Vision Problems & Parkinson's Disease
Some patients with PD and parkinsonism may have difficulty reading. After common problems such as cataracts and macular degeneration have been ruled out, it can be helpful to evaluate a patient’s ability to shift the eyes from the distant to the near. This evaluation may reveal that a patient’s capacity for converging eye movements is reduced. Convergence insufficiency makes it difficult to keep both eyes pointed together at a near target.
It is not known how many people with parkinsonism have this problem, but it is one of the most common eye movement disorders. People may only describe eye strain while they read, but more pronounced symptoms may appear, including a reduced ability to read, eye fatigue and sometimes double vision or a tendency to involuntarily close one eye while reading.
Convergence insufficiency, when identified as a cause of reading problems, may be improved with exercises designed to strengthen eye movements (the turning motion of the eyes toward or away from each other). In many cases, however, this will not suffice, and improving near vision may require the use of prisms in dedicated reading glasses.
Prisms are optical devices that can be ground into regular eyeglasses. They bend the light so that the amount of convergence necessary for near vision is reduced. In severe cases, however, even this may not provide adequate relief, and the only remaining option is to cover one eye with a patch or cover glasses with occluding tape so the patient only reads with one eye.
Reduced Blinking & Eye Movement Disturbances
Other eye movement disturbances have been described in parkinsonism. These include an impaired ability to pursue a moving target with the eyes, difficulty initiating gaze shifts or taking the eyes off a face. Also, the ability to maintain eccentric gaze is impaired, and the blink frequency tends to be reduced. Of these abnormalities, only the latter tends to show significant symptoms, as reduced blinking can cause a feeling of dry eyes. This may be further enhanced by reduction in tear secretion, which is not uncommon in parkinsonism. Management of dry eyes usually involves the use of artificial tears. It is rare that additional measures are needed to combat symptoms of dry eyes in patients with parkinsonism.
Patients with parkinsonism are also susceptible to visual hallucinations. These can be related to the underlying neurological illness or medications used for treatment. PD patients who have visual hallucinations respond well to antipsychotic medications such as quetiapine. Hallucinations should always be reported to the physician.
Vision Problems with PSP (Progressive Supranuclear Palsy)
Slowness in looking up or down with moving the head is a symptom in a severe parkinsonian disorder called progressive supranuclear palsy (PSP). Patients with PSP have trouble initiating gaze shifts in the up and downward direction, and the speed and extent of such gaze shifts reduce as the disease progresses.
The negative effects on vision and visual orientation are profound. Patients can eventually loose their ability to look down through the reading part of their glasses, causing an inability to read. In addition, they become susceptible to falls by not seeing where they step on level ground or on stairs. This adds greatly to mobility and balance problems, which are already prominent with PSP.
Unfortunately, there is no treatment for this eye movement disorder. To make reading easier, special reading glasses that cover the entire field of vision can be prescribed, and reading material may have to be placed at eye level in a special stand.