Individuals with Parkinson's Disease (PD) contend with a wide range of symptoms, including tremors and impaired movement, cognitive decline, speech difficulty, fatigue, and more. In addition to these better known symptoms, many people with Parkinson's experience "facial masking," a reduction in their facial expressiveness due to muscular stiffness or slowness.
Experts say that, while facial masking can sometimes be the result of stiffness around the cheeks and mouth, one particularly subtle change that many Parkinson's patients experience in their eyes is sometimes to blame. Frequently flying under the radar, this strange eye symptom can cause vision loss and increased discomfort over time. Read on to learn about this early sign of Parkinson's Disease, and how it may affect you.
If you blink infrequently, it may be an early sign of Parkinson's.
You may not give much thought to your blink reflex, but experts say that maintaining a steady blink rate—typically about 16 to 18 times per minute—is important for eye health. In PD patients, this rate can sometimes slow substantially due to muscular changes, leading to increased facial masking, eye discomfort, and even impaired vision.
"Problems can come from difficulty in moving the eyes and eyelids, as well as problems with blinking and dryness," writes ophthalmologist Elliott Perlman, MD, for the American Parkinson's Disease Association (APDA). "Most of these conditions arise from Parkinson's Disease itself, while others may be caused by the medications required to treat PD," he adds.
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A slow blink rate may help replenish dopamine.
People develop Parkinson's disease when they lose dopamine or dopaminergic neurons in the substantia nigra area of the brain. The dopamine system plays an essential role in muscle function and motor physiology—hence its reputation as a movement disorder.
Surprisingly, some experts believe that reduced blink rates are more than just the result of muscle slowness or stiffness resulting from a lack of dopamine. They may in fact be the body's way of trying to increase one's light exposure, which in turn helps the body develop more dopamine.
One study published in the International Journal of Neuroscience explains that blinking helps to regulate light-dark exposure, which helps "fine tune" melatonin and dopamine production. "Decreased blinking (as is observed in patients with Parkinson's disease) could reflect a compensatory mechanism to increase light exposure, reduce melatonin production and ultimately increase dopamine functions," the study concludes.
However, it can cause ocular discomfort and poor vision.
Blinking at a normal rate is an essential part of eye health because it helps to redistribute tears on the eye's surface. Without constant redistribution, tears quickly evaporate, causing the eye surface to become dry and painful. As a result, some people experience a burning sensation associated with this symptom, while others experience a "foreign body sensation"—the feeling that something is stuck in their eye. Over time, this can degrade one's vision, and lead to difficulty with reading and other ocular functions.
According to the APDA, artificial tears can help alleviate these symptoms in Parkinson's patients, including visual blurring and ocular discomfort.
The opposite can also happen in PD patients.
Those who suffer from blepharospasm may benefit from seeing an ophthalmologist or neuro-ophthalmologist, who can inject a botulinum toxin in the muscle surrounding the eye every three to four months. This treatment, performed by a movement disorders specialist, is known to be very effective in slowing blink rates and improving eye function.