UNDER PRESSURE!

GLAUCOMA

Glaucoma is a disease that is usually, but not always, associated with elevated pressure within the eye, in which damage to the main nerve of the eye, the optic nerve can lead to loss of vision and even blindness. In some cases, it can occur in the presence of normal eye pressure, and is then thought to be caused by poor blood flow to the optic nerve.

There are many different types of glaucoma. Most, however, can be classified as either open-angle glaucomas, which are usually chronic, or closed angle glaucomas, which can occur suddenly (acute) or over a long period of time (chronic). Glaucoma usually affects both eyes, but can progress more rapidly in one eye than in the other.

Signs and Symptoms

Glaucoma is often called the “sneak thief of sight” because eye pressure can build up and destroy sight with no obvious symptoms in the early stages.Peripheral vision (side vision) decreases as the disease progresses, until one is left with tunnel vision and irreversible nerve damage. The eyes appear normal to the patient and those around him. On examination, the optometrist will identify elevated intraocular pressure, optic nerve abnormalities or peripheral visual loss.

On the other hand, the symptoms of acute angle-closure glaucoma are often dramatic, with the rapid onset of severe eye pain, headache, nausea and vomiting, and visual blurring.The eyes of patients will appear red, and the pupil of the eye may be large and nonreactive to light. The cornea may appear cloudy to the naked eye.

Causes

Elevated pressure in the eye is the main factor leading to glaucomatous damage to the optic nerve. The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is constantly being produced, flowing through the pupil, and draining through tiny channels. If the drainage channels become blocked or too much fluid is produced in the eye, the pressure in the eye becomes raised. Because the eye is a closed system, it cannot remove the increased fluid. Pressure builds upand damage to the optic nerve may result.

Risk Factors

Because there are no early symptoms, regular eye examinations and awareness of your own risk factors are paramount for early detection and successful treatment. While everyone is at risk for glaucoma, certain people are at a higher risk and need to be checked more frequently. Risk factors include a family history of glaucoma, diabetes, a high degree of short-sightedness, history of injury to the eye, and long term use of cortisone (steroids).

Diagnosis

There are several painless tests that can be done by your optometrist to determine the intraocular pressure, the status of the optic nerve, drainage angle, and visual fields:

Tonometry determines the pressure in the eye by measuring the tone or firmness of its surface.

Pachymetry measures the thickness of the cornea. After the eye has been numbed, the pachymeter tip is touched lightly to the front surface of the eye.

Gonioscopy is done by numbing the eye and placing a special type of contact lens with mirrors on the eye. This allows the optometrist to examine the drainage angle and drainage area of the eye.

Ophthalmoscopy is an examination in which the optometrist looks directly through the pupil into the eye. This procedure is done to examine the optic nerveat the back of the eye. Special cameras can be used to take photographs of the optic nerve to compare changes over time.

Visual field testing maps the visual fields to detect any early (or late) signs of glaucomatous damage to the optic nerve. Visual fields are measured by a computer one eye at a time. A computerised map of the visual field is produced, outlining the areas where the eye can or cannot see.

Optic nerve tomography and nerve fibre analysis create a three-dimensional image of the optic nerve to evaluate the nerve fibre layer and better evaluate optic nerve damage.

All of these tests are repeated at regular intervals to assess the progress of the disease and the effect of the treatment.

Treatment

Early diagnosis and treatment is the key to preserving the sight in people with glaucoma. Although nerve damage and visual loss cannot usually be reversed, glaucoma can generally be controlled. It is usually treated with eyedrops, although lasers and surgery can also be used. Most cases can be controlled well with these treatments, thereby preventing further nerve damage and loss of vision.

One or more types of eye drops may have to be used several times a day to lower intraocular pressure. These work by either reducing the production of aqueous fluid or increasing the drainage of fluid from the eye.

World-wide research is constantly being conducted in the area of glaucoma. Increased efforts to enhance public awareness of glaucoma, screenings for those individuals at risk, earlier diagnosis and treatment, and better compliance with treatment are our best hopes to reduce vision loss from glaucoma.