Macular Degeneration
AMD damages the part of the retina responsible for central vision and for seeing fine detail, and makes it difficult to see small details of objects. Side vision is not affected. If both eyes are affected, reading and other tasks requiring fine vision may become very difficult, but because side vision remains, people with AMD can usually take care of themselves.
AMD is the result of ageing processes in the eye. Some of the layers of the retina thicken and waste material which is usually removed from the retina forms deposits, distorting the retina. This distortion can cause damage to the other layers of the retina. In about 10 per cent of cases, new blood vessels grow into the macula from beneath. These newly-formed (neovascular) vessels are fragile and often leak blood into the retina, where the blood causes scar tissue to form. The scarring severely blocks central vision. Other forms of macular degeneration are inherited and not associated with ageing.
Age-related macular degeneration is the major cause of vision impairment and blindness in Australia for people over the age of 50. Early AMD occurs in about 14 per cent of those aged 55 to 64 years, 18 per cent of those aged 65 to 74 years, and 30 per cent of those aged over 75 years. Men and women are equally affected. AMD accounts for almost 50 per cent of legal blindness and up to 70 per cent of seriously impaired vision in people over the age of 70 years.
People with AMD may notice that they can no longer read as quickly as previously even with their reading spectacles, or they may notice that their vision has deteriorated. Many patients do not realise that they have a problem until their vision becomes blurred. Optometrists perform a number of tests in an examination, which enable them to detect the presence of AMD in the early stages.
The optometrist examines the macula carefully with a range of specialised instruments such as an ophthalmoscope, retinal camera or slit-lamp with a high-powered lens. These instruments allow examination of the interior of the eye, including the macula. Sometimes the optometrist may place a drop in the eye to dilate the pupil to get a better view of the internal structures. Through the ophthalmoscope the optometrist will look for changes in the macula, such as accumulation of waste material or new blood vessels.
Another test that may be used is a grid pattern known as an Amsler chart. This is a regular grid that looks like a piece of graph paper. Patients with AMD often report that sections of the grid appear to be distorted or missing.
Optometrists will usually refer patients whom they suspect have AMD to an ophthalmologist (eye surgeon) for confirmation of the diagnosis. The ophthalmologist may perform a test called fluorescein angiography. In this test a fluorescent dye is injected into the patient’s bloodstream and the ophthalmologist observes the progress of the dye through the blood vessels in the retina. This reveals any leaking blood vessels.
Recent advances in treatment of the early stages of neovascular AMD involve injection of anti-VEGF (vascular endothelial growth factor) substances that prevent the formation and growth of abnormal blood vessels. This is the first treatment of AMD that has been shown to improve vision in some cases but complete or permanent resolution of abnormal blood vessels is not possible. The treatment needs to be repeated as part of ongoing management of the disease. Associated risks of anti-VEGF treatment include formation of cataract and ocular inflammation.
Photodynamic therapy (PDT) is a well-established treatment for vascular forms of AMD. Laser surgery may be used where new blood vessels have appeared in the macula area. A focused, intense beam of laser light is used to seal leaking blood vessels and prevent new vessels growing. This treatment is most effective when it is applied in the very early stages of the disease, before extensive damage has been done.
There is little that can be done to cure AMD, particularly in its more advanced stages. One study found that antioxidant vitamin and mineral supplementation assisted in halting the progression of AMD in a small percentage of patients. These supplements should be taken under the supervision of a health care professional as they may be associated with harmful effects.
People with AMD can be helped to continue functioning normally. Many will eventually be classified as having low vision. Help in the form of low vision devices is available from optometrists and specialist low vision clinics. Low vision devices enable patients to make the most of their vision and include miniature telescopes, high-powered reading spectacles, hand-held and stand magnifiers, closed circuit televisions and other simpler aids such as large-print books.
For treatment of AMD to be effective, it must be diagnosed as early as possible. Regular eye examinations are the key to early detection of retinal changes and other signs of disease. If you notice any change in the quality of your vision, have your eyes examined immediately. Regular examinations are particularly important for people over the age of 50 years and people whose families have a history of eye problems. Other important preventative measures include minimising exposure to UV light and cigarette smoke, both of which are associated with AMD. A low-fat diet rich in green leafy vegetables, nuts and fish may be beneficial in reducing the impact of AMD.