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Eye tests predict Parkinson’s-linked cognitive decline 18 months ahead

Simple vision tests can predict which people with Parkinson’s disease will develop cognitive impairment and possible dementia 18 months later, according to new UCL research.

The study, published in Movement Disorders, adds to evidence that vision changes precede the cognitive decline that occurs in many, but not all, people with Parkinson’s.

In another new study published today in Communications Biology, the same research team found that structural and functional connections of brain regions become decoupled throughout the entire brain in people with Parkinson’s disease, particularly among people with vision problems.

The two studies together show how losses and changes to the brain’s wiring underlie the cognitive impairment experienced by many people with Parkinson’s disease.

Lead author Dr Angeliki Zarkali (Dementia Research Centre, UCL Queen Square Institute of Neurology) said: “We have found that people with Parkinson’s disease who have visual problems are more likely to get dementia, and that appears to be explained by underlying changes to their brain wiring.

“Vision tests might provide us with a window of opportunity to predict Parkinson’s dementia before it begins, which may help us find ways to stop the cognitive decline before it’s too late.”

For the Movement Disorders paper, researchers studied 77 people with Parkinson’s disease and found that simple vision tests predicted who would go on to get dementia after a year and a half.

The Communications Biology study involved 88 people with Parkinson’s disease and 30 healthy adults as a control group, whose brains were imaged using MRI scans.

In the healthy brain, there is a correlation between how strong the structural (physical) connections between two regions are, and how much those two regions are connected functionally. That coupling is not uniform across the brain, as there is some degree of decoupling in the healthy brain, particularly in areas involved in higher-order processing, which might provide the flexibility to enable abstract reasoning. Too much decoupling appears to be linked to poor outcomes.

The researchers found that people with Parkinson’s disease exhibited a higher degree of decoupling across the whole brain. Areas at the back of the brain, and less specialised areas, had the most decoupling in Parkinson’s patients.

Parkinson’s patients with visual dysfunction had more decoupling in some, but not all brain regions, particularly in memory-related regions in the temporal lobe.

Dr Rimona Weil (UCL Queen Square Institute of Neurology), senior author of both papers, said: “Our findings could be valuable for clinical trials, by showing that vision tests can help us identify who we should be targeting for trials of new drugs that might be able to slow Parkinson’s. And ultimately if effective treatments are found, then these simple tests may help us identify who will benefit from which treatments.”