Visual Sequelae of Parkinson's Disease
Parkinson’s disease (PD) is a neurodegenerative movement disorder with a number of factors that will impact on the overall well-being of an individual over and above the evident symptoms of tremors, difficulty walking, posture and balance, and speech trouble. In an article recently published in the Canadian Journal of Ophthalmology, Askoy and colleagues point out some of the more evident visual difficulties of decreased blink rate and dry eyes and how they seem to correlate with the thinning of the cornea.
The importance of corneal thinning to the eye care practitioner relates to measurement of intraocular pressure which, without other evident signs, contributes to the diagnosis of ocular hypertension or early glaucoma, a condition which is common in PD. The message here is that any eye examination of a patient with severe PD should include pachymetry to measure corneal thickness. However, there are additional visual sequelae in PD that also need to be recognized and, indeed, where possible, treated or managed. Many of these changes in the visual system will have an impact on the patient’s activities of daily living and can exacerbate the cognitive changes that are also a part of PD. For example, depth perception difficulties, intermittent diplopia, dry eyes, photophobia, blurred vision, and general eye movement deficits can impact the already challenging problem with walking, leading to a greater risk of falling. Over and above that, not having an updated eye glass prescription can cause blurred vision and can contribute to poor visual awareness of the environment, while something as simple as eliminating a bifocal to minimize missteps when walking, can easily be managed. Not so easily managed, however, is the way in which these visual dysfunctions affect driving, especially with the akinesia associated with PD. Near activities like reading can also be affected by some of the visual sequelae of PD. Saccadic dysfunction, convergence insufficiency, and difficulty with vertical gaze can make reading a challenge. However, prescribed single-vision glasses for near activities (with prism for convergence difficulty when appropriate) and techniques such as rapid serial visual processing can enhance these near tasks. There are also visual training activities that may minimize the impact of eye movement dysfunctions in those patients who can tolerate a more interactive treatment.
So, the unintended positive consequence of this article that makes practitioners aware of blink rate, dry eyes, and corneal thickness is to also remind them of the many other visual sequelae of PD. These sometimes “under-recognized” visual dysfunctions deserve assessment, not only at the primary care level, but with a comprehensive eye health and visual assessment as well.
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