Dry Age- Related Macular Degeneration

Age related macular degeneration (AMD) is an eye disorder that is the leading cause of vision loss in the developed world in people above 50 years old and the third leading cause of vision loss globally.

As the name implies, this disease is caused by age related degenerative changes within the central portion of the retina called the macula.

The retina is the inner layer of the back of the eye that receives the visual input we see and transfers it to the brain via the optic nerve for image interpretation.

The macula is the retina’s central portion and responsible for the sharp, focused vision that we need in our daily activities such as reading, driving, recognizing faces and colors, and seeing objects in fine details. AMD affects approximately 11 million individuals in the United States (U.S.) alone, with a global prevalence of 170 million.

Aging is the greatest risk factor for AMD. As the proportion of older people in the population increases, the prevalence of AMD in the U.S. is anticipated to increase to 22 million by the year 2050. The global prevalence is expected to increase to 288 million by the year 2040. In the U.S., the prevalence of AMD is similar to that of all invasive cancers combined and more than double the prevalence of Alzheimer’s Disease.

Types of AMD

There are two major types of AMD, known as the dry type (atrophic) and the wet type (exudative). Dry AMD, which is the focus of our article, is more common and accounts for 85 to 90 % of AMD cases.

It is characterized by progressive accumulation of yellowish deposits called drusen under the retina. The normal retina discards and recycles drusen through different biochemical pathways. However, in people with dry AMD, these biochemical pathways are dysfunctional, resulting in the buildup of drusen with damage to the retina’s light sensing cells.

Consequently, patients start to complain of central vision distortion/loss that worsens slowly over time. As the disease progresses, patches of the macula waste away (atrophy), resulting in irreversible damage to the retina’s light sensing cells with severe vision loss.

Because the patches were thought to resemble countries on a map, they were called ‘Geographic Atrophy’ (GA), which is the most advanced form of dry AMD. Dry AMD typically affects vision in both eyes, although vision loss often occurs in one eye before the other.

In 10 to 15 % of affected individuals, the progressive accumulation of drusen induces abnormal growth of fragile blood vessels from a thick vascular layer underneath the retina, known as the choroid. These abnormal blood vessels are called choroidal neovessels (CNV), which is the hallmark of conversion from dry to wet AMD.

As its name suggests, the wet form is characterized by leakage of blood, lipids, and fluid from these abnormal blood vessels underneath the macula. This results in severe vision loss that can progress rapidly. The current treatment modalities for wet AMD are based on suppressing these abnormal vessels by injecting certain medications inside the eye that are capable of inducing the regression of these abnormal blood vessels.

Symptoms of dry AMD

Patients with dry AMD might complain of vision changes that are painless and slowly progressive over time. Dry AMD usually develops first in one eye and then affects both eyes. Symptoms include:

• Visual distortions where straight lines may appear wavy.
  
  
• Decreased or blurred central vision in one or both eyes. The patient usually notices gaps in items on which the eye naturally focuses, such as words on pages, road signs, and faces.
  
  
• Decreased brightness of colors and the need for brighter light when reading or doing close work.
  
  
• Increased time to adapt to dim light.

You need to see your eye doctor in case you notice any of the above-mentioned vision changes. It is important to point out that if only one eye is affected, you may not notice any changes in your vision because your good eye may compensate for the weak eye.

Although there is no effective cure for dry AMD, early detection and self-care measures may slow vision loss progression.

Causes of AMD

The causes of AMD remain poorly understood. Research suggests that this eye condition’s development involves an interplay between genetic predisposition, immunological process, and other factors such as smoking and diet.

Many of these genes and factors have been identified, but many are still largely unknown, which precludes a complete understanding of this eye disorder.

Risk factors

• Age is the most important risk factor for developing AMD. The disease is more likely to occur in people above the age of 50. It is estimated that 10% of people above the age of 65 and 25% of people above 75 have AMD. Other risk factors include:
  
  

• Family history of AMD: As the disease has been linked to many genes, a hereditary component plays a role in disease development. 
  
  
• Race: AMD is more common in whites and lowest in African Americans.
  
  
• Sex: AMD is more common in females. 
  
  
• Smoking: Smoking cigarettes or being regularly exposed to smoke significantly increases the risk of AMD. Cigarette smoking has been consistently demonstrated to be the most significant modifiable risk factor.
  
  
• Obesity: Some studies suggest that men with increases waist-to-hip ratio have a higher risk of developing AMD.
  
