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Glaucoma - the thief of sight

Glaucoma - the thief of sight

You may have glaucoma but you’re far from alone. Around 30,000 other New Zealanders have this condition. If it is not treated, glaucoma can impair your eyesight. However when glaucoma is recognised and treated early, loss of sight may be prevented. The average person over the age of 40 has about a 1% chance of developing glaucoma. However, those who have a parent with glaucoma have alot greater chance of developing the disease. Everyone over 40 should be checked for glaucoma at least every five years, and those with a family history more frequently. You probably have many questions about glaucoma and its treatment. At Eye Institute we’re always happy to answer your questions at any time. But in the meantime, we hope this booklet will help you understand the condition. Modern glaucoma treatments are very effective. Understanding the disease will help you to follow the glaucoma management programme prescribed for you.

 

Cataract Surgery Information
Diabetic Retinopathy
Dry Eyes or Sjögren’s Syndrome
Epiretinal Membranes
Eyelid Surgery and Appearance Medicine
Glaucoma - the thief of sight
Flashes & Floaters and Retinal Detachment
Implantable Contact Lens FAQ's
Keratoconus
Laser Capsulotomy
Macular Degeneration
Macular Hole
Pterygium & Pinguecula
Retinal Vein Occlusions
Vitrectomy Surgery

FIGURE 1: ANATOMY OF THE EYE
Eye Anatomy

How your eye works
The eye functions much like a camera. The cornea is the clear tissue at the front of the eye. Through the cornea you can see the iris, which is the coloured part of the eye. The black hole in the centre of the iris is the pupil, which can vary in size to regulate the amount of light entering the eye. The lens is located behind the pupil and cannot be seen without amicroscope.

The cornea and the lens combine to focus light rays on to the retina at the back of the eye. The retina converts the light into electrical impulses which then pass up the optic nerve to the brain.

The front part of the eye is filled with a fluid which is called aqueous humour. Its production, and drainage out of the eye are controlled so that the eye is maintained within a normal pressure range. In glaucoma the pressure is often (but not aways) raised, usually because of abnormalities in the drainage canal. The place where the optic nerve leaves the eye is called the optic disc, and this can be seen in the eye using specialist instruments. An abnormal-looking optic disc is an early sign of glaucoma.

 

NORMAL OPTIC DISC
Optic Disc
GLAUCOMATOUS OPTIC DISC
Glaucomatous Optic Disc
Glaucoma - a disease of the optic nerve
Each optic nerve is made up of almost a million fibres which originate in the retina. In glaucoma, some of these nerve fibres become damaged. This results in blind areas in the vision which in the beginning affect the peripheral or side vision. If not treated, more and more nerve fibres become affected, causing a shrinkage of the field of vision which leads to tunnel vision and eventually to blindness. Fortunately this rarely occurs if glaucoma is treated early.

Types of Glaucoma

  • Open-angle glaucoma - This is by far the most common type and is what we have been discussing so far. Early detection and treatment are the best way to prevent loss of vision.
  • Acute closed-angle glaucoma - This occurs when there is a sudden blockage of the drainage canals in the eye. As a result, the pressure builds up rapidly causing blurred vision, coloured halos around lights, headache, and often severe pain. This is an emergency situation since the rapid increase in pressure can severely damage the optic nerve in a few hours.
What Glaucoma is NOT
  • Not some kind of cancer or tumour
  • Not an infection
  • Not caused by too much reading or reading in poor light
  • Not caused by improper diet
  • Not caused by wearing contact lenses
How do you know if you have Glaucoma? 
Glaucoma has been called the sneak thief of sight. There is nothing that you will notice until the defects in the side vision are obvious to you and by that time they may be very large or one of your two eyes may even be almost blind. That is why it is so important to be tested for glaucoma. Your eye specialist will suspect glaucoma if the pressure in your eye is abnormally raised or if there is an abnormal appearance to the optic disc. Raised pressure is caused by degeneration in the channels through which fluid drains out of the eye. The raised pressure causes gradual damage to the optic nerve fibres. However, glaucoma may occur even if the pressure is within the normally accepted limits (10-21 mmHg). Nevertheless, effective lowering of the pressure with either medications or surgery prevents glaucoma from worsening.

AN ABNORMAL VISUAL FIELD WITH ALMOST NO VISION ABOVE CENTRE.
ABNORMAL VISUAL FIELD
HEALTHY EYE
Healthy Eye Healthy Eye
UNHEALTHY EYE WITH GLAUCOMA
Unhealthy eye with Glaucoma Unhealthy eye with Glaucoma
Monitoring Glaucoma
Once your eye specialist has made diagnosis of glaucoma, you will have detailed tests of your side or peripheral vision. This test involves sitting in front of the machine and pushing a button when you see pinpoints of lights in your side vision, while you keep looking straight ahead.

You may also have a Heidelberg Retina Tomograph (HRT-II) performed to examine in detail your optic nerve. This may be one of the greatest technological advances in the management of glaucoma. It is a scanning laser camera that allows a 3-D topographic map to be created of your optic nerve. The HRT-II does not require the pupil to be dilated or the eye to be exposed to bright flashes. This specialised camera allows exact measurements to be made. This test can be repeated periodically and thus allow the earliest detection of any deterioration.

How is Glaucoma treated?
Strictly speaking, glaucoma cannot be cured, but it can be controlled so that further damage is slowed or halted. In the case of primary open-angle glaucoma, this requires a lifelong commitment to treatment and regular checks by your eye specialist. The aim of treatment is to lower the pressure in your eyes to a level at which further damage to the optic disc and to the visual field does not occur.

There are many treatment options for glaucoma, including eye drops, tablets, laser treatment and surgery. The safest and most effective choice will be discussed for each individual’s glaucoma.
  • Glaucoma Eye Drops
    To be effective, eye drops must be taken regularly and continuously. There is an increasing range of eye drops available which lower the pressure in the eye and thus slow or halt the progression of glaucoma. Some function by reducing the production of aqueous humour, while others increase its outflow. Some of these drops have a long duration of action and need to be used only once daily, while others need to be used twice or four times daily.

    Your doctor will advise you which drops are best for your individual situation. If the drops do not adequately control your glaucoma, stronger or additional drops can be tried.

    Many but not all cases of glaucoma can be controlled for a long time with appropriate eye drops. However if your glaucoma worsens despite using eye drops, then laser treatment or surgery may be needed.

  • Laser Treatment at Eye Institute 
    Laser trabeculoplasty is a relatively minor operation in which some of the blockages to the drainage canals are opened by focusing an intense beam of light on to the clogged drainage canals. The procedure is performed under local anaesthetic.

  • Glaucoma Surgery at Eye Institute 
    This involves creating a new channel for fluid to drain out of the eye. It is usually very effective in reducing the pressure in the eye and indeed after the surgery there may be no need for further medications.
Ongoing commitment
If you have glaucoma, it will be with you for the rest of your life. Fortunately there is now a wide range of treatments available to control the condition. However your role is crucial in taking the treatment advised and in maintaining regular follow-up checks indefinitely. After all, your eyesight is worth it. When glaucoma is diagnosed, your eye specialist will communicate with your general practitioner to advise of the treatment proposed. This is important, as glaucoma medications do enter the bloodstream, and may interact with other medications you are taking, or aggravate an important condition such as a heart problem or asthma.

If you have any questions, it is important that you ask us at Eye Institute. If one of our staff cannot help you straight away, they will pass your enquiry on to one of our specialists.