Cataracts are the clouding of the lens inside the eye. Most cataracts form as a normal part of getting…
What is macular degeneration?
Macular degeneration (MD) is a group of eye conditions in which the central retina (called the macula) is damaged. This can make it difficult to read and see fine detail. Because peripheral (side) vision is not affected, MD does not cause total blindness. MD usually occurs in people over 50 years of age. It is the leading cause of serious vision loss in Australia. Due to the ageing population, the number of people with MD is likely to increase significantly over the next few decades.
Damage that occurs to the macula in MD is related to ageing processes in the eye that lead to damage of the retina. The retina is a thin layer of tissue that lines the inside of the back of the eye. Rather like the film in a camera, the retina contains cells that pick up light and send signals to the brain so that you can see.
The retina contains two zones:
- The macula - a very small section in the centre of the retina that processes very fine detail. This is the part of the retina that is important when you read, and;
- The peripheral retina - which processes most of your vision. This part of the retina is important for seeing the big picture and for being able to move around. If the peripheral retina is damaged, it can result in tunnel vision.
There are two types of MD: dry and wet.
Cause of dry MD
The light-sensing cells of the retina produce waste material. Usually this waste material is removed from the retina, but over time it can accumulate and form small yellow deposits, called drusen. This can lead to patches of the light-sensing cells being damaged and distortion of the retina.
Cause of wet MD
In wet MD, blood vessels from the layer beneath the retina grow into the macula. Because the blood vessels are new, they tend to leak blood and fluid, and this damages the light-sensing cells and causes scarring of the retina.
Risk factors for macular degeneration include:
Because MD is associated with the ageing process, symptoms are rare before the age of 50 and much more common in people over the age of 75.
Having family members who have MD increases the risk of developing the condition.
Smoking causes damage to delicate eye structures including the retina. It can cause the onset of MD and increase the rate at which the condition progresses.
Diet has been associated with the risk of developing MD. People whose diets contain a lot of high-glycaemic carbohydrates have been shown to be more likely to develop MD than people who eat low-glycaemic diets. Nutrients that may help to reduce risk of developing MD include:
- Omega-3 fatty acids (oily fish such as salmon, trout and sardines);
- Lutein and zeaxanthin (a range of vegetables, particularly dark leafy greens such as spinach, silverbeet and kale);
- Zinc (nuts, legumes and seafood);
- Vitamin E (nuts and wholegrains);
- Vitamin C (citrus foods, tomatoes and berries), and;
- Selenium (some nuts, particularly brazil nuts).
Signs and symptoms
Symptoms of MD can include:
- Difficulty with activities involving fine detail such as reading or sewing;
- Distorted central vision (for example, straight lines may appear wavy), and;
- Blank or dark spots in your vision.
In its early stages, symptoms of dry MD may develop very slowly. However, symptoms of wet MD tend to develop more quickly and vision problems associated with this form of the condition tend to be more severe.
Methods for diagnosis
Regular eye examinations by an optometrist or ophthalmologist can detect early signs of MD. If an optometrist is concerned that you may have signs of MD, they will refer you to an ophthalmologist for further examination. In some of the tests below, eye drops that dilate the pupil may be necessary. These drops can blur vision for several hours afterwards and driving is generally not recommended during this time.
Visual acuity measures the ability to see fine detail. Tests usually involve reading letters off a chart (to test distance vision), or a card (to test near vision).
You may also be asked to look at a small hand-held card with a central target and a grid. This is called an Amsler chart and can be used to detect distortion of vision (in which straight lines appear wavy).
Ophthalmoscopy is used to view the back of the eye, in particular the optic disc (the end of the optic nerve) and the retina. Eye drops may be used to dilate the pupils to improve visualisation of the eye. In some cases, a photograph of the back of the eye may be taken to record the appearance of the retina and help your ophthalmologist or optometrist monitor any progression of MD.
Fluoroscein angiography involves taking photographs of the back of the eye, after a small amount of fluorescent dye has been injected into the bloodstream, usually into a vein at the elbow. The dye makes it easier to see any blocked or leaking blood vessels in the retina or the choroid (two layers at the back of the eye).
Optical coherence tomography (OCT)
OCT is an imaging technique that reveals the thickness and structure (cross-sections) of the central retina. It can be used to assess and monitor changes in the retina due to MD.
Types of treatment
There is no cure for MD; however, treatment can help to slow or prevent the condition getting worse. Unfortunately, once significant damage has occurred to the retina, it is usually not possible to restore normal vision, although some treatments can lead to improvement in vision. For people with significant vision loss, a variety of low-vision aids and products are available to help with reading and other daily tasks. Low-vision clinics and services can offer advice on which products may be most suitable and provide support for people adapting to life with vision loss. Other treatments depend on the type of MD and how far it has progressed.
Treatment for dry MD
There is no current effective medical treatment for dry MD.
For people in the early stages of dry MD, regular monitoring by an optometrist or ophthalmologist may be all that is needed. Making sure your glasses prescription is up to date and having good lighting when you read or do close, fine-detail activities, such as sewing, can help to manage symptoms.
How often monitoring is needed will depend on your particular situation. Your optometrist or ophthalmologist may ask you to monitor your own vision regularly at home by using an Amsler chart.
People who smoke are usually strongly encouraged to stop as soon as possible. Because of the possible links between lifestyle and MD, maintaining a low-fat healthy diet and performing regular exercise may be suggested. Shielding your eyes from too much sunlight (ultraviolet light exposure) may also be recommended.
There is evidence that two particular combinations of vitamin supplements - known as AREDS and AREDS2 - may help to slow or prevent progression of MD in some people. These supplements are not suitable for everyone and may cause harmful side effects. Your doctor or ophthalmologist can advise whether they are suitable for you.
Treatment for wet MD
Anti-vascular endothelial growth factor (VEGF) medications
VEGF is a substance made by cells that encourages the growth of abnormal blood vessels. Anti-VEGF medications, such as ranibizumab, aflibercept and bevacizumab, can help to reduce blood-vessel growth that occurs in wet MD. Treatment cannot cure the condition, but can help to maintain vision for longer; some people also do experience improvement in vision.
These medications are injected directly into the eye and their effect is not permanent, so treatment will usually need to be repeated. Injections are usually done in an ophthalmologist's rooms, or as a day surgery procedure.
Laser photocoagulation treatment for wet MD focuses a small beam of light at the back of the eye to destroy and seal leaking blood vessels, and prevent new ones from forming.
Because the laser can damage tissue surrounding the blood vessels, complications of this treatment can include some vision loss, the extent of which will depend on how much treatment is required and where in the retina the blood vessels are situated. This treatment is used much less often now than in the past to treat wet MD.
Photodynamic therapy is a form of laser treatment for wet MD. It is combined with a light-sensitive medication that is injected into the bloodstream to help target the effects of the laser on abnormal blood vessels. It is sometimes used along with anti-VEGF medications. After treatment, you will need to avoid exposure to direct sunlight for 24-48 hours.
Treatments for wet MD can have complications that depend upon the stage of the condition and the type of treatment used. Your ophthalmologist can discuss any complications that may be relevant to you.
There is no cure for MD, but because peripheral (side) vision is not affected, it does not cause complete blindness. It can lead to low vision and, in some cases, legal blindness. For a person with MD, this will often mean a profound reduction in their ability to read, drive, or see fine detail, such as people's faces. However, their peripheral vision will allow them to get around and do many activities as they normally would.
MD cannot be prevented, but some risk factors can be limited. Regular eye examinations, particularly for people over the age of 50, can help to detect early signs of MD.
Other things you can do that may help reduce your risk include: