Macular Degeneration

February 2, 2017

Macular degeneration, also known as AMD, is a disease that affects the retina. If left untreated, is the leading cause of severe, permanent vision loss in Americans over 50. More than eight million people have earlier stages of AMD. This disease of the macula, the central and most sensitive part of the retina, can rob people of central vision. Left with only peripheral vision, they may struggle to identify faces, read books and watch TV, because they can see the side or peripheral vision, but not straight ahead.

The Eye

The retina is made up of two main layers. There is an inner layer of ‘seeing cells’ called rods and cones. These cells react to light and send electrical signals down tiny nerve fibres (which collect into the optic nerve) to the brain. The outer layer – the retinal pigment epithelium (RPE) – is a layer of cells behind the rods and cones. The RPE is an insulating layer between the retina and the choroid. These cells help to nourish and support the rods and cones. They pass nutrients from the blood vessels in the choroid to the rods and cones. They also take waste materials from the rods and cones to the blood vessels in the choroid. The RPE can be thought of as a filter, determining what substances reach the retina. Many components of blood are harmful to the retina and are kept away from it by a normally functioning RPE. The rods and cones are responsible for vision in different conditions. There are many more rods than cones, and rods are smaller cells than cones –

The cone cells (‘cones’) help us to see in the daylight, providing the basis for colour vision.
The rod cells (‘rods’) help us to see in the dark – ‘night vision’.

The macula is a small but vital area of the retina at the back of your eye. It is about 5 mm in diameter. The macula is the part of the retina that is the most densely packed with rods and cones. The macula is essential for central vision. In the middle of the macula is an area called the fovea, which only contains cones.

The choroid is a layer of tissue behind the retina which contains many tiny blood vessels. These help to take oxygen and nutrients to the retina.

Bruch’s membrane is a thin membrane which helps to form a barrier between the choroid and the delicate retina.

The sclera is the outer thick white layer of the eye.

When a person looks at an object, light from the object passes through the cornea, then the lens, and then hits the retina at the back of the eye. The light from the object focuses on the macula. A person needs a healthy macula for detailed central vision.

AMD is a condition that occurs when cells in the macula degenerate. This occurs with partial breakdown of the RPE and the cells become damaged and die. Damage to the macula affects your central vision which is needed for reading, writing, driving, recognising people’s faces and doing other fine tasks. The rest of the retina is used for peripheral vision – the ‘side’ vision which is not focused. Therefore, without a macula you can still see enough to get about, be aware of objects and people, and be independent. However, the loss of central vision will severely affect normal sight. There are two types – ‘dry’ and ‘wet’ AMD – described below.

People with macular degeneration gradually find it much harder to read, write, recognize faces and drive. The macula, or macula lutea (Latin: macula = spot + lutea = yellow) is an oval shaped yellow spot near the center of the retina of the eye.

Types of Macular Degeneration

There are two basic types of Macular Degeneration: “dry” and “wet.” Approximately 85% to 90% of the cases of Macular Degeneration are the “dry” (atrophic) type, while 10-15% are the “wet” (exudative) type.

Stargardt disease is a form of macular degeneration found in young people, caused by a recessive gene.

Causes

The specific factors that cause macular degeneration are not conclusively known, and research into this little understood disease is limited by insufficient funding. At this point, what is known about age-related Macular Degeneration is that the causes are complex, but include both heredity and environment. Scientists are working to understand what causes the cells of the macula to deteriorate, seeking a macular degeneration treatment breakthrough. They know the causes are not the same for Age-related Macular Degeneration as they are for Stargardt disease. Stargardt disease has a specific genetic cause in most cases, whereas AMD involves both genetic and environmental factors.

Risk Factors

Age is a major risk factor for AMD. The disease is most likely to occur after age 60, but it can occur earlier. Other risk factors for AMD include –

Smoking – Research shows that smoking doubles the risk of AMD.
Race – AMD is more common among Caucasians than among African-Americans or Hispanics/Latinos.
Family history and Genetics – People with a family history of AMD are at higher risk. At last count, researchers had identified nearly 20 genes that can affect the risk of developing AMD. Many more genetic risk factors are suspected.
Foods that contain free radicals – Trans fats, hydrogenated fats and grilled foods contain free radicals that can cause damage to the vision.
- Caffeine -Has been shown to reduce blood flow to the eye.
- Alcohol – Liver toxicity can lead to eye problems, therefore it is best to avoid alcohol.
- Sugar – Speeds the aging process and causes cellular oxidation leaing to macular degeneration.

