AMD and other eye conditions associated with Parkinson’s Disease

Are macular degeneration and Parkinson’s disease connected?

A recent study published in the medical journal BMC Ophthalmology concluded that patients with age-related macular degeneration (AMD) may have a higher risk of developing Parkinson’s disease (PD). Plus, Parkinson’s disease has been found to be associated with a number of other eye and vision issues.

Results from the study

The study was based in Taiwan and analyzed more than 20,000 individuals. About half of the people in the study were diagnosed with age-related macular degeneration. The other half did not have AMD. These individuals were followed for about five years. 

After adjusting for other factors, researchers found that men and women who had been diagnosed with AMD had a higher risk of developing Parkinson’s disease over the 12 years this group was followed.

Increased risk for certain groups

For individuals over 60 with AMD who also had other medical conditions, the risk of developing Parkinson’s disease rose significantly. These medical conditions included:

• Diabetes

• High blood pressure

• Osteoporosis

People with AMD who were also on certain medications were also found to be at a much higher risk for developing Parkinson’s disease. These medications include calcium channel blockers (often prescribed for high blood pressure) and statins (often prescribed for high cholesterol).

What is age-related macular degeneration?

AMD is an eye disease that affects the center of your vision. It impairs your ability to clearly see the details of what you are looking at. AMD is the most common cause of vision loss in adults over 50.

Symptoms

Although it is rare to go blind from this condition, AMD can cause a progressive decline in central vision. This leads to difficulty reading small print, driving or seeing faces clearly. 

Early in the disease, someone with AMD may not experience any symptoms. This is why it is important to schedule routine comprehensive eye exams, particularly for individuals over 50 years of age. An eye doctor can monitor any changes in your eye health and provide strategies to slow down the progression of this condition.

Cause

AMD is caused by a gradual degeneration of the macula, resulting in decreased visual acuity. The macula is located near the center of the retina— the light-sensitive tissue forming the inner layer of the back of the eye. 

The macula provides our most detailed and sharp vision. This is why tasks that require clear central vision are so severely impacted. 

There are two types of AMD:

Dry AMD 

With age, the macula can become thinner, resulting in dry, or atrophic, AMD. Small clusters of proteins, called drusen, accumulate around the macula. 

It is a slow progressing condition that advances through an early, intermediate and late stage over a period of several years. About 80% of people with macular degeneration have the dry form of AMD. 

Wet AMD

This type of AMD is called “wet” because of blood and fluid that can leak from abnormal blood vessels that have begun to grow under the retina. Scarring and tissue damage occur more rapidly, resulting in faster vision loss than with the dry form of AMD.

Treatment

Although there is no treatment for dry AMD, it causes less damage to the retina than wet AMD. Treatments for wet AMD are available. These focus on slowing the growth of abnormal blood vessels and the damage from fluid leaks and scars. 

What is Parkinson’s disease?

Parkinson’s disease is a progressive brain disorder that causes a number of physical and behavioral signs and symptoms. These signs and symptoms can vary with each individual. 

Parkinson’s disease usually occurs in people who are over the age of 60. However, up to 10% of people with this condition experience early-onset, before the age of 50. Parkinson’s disease affects men twice as much as women. But the disease progresses faster in women and they are more likely to die of it.

Symptoms

The symptoms and signs of Parkinson’s disease develop slowly over a period of several years. The rate of progression and degree of these symptoms vary with each individual. Common symptoms include:

• Tremors

• Rigidity

• Uncontrollable physical movements or slowed movements

• Difficulty with walking, lack of arm swinging when walking and poor balance

• Difficulty talking or lack of facial expression

• Difficulty swallowing

• Fatigue 

• Memory difficulties

• Sleep issues, depression and anxiety

Cause

An area of the brain called the substantia nigra is affected by Parkinson’s disease. The nerve cells, or neurons, in that region of the brain become damaged. This results in low levels of the neurotransmitter dopamine in the brain. Scientists are investigating what causes this to happen.

Abnormal proteins, called Lewy bodies, accumulate in the neurons of the substantia nigra in patients with Parkinson’s disease. A particular protein that cannot be broken down by cells is found clustered together within these Lewy bodies. This protein is called alpha-synuclein (a-synuclein). It is an important focus of current Parkinson’s disease research. 

Treatment

People who have been diagnosed with Parkinson’s disease should work closely with their doctor. Together, they can find the appropriate therapies to help manage their condition. 

At this time, medications that help to increase the level of dopamine in the brain are the typical course of treatment. While these medications improve symptoms, they do not slow down the progression of the disease. 

What are the similarities between AMD and Parkinson’s disease?

AMD and Parkinson’s disease have some similarities in how they affect and damage the body. 

Both Parkinson’s disease and age-related macular degeneration are degenerative and have older age as a risk factor. In addition, these two conditions overlap in the following ways:

Dopamine

Both the retina and the brain are dependent on the neurotransmitter dopamine to perform their functions. Dopamine levels become low in Parkinson’s disease. 

Low levels of dopamine can affect the nerve cells in the retina. This includes reducing their ability to transmit information along the visual pathway. 

Inflammation

Inflammation is an immune response to help the body remove harmful substances and to begin healing injured tissue.  A number of studies have found that neurodegeneration and inflammation play a role in both AMD and PD. 

Complement factors are proteins that help the immune system by supporting antibodies. These proteins also increase inflammation. And they have been found in high concentrations in people with AMD.

Autophagy dysfunction 

Autophagy is how the body clears out debris. If this debris doesn’t become cleared, cell damage can occur. Nerve cells (neurons) are particularly susceptible because they don’t have very much turnover. 

