Age-Related Macular Degeneration
Age-related macular degeneration causes the loss of central vision and is the most common basis of loss of sight in people aged over 50. Central vision is concerned with objects straight in front of you and is involved in detailed activities, including reading, painting and sewing. Age-related macular degeneration (known as AMD or ARMD) does not affect peripheral vision, which is the ability to see things that are not straight in front of you. ARMD is a gradual condition and it usually progresses from objects being mildly blurred to more severe blurring of vision; there can become apparent a black patch in the centre of your field of vision, but it does not cause blindness. ARMD affects people in different ways. Some people develop symptoms over months while others will gradually experience a loss of vision over a period of years.
There are two types of ARMD: wet and dry. Wet ARMD tends to be more serious but easier to treat than dry ARMD.
About the macula
Age-related macular degeneration affects the macula, a tiny part of the retina, which is located at the rear of the eye. The macula contains the highest concentration of rods and cones, which allow people to see in the light (cones) and dark (rods). When you look at something light passes through the cornea and lens, before reaching the retina and focusing on the macula. A healthy macula processes the light and enables you to see a clear image.
Types of age-related macular degeneration
There are two forms of age-related macular degeneration, which are wet and dry. Dry ARMD tends to be much more common, accounting for around 85-90 percent of cases.
Dry ARMD occurs when the cells in the retinal pigment epithelium (RPE) become thinner, which is known as atrophy. The RPE cells are essential for the function of the rods and cone and if they start to deteriorate, the rods and cones will also begin to degenerate and cause problems with vision. Dry ARMD usually develops slowly and it can take several years for vision to become badly affected.
In patients with dry ARMD, tiny deposits called drusen form underneath the retina; these collect as a result of the cells in the RPE not functioning properly.
Wet ARMD is a great deal less common than dry ARMD accounting for only 10-15% of cases. Wet ARMD tends to be more serious than dry ARMD but it is often easier to treat. Wet ARMD develops much quicker than dry ARMD and the symptoms can become severe in a matter of months. In rare cases, when a blood vessel haemorrhages, loss of vision can develop in a period of days.
The condition occurs when the cells in RPE start to degenerate and new blood vessels grow from vessels in the choroid part of the eye. These new vessels are abnormal and break through another component of the eye, known as the Bruch’s membrane, into the macula causing damage to the rods and cones and subsequently affecting vision. The abnormal blood vessels are often fragile and there is a high risk of them leaking.
Wet and dry types of ARMD are classified according to the severity of the condition. Cases are diagnosed as either early stage, intermediate or advanced stage. Most cases of intermediate or advanced ARMD are caused by wet ARMD. Dry ARMD can also develop into wet ARMD.
Causes and risk factors
Dry ARMD is caused by the cells in the RPE not functioning properly. As a person ages the cells start failing to deliver enough nutrients to the rods and cones and clear enough waste, and this causes deposits called drusen to develop underneath the retina. In time the RPE cells and rods and cones deteriorate, which causes vision to become impaired.
Wet ARMD is caused by the deterioration of the RPE cells, as well as the development of new blood vessels, which are abnormal and have a high risk of leaking and bleeding.
It is not fully understood why the retinal cells stop working properly, but some risk factors have been identified. These include:
- Family history.
- High blood pressure (although evidence is not conclusive).
- Exposure to sunlight (although research is ongoing).
- Race: studies suggest that Caucasian people are more likely to develop ARMD than people from other races.
How common is ARMD?
ARMD is the most common type of macular degeneration and tends to affect older people. The risk rises with age and around 1 in 100 people aged between 65 and 75 have ARMD and 1 in 8 people over the age of 85 have severe ARMD (when loss of vision is serious). ARMD tends to be more common in women over the age of 75 than men of the same age.
If you develop ARMD in one eye there is a higher risk of you developing ARMD in the other eye; around 60 % of people develop the condition in both eyes.
Symptoms of ARMD
The most frequent signs of early stage ARMD is blurring in your central vision, which can make it more difficult to read, drive and do detailed activities. You may detect that you need a brighter light when reading or you experience blurring when reading or watching television and colours may also not be as bright. One important symptom to look out for is distortion, which is most commonly found when you look at straight lines and they appear wavy.
