Macular degeneration is a degenerative disease of the retinaThe retina is the receptor of light at the back of the eye. It fulfils the same function as the film in a film camera or the image sensor in a digital camera. The retina translates the images into electrical signals that are sent via the optic nerve to the visual cortex in the brain, where it is interpreted as the images we see. See Info on Eyes – Anatomy., which affects the macula. The macula is the small central part of the retina, which is responsible for sharp visual acuity in the center of the visual field. This condition is the most prevalent after the age of 60 years. Early or juvenile onset macular degeneration is a less common.
There are two basic types of age-related macular degeneration (AMD)
This is the most common form. It is also known as atrophic, non-exudative or drusenoid macular degeneration. This type accounts for 90% of macular degenerations. It is characterized by the build-up of drusen (small yellow lipofuchsin deposits) beneath the retina within the macular area. As a result, the overlying layer of photoreceptor cells within the macular area starts to atrophy, or die, as the cells break down.
It is also known as choroidal neovascularisation, subretinal neovascularisation, exudative form, or disciform degeneration. Wet AMD accounts for ten percent of patients with AMD. It is characterized by abnormal blood vessel growth beneath the macula, within a potential space between the retina and a thin layer of tissue called the choroid. The choroid is the main source of oxygen supply to the retinal photoreceptors, and it is the only blood supply for the macula. New, fragile blood vessels develop which may leak fluid and bleed, which may lead to a deterioration of the choroid and retina.
The symptoms of macular degeneration vary greatly and range in severity. The most common symptoms are:
- Blurring of vision with particular difficulty discerning details, both up close as well as at distance.
- Blind spots, resulting in dark or empty areas within the centre of the field of vision.
- Distortion of lines and shapes.
- Diminished colour.
- Unaffected peripheral, as well as night vision.
To obtain a clinical diagnosis, the interior of the eye is examined through the dilated pupil with special lenses. In addition to this, a number of diagnostic tests may be performed. These include:
- Visual acuity tests.
- The Amsler grid test (which is used to locate and verify the extent and severity of sight loss – these areas of visual loss are called scotomas).
- Colour tests (which can help to determine the functional status of your cone photoreceptor cells).
- A dark adaptation test (which will measure how well your eyes adjust to different lighting conditions).
- A fluorescein angiogram (which allows inner eye structures to be visualised). A non-toxic dye is injected into a blood vessel in the patient's arm. The dye is then carried through the bloodstream, including the blood vessels of the eyes. Serial photos or video-angiography of the macula and retina are then taken in quick succession, which is used to identify new blood vessel growth as well as leakage from blood vessels within the eye. New blood vessel growth is a feature of wet age-related macular degeneration, which is explained in detail in the section below describing the different forms of macular degeneration.
- An indocyanine green angiogram (ICG), which is very similar to a fluorescein angiogram. This test differs in that it enables the ophthalmologist to obtain images from the choroidal vasculature, which lies beneath the retina. The choroid may often not be fully visible by means of a fluorescein angiogram.
- 'Blue Peak' autofluorescence. This examination is done by means of illuminating the retina with a very special blue laser. It enables the ophthalmologist to visualize pathology within the retinal pigment epithelium (RPE).
- An Optical Coherence Tomography (OCT). This ultra-modern test utilizes the properties of light, bouncing back from the retina when projected onto it. It is a non-invasive test which provides visual information on the various structures within the eye, and can be used as a standalone test, or in conjunction with a fluorescein angiogram, ICG or autofluorescence test.
Can macular degeneration be prevented?
At present, there is no treatment or cure for retinal degenerations. There are many promising areas of research that one day may offer preventative therapies for macular degeneration. For now, the most important thing one can do is to have regular eye examinations, which may allow these conditions to be detected and diagnosed early. As mentioned above, we are able to detect what the status of your retina is by using special instruments and tests. One of the important goals is to prevent the progression of macular degeneration from the dry to the wet form. The following may prove useful:
- Avoid intense, bright sunlight. Good quality sunglasses, hats and visors can help people to protect their eyes from the sun. It is postulated that ultra-violet light plays a central role in the development of macular degeneration.
- Cigarette smoking has been linked in some studies to an increased risk for the development of AMD. It is recommended that persons stop smoking to decrease their chance of developing AMD.
- If the diagnosis of dry AMD is established, it is of utmost importance to avoid progression to wet AMD. A simple way to monitor your vision is by using an Amsler grid. During a consultation with us, the use of this tool will be explained in detail, and the symptoms of progression will be discussed to allow the patient to seek help at an early stage of development of wet AMD. It is possible to prevent, or at least significantly retard, progression from dry to wet AMD with current technology.
Most people with macular degeneration only lose their central vision, but do retain some peripheral vision. Each case differs. However, many will be classified as 'legally blind'.
There is currently no effective treatment for dry AMD. There is no evidence that laser treatment is of any value for people with these conditions.