Autophagy dysfunction is thought to contribute to the abnormal accumulation of protein in both AMD and PD. 

Oxidative stress

Inflammation and autophagy dysfunction both cause oxidative stress. This is an imbalance between the production of damaging free radicals (highly reactive oxygen molecules) and the body’s ability to counter them with antioxidants. 

The brain cells and retina cells both consume a large amount of oxygen. As a result, oxidative stress is commonly found in AMD and PD. Over time, an excess of free radicals due to oxidative stress can lead to these and other diseases, as well as accelerated aging of tissues. 

Thinning of the retinal nerve fiber layer (RNFL)

The RNFL is a layer of the retina that is composed of cells called retinal ganglion cells. These cells go on to form the optic nerve, which connects the eye to the brain.  

Optical coherence tomography (OCT) is a test that detects the thickness of the retinal nerve fiber layer. Many OCT clinical studies have found that advanced AMD is associated with a thinner retinal nerve fiber layer. 

OCT studies have found that individuals with Parkinson’s disease also experience a thinning of the RNFL. In fact, the longer an individual has PD, the greater the amount of thinning that can occur. Scientists believe that this is due to damage to the neural cells in the retina that results from the neurodegeneration caused by PD.

Doctors have found that measuring RNFL thickness using OCT may be a beneficial tool in following the progression of Parkinson’s disease as well as advanced AMD. 

Difficulty reading caused by AMD and PD

People with AMD find that reading can become difficult. This is because their central vision that provides details and the sharpest visual acuity has been diminished.

Some people with Parkinson’s disease also find that reading becomes difficult. This is because the disease affects eye movements that are important for reading:

• Convergence eye movements –These are inward eye movements when looking at something close up, like a book or a tablet. PD decreases an individual’s ability to converge their eyes when looking up close (convergence insufficiency). And this results in double vision.

• Saccadic eye movements – These rapid eye movements help a reader jump from one line of text to the next, and can become slow in PD.

• Pursuit eye movements – These occur when your eyes follow a moving object. Decreasing pursuit ability makes it hard for someone to read scrolling text.

Other eye and vision issues associated with Parkinson’s disease

Parkinson’s disease is associated with several vision issues. There is a higher risk of vision impairment because it can cause neurodegeneration both at the retina and in the part of the brain that processes vision — the visual cortex. 

Symptoms caused by neurodegeneration

• Double vision – This is due to decreased control of eye muscles. 

• Poor color vision – This often affects the ability to perceive blue and yellow. 

• Diminished spatial awareness – This is due to neurodegeneration in the visual cortex. 

• Decreased contrast sensitivity – This often affects vision in low light conditions.

• Blepharospasm – This can cause the eyelids to have difficulty opening.

• Decreased blink rate – This can lead to dry eyes and blepharitis (eyelid inflammation resulting in irritation and discomfort).

• Poor depth perception – This can make walking on stairs and other surfaces difficult.

Additional vision issues

• Blurry vision – This can impair someone’s ability to see and move around safely.

• Difficulty adapting to light changes – This can make it difficult to see when moving from one room to another or changing locations between indoors and outdoors.

Fluctuating eyesight and vision issues can increase the risk of falling in people with Parkinson’s disease who have unsteady posture and gait.

How an eye doctor can help 

It is important to note that eye and vision issues don’t only impact an individual’s ability to read.  They can also greatly impact the ability to perform activities of daily life. As a result, receiving routine eye and vision care is essential for those with AMD and Parkinson’s disease.

Eye exams for Parkinson’s disease

It is important for an individual with PD to have a group of trusted doctors. This includes a primary care doctor, a neurologist and an eye doctor, such as a neuro-ophthalmologist. In addition to monitoring your eye health, some vision and eye symptoms can be treated by your eye doctor:

• Single vision glasses and bifocal glasses – To address uncorrected refractive error

• Prism glasses – To help correct double vision

• Tinted glasses – To help with visual and sensory deficits

• Art therapy – To help with visual and sensory deficits

• Blepharitis treatment – With lid scrubs, warm compresses and prescription ointments 

• Dry eye treatment – With artificial tears or ointments 

• Botulinum toxin injection – To relieve blepharospasm

Eye exams for age-related macular degeneration

Patients with AMD should be routinely followed by an eye doctor. Depending on the type and severity of macular degeneration, there are a number of different AMD treatments. These treatments can preserve vision and slow down the progression of the disease.

Why should I have routine eye exams if I have Parkinson’s disease or AMD?

It is essential to schedule routine check-ups with both your eye doctor and your primary care doctor.

Both AMD and PD are degenerative conditions. They also have some common disease pathways and are more likely to occur with age. Your doctors will be able to monitor your health and provide guidance to ensure that your eyes and body are as healthy as possible. 

A recent study has found that patients with AMD have a higher risk of developing Parkinson’s disease than those who do not have AMD. But this does not mean that if you have AMD you will develop Parkinson’s disease. The study simply concludes that you may be at a somewhat higher risk. 

In addition to AMD, vision problems are generally more common in people with Parkinson’s disease. These include double vision, poor color vision, decreased contrast sensitivity, diminished spatial awareness, poor depth perception, dry eyes and blepharitis. 

The best way to take care of your vision and eye health with AMD or PD is to be routinely monitored by a qualified eye doctor. If it has been more than a year since your last eye exam, take steps to schedule a comprehensive eye exam.

Page published on Wednesday, July 13, 2022