Eye & Vision Issues in Parkinson's Disease
by Andrew A. Berman, MD
FOLLOWING ARE SOME OF THE EYE AND VISION PROBLEMS THAT PEOPLE WITH PARKINSON'S DISEASE MAY EXPERIENCE, ALONG WITH AN EXPLANATION OF WHAT CAUSES THESE CONDITIONS AND HOW THEY CAN BE TREATED.
WHAT IS A NEURO-OPHTHALMOLOGIST?
A neuro-ophthalmologist is either an ophthalmologist or a neurologist who has additional post-residency training in neuro-ophthalmology. Neuro-ophthalmologists attempt to bridge the gap between the two disciplines by diagnosing and treating the ophthalmic or vision manifestations of neurological disease. As we know, Parkinson's disease (PD) is a neurological disorder caused by the death of dopaminergic neurons in the substantia nigra and therefore depletes dopamine in a part of the brain called the putamen as well as the visual cortex and some cells in the retina. Therefore people with PD may have ophthalmic complaints such as blurred vision, trouble reading, double vision and dry eyes. For these reasons it is the neuro-ophthalmologist who is frequently asked to care for the PD patient.
There are three fundamental types of eye movements. The saccadic eye movements are the rapid eye movements that redirect our gaze to pick up an object of interest. They are also important in following the lines of a printed page. Pursuit eye movements stabilize the object on our retina and follow it as it moves slowly through space. Vergence eye movements serve to move the eyes in different directions (either together, which is convergence, or apart, which is divergence), keeping an image stable on our retina as it moves toward or away from our eyes. This type of eye movement helps us avoid double vision. In Parkinson's disease, the saccades tend to be slow (or hypometric) and show delayed initiation. Some people with PD require a blink to change their saccadic position (this is called Wilson's sign). As you can imagine, this makes it hard to fixate changing targets in the environment and to read as well. Often these can normalize with L-dopa, but if a person has Levodopa-induced dyskinesias, the saccades can become hypermetric. When pursuit movements become decreased, this can produce what is called cog-wheel (jerky) slow eye movements. Insufficient convergence of the eyes can cause insufficiency of accommodation, which is the eye's response to a near stimulus. This inadequacy or slowness of accommodation can result in eyestrain, headaches and double vision (diplopia) when working on near tasks. Unfortunately, this condition can be exacerbated by medications used to treat the tremors and the spasms often seen in PD.
EXTERNAL EYE DISEASE
The blink reflex, which is normally about 16 to 18 times per minute, may decrease to 1 to 2 times per minute. This causes the ocular surface to become dry in a setting of already reduced and abnormal tear film production, creating a condition called "dry eyes." This may lead to a foreign body sensation, blurred vision, itching and burning. Some theorize that this may contribute to excessive blinking and lid spasms, called benign essential blepharospasm. Occasionally, people with PD may experience apraxia of eyelid opening, which is an inability to open the eyes voluntarily. As a result of the dysfunction of the autonomic nervous system, seborrheic blepharitis and dermatitis may occur which can cause irritation and inflammation of the upper and lower lid. Inflammation of the cornea and ocular surface may also occur. This condition exacerbates the symptoms of dry eyes.
There are dopaminergic receptors in the retina. The dysfunction of these receptors can lead to a loss of contrast sensitivity for some people. There can also be color vision deficits, usually along the blue-yellow axis. If a person experiences hallucinations, visual disturbances may be a contributing factor in addition to medications.
As physicians, we always have to be aware of our patients' medications— their dosages, effects and side effects. A good history of medications is paramount. It is important to know how the person's symptoms are affected by the medication dosages and by their schedule. For instance, I have patients who need different types of glasses depending upon where they are in their medication cycle. First and foremost, the management of eye problems requires an accurate and thorough eye examination and correction of refractive errors. Most of the time, when eye movement abnormalities are found, it is best to prescribe one pair of glasses for distance and another for reading. This is in preference to a bifocal. However, if patients insist on bifocals then I will recommend a standard "lined" bifocal rather than a progressive bifocal. For those with convergence insufficiency, I will prescribe prisms in their glasses. Prisms help to bend light to the proper focal point on the retina when the eyes cannot move properly to accomplish the same thing. This helps with the ocular fatigue and double vision as well. Although ocular external disease and dry eyes cannot be cured, they can be effectively treated. This management usually involves warm, moist compresses, lid scrubs, and at times, medicated ointments. The dry eyes can be treated with Artificial Tear substitutes in both an eyedrop and an ointment form. In some patients, punctal occlusion (blocking the drainage opening) may be done to increase the contact time of the tears with the ocular surface. All of these techniques can go a long way toward making the eyes look and feel better and increase a patient's vision. People with Parkinson's who have blepharospasm (involuntary spasms of the eyelids) will benefit from injections of botulinum toxin (Botox). Although it is usually repeated every three to four months, it can be very helpful in restoring a patient's ability to function. Those who experience apraxia of lid opening (involuntary closing of the eyes) can use lid crutches or cosmetic lid tape to help keep their eyes open. Although it is difficult to treat the sensory deficits which at times can affect people with PD, sometimes certain tints for lenses can be helpful. Hallucinations may respond to some central nervous system depressants. Finally, in addition to everything already discussed, the person with PD can still get the garden variety ophthalmic diseases. Diseases such as glaucoma, cataracts and macular degeneration must also be properly diagnosed and managed. With proper attention to the particular problems, as well as routine eye care, patients with Parkinson's disease can protect and improve their vision and can enjoy a fine quality of life.
Dr. Berman is a neuro-opthalmologist in private practice in Skokie, IL. To find a neuro-opthalmologist in your area go to www.aao.org.