Age-related Macular Degeneration (AMD)

What is the macula?

The macula is the area at the very centre of the retina. About 5 mm across, it is the most sensitive and important part of the retina - responsible for what we see directly in front of us. We need a healthy macula to see fine detail when reading and writing. It is the part of the retina which sees colour best. The ‘optical centre’ of the macula is the fovea which is the area responsible for sharpest vision.

In order to understand AMD it is helpful to know a little about the normal structure of the retina.

The retina is made up of a number of layers;

1. The neural retina – consisting of light sensitive cells (photoreceptors - rods and cones) and the nerves that connect them to the brain
2. The retinal pigment epithelium (RPE) – this layer of cells removes waste products from the retina and provides nutrients for the retina.
3. Bruch’s membrane – this is the tissue which separates the RPE cells from the underlying blood vessels in the layer of the eye known as the choroid.

Healthy retina:

What is Age-related Macular Degeneration?

As its name suggests, AMD is a degenerative condition of the macula linked to getting older. It is the most common cause of loss of vision in patients aged over 65 in the developed world. Broadly speaking, AMD can be divided into two types: “dry” and “wet”.

Dry AMD

This is the most common form of AMD (90% of cases) and is caused by degeneration in the RPE layer. When the RPE is damaged, waste products from the photoreceptor cells build up under the RPE (these yellowish/white deposits are known as drusen). The overlying photoreceptors begin to die and the central vision slowly deteriorates.

Wet AMD

This accounts for approximately 10% of cases of AMD. In “wet” AMD, a weakness in Bruch’s membrane allows small blood vessels from the choroid to grow either under the RPE or between the RPE and the photoreceptors. If fluid leaks from these abnormal blood vessels, or if they rupture and bleed, the macula will suddenly become damaged. Liquid under the retina causes elevation and stretching of the macula, resulting in distortion of the vision; straight lines becoming “wavy” and twisted.

AMD usually involves both eyes, although one may be affected long before the other. Wet and dry AMD are not completely separate conditions and in fact many patients have a combination of dry and wet AMD.

What are the symptoms?

Often the symptoms of AMD are not recognised when only one eye is involved, as the normal sight in the better eye compensates for the loss of sight in the affected eye. In the early stages your central vision may be blurred or distorted, with objects looking an unusual size or shape and straight lines appearing wavy or fuzzy. This may happen quickly or develop over several months. You may actually see lights, shapes and colours that are not there. Age-related macula degeneration is not painful. As AMD affects the centre of the retina people with advanced AMD will often notice a blank patch or dark spot in their central vision. This makes reading, writing and recognising small objects or faces difficult.

AMD almost never leads to total blindness because only the central retina is affected therefore the side (peripheral) vision is spared. This peripheral vision is extremely valuable as it allows patients with AMD to get around and keep their independence.

What can you do to minimise the risk of developing AMD or to slow the progression of AMD?

Risk factors for developing AMD include the following;

• smoking
• circulatory diseases and hypertension
• poor diet, especially one which is deficient in carotenoid rich vegetables, such as spinach, peas, beans, tomatoes, curly kale.

Vitamins in AMD

Patients often ask whether taking vitamin supplements can help if there is a risk of AMD. While we know that a healthy diet is likely to help there have been some very large scientific studies in recent years that have given us guidelines about vitamin supplementation. The Age-Related Eye Disease (AREDS) study conclusively showed that high doses of anti-oxidant vitamins (B,C and E) together with zinc could reduce the risk of serious vision loss in the second eye of about 28% of patients who had already lost their central vision from wet AMD in their first eye. For this reason, ophthalmologists are likely to recommend taking appropriate vitamin supplements if there is a high risk of wet AMD. If you smoke or have stopped smoking in the last 5 years there might be an increased risk of lung tumours while taking the AREDS vitamins and your ophthalmologist will discuss this with you so that an alternative supplement might be recommended.

What should you do if you think you have AMD?

Patients over the age of 40 should have regular eye tests every 1 -2 years. If your optician sees any early signs of AMD they may suggest early referral to an ophthalmologist. Careful consideration of your diet is also reasonable but early AMD signs do not require extra vitamin supplements.

If you have macular drusen you should be prepared to test your central vision in either eye separately from time to time (perhaps once a month). The easiest test is to make sure each eye can still read quite small print with your reading glasses on. It is also useful to check for any signs of distortion - where straight lines become wavy. This can be done by looking at a window or door frame, some graph paper or a special chart which your optician may recommend to you - known as an Amsler chart. Any abnormlities should be reported to your optician without delay and if there is concern they will refer you to an ophthalmologist.

Patients who are suspected to have early wet AMD should see an ophthalmologist within a few days of the first onset of symptoms to try to minimise any chance of significant loss of vision.

At the eye clinic

Your ophthalmologist will take a detailed medical history from you, test your vision and have a careful look at your macula after using eye drops to dilate both pupils. If required, they can arrange further investigation – usually a fluoresecin angiogram to look for signs of leaking blood vessels. Results of the angiograms are usually immediately available and a decision can be made about further treatment.

Treatments for Wet AMD

There are a number of treatment options for wet AMD. The recommended treatment depends exactly on the type of wet AMD that you have and is a highly specialised area.

Treatments include:-

1. Conventional laser treatment. This has been used for a number of years and has been appropriate for patients who have blood vessel leakage well-away from the fovea.
2. Photo Dynamic Therapy (PDT). This is a newly-established treatment where a low power invisible laser is used to treat leaking blood vessels which have been filled with a special photo-sensitive dye called Verteporfin (Visudyne). The dye is injected into an arm vein and shortly after the laser treatment is applied. The laser will selectively close the diseased leaking vessels and not damage neighbouring healthy retinal tissue.
3. Macugen. This is a new drug that is not yet widely available. This drug is a special chemical that is injected into the eye under local anaesthetic where it will prevent growth of leaking vessels in the macula. At the time of writing it has results that are similar to PDT but it may be useful in a wider range of patients.
4. Lucentis (ranibizumab). This is another new drug similar to Macugen that is still going through the trial phases. Early results are more encouraging than Macugen with a significant number of patients experiencing improvements in vision that can be maintained for 2 years. This drug is not yet licensed for use in Europe. Both Macugen and Lucentis will require government approval before being made available on the NHS.
5. There are a number of other agents which are being studied at the moment including Anecortave, Avastin and Triamcinolone. It is possible that these treatments might be used in combination with any of the above and there is likely to be much refinement of treatment with time.
6. Surgery. Known as Macular Translocation (MT 360), surgery for macula degeneration is highly specialised and is designed to move a healthy piece of undamaged retinal pigment epithelium to replace the damaged tissue at the macula. The surgeon has to create a retinal detachment, move the underlying RPE and re-attach the retina so that the fovea lies on an area of healthy RPE. Successful surgery has been reported in a number of centres in the UK and the USA with preservation of vision good enough to read. However, surgery is highly complex and not guaranteed to work. It is considered for patients who have only one eye which will not respond to any other form of medical treatment. There will be a careful discussion of the risks and possible benefits before embarking on this type of treatment.

There have been many developments in the treatment of AMD in recent years and these are expected to increase in pace over the coming decade. It is important that patients receive up-to-date consultant advice about treatment of AMD from retinal specialists should they suffer onset of blurred or distorted eye sight.