by Elliott Perlman, MD
PD patients often have a lot of difficulty with their vision, although, when I examine them in the office, the visual acuity is often normal. Problems can come from difficulty in moving the eyes and eyelids, as well problems with blinking and dryness. Most of these conditions arise from Parkinson’s Disease itself, while others may be caused by the medications required to treat PD.
Many Parkinson’s Disease patients complain of trouble reading. One common cause of this is called “convergence insufficiency”. In order to see clearly up close, normal eyes must converge or cross inwards to see a single image. If convergence is defective, a person will have double vision when trying to see close up. Sometimes placing prisms in the reading glasses can alleviate this problem. Often, however, just covering one eye may be the only way to eliminate the symptom.
Another common cause of reading difficulty in Parkinson’s Disease patients is they often have a decreased blink rate (the number of times you blink per minute). Parkinson’s Disease patients can temporarily overcome this problem by consciously blinking more frequently, but this effort is impossible to sustain. Normal blinking helps redistribute the tears on the eye surface, much like a windshield wiper spreads rain on a windshield. With slow blink rates, the tears evaporate more rapidly and vision deteriorates. Also, symptoms of dryness, burning sensation or foreign body sensation may arise from this high tear film evaporation rate. Long-acting artificial tears may be helpful with the blurring and ocular discomfort.
Other eyelid movement problems can contribute to visual difficulty in Parkinson’s Disease patients. Parkinson’s Disease patients may have intermittent blepharospasm, especially when the eyelids or brows are touched. The patient involuntarily squeezes his eyes shut and may have difficulty opening them as well. This is why Parkinson’s Disease patients often have difficulty during eye exams, when the doctor is holding the eyelids open for examination or to measure eye pressures.
Over 30% of Parkinson’s Disease patients report visual hallucinations, which probably do not reflect any disease of the eye. They are often attributed to side effects of medications and are mildly increased in people with impaired vision.
In summary, although Parkinson’s Disease patients can have many ocular symptoms, their general eye health is comparable to other non Parkinson’s Disease patients of the same age. Moreover, many of the problems are treatable with such non-invasive therapies as changes of glasses and over-the-counter tear preparations.
Dr Elliott Perlman, MD Rhode Island Eye Institute 150 E. Manning St. Providence, RI 02906