by far the most common type of glaucoma.

The front part of the eye is filled with a clear fluid called the aqueous humor. This fluid is constantly made in the back of the eye. It leaves the eye through channels in the anterior (front) chamber of the eye, and eventually drains into the bloodstream. The channels that drain the aqueous humor are in an area called the anterior chamber angle, or simply the angle.

In open angle glaucoma, the channels in the angle gradually narrow with time, making it hard for the fluid to drain properly. The buildup of fluid causes increased pressure in the eye. This increased pressure pushes on the junction of the optic nerve and the retina at the back of the eye, reducing the blood supply to the optic nerve.

As the optic nerve deteriorates due to decreased blood supply, blind spots develop in the field of vision. Peripheral (side) vision is affected first. This is usually not noticed until quite a bit of vision is lost. If the disease is not diagnosed and treated, a lot of vision may be lost before the person becomes aware of a problem.

Open angle glaucoma tends to run in families. Your risk is higher if you have a parent or grandparent with open angle glaucoma. People of African descent are at particularly high risk for this disease.

Angle closure (acute) glaucoma is caused by a shift in the position of the iris of the eye that suddenly blocks the exit of the aqueous humor fluid. This causes a quick, severe, and painful rise in the pressure within the eye (intraocular pressure). Most people with angle closure glaucoma will also have redness and swelling in the affected eye. Nausea and vomiting may occur. Angle closure glaucoma is an emergency. This is very different from open angle glaucoma, which painlessly and slowly damages vision.

If you have had acute glaucoma in one eye, you are almost certainly at risk for an attack in the second eye, and your doctor is likely to recommend preventive treatment.

Dilating eye drops and certain systemic medications may trigger an acute glaucoma attack if you are at risk.

Secondary glaucoma is caused by other diseases, including eye diseases such as uveitis, systemic diseases, and drugs such as corticosteroids.

Congenital glaucoma, which is present at birth, is the result of abnormal development of the fluid outflow channels of the eye. Surgery is required for correction. Congenital glaucoma is often hereditary.

Symptoms

OPEN ANGLE

• Most people have no symptoms
• Gradual loss of peripheral (side) vision

ACUTE

• Severe eye pain, facial pain
• Decreased or cloudy vision
• Red eye
• Swelling of the eye
• Pupil does not react to light
• Nausea and vomiting (may be the major symptom in the elderly)

CONGENITAL

• Tearing
• Sensitivity to light
• Red eye
• Enlargement of one eye or both eyes
• Cloudiness of the front of the eye

Signs and tests

An examination of the eye may be used to diagnose glaucoma. However, checking the intraocular pressure alone (tonometry) is insufficient because eye pressure changes. Examination of the inside of the eye by looking through the pupil, often while the pupil is dilated, is needed.

Usually a complete examination of the eyes will be done.

Tests may include:

• Retinal examination
• Intraocular pressure measurement by tonometry
• Visual field measurement
• Visual acuity
• Refraction
• Pupillary reflex response
• Slit lamp examination
• Optic nerve imaging (photographs of the interior of the eye)
• Gonioscopy- use of a special lens to see the outflow channels of the angle