Age-related Macular Degeneration (armd)
Macular degeneration is the name given to certain conditions affecting the retina, which causes loss of central vision. The macula is the small central part of the retina of the eye, which allows detailed vision. Age-related macular degeneration is the leading cause of legal blindness in people over the age of 60. Early onset macular eye degeneration is much less common. Diseases that are characterised by eye degeneration of some portion of the retina are difficult to describe because they occur in many variations and progress at different rates for different people. This page will generally explain macular eye degeneration to people who have the condition.
What is Macular Degeneration?
Macular degeneration is the name given for several similar conditions that are characterised by a breakdown of the macula. The macula is only about 3 to 5 mm wide and makes central vision, the vision directly in front of you, possible. It is responsible for visual acuity, which is the ability to see things clearly and discriminate the fine details of objects.
What is a Macular Hole?
Most macular holes develop in otherwise healthy eyes and are age-related. It also causes impairment of central vision (just like macular degeneration) and both eyes are affected in about 10% of cases. People who are very short-sighted are more prone to developing macular holes. Macular holes may also develop following ocular trauma.
Causes of Macular Degeneration:
There are two basic types of Macular Degeneration:
- Juvenile / early onset macular eye degeneration
- Age-related Macular Degeneration (AMD)
These are thought to have different causes. Juvenile Macular Degeneration appears to be largely genetic and is rare. With AMD, it is difficult to establish the cause, but there may also be genetic causes.
What are the symptoms?
It varies greatly and ranges in severity from one person to another. The most common symptoms are blurring of vision with particular difficulty discerning details, both up close and from a distance. It may cause blind spots, resulting in dark or empty areas in the centre of the field of vision. It may also cause distortions of lines and shapes and colour vision may be diminished. Peripheral and night vision usually remains unaffected.
Can AMD be prevented?
At present there is no known way to prevent the occurrence of AMD. There are many promising areas of research that one day may offer preventative therapies for AMD.
Does AMD lead to total blindness?
Most people with AMD do retain some peripheral vision, and they learn to optimise the use of their remaining vision. Each case differs, however many will be classified as "legally blind", with visual acuity of 20/200 or worse. Many people with mild forms of AMD may drive, but it is best to discuss your visual limitations with your eye care professional.
How is AMD diagnosed?
The early signs of AMD are usually detectable in a thorough eye exam, even before the disease begins affecting the vision. The tests include visual acuity measurement, the Amsler grid test, colour vision testing, optical coherence testing (OCT) and a Flourescein Angiogram (FA). FA allows the examiner to visualise the inner eye structures, by injecting a non-toxic dye (Fluorescein) into the patient’s arm. The dye moves through the bloodstream, including the blood vessels of the eye, showing up abnormal blood vessel growth and leakage from blood vessels.
Types of AMD:
Dry AMD: This is the more common type of AMD and accounts for 90% of AMD. It is characterised by the build-up of drusen (small yellowish deposits) beneath the macula. The layer of photoreceptor cells in the macula begins to die, resulting in distortion of vision when reading. Dry AMD usually does not cause total loss of reading vision.
Wet AMD: This accounts for 10% of patients with AMD. In wet AMD, new abnormal blood vessels begin to grow beneath the macula. These blood vessels may leak fluid and blood, and then cause the choroids and retina to deteriorate. This causes the retinal layer to blister under the macula, and the photoreceptor cells to degenerate. At this stage there is marked disturbance of vision in the affected eye.
Risk factors relating to AMD:
These include a history of hypertension (high blood pressure) and/or cardiovascular disease, smoking, a family history of AMD, hyperopia (farsightedness), light skin and eye colour, and cataracts. The presence of these risk factors in people with AMD has been noted, but the relationship of the various factors to the disease itself has not been systematically studied and it is not clear as to why the links are present. Both men and woman are at equal risk for AMD.
Family patterns have been observed, indicating that inheritance is involved to some extent. Some surveys have estimated that 15 to 20% of AMD patients have one or more first-degree relatives who are also affected.
Research estimates that 25% of Caucasians over the age of 65 may be affected by AMD. It is one of the most common problems affecting the retina, and as the population enjoys a longer life, the number of those affected by AMD will increase as well.
How quickly does AMD progress?
Most cases progress very slowly over a period of years. However, wet AMD typically progresses far more rapidly than dry AMD.
Is there any treatment for AMD?
Macular degeneration surgery has made some breakthroughs with the use of Laser photocoagulation. This can help some people with wet AMD. In this treatment, laser light rays are directed into the eye and focused on a small spot on the retina. The laser destroys the abnormal blood vessels growing beneath the macula and seals leaking areas. This treatment cannot restore vision already lost from AMD, so it is critical that it be applied as early as possible, before vision impairment has progressed. A badly damaged macula will not benefit from laser treatment. Laser photocoagulation is only suitable for a minority of patients and is not appropriate for patients who have blood vessel growth at the centre of the macula.
Photodynamic therapy (PDT) with Avastin or Lucentis injection is a treatment modality that may benefit some cases of wet AMD. PDT reduces the risk of further vision loss, and cannot restore vision already lost. Early treatment leads to better outcomes.