Age-related macular degeneration (AMD): Types, causes, risk factors, and symptoms

Macular degeneration is a disease that affects the retina, a layer at the back of the eyeball. This layer contains light-sensitive cells. It helps us see the world around us.

Age-related macular degeneration (AMD) affects a person’s central vision. Images that used to be clear may start appearing blurred, and dark spots may appear, which get progressively bigger.

Straight lines may appear curved or distorted, and colors are darker or less vivid than they used to be.

It becomes harder to read, write, recognize faces, and drive. However, there is usually enough peripheral vision to allow other activities of daily life. Total vision loss is unlikely.

It affects older adults and is a major cause of partial blindness among people aged 50 years and over.

Types


AMD can lead to a growing loss of central vision as people age.

There are two types of macular degeneration: wet and dry.

  • Dry macular degeneration: This type develops gradually. There is no treatment. There are things the patient can learn to cope with it. The dry form accounts for 85 to 90 percent of cases.
  • Wet macular degeneration: Also known as neovascular AMD, this happens when new blood vessels develop under the macula. These can cause blood and fluid to leak. Wet AMD is a more serious form AMD, and severe vision loss can result. It can develop more quickly. If symptoms appear, immediate treatment is needed.

Causes

The exact cause of AMD is not known, but it has been linked to a number of risk factors. These include having excess weight and high blood pressure, smoking, and having a family history of the condition.

Risk factors

Figures for 2010 showed that in the United States, AMD affected 2.1 percent of people aged over 40 years. Among white people, this figure was 2.5 percent, rising to over 14 percent among those aged over 80 years. Figures for other ethnic groups are lower.

In rare cases, younger people can develop macular degeneration. This type, known as juvenile macular degeneration, includes Stargardt’s disease (STGD) and Best’s disease. It usually stems from a genetic condition.

According to the American Academy of Ophthalmology (AAO), key factors that appear to play a role include:

Age: The risk increases after the age of 60 years.

Ethnicity: Caucasians are more likely to develop AMD than other groups.

Family history: Around 15 to 20 percent of people with AMD have a close relative with the condition.

Smoking cigarettes: Current smokers may have a risk of AMD that is four times higher than that of those who have never smoked.

Obesity: Excess weight or obesity, together with linked factors — such as high blood pressure and high cholesterol levels — appear to add to the risk.

AMD and cardiovascular disease (CVD) share some common risk factors. Lifestyle choices that reduce the risk of CVD, such as not smoking and limiting the intake of dietary fats, may also help reduce the risk of AMD.

Other factors may include:

  • Dietary fat: Studies indicate that those who consume a lot of saturated fats are more at risk of AMD.
  • Light exposure: Some studies indicate that high-energy visible light and ultraviolet (UV) light, including sun exposure, may be a contributory factor, but other studies do not. Research published in JAMA Ophthalmology in 2001 concluded that there was no link. However, most eye doctors recommend wearing sunglasses that protect from UV light.

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Symptoms

The changes that result from AMD are gradual. Most people do not realize they have it until the later stages, when vision loss starts to occur.

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 AMD symptoms:

Symptoms of dry AMD may not appear for up to 10 years after onset, and longer if AMD affects only one eye.

When symptoms do appear, they may include:

  • the need for a brighter light when reading
  • written or printed texts appearing blurry
  • slow recovery of visual function after exposure to bright light
  • colors seeming less vibrant than they used to
  • increasing difficulty recognizing people’s faces
  • hazier, less defined vision

Wet AMD symptoms:


Seeing the two boys with normal vision.


How a person with AMD sees the same two boys.
Photos by National Eye Institute

All the above symptoms may be present, and also the following:

  • metamorphopsia, in which straight lines appear crooked or wavy
  • a blind spot in the central vision (central scotoma) that will get bigger without treatment

Symptoms appear and progress more rapidly than with dry AMD.

According to the National Eye Institute (NEI), early AMD does not always progress to the later stages.

  • Among those with early AMD in one eye, where the other eye is not affected, around 1 in 20 will have advanced AMD after 10 years.
  • Around 14 percent of people with early AMD in both eyes will have late AMD in one or both eyes after 10 years.

Regular eye tests can help detect early AMD, and steps can be taken to reduce the risk of it progressing.

Diagnosis


The macula is at the center of the retina and provides the most detailed central vision.

If vision problems start to occur, it is important to see an eye doctor, an optometrist, or an ophthalmologist.

The eye specialist will examine the eyes, especially the back of the eyes, where the retina and macula are.

Then there will be a series of tests:

Amsler grid: The patient looks at a special grid, which consists of vertical and horizontal lines. If AMD is present, some of the lines on the grid may seem distorted, broken, or faded.

The result will give a better idea of how much damage has occurred. Most people with detectable symptoms find the lines nearest the center of the grid seem distorted, faded, or broken.

Fluorescein angiography: This test confirms the type of AMD. It is usually carried out if the specialist suspects wet AMD.

