Parkinson’s detectable through eye exam?

It's neither an avant-garde brain scan nor invasive test that could revolutionize detection of Parkinson's disease among asymptomatic patients, but routine imaging found in the office of a doctor of optometry.

New research published Aug. 18 in the journal Acta Neuropathologica Communications details how the in vivo diagnostic imaging afforded by optical coherence tomography (OCT) may help detect miniscule retinal changes associated with Parkinson's long before the first symptoms become evident.

Categorized by bodily tremors, bradykinesia and impaired coordination, Parkinson's affects nearly 1 million Americans, but its cause is unknown. Onset begins subtly when dopaminergic cell death accumulates proteins called Lewy Bodies in the brain. However, outward symptoms only present once 70% of dopaminergic cells die, making early detection equally crucial and difficult.

Therefore, scientists at University College London (UCL) investigated retinal ganglion cell (RGC) apoptosis as a surrogate marker for changes in the brain. Mimicking Parkinson's cell death in rodent models, researchers used longitudinal in vivo imaging with detection of apoptosing retinal cells (DARC) and OCT to measure cell death before and after administration of the anti-diabetic drug, rosiglitazone.

Researchers found that this nerve-cell-protecting drug helped reduced retinal cell death, further suggesting that rosiglitazone may have potential as a Parkinson's treatment option.

"Moreover, the results advocate use of the retina as an endpoint for the evaluation of possible therapeutic strategies in [Parkinson's disease]. This work highlights the advantages of using real-time parameters to evaluate tissue changes in the retina (DARC and OCT) in this [Parkinson's disease] model, methodologies that, due to their noninvasive nature and widespread availability, could easily be applied to the patient," the study concludes.

In other words, OCT's ability to provide an accurate and noninvasive cross-sectional view of living tissue directly related to the brain, and its widespread availability and use among eye doctors, could make it invaluable to determining effective intervention timing for this neurodegenerative disease.

Eyes: Windows to our health

Although the UCL research is still relatively new, the vast potential implications for doctors of optometry and comprehensive eye examinations isn't. In fact, the study bolsters one important connection that optometry has long known.

"The eye is a direct extension of the brain," says Andrew Morgenstern, O.D., AOA consultant and former optometric subject matter expert for the Vision Center of Excellence at Walter Reed National Military Medical Center. "This study reaches a logical conclusion. As doctors of optometry, we're looking at brain tissue with each eye examination we conduct, so it makes sense for doctors of optometry to be knowledgeable, educated and aware of not only brain diseases, but also the technology that evaluates those diseases."

Using the eye as a proxy for neural health isn't a novel supposition—it's a fast-evolving realm of scientific inquiry, especially as brain diseases and injuries take center stage.

Earlier this year, University of Minnesota researchers used spectral imaging of the retina to detect amyloid plaque buildup—a key marker for Alzheimer's disease—in a live mouse model. Separately, the visual system's connection to traumatic brain injuries (TBIs) draws increasing scrutiny, and AOA offers members valuable resources to know how to properly diagnose and manage these cases.

• Access the Brain Injury Electronic Resource Manual (BIERM) Volume 1A: Traumatic Brain Injury Visual Dysfunction Diagnosis
• Access the BIERM Volume 1B: Traumatic Brain Injury Visual Dysfunction: Optometric Management and Advanced Topics

"Simply put, eye doctors are the only doctors who get to look at the brain directly without scanning or cutting into the body," Dr. Morgenstern says. "This validates why a regular, comprehensive eye examination is so beneficial to overall health."

Read more about OCT's impact on optometry in the October 2015 edition of AOA Focus, or optometry's role in TBI in the September 2014 edition of AOA Focus.