Eye Test May Predict Parkinson-Related Cognitive Decline 18 Months Before Onset

Patients with Parkinson disease experiencing visual dysfunction were associated with worse cognitive performance after 18 months and were at higher risk of developing mild cognitive impairment compared with those with normal vision, according to study findings published in Movement Disorders.

Along with the exacerbation of motor and nonmotor issues such as pain and depression, the degradation of dopaminergic cells seen in PD also includes those in the retina, in which thinning of the retina walls can lead to significant vision and eye issues.

Moreover, additional research has suggested that eye exams may provide a novel approach to diagnose PD in early stages, highlighting the potential significance of structural changes within the eye in the pathogenesis and progression of PD.

As researchers of the present study note, visual dysfunction has been associated with greater risk of dementia in PD, but it is not known whether this translates to structural change over time.

“In patients with PD, white matter changes are seen and can be measured using diffusion-weighted imaging,” the authors wrote. “These increase with worsening cognition and may precede gray matter atrophy.”

Leveraging white matter, which is influenced by retinal dysfunction, researchers tracked longitudinal changes via fixel-based analysis in 77 patients with PD, categorized as having low visual function (n = 22) or normal vision (n = 55), as well as 25 controls. Participants underwent clinical assessments and brain imaging at baseline and after 18 months. Of the patients with PD, 50 had normal cognition throughout the study period, 13 had mild cognitive impairment at baseline, and 13 developed mild cognitive impairment by the follow-up after having normal baseline cognitive performance.

“We compared microstructural changes in fiber density, macrostructural changes in fiber bundle cross-section and combined fiber density and cross-section, across white matter, adjusting for age, sex, and intracranial volume,” explained the study authors.

In their findings, patients with PD experiencing visual dysfunction exhibited diffuse microstructural and macrostructural white matter changes at baseline, and after 18 months, were more likely to develop mild cognitive impairment compared with those with normal vision (P = .008).

Baseline low visual performance was additionally associated with:

• further reductions in fiber cross-section at longitudinal follow-up,
• more extensive white matter changes at baseline than those seen in patients with mild cognitive impairment, and
• macrostructural changes involving the fronto-occipital fasciculi, external capsules, and middle cerebellar peduncles bilaterally.

Conversely, no longitudinal white matter change was observed in patients with mild cognitive impairment at baseline.

“These findings provide insights into the temporal pattern of white matter degeneration associated with cognitive impairment in PD and highlight an at-risk population for possible therapeutic intervention,” concluded the study authors.

Reference

Zarkali A, McColgan P, Leyland LA, Lees AJ, Weil RS. Visual dysfunction predicts cognitive impairment and white matter degeneration in Parkinson's disease. Mov Disord. Published online January 9, 2021. doi:10.1002/mds.28477