July 2018

NEWS & OPINION

Pilot study shows changes in corneal innervation and trigeminal nerves of newly diagnosed patients with Parkinson’s disease


by Liz Hillman EyeWorld Senior Staff Writer


Histological cross section of the cornea
Source: Karl Brasse, MD

“In this study we showed that confocal-based investigation of corneal innervation changes can be a feasible, noninvasive way to obtain useful information about neurological impairment occurring in PD patients.”
—Alessandro Arrigo, MD

Methods could provide a noninvasive way to study neurological changes

There is a growing body of research showing that non-motor symptoms of Parkinson’s disease (PD), including effects on the visual system, could precede the effects more commonly associated with the condition.1
A pilot study published in the journal Cornea shows “profound” corneal innervation and trigeminal alterations in patients with early Parkinson’s disease, compared to healthy control subjects.2
“Nowadays, Parkinson’s disease (PD) cannot be considered only a neurologic motor impairment,” Alessandro Arrigo, MD, Department of Ophthalmology, San Raffaele University, Milan, Italy, and Department of Biomedical Sciences and Morphological and Functional Imaging, University of Messina, Messina, Italy, told EyeWorld. “Indeed, it is characterized by a number of non-motor alterations, including visual ones. In a recent paper, we showed strong alterations of the entire intracranial visual system in a cohort of newly diagnosed treatment-naive patients, thus providing further support to the hypothesis that PD largely involves brain structures.
“In this context, taking into account that anterior segment-related symptoms (dry eye-related ones) are common clinical complaints by PD patients, we considered it interesting to study corneal innervation involvement in PD patients,” Dr. Arrigo continued. “The new confocal techniques offer the unique opportunity to assess corneal innervation changes noninvasively. Moreover, since corneal nerves are part of the trigeminal innervation, we decided to adopt MRI investigations to assess its possible involvement.”
The small study involved three drug-naive patients who were early in their diagnosis with Parkinson’s disease and 14 age-matched controls. An ocular exam was performed, including assessment of visual acuity, pupillary light reflexes, extrinsic ocular movements, corneal sensitivity, and completion of an Ocular Surface Disease Index questionnaire. Corneal innervation was evaluated using a confocal microscope and MRI assessed water diffusion property changes of the trigeminal nerves.
According to the study, the confocal scans revealed “significant alterations both of deep and subbasal corneal plexa” in the patients with PD. MRI analysis also showed significant differences in the trigeminal nerves of patients with PD compared to control patients, represented by changes in the “anisotropic component of white matter fibers, thus providing an indirect measure of axonal structural integrity loss,” according to the investigators. They also evaluated retinal alterations and found, as previous research has noted, that they occur at an early stage in PD diagnosis.
“In this study we showed that confocal-based investigation of corneal innervation changes can be a feasible, noninvasive way to obtain useful information about neurological impairment occurring in PD patients,” Dr. Arrigo said. “We should consider that the eye is the only organ providing the opportunity to study in a noninvasive way cellular, vascular, and neurological changes. The eye offers a direct window to these systems, otherwise hidden and not reachable to conventional investigations used in clinical practice.”
Dr. Arrigo said larger studies are needed to assess the early pathological changes in the visual system of patients newly diagnosed with PD with follow-up to show progression of these alterations.
What this research, if validated by larger studies, shows is “that what is hidden in the human body is easily available for deep and detailed, noninvasive microstructural investigations in the eye,” Dr. Arrigo said. “The research should move it in the direction to include ophthalmologic investigations in apparently non-related diseases. Moreover, a stronger relationship between ophthalmologists and other medical specialties should be established in order to potentially obtain fundamental information and advances in knowledge, in order to improve patients’ quality of life.”

References

1. Arrigo A, et al. Visual system involvement in patients with newly diagnosed Parkinson disease. Radiology. 2017;285:885–895.
2. Arrigo A, et al. Early corneal innervation and trigeminal alterations in Parkinson disease: A pilot study. Cornea. 2018;37:448–454.

Editors’ note: Dr. Arrigo has no financial interests related to his comments.

Contact information

Arrigo: alessandro.arrigo@hotmail.com

Pilot study shows changes in corneal innervation and trigeminal nerves of newly diagnosed patients with Parkinson’s disease Pilot study shows changes in corneal innervation and trigeminal nerves of newly diagnosed patients with
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