The doctor will inject a special dye is injected into the patient’s arm then look into their eyes with a special magnifying device. They will take a series of pictures of the eye. The pictures will indicate whether the blood vessels behind the macula are leaking.

Wet AMD happens when blood vessels leak behind the macula.

Optical coherence tomography: Special light rays scan the retina and take an image of it. The image gives the specialist more data about the macula. If the macula has become thicker, thinner, or changed in any way, the image may reveal this.

Treatment

Regular eye checks are recommended to detect macular degeneration before vision loss begins.

Treatment cannot restore vision, but it can slow vision loss.

Dry AMD

Dry AMD does not usually result in total vision loss, and peripheral vision will normally remain.

Support and lifestyle adaptations can make it easier to cope with the loss of vision and to maximize the vision that remains.

Tips may include:

  • using a magnifying lens
  • getting large print books
  • using intensive reading lights

Wet AMD

Some treatments can stop the progression of wet, or neovascular, AMD, but treatment must be immediate for it to be effective. Any eyesight lost is very hard to regain.

Anti-VEGF medication

Anti-vascular endothelial growth factor medication (VEGF) is a chemical that contributes to the formation of new blood vessels in the eyes of people with wet AMD. Anti-VEGF drugs block this chemical so that it cannot produce any more blood vessels.

Examples of these drugs include ranibizumab (Lucentis), and bevacizumab (Avastin).

Anesthetic is applied, and then the doctor injects the drug into the eye with a very fine needle.

The treatment needs repeating every few weeks.

In some cases, anti-VEGF treatment has restored some vision, but this depends on the individual and the symptoms they have.

Anti-VEGF treatment does not usually have any side effects, but pain, swelling, redness, and blurred vision may occur after the injections.

In very rare cases, treatment can lead to complications, such as damage to the retina, damage to the lens of the eye, and infection.

Photodynamic therapy

Verteporfin, a light-sensitive medication, is injected into the person’s arm. Veteporfin attaches itself to the proteins in the veins. It can detect abnormal blood vessels in the macula.

A laser is shone through the eye for about 1 minute. When verteporfin is activated by the laser, the abnormal blood vessels in the macula are destroyed. This happens without any damage to surrounding eye tissue. If the vessels can be destroyed, blood or fluid cannot leak out and damage the macula any further.

Some patients need photodynamic therapy every few months. Whether this type of treatment is given depends on where the target blood vessels are located and how badly they have affected the macula.

This treatment is less commonly used than anti-VEGF injections.

Laser therapy

Sometimes, an eye doctor will use a laser to treat the abnormal blood vessels in the retina. This is also not used as often as other therapies but may be appropriate in some cases.

Home remedies

Research has suggested that some supplements may help delay the progression of AMD.

Vitamins, minerals, and antioxidants

Studies have shown that the following ingredients may be effective if taken during the intermediate or later stages:

  • vitamin C (500 mg)
  • vitamin E (400 IU)
  • zinc oxide (80 mg)
  • copper oxide (cupric oxide 2 mg)
  • lutein (10 mg)
  • zeaxanthin (2 mg)

The supplements, known as an Age-Related Eye Disease Studies (AREDS and AREDS2) supplement, can be purchased without a prescription, but patients should discuss them with a doctor first and ensure they obtain the correct type.

Vitamins are not a cure for AMD, but they may help slow disease progression.

Omega-3 fatty acids

A meta-analysis published in 2008 linked a high dietary intake of omega-3 fatty acids, found in flax and fish oils, with lower levels of AMD. However, the researchers said the evidence was not strong enough to support the use of omega-3 supplements to prevent the disease.

Another review, published in 2015, concluded that there was no link between the two.

Stem-cell therapy

Studies have suggested that human stem cells might one day enable the retina to repair itself.

In March 2018, The BMJ reported that two people with very severe wet AMD had recovered their sight after stem-cell therapy.

Implantable telescope

Another investigation found that an implantable miniature telescope (IMT) might improve the vision of people with advanced AMD. Benefits include the recovery of some sight and a greater scope for independence. However, the field of vision will be reduced, and the person will still not be able to drive a car.

Complications

AMD can lead to a number of complications.

Adapting to vision loss: Vision loss can be hard to accept, especially when previously straightforward tasks, such as reading, become difficult. This can lead to feelings of stress, depression, and anxiety. Talking to a health professional might help an individual find new ways to cope.

Driving: Having AMD can affect a person’s ability to drive. An eye doctor can advise a person if their vision changes will affect their ability to drive.

Cardiovascular risk: AMD shares some risk factors with CVD, and studies have found that those with AMD are more likely to experience symptoms of CVD.

Visual hallucinations: If vision decreases severely, these can affect some people. This may be because the brain compensates for visual data it is not receiving by creating fantasy images, often images from memory.

Some patients are afraid to talk about this because they are worried that it may indicate some kind of mental illness. It is important to know that these hallucinations reflect vision problems and not an altered mental state.

Video: What is AMD?

The video below explains what macular degeneration is and how it affects vision.

Source: Age-related macular degeneration (AMD): Types, causes, risk factors, and symptoms

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