The treatment options may be categorized in two categories:
1. Supportive management
This mainly entails the use of low vision aids. These may be divided into optical and non-optical aids.
- The white cane is probably the most visible aid, and some people with macular degeneration find it a useful navigational aid when their vision loss progresses beyond a certain stage. The cane is a form of non-optical aid; that is, it does not have an actual effect on your eyes, although it may help you 'see' or cope with vision loss. Other non-optical aids include guide dogs, audiotapes, and large print books.
- There are also electronic aids. These include closed-circuit televisions (CCTV), reading machines, and talking computers. An increasing number of computer programmes are addressing the needs of the visually impaired, making it possible to easily enlarge type on the screen or provide an audio or Braille version to go with what is shown on the screen.
Optical aids are devices that work to improve vision to some extent. These include Corning and NOIR glasses, the Fresnel prism, telescopes and magnifiers. With advancing technology, some of these devices are becoming increasingly sophisticated and offer new opportunities to people with retinal degenerations to maximize their available vision.
To determine which aids may be most useful, it is suggested to undergo a thorough low vision evaluation from a specialist in the field. One may also contact the RP Foundation of South Africa for more information on low vision services.
Orientation and mobility training may also be provided in addition to the use of low vision aids.
2. Treatment aimed at the prevention of further deterioration.
- Laser photocoagulation: This may be beneficial to patients with wet AMD. A laser beaim is directed into the eye and focused the area of pathology within the macula. The abnormal blood vessels growing beneath the retina are destroyed with the laser, which then seals leaky 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 due to wet AMD. A badly damaged macula will not benefit from laser treatment.
- Intra-ocular injection of special medication. The latest addition to the ophthalmologist's armamentarium to treat sub-retinal neovascularization, is the injection of anti-VEGF (vascular endothelial growth factor) substances. It has been established that choroidal neovascularization occurs in response to a cascade of chemical mediators within the eye. A variety of new drugs have been developed in recent times to block the proliferation of abnormal blood vessels in the eye. Although still in it's infancy, this methodology holds great promise for the treatment of AMD.
- The implantation of an intra-ocular Fresnel prism lens. In patients with stable forms of AMD and a functioning area in the para-macular region, the implantation of an intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options. with a built-in prism may be of benefit. In these eyes, the retinal image is directed away from the affected retina, onto an area of the macula that still functions. This may lead to displacement of the scotoma, and an improvement in visual acuity.
- Surgical removal of choroidal neovascularization, subretinal blood and rotation of the retina. Various surgical techniques have been developed to remove subretinal pathology. Although some improvement and stabilization of lesions have been demonstrated, these interventions have proved not to be the first line of management, and are reserved for cases with special indication. The outcomes with these interventions were reserved in the past.
- The implantation of electronic micro-chips and retinal stem cells. These are among the fields of ongoing research (please see below).
Through the efforts of the International RP movement, a number of highly qualified scientists are working full-time on macular degeneration and other diseases of retinal degeneration. With the financial support from various RP Foundations, clinical specialists and laboratory scientists are working at more than 40 medical and research institutions in the USA, Europe and South Africa, on more than 110 research projects related to retinal degeneration.
Antioxidants and Vitamin Therapies
One working hypothesis is that a cause or contributing factor to macular degeneration involves the formation of chemicals in the body called free radicals. Free radicals are thought to result, in part, from exposure to sunlight and other forms of ultraviolet light. They cause cellular damage by taking electrons from molecules in healthy cells. This process, called oxidation, has been linked to a variety of health problems including heart disease and cancer. Substances called antioxidants may counteract the oxidation process; the body produces its own antioxidants, and these are helped by antioxidants that we ingest through food or vitamin supplements. Vitamins C, E and carotenoid, including beta-carotene, are examples of potent antioxidants. However, it is unknown which of these are helpful to AMD.
The work investigating a link between vitamins and macular degeneration is still in its preliminary stages. Recommendations regarding nutritional supplementation and light avoidance for patients with macular degeneration are expected to emerge from studies now in progress.
Retinal stem cell transplantation
The transplantation of retinal cells has shown some encouraging results in animals studies, although it is important to emphasize that this is not a treatment modality available for use in humans. Retinal stem cell transplantation is still in it's preliminary stages of investigation in the laboratory. Before a procedure can be tested in humans, long-term beneficial effects must be proven and possible side effects must be determined. Such research may take several more years.
The good news is that studies so far have found that when photoreceptor cells are transplanted into the retinas of animals, some features of normal photoreceptors are either maintained or developed after transplantation. However, there is no conclusive evidence that retinal cell transplants or similar procedures in animals with a retinal degeneration, will result in long-term improved or restored vision in humans. Nevertheless, the research done so far has been promising enough for the American Foundation Fighting Blindness to expand a grant award programme aimed at scientists who are investigating several areas of basic science that could lead to new therapies that might repair or replace damaged retinal cells.Also visit: www.mdsupport.org