Symptoms

The symptoms can be so gradual and subtle that many people do not know they have it for quite a long time. The main symptom is blurring of the person’s central vision. Peripheral vision (outer vision) is not affected. The blurred central vision is still there, even when the person wears glasses.

Dry Macular Symptoms –

The patient may not notice anything unusual for up to ten years after onset
If just one eye is affected, it may take even longer before somebody knows he/she has it
People with dry AMD tend to need a brighter light when reading
Written or printed texts seem blurry
Slow recovery of visual function after exposure to bright light
Colors do not appear as vibrant as they used to
It becomes more difficult to instantly recognize people’s faces
The sufferer’s vision is less defined, hazier.

Wet Macular Symptoms –

The patient may experience all the symptoms mentioned above, plus –

Symptoms appear faster
Metamorphopsia – straight lines may seem crooked or wavy
Central vision blind spot (central scotoma) – the middle of the person’s visual field is a total blind spot. If left untreated, this blind spot will get bigger.\

Complications

Severe AMD can cause legal blindness. Low vision aids may help if you have partial blindness. Sometimes blood vessels build up underneath the retina, causing the retina to become detached or scarred. If this happens, the chances of preserving your central vision are poor. This condition, called subretinal neovascularization, happens in about 20% of cases of AMD. It often comes back even after laser treatment.

Treatment

Laser Surgery – Laser surgery uses a laser to destroy the fragile, leaky blood vessels. Only a small percentage of people with wet AMD can be treated with laser surgery. Laser surgery is performed in a doctor’s office or eye clinic.

Photodynamic Therapy – With photodynamic therapy, a drug called verteporfin is injected into your arm. It travels throughout the body, including the new blood vessels in the eye. The drug tends to stick to the surface of new blood vessels.

Drug Treatment for Wet AMD – Wet AMD can now be treated with new drugs that are injected into the eye (anti-VEGF therapy). Abnormally high levels of a specific growth factor occur in eyes with wet AMD and promote the growth of abnormal new blood vessels. This drug treatment blocks the effects of the growth factor. Two such drugs are approved to treat AMD:

Pegaptanib (Macugen)
Ranibizumab (Lucentis)

Complementary and Alternative Treatment

AREDS formula (vitamin C, vitamin E, beta-carotene, and zinc, plus copper) – The Age-Related Eye Disease Study (AREDS) found that a combination of antioxidant vitamins plus zinc helped slow the progression of intermediate macular degeneration to an advanced stage.

Lutein and zeaxanthin – High levels of these two antioxidants that give plants orange, red, or yellow color may help protect against AMD, either by acting as antioxidants or by protecting the macula from damage from light.

Omega-3 fatty acids (fish oil) – Studies show that eating fatty fish at least once a week cuts the risk of AMD in half. Another larger study found that consuming docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), two types of omega-3 fatty acids found in fish, 4 or more times per week may reduce the risk of developing AMD.

Ginkgo – Ginkgo contains flavonoids, which researchers think may also help AMD.

Bilberry – These are also high in flavonoids, so researchers think that they may help prevent and treat AMD.

Milk thistle – Silymarin, from milk thistle, is a major supporter of liver function. The liver is a key organ for maintenance of eye health because the fat soluble vitamins and the B vitamins are stored there.

Frankincense oil has been demonstrated to improve eyesight, helichrysum oil improves vision and supports nerve tissue and cypress essential oil improve circulation which can improve macular degeneration.

Reference –

http://www.rnib.org.uk/eye-health-eye-conditions-z-eye-conditions/age-related-macular-degeneration-amd

http://www.brightfocus.org/macular

http://www.aao.org/eye-health/tips-prevention/amd-macular-degeneration

http://patient.info/health/age-related-macular-degeneration-leaflet

http://www.hopkinsmedicine.org/wilmer/conditions/mac_degen.html

http://umm.edu/health/medical/altmed/condition/macular-degeneration

http://mdnz.org.nz/

http://www.nhs.uk/conditions/macular-degeneration/Pages/Introduction.aspx

http://www.aao.org/eye-health/tips-prevention/amd-macular-degeneration

http://www.brightfocus.org/macular

https://www.macularsociety.org/