This is the first time anyone has shown these findings several years before diagnosis, and these results were made possible by the largest study to date on retinal imaging in Parkinson’s disease.

The use of data from eye scans has previously revealed signs of other neurodegenerative conditions, including Alzheimer’s, multiple sclerosis and, most recently, schizophrenia, in an emerging and exciting field of research referred to as “oculomics”.

Eye scans and eye data have also been able to reveal a propensity to high blood pressure; cardiovascular disease including strokes; and diabetes.

Doctors have known for a long time that the eye can act as a ‘window’ to the rest of the body, giving a direct insight into many aspects of our health.

High-resolution images of the retina are now a routine part of eye care – in particular, a type of 3D scan known as ‘optical coherence tomography’ (OCT), which is widely used in eye clinics and high-street opticians.

In less than a minute, an OCT scan produces a cross-section of the retina (the back of the eye) in incredible detail – down to a thousandth of a millimeter.

These images are extremely useful for monitoring eye health, but their value goes much further, as a scan of the retina is the only non-intrusive way to view layers of cells below the skin’s surface.

Lead author Dr Siegfried Wagner (UCL Institute of Ophthalmology and Moorfields Eye Hospital), who is also principal investigator of several other AlzEye studies, said: “I continue to be amazed by what we can discover through eye scans. While we are not yet ready to predict whether an individual will develop Parkinson’s, we hope that this method could soon become a pre-screening tool for people at risk of disease.

“Finding signs of a number of diseases before symptoms emerge means that, in the future, people could have the time to make lifestyle changes to prevent some conditions arising, and clinicians could delay the onset and impact of lifechanging neurodegenerative disorders.”

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