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Macular Degeneration (AMD)

The macula is a name for the central part of the retina. The retina is the light sensitive membrane at the back of the eye. The retina converts light into nervous impulses. These are taken away from the eye in the optic nerve to the brain. In the brain the impulses are processed into our vision. The central retina (macula) is the most sensitive part of the retina. It is the part we use for detailed vision, colour perception and reading.


The retina is one of the most active tissues in the body. The macula is the “busiest” part of the retina and because of this as we age it is more prone to malfunction. This malfunction manifests as a degeneration and as it affects mainly older people is called “age related macular degeneration” or AMD. There are two main types of AMD, dry and wet

 

Dry macular degeneration

This is by far the most common type of AMD, 90% of all cases are the dry type.  Essentially the layers of the central retina start to atrophy (wither). One of the earliest changes is accumulation of cellular debris in the deep layers of the macula. These accumulations look like multiple pale yellow spots and are called drusen. People with drusen often have perfectly normal vision.

However a proportion of people with drusen will start to notice their vision, especially reading vision, slowly deteriorating. As the macula atrophies their central vision worsens and they have difficulty recognising people’s faces. Parts of the macula look pale and atrophied along with other areas appearing pigmented. At its worst the affected eye cannot read at all. The peripheral vision always remains intact.

Drusen Dry AMD
Drusen Dry AMD

Dry AMD often affects both eyes though usually one side is worse than the other. Some people eventually end up with both eyes severely affected. However even then the peripheral vision is normal. They can get around and never go into a world of darkness.

A major problem for many people with AMD is driving. If the better eye falls below the driving standard they cannot continue to drive. It is that person’s legal responsibility to ensure they attain the visual standard whilst continuing to drive. The DVLA can advise on this.
There is no treatment that can reverse the process and give back the detailed vision. There are many ways to make the most of the remaining peripheral vision. Up to date glasses can help a little, though they won’t return the vision to normal. Glasses are the equivalent to the lens in a camera; if the film is damaged (like the retina in AMD) simply changing the lens will not fix the picture. If there is a cataract, surgery for this may improve the vision and is often worth considering. However even successful cataract surgery will not return the vision to normal. Optical aids such as magnifying glasses or telescopes can help with reading. Opticians can provide these aids and check for cataracts, so it’s important to keep up to date with eye tests.

Some studies have shown that taking certain vitamins can help slow down the course of AMD. The affect is not major and they cannot reverse whatever damage has already been done. Tiny telescopic devices can be implanted in the eye (like an implant in cataract surgery). Some people find these helpful but by no means all. None of the new treatments for wet AMD (see wet AMD) have any effect in people with dry AMD.

If both eyes are affected and the reading vision falls below a certain limit, people with dry AMD can be eligible to be registered partially sighted or even blind. Once again this does not mean they are in a world of darkness, it does mean they are entitled to extra help. There are many national and local organisations that can help someone to get the help they need such as the Derbyshire Association for the Blind www.dab.org.uk/

Wet macular degeneration

Wet macular degeneration (wet AMD) is a different disease process to dry AMD. In some people’s central retina, the constant stress of the visual process stimulates the overproduction of certain chemicals. These chemicals are growth factors (known as VEGF) that promote the growth of blood vessels. Unfortunately the resulting vessels are in the wrong place and are also abnormally frail. As they grow, unlike normal retinal blood vessels, they leak fluid into the retinal layers. This fluid distorts the retinal layers and results in distorted central vision, one of the early symptoms of wet AMD.  Frequently these frail vessels bleed into the retinal layers as well. Once there is blood in the retina, scar tissue starts to form and this usually results in permanent loss of the central vision. The whole process tends to be more rapid and severe than dry AMD. Drusen (see dry AMD) can be a feature of the wet type too.

Wet AMD

Wet AMD

Drugs have been developed that neutralise these growth factors. These drugs are known as anti-VEGF agents.  In order to work the drug has to be injected into the eye. Once working repeated injections are required, often over a period of years. In appropriate cases they are effective in stopping the disease getting worse, occasionally reversing the process and improving vision. The treatment does not work in every case however.

One of the earliest symptoms of wet AMD is distortion. Straight lines such as window frames appear distorted. If this starts to happen you should arrange to see your

Optician urgently. If they suspect wet AMD they will contact the eye department and arrange an appointment. Derby offers a full macular degeneration service. Once referred, the macula (central retina) is checked for the presence of fluid. A special photographic test (fluorescein angiogram) involving a dye being injected into the arm is used to look for abnormal blood vessels. If wet AMD is confirmed and deemed suitable for treatment, an injection of anti-VEGF drug into the eye will be arranged. Surprisingly this is nowhere near as painful as it sounds. You will be monitored closely over the next few months to ensure the treatment is working. Repeated injections are usually required.

If the treatment fails or is inappropriate, the resulting visual loss is much the same as for severe dry AMD. The peripheral vision is unaffected and the eye never goes into a world of darkness. As in AMD optical aids can help with reading though it will always be difficult.

Useful link: www.rnib.org/Pages/Home.aspx

 

General eye problems

Adult Squint
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AMD
/
Presbyopia and normal ageing of the eye
/
Cataract
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Cataract FAQ's
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Refractive surgery of the lens and correction of presbyopia
/
Dry eye
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Glaucoma
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Retinal Vein Occlusion

 

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