As the condition progresses you may also experience the following symptoms:
- Difficulty recognising faces.
- A blind spot in your central vision.
ARMD does not cause pain.
When should I seek help?
If you experience blurred vision, distorted vision or a loss of sight, you should arrange to see your doctor or an optometrist as quickly as possible. If you are over the age of 60 you should have regular routine eye tests, even if you do not experience any symptoms.
How is ARMD diagnosed?
If you have symptoms of ARMD you will be referred to an eye specialist (an ophthalmologist). They will ask you questions about your symptoms, examine the rear of the eye using an instrument called a strip lamp microscope and ask you to look at pictures, usually with straight horizontal and vertical lines. Your doctor will also take digital images of your eye, specifically the retina, and look for other symptoms related to ARMD.
If your specialist suspects that you have wet ARMD a test called fluorescein angiography will be carried out. This involves injecting dye into a vein in the arm. It enables the ophthalmologist to see whether the blood vessels leak the dye into the macula.
Another test, called ocular coherence tomography, may also be conducted. This test is becoming increasingly common as it can provide doctors with extremely detailed 3D images of the retina and macula. The images allow doctors to detect any abnormalities relating to the macula. The test is useful if a doctor is unsure if a patient has wet or dry ARMD.
Treatment for dry ARMD
At the moment there is no specific treatment for dry ARMD, but there are things that can be done to prevent further damage and optimise vision. These include giving up smoking, wearing sunglasses, eating a healthy, balanced diet and taking vitamin supplements. If you need information about dry ARMD you can contact the RNIB. Your local hospital eye department will also be able to provide support and you will be advised to attend regular appointments to enable doctors can keep an eye on your condition.
Treatment for wet ARMD
Treatments for wet ARMD can stop or slow the development of the condition and a new treatment called anti-VEGF drugs may even be able to reverse some loss of vision. Anti-VEGF drugs work by blocking the actions of a chemical called vascular endothelial growth factor and helps to stop the formation of new, abnormal blood vessels damaging the macula in people with wet ARMD. Examples of anti-VEGF drugs include pegaptanib, ranibizumab and bevacizumab. Other drugs are currently being developed and clinical trials are taking place. So far NICE (the National Institute for Clinical Excellence) has approved the use of ranibizumab.
Research suggests that ranibizumab improves vision in 1 in 3 people, preserves vision and prevents further degeneration in most people. However, around 1 in 10 people do not respond to the drug.
Photodynamic therapy: this therapy involves injecting a drug known as verteporfin into the arm. The drug then bonds to proteins in the abnormal blood vessels in the macula and once this has occurred, a light beam is shone into the eye activating the drug, which destroys the abnormal blood vessels. Photodynamic therapy is not suitable for everyone.
Laser photocoagulation: this therapy involves aiming a laser beam at the new blood vessels. The laser destroys the vessels and helps to prevent further damage to the eye. This procedure is only suitable for a small proportion of people and it also causes a permanent patch of black or grey to develop affecting vision.
Nutritional supplements: a special blend of vitamins and minerals has been found to be effective in the treatment of ARMD, which includes vitamins C, A, E, zinc oxide and cupric oxide. Two products containing this combination are currently licensed and available in the UK; they are Bausch and Lomb PreserVision and Viteyes Original.
Other treatments are currently being investigated and researched.
Coping with ARMD
It can be difficult to get used to having impaired or blurred vision. It is important to see a doctor or optometrist if you discern any alterations in your vision and always attend regular examinations. If you need additional help when reading use a magnifying glass and always ensure there is plenty of light. If you need help or information you can contact the RNIB or Macular Disease Society.
Here are some tips to try to prevent damage to your eyes and slow the progression of ARMD:
- Try to keep your eyes protected by wearing sunglasses when you go out.
- Give up smoking (if this is applicable).
- Eat a healthy, balanced diet.
- Try to lead a healthy lifestyle.
- See your doctor if you become aware of any changes in your vision.