Glaucoma

Glaucoma is the name given to a group of eye diseases, all of which have in common damage to the optic nerve in the back of the eye. Elevated pressure inside the eye is the most frequent risk factor for glaucoma development, although a small percentage of eyes will develop glaucoma with normal eye pressure. If left untreated, glaucoma will damage the vision, initially by constricting the peripheral visual field. Later, it can lead to blindness. When detected early, treatment will prevent or reduce the loss of vision in most patients.

 

The fluid inside the front of the eye is constantly being produced by the ciliary body behind the pupil. It flows through the pupil into the anterior chamber of the eye, and drains out of the periphery of the iris through the trabecular meshwork. This is a dynamic process that maintains eye pressure within a narrow range throughout the day. If the rate of fluid production exceeds the rate of fluid drainage then the eye pressure increases. This, in turn, can result in damage to the delicate fibres in the optic nerve that join the eye to the brain.

 

Glaucoma

Glaucoma

 

Glaucoma is diagnosed based on a combination of features including family history, visual acuity, intraocular pressure readings, corneal thickness (pachymetry), gonioscopy (examining the trabecular meshwork in the front of the eye using a mirrored contact lens), and visual field testing, plus other ancillary tests that examine the optic nerve in more detail using techniques such as laser, ultrasound or polarised light. In some cases, the diagnosis is straightforward. In other cases, particularly early in the course of the disease, the diagnosis may not be certain; a review at a later time may be needed to definitively diagnose or exclude glaucoma.

 

Open-Angle Glaucoma

This is the most common form of glaucoma and usually develops slowly over many years. It often runs in families. There is no pain associated with this condition and, as it develops slowly, most people are unaware of its presence. This is the reason regular eye examinations are so important, particularly if you have a family history of glaucoma, as well as for everyone over 50 years of age.

 

In open-angle glaucoma, the rate of fluid draining through the trabecular meshwork is reduced and the eye pressure slowly rises. This can be treated with eye drops that reduce the rate of fluid production in the eye (beta-blockers, alpha-agonists, carbonic anhydrase inhibitors) or that increase the fluid drainage out of the eye (prostaglandin analogues, miotics). Laser to the trabecular meshwork is another way of increasing fluid drainage out of the eye and is simple, safe and effective.

 

If open-angle glaucoma progresses, despite eye drops and laser, then surgery may be required to create an alternative pathway for fluid to drain from the eye. This procedure is known as trabeculectomy.

 

Angle-Closure Glaucoma

This type of glaucoma usually causes a sudden elevation of the eye pressure due to blockage of the fluid drainage through the pupil into the front of the eye. If this occurs, the affected eye may become acutely painful and the vision quickly becomes blurred. This will often be accompanied by nausea and vomiting. Treatment of an attack of angle-closure glaucoma is an emergency, as permanent damage to the optic nerve can result within hours of onset due to the high levels of eye pressure involved.

 

Treatment of acute angle-closure glaucoma involves the use of intensive pressure-lowering eye drops, tablets, and laser to the iris to bypass the blockage in the eye. If these measures are unsuccessful, emergency surgery may be needed. Examination of the eye prior to an attack of angle-closure glaucoma may reveal the future likelihood of such an event and a prophylactic laser treatment (iridotomy) can be performed to prevent an attack.

 

Congenital Glaucoma

Failure of the structures in the front of the eye to develop normally may result in elevated intraocular pressure in an infant. Enlargement and discoloration of the cornea, or tearing may be the earliest signs. This type of glaucoma is usually treated with surgery.

 

Secondary Glaucoma

Elevated intraocular pressure can occur if other eye diseases are active in an eye.

 

  • Uveitic glaucoma occurs in eyes that experience prolonged inflammation.
  • Pigmentary glaucoma occurs in eyes where the pigment on the back of the iris is rubbed off over time as the iris dilates and constricts on top of the natural lens of the eye. This pigment then blocks fluid from draining out of the eye through the trabecular meshwork, leading to high eye pressure.
  • Neovascular glaucoma occurs when abnormal blood vessels grow inside the front of the eye in response to vascular diseases in the back of the eye such as retinal vein occlusions and diabetes. The abnormal blood vessels block the trabecular meshwork leading to very high eye pressure. Neovascular glaucoma can be very challenging to treat.
  • Pseudoexfoliation glaucoma (often abbreviated to PXF or PEX glaucoma) occurs when a dandruff-like material is produced in the front of the eye. The material blocks fluid drainage through the trabecular meshwork. This type of glaucoma has a strong genetic component.

 

Illustrations shown are provided courtesy of the Royal Australian and New Zealand College of Ophthalmologists (RANZCO) and Mi-Tec Publishing. The complete RANZCO patient education pamphlet is available from your ophthalmologist