Image: Visual system colored according to tract directionality: red for L to R, green for A to P, and blue for inferior to superior (Photo courtesy of UNISR).
A new study suggests that visual system alterations occur in early stages of Parkinson’s disease (PD), and that the entire intracranial visual system may be involved.
Researchers at the University of Messina (Italy), University Vita-Salute San Raffaele (UNISR; Milan, Italy), City University of New York (CCNY; NY, USA), and other institutions recruited 20 patients with newly diagnosed PD and 20 age-matched control subjects in order to assess intracranial visual system changes in drug-naïve patients. T1-weighted and diffusion-weighted magnetic resonance imaging (MRI) scans were used to assess changes in the visual system.
Changes in white matter diffusion profile were assessed via diffusion-tensor imaging–based parameters and constrained spherical deconvolution–based connectivity analysis, and by means of white matter voxel-based morphometry (VBM). Alterations in occipital gray matter were investigated by means of gray matter VBM. In addition, morphologic analysis of the optic chiasm was conducted by manual measurement of regions of interest. All study participants also had ophthalmologic examinations.
The results showed significant alterations in optic radiation connectivity distribution, with decreased lateral geniculate nucleus V2 density, a significant increase in optic radiation mean diffusivity, and a significant reduction in white matter concentration in early PD patients. VBM analysis also showed a significant reduction in visual cortical volumes, including in the chiasmatic area, where the left and right optic nerves intersect. The study was published on July 11, 2017, in Radiology.
“Just as the eye is a window into the body, the visual system is a window into brain disorders. These non-motor Parkinson’s symptoms may precede the appearance of motor signs by more than a decade,” said lead author Alessandro Arrigo, MD, of UNISR. “Visual processing metrics may prove helpful in differentiating Parkinsonism disorders, following disease progression, and monitoring patient response to drug treatment. We’re excited by our findings; however, this is just a starting point.”
The visual system detects and interprets information from visible light to build a representation of the surrounding environment, enabling organisms to process visual detail as well as other, non-image photo response functions. Its tasks include the physical reception of light; formation of individual monocular representations; buildup of a nuclear binocular perception from a pair of two-dimensional projections; identification and categorization of visual objects; assessing distances to and between objects; and guiding body movements in relation to the objects seen.
University of Messina
University Vita-Salute San Raffaele
City University of New York