  
• Diet: A recent systematic review of the literature performed by the Royal Australian and New Zealand College of ophthalmologists suggests a Western diet pattern with a higher intake of red meat, processed meat, high-fat dairy products, fried potatoes may increase the risk of development and progression of AMD.
  
  
• Cardiovascular disease: If you have uncontrolled high blood pressure, high cholesterol levels, a history of stroke, or heart attacks, you may be at higher risk of AMD.

Diagnosis of AMD

AMD diagnosis requires a comprehensive eye exam with a possible need for additional testing to confirm the diagnosis. 

• Visual acuity test and test for defects in your central vision: Routine eye exam usually starts with visual acuity assessment. During an eye examination, your eye doctor may use a special tool called Amsler grid to detect any defects or distortion in central vision. Amsler grid is a simple square containing a grid pattern and a dot in the middle. AMD can cause irregularities, waviness, and distortion of the straight lines in the grid.
  
   
• Examination of the retina ( back of the eye): Your eye doctor will put drops in your eyes to dilate your pupils and use special instruments and lenses to examine the back of your eye. The eye doctor will look for drusen, yellowish deposits under the retina, which are the hallmark of dry AMD. Other clinical exam findings include abnormal pigmentation in the center of the retina (macula), thickening or thinning of the retina. 

Additional testing

The eye doctor may also do several other tests to confirm the diagnosis or obtain a baseline test to follow up on the disease’s progression. These tests include:

• Optical coherence tomography (OCT): OCT is an indispensable tool for diagnosing and following up with disorders at the retina, which is the back of the eye. It is a noninvasive imaging modality capable of obtaining detailed cross-sectional images of the retina within a few seconds. It identifies variable abnormalities that might occur in the back of the eyes with AMD, such as drusen, retina thinning areas, thickening, or accumulation of fluid/blood within or underneath the retina. Detection of fluid/blood by OCT is used to differentiate between dry and wet AMD.
  
  
• Fundus Fluorescein angiography (FFA): This test is used to highlight the blood vessels of all layers of the back of the eye. During this test, the colored dye will be injected into a vein in your arm. The dye travels through the blood circulation to reach the blood vessels of the back of the eye. A special camera takes several pictures at different time points as the dye travels through the back of the eyes’ blood vessels. FFA is usually used when the eye doctor suspects wet AMD as FFA can detect leakage and abnormal blood vessels, which are characteristics of wet AMD.
  
  
• Optical coherence tomography angiography (OCTA): OCTA is a noninvasive imaging technology that can delineate the normal and abnormal blood vessels at the back of the eye. This is like fluorescein angiography but without a dye, which might be preferred in certain situations.

Stages of dry AMD

After completing a full eye exam, the eye doctor can stage dry AMD into the following categories:

• Early AMD – Because most people do not have vision complaints in early AMD, this stage is usually discovered incidentally during a routine eye exam. This explains the importance of routine eye exams, especially if you have one or more of the risk factors that are discussed above. Early AMD is diagnosed by the presence of small-sized drusen (the yellow deposits beneath the retina) or a few intermediate-sized drusen.
  
  

• Intermediate AMD – At this stage, the drusen get larger and increase in number. Patients might start to complain of vision changes at this stage, such as the need for brighter light for reading and doing close work.
  
  
• Advanced AMD or Geographical Atrophy– At this stage, irreversible damage and atrophy of the light-sensing cells in the back of the eye cause severe vision loss. Vision loss starts with a blurred spot in the center of your vision that gets larger and darker over time, occupying more of your central vision.

Complications of dry AMD

Severe vision loss

In advanced cases of dry AMD, patients have severe vision loss in both eyes. This impairs the ability to perform daily activities and function independently, which affects the overall quality of life. Consequently, feelings of isolation, sadness, and even depression can result.

Not only can AMD affect your mental and psychological well-being, but it also can increase your risk for physical injuries due to low vision. Special attention should be paid in low light conditions as it may be hard to see certain objects such as steps, electrical cords, or upturned carpets, which may cause you to stumble and fall. 

Conversion to wet AMD

Growth of abnormal blood vessels (choroidal neovascularization) at the back of the eye underneath the retina will convert the dry form of AMD to the wet form. This results in fluid and blood leakage within and underneath the retina with rapid deterioration of vision, which is different from the slow progressive decline of vision caused by dry AMD.

Treatment is available for this condition and is achieved by repeated injections of certain medications that target and suppress these abnormal blood vessels inside the eye. These medications belong to a big family of therapeutics called Anti-vascular Endothelium Growth Factors- (Anti-VEGF).

Visual hallucination

Sometimes advanced AMD can cause visual hallucinations, called Charles Bonnet Syndrome. These hallucinations can include seeing patterns or more complex images such as people, animals, flowers, and buildings. The mechanism behind these hallucinations is poorly understood, but it is not related to a psychiatric condition, metabolic abnormalities, or brain injury.

Prevention

It is essential to have annual routine eye exams to detect early signs of macular degeneration. Moreover, lifestyle plays a role in reducing the risk and/or slowing the progression of AMD. Multiple studies recommend the following measures that might protect your eyes against the risk of developing AMD.

• Avoid smoking: Smoking is the most important modifiable risk factor for developing AMD. Smoking is known to increase the number of damaging chemical compounds and decrease the number of protective nutrients delivered by the bloodstream to the eye. Quitting smoking reduces the risk of AMD. In fact, the risk of developing AMD is the same in smokers compared with non-smokers after 20 years of smoking cessation. 
  
  
• Maintain a healthy weight and exercise regularly
  
  
• Choose a diet rich in fruits and vegetables and limit the consumption of processed food.
  
  
• Include fish in your diet. Omega-3 fatty acids, which are found in fish, may reduce the risk of macular degeneration. Nuts, such as walnuts, also contain omega-3 fatty acids.
  
  
• Keep your other medical conditions under control: more specifically, cardiovascular disorders such as high blood and elevated cholesterol levels. Take your medications regularly with strict follow up of your doctor’s instructions.
  
  
• Avoid excessive UV light exposure: Studies are controversial over the role of UV rays in developing AMD. However, UV-protective eyeglasses are recommended as there are no adverse effects from wearing them.

Treatment

There is currently no cure for dry AMD. All available treatments aim to reduce the risk of developing the disease or minimize its progression. The treatment for early dry AMD is generally nutritional therapy, with a healthy diet high in antioxidants to support the macula cells, in addition to lifestyle modifications, as discussed above.

Your eye doctor prescribes AREDS2 supplements if AMD is further advanced to the intermediate and advanced stages but still dry. They work by adding higher quantities of certain vitamins and minerals, which may increase healthy pigments and support cell structure at the back of the eye.

AREDS 2 supplements and dry AMD

AREDS 2 (Age-Related Eye Disease Study 2) was a very large clinical trial that assessed the benefits and potential risks of taking a certain combination of vitamins and minerals, called AREDS 2 formula, on the progression of dry AMD.

This study found that AREDS 2 supplements could reduce the risk of progression from intermediate to advanced AMD stages. In people who have significant loss of vision in one eye due to dry AMD, these supplements might reduce the risk of vision loss in the less affected eye.

The following are the components of the AREDS 2 formula:

• Zinc (80 mg)
  
  
• Copper (2 mg)
  
  
• Vitamin C (500 mg)
  
  
• Vitamin E (400 IU)
  
  
• Lutein (10 mg)
  
  
• Zeaxanthin (2 mg)

It is important to remember that AREDS 2 supplements are not a cure or prophylaxis for dry AMD. Still, they may help slow the disease progression in some people who meet certain criteria determined by your eye doctor.

Low vision rehabilitation

AMD usually affects central vision with the preservation of side/peripheral vision. In cases with advanced AMD, it is essential to work with a low vision rehabilitation team to maximize the use of your remaining visual functions. The low vision rehabilitation team can also help you find ways to adapt to your changing vision and maintain a safe environment at home, which is crucial to decrease the risk of falls and physical injuries due to low vision.

Surgery to implant telescopic lens

For selected people with advanced dry AMD, surgery to implant, a telescopic lens in one eye might be considered. The telescopic lens, which looks like a tiny plastic tube, is equipped with special lenses that magnify the visual input you are trying to see. While the telescopic lens implant may improve both distance and near vision, it has a very narrow field of view. 

Conclusion 

Dry AMD is a significant cause of vision loss in the elderly population all over the world. While there is still no available cure for this eye disorder, a healthy lifestyle, smoking cessation, a balanced diet, and exercise can reduce the risk of developing this blinding condition.

Moreover, AREDS 2 supplements prescribed by your eye doctor might slow the progression of certain stages of dry AMD. In advanced AMD stages, vision rehabilitation services can maximize your visual functions and provide you with safety tips that can help you function independently.