Age related macular degeneration (AMD) most commonly affects people who are over the age of 50. By the age of 75, 30% of people have signs of early AMD and 7% will have more advanced AMD. Currently there are approximately 240,000 people in the UK who have visual impairment caused by AMD.
The exact cause of AMD is not yet known. However, several factors are associated with the condition. AMD is more common in women than men, but probably because women live longer than men. Some genes have been associated with the development of AMD. This has come to light in families where several generations have been affected. However, not all AMD is thought to be inherited. Smoking greatly increases the chance of developing AMD and some studies have suggested that high levels of ultraviolet light throughout life may also be associated with an increased risk of developing AMD. There is no agreement on the influence that diet may have on the development of AMD, but there is some evidence that vitamins A, C, and E, as well as zinc, may slow the progression of AMD in some people.
The macula is a tiny part of the retina, the inner lining of the back of the eye, which is only the size of a pin head. This area has a high concentration of specialised cone photoreceptor cells, which have the role of discerning fine details, necessary for reading and for recognising colour. When this area is damaged by AMD, the central vision becomes distorted and the ability to read diminishes.
Types of AMD
There are two types of AMD, ‘dry’ and ‘wet’. Dry AMD is the more common type and usually develops very slowly. At worst, a blank patch develops in the middle of the vision but the surrounding retina works normally. Eventually reading vision may be poor but total blindness does not occur.
Wet AMD is similar to dry AMD in that the macular function becomes poor, affecting the ability to read. However, the difference is that in wet AMD the blood vessels behind the retina start to grow new, unstable branches to try to improve the problem. Unfortunately, these new blood vessels grow in the wrong place and cause bleeding and swelling of the retina. The swelling is responsible for the distortion caused by AMD and the blood leads to scar tissue formation and loss of vision.
The diagnosis of AMD is usually made opticians, either because the vision has rapidly worsened or become distorted (especially in cases of wet macular degeneration) or has been found incidentally by the optician due to a reduction in the quality of vision which has been more subtle (especially in cases of dry AMD).
The optician will then organise an appointment with a Consultant Ophthalmologist for further tests. It is common practice now to have an OCT scan of the retina at this second appointment to measure the thickness of the retina to assess whether there is any abnormal fluid within the retina. This test is often complemented by a fluorescein angiogram. This second test involves taking photographs of the retina following the administration of an injection of fluorescein dye into a vein on the back of the hand.
Currently there is no treatment for dry macular degeneration, but fortunately it usually progresses very slowly. A number of treatments are now available for wet AMD, with the aim of stopping the growth of new blood vessels in the retina. The most important recently available treatment is an anti-vascular endothelial growth factor (anti-VEGF) drug called Lucentis. Lucentis works by blocking the chemical messengers which stimulate the growth of new blood vessels in the retina. This stabilises the AMD as the vessels no longer bleed. There is another anti-VEGF drug called Avastin, which although successfully used in the treatment of AMD is not licensed for this purpose.
Lucentis is given by injection into the eye, a procedure which has very little discomfort associated with it. The injections are given on a monthly basis until the AMD is stable. Usually the anti-VEGF injections have a high success rate and for most stop the vision from getting worse. Approximately 40% of people see an improvement in their vision.
Anti-VEGF treatments are the first treatment used for wet AMD. However, if the response is not adequate then another form of treatment should be considered. Photodynamic therapy uses a combination of a cold laser light shone onto the abnormal blood vessels combined with an intravenous injection of a light sensitive drug called Verteporfin. The laser light activates the Verteporfin which seals off the abnormal blood vessels.