Researchers at University College London have published two studies of people with Parkinson's disease revealing that those with visual problems are more likely to develop dementia months later.
Many studies have already suggested that a simple examination of the eye could detect an early warning sign of Alzheimer's disease, amyloid plaques in the retina. And if the same vision test could also be used for the prognosis of Parkinson's disease, the second most common neurodegenerative disease in France after Alzheimer's disease, which is also a major cause of disability in the elderly. Researchers at University College London published a study in Movement Disorders stating that changes in vision can precede the cognitive decline that occurs in many people with Parkinson's disease.
"People with Parkinson's disease who have visual problems are more likely to develop dementia, and this appears to be due to underlying changes in their brain wiring. Vision testing could provide a window of opportunity to predict Parkinson's dementia before it starts, which may help find ways to stop cognitive decline before it's too late. "The study's lead author, Dr. Angeliki Zarkali, explains. The researchers studied 77 people with Parkinson's disease and found that a vision test can tell which patient will develop dementia a year and a half later.
A link between cognitive and vision decline
Dementia is a common aspect of Parkinson's disease, which is estimated to affect approximately 50% of people within 10 years of diagnosis. "These results add weight to previous studies conducted at one time that suggested that performance on vision tests, involving commonly used eye charts and distorted images of cats and dogs, was linked to the risk of cognitive decline. "The researchers point out. "The study also found that those who developed Parkinson's dementia had losses in brain wiring, including areas related to vision and memory. »
Patients with Parkinson's disease and visual dysfunction showed poorer cognitive performance at follow-up and were more likely to develop mild cognitive impairment compared to those with normal vision. A second study published in Communications Biology involved 88 people with Parkinson's disease, 33 of whom had visual dysfunction and were therefore considered at high risk of dementia, and 30 healthy adults. All participants agreed to undergo a brain MRI scan so that researchers could examine changes in the structural connectivity of the brain.
Valuable help for clinical trials
In the healthy brain, there is a correlation between the strength of the structural (physical) connections between two brain regions and the extent to which these two regions are functionally connected. This coupling is not uniform across the brain, as there is a degree of "decoupling", particularly in areas involved in higher-order processing, to provide the flexibility needed to allow abstract reasoning. But excessive decoupling appears to be linked to poor cognitive outcomes, as researchers have found that people with Parkinson's disease have a higher degree of decoupling throughout the brain.
In addition, patients with Parkinson's disease who had visual dysfunction had greater decoupling in certain areas of the brain, particularly in areas related to memory. "These two studies help us understand what happens in the brains of people with Parkinson's disease who experience cognitive decline, as it appears to be due to a breakdown in the wiring that connects different regions of the brain," says Prof. Angeliki Zarkali. If further studies are needed to confirm these findings, the researchers hope that their discovery will prove useful in clinical trials conducted in patients suffering from the disease.
Indeed, vision tests could help researchers identify people who should be given priority access to new drugs to slow the progression of their disease. And if new treatments come to light, then these tests would also help them identify which patients should benefit from which drugs. According to the French health insurance system, Parkinson's disease, a chronic disease that progresses over several years or decades and whose causes are still uncertain, affects 1% of the population over the age of 65: 100,000 to 120,000 people are affected in France. It begins on average between the ages of 55 and 65, sometimes appearing after the age of 75 and in rare cases before the age of 45.
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