Parkinson's disease involves the degeneration of nerve cells in the brain – and its main symptoms are tremors and shaking when standing, sitting or lying still.
The area of the brain that is affected is known as the basal ganglia which is responsible for regulating movement and coordination. Chemical neurotransmitters send signals to and from the basal ganglia. One of the main neurotransmitters involved is dopamine.
Now researchers report that changes in vision may be an early indicator of Parkinson's.
Non-motor symptoms in Parkinson's disease patients include visual
changes, such as an inability to perceive colours, a change in visual
acuity, and reduced blinking, which can lead to dry eye, the study
The neurodegenerative condition is caused by the loss of neurons in several brain structures, resulting in tremors, rigidity or stiffness, along with impaired balance and coordination, the Italian researchers explained.
Symptoms often undiagnosed
But, "although Parkinson's disease is primarily considered a motor disorder, several studies have shown non-motor symptoms are common across all stages of the disease," said lead researcher Dr Alessandro Arrigo. He is a resident in ophthalmology at the University Vita-Salute San Raffaele of Milan.
"However, these symptoms are often undiagnosed because patients are unaware of the link to the disease and, as a result, they may be undertreated," Arrigo added.
These symptoms "may precede the appearance of motor signs by more than a decade," Arrigo said.
The graphic below shows differences in the brain caused by Parkinson's disease involving the substantia nigra, a basal ganglia structure:
This study included 20 newly diagnosed Parkinson's patients who had not yet received treatment, and a "control" group of 20 people without the disease. Brain scans revealed that the Parkinson's patients had significant abnormalities within the visual system brain structures.
The study findings were published online in the journal Radiology.
Assessing visual system problems in patients "may prove helpful in differentiating Parkinsonism disorders, following disease progression, and monitoring patient response to drug treatment," Arrigo said in a journal news release.
Further research is needed to learn more about the timing of visual system degeneration, along with specific changes, Arrigo said.
Treating Parkinson's disease
What is Parkinson's disease?
Causes of Parkinson's disease