Although Parkinson’s disease does not directly affect the optic nerve or the physical mechanisms of vision, the disease often affects the muscles that control the eyelids. This effect can result in reduced blink rate (one of the earliest symptoms of Parkinson’s disease), blepharospasms (involuntary and sometimes protracted closure resulting from intense, extended muscle contractions), excessive tearing that causes blurry vision, and rigidity of the lower eyelid. bradykinesia and dyskinesia that affect other muscles, such as freezing, also can affect eye movements and the ability to focus or to distinguish among objects. Although the optic tracts remain intact, neuromuscular impairments interfere with the mechanics of eye function.
anticholinergic medications taken to treat tremors can cause dryness of the eyes and either constricted or dilated pupils (both of which affect depth perception and the eye’s ability to focus). Anticholinergics and levodopa can cause increased pressure within the eye (intraocular pressure), causing rapid-onset glaucoma in rare individuals who are susceptible to closed angle glaucoma. By the time there are vision-related symptoms, it may be too late to prevent significant visual impairment or blindness. Glaucoma typically manifests no symptoms until the disease is fairly advanced. Anyone who is taking anti-parkinson’s medications should have regular eye examinations that include checks for glaucoma. Most people with glaucoma have the open angle variety, and can usually take sinemet or anticholinergics without ill effect, but they require close supervision by an ophthalmologist (a physician who specializes in the medical and surgical treatment of eye disease).
Other problems with reading arise as Parkinson’s progresses and the person has increased difficulty with fine motor control in the hands and fingers, and it becomes more challenging to hold a book or magazine or to turn its pages. Tremors can cause constant movement, making seeing or focusing on words difficult. Large-print books can overcome this problem to some extent. Assist devices that provide hands-free support help hold books and other materials flat and steady; there are page-turning aids as well.
Audiobooks (books on tape) allow an avid reader to continue enjoying books. Many titles available in print are also available on audiotape. Reading aloud to a loved one who has Parkinson’s disease provides a good opportunity to share an activity together. Some public libraries, senior centers, and organizations that assist the visually impaired have “read aloud” programs in which volunteers read to groups and individuals. Some people with Parkinson’s disease may enjoy plays, movies, and other nonreading forms of entertainment as alternatives to reading.
Eye problems that cause reading difficulties can interfere with a person’s ability to perform job functions, read directions on medication labels, and drive a motor vehicle. Adjusting medication dosages or trying different drugs sometimes improves control over the muscles of the eyelids and eye itself, and using lubricating eye drops can help to mitigate eye dryness and irritation.