Visual Signs May Herald Parkinson Disease

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Mayo Clinic Researchers have found that visual abnormalities are among the most frequent nonmotor symptoms in the early stages of Parkinson disease (PD).¹ In some cases, visual symptoms could indicate PD onset before more specific physical signs and symptoms develop. They may even predict disease progression.

“Parkinson can affect almost any part of the visual system, including subtle changes in the retina, ocular motor function, and cortical visual processing,” said John J. Chen, MD, PhD, at the Mayo Clinic in Rochester, Minnesota.

The early signs. In a literature review, Dr. Chen and his colleagues described the ophthalmic abnormalities that can be seen in PD and outlined how dopaminergic therapy can influence these symptoms. For instance, they noted that impairments in color vision and con­trast sensitivity in PD patients may be related to the loss of dopaminergic neurons in the retina.

“These visual manifestations are important to rec­ognize because some of them will be symptomatic in our patients, while others may end up being a prodro­mal symptom that can help with the PD diagnosis,” Dr. Chen said.

Prodromal clues? The prodromal visual manifesta­tions of PD are “the most exciting part of the study,” he said. “Some of these may precede the development of PD and could possibly be used as a biomarker to predict or follow progression.”

To that end, Dr. Chen is conducting a pilot study to explore the use of optical coherence tomography in patients with REM (rapid eye movement) sleep behav­ior disorder, which is strongly associated with a risk for conversion to PD.²

Clinical implications. Most ophthalmologists know that patients with PD often have dry eye from poor blink rate and may also have some ocular motility abnormalities, Dr. Chen said. But PD can cause other visual abnormalities that often go unrecognized—not only impaired color vision and contrast sensitivity but also problems with stereopsis, saccades, and smooth pursuit eye movements. Patients may even develop visual hallucinations.

“These are important to identify,” Dr. Chen said, “be­cause these symptoms can be explained to the patient” as part of the disease process. Moreover, he said, “they may even lead to a diagnosis of unrecognized PD” in some cases.

—Miriam Karmel

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1 Turcano P et al. J Neurol. 2019;266(9):2103-2111.

2 Postuma RB, Berg D. Nat Rev Neurol. 2016;12(11):622-634.

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Relevant financial disclosures—Dr. Chen: None.

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