New concept may explain vision problems in Parkinson's disease

(Medical Xpress)—Are patients with Parkinson's disease "blind to blindsight?" That's not a trick question, but the focus of an inquiry by neuroscientists from Rush University Medical Center as well as the Centre Hospitalier and University of Luxembourg.

The "blind to blindness" concept is described in the June issue of the journal Brain by Dr. Nico J. Diederich, from Centre Hospitalier and University of Luxembourg, who is a visiting scholar at Rush University. He was joined by the Rush researchers Glenn Stebbins, PhD, and Dr. Christopher G. Goetz, and neuropsychologist Christine Schiltz, PhD, from the University of Luxembourg.

The scientists developed the concept of "blind to blindsight" to integrate data on visual impairments that contribute to the disability and diminished quality of life