Dry eye disease (DED) is common in people with Parkinson’s disease, with more than 60% of patients reporting that they experience its symptoms, according to a recent meta-analysis.
Clinical signs of this disease, which include a lower rate of blinking, reduced corneal thickness, a lesser tear secretion, and a faster tear drying time, were also significantly more prevalent among Parkinson’s patients than healthy people.
While more work is needed to establish the relationship, these findings highlight a “need for healthcare providers to be vigilant regarding comorbid [co-occurring] DED and regularly offer DED screening and intervention for patients with [Parkinson’s],” the researchers wrote.
The study, “Prevalence and characteristics of dry eye disease in Parkinson’s disease: a systematic review and meta‑analysis,” was published in Scientific Reports.
Significant differences seen in tear secretion, corneal thickness
Parkinson’s is driven by the degeneration of dopamine-producing nerve cells in the brain. The loss of dopamine, a signaling molecule, leads to the disease’s characteristic motor symptoms, as well as a range of non-motor symptoms.
Various eye problems, including poorer visual acuity, difficulties with color perception, and a slower blinking rate, are often among those non-motor symptoms.
Dry eye disease, which occurs when the eyes are not sufficiently moistened by tears, can lead to chronically dry eyes that cause discomfort and risk vision loss, significantly disrupting daily life.
It’s estimated that DED’s prevalence in Parkinson’s is between 53% and 60%, but the relationship is not well studied.
“Due to insufficient reports on the … occurrence of DED in patients with [Parkinson’s], initiatives to establish a multidisciplinary care system, wherein regular ocular examinations and DED screening are incorporated within the routine management of [Parkinson’s], are limited,” the researchers wrote.
Delays in diagnosing dry eye disease can lead to severe and potentially permanent impairments in vision, they added.
Researchers in Japan conducted a systematic review of published studies to better understand the prevalence of DED in Parkinson’s.
Their analysis included 13 studies published from 2004 to 2022, which collectively involved 1,519 Parkinson’s patients and 639 people without the neurodegenerative disease, serving as healthy controls.
Five of these studies reported the subjective prevalence of DED in Parkinson’s patients. While findings were variable among them, 61.1% of patients overall — 667 of 1,061 people — reported experiencing dry eyes.
Subset analyses also compared the prevalence of clinical signs of DED in Parkinson’s patients versus healthy controls.
Across six studies, Parkinson’s patients (230 people) had a significantly lower blink rate — associated with eye dryness — than did 217 healthy people, results showed.
A need for vigilance in checking for, treating dry eye disease
Corneal thinning, a thinning of the transparent layer covering the front of the eye, can result from DED. Three of the studies, covering 199 people with Parkinson’s and 144 people without it, showed significantly thinner corneas in patients than controls.
Parkinson’s patients relative to controls also showed a significantly faster drying of the eye’s surface after blinking in seven studies, and lower tear secretion in six studies, the researchers reported. The low rate of tear production reached significance when analyzed with patients under anesthesia.
To address variability across studies in terms of blink rate and drying of the eye’s surface, the results were analyzed in patients grouped by Parkinson’s severity, as assessed by the Hoehn and Yahr Scale. Findings were not different across these subgroups.
“Our findings emphasize the need for clinicians to be vigilant of the presence of DED when managing patients with [Parkinson’s] and to appropriately adjust the threshold for monitoring and early intervention in these high-risk populations,” the researchers wrote.
Due to a large amount of variability across the studies analyzed, however, these results should be “interpreted cautiously,” the scientists noted. Sources of this variability could include patient demographics, sample sizes, and medication influences.
More work, including “future large-scale studies,” is needed to understand the mechanisms that underly dry eye disease in Parkinson’s and whether Parkinson’s treatments affect eye symptoms.
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