A fascinating study by researchers at the University of the Basque Country. Thinning of the retina, measured using sophisticated equipment, makes it possible to detect Parkinson's disease and identify patients who are at a higher risk of cognitive impairment.
The biggest worry for patients who have been given a diagnosis of Parkinson’s or another neurodegenerative disease has to do with the future: “Now what? “What should I expect? What will happen to me?” Neurologists, however, are often unable to provide precise answers to these questions, “because,” as Ane Murueta-Goyena, researcher at the University of the Basque Country, explains, “the evolution of the disease tends to be highly varied: some patients experience no really serious change over the years, while others may wind up with dementia or in a wheelchair.”
Being able to identify early those Parkinson’s patients who are at a higher risk of cognitive impairment would be of considerable benefit, because it would make it possible to put every treatment tool to use at as early a stage as possible. A new path in this direction, according to Ane Murueta-Goyena's team, could be an analysis of the characteristics of the retina.
This exam is already used to diagnose Parkinson's (and is being trialled as a diagnostic tool for Alzheimer’s-related dementia as well), but until now it has only been able to provide confirmation of a disease hypothesis, not predict how the condition will evolve. Now, however, the researchers at the University of the Basque Country have gone further, also “exploring”, as we mentioned above, the possibility of predicting cognitive impairment—with significant results, which have been published in the npj Parkinson’s Disease scientific journal, belonging to the Nature group.
But why the retina, specifically?
A “window to the brain
This essential membrane, located at the back of the eye and in direct contact with the nerves that convey visual information to the central nervous system, is a sort of perpetually open window through which to observe the brain’s condition. By examining the retina using a completely harmless technique called optical coherence tomography (the same method used to monitor the evolution of a number of different eye diseases, such as macular degeneration), the University of the Basque Country researchers were able to learn which patients were going to experience a rapid decline in cognitive and motor terms and which were not.
Specifically, the researchers analysed data from 156 patients with Parkinson's and 72 healthy control subjects (over the course of six years, from 2015 to 2021), with very characteristic findings in terms of disease evolution. Initially, as a matter of fact, the thickness of one of the locations measured (the parafoveal ganglion cell inner plexiform layer, to give it its technical name) decreases at twice the rate in Parkinson's patients in comparison to the control subjects, until reaching minimum values. At that point, however, retinal degeneration stabilises, and a reverse phenomenon occurs: in those patients who will worsen, the retinal thinning slows, while the cognitive and motor decline continue to progress; the slower the changes to the retina, the more severe and rapid the other types of deterioration. Meanwhile, at another measurement location (the peripapillary retinal nerve fibre layer), the retinal thinning and worsening of the Parkinson's always progressed at the same speed.
Highly precise parameters
According to the researchers, the first measurement location, both alone or in combination with the second, could become a very important tool for early diagnosis, especially in terms of setting out, from the start, the treatment strategy best suited to each individual patient.
Optical coherence tomography is available in many ophthalmology departments. Therefore, if these data are confirmed, this exam could become a differential diagnostic tool, one recommended when Parkinson's is first diagnosed, but it could also be well-suited for the sort of mass screening that could be offered to the entire population upwards of a certain age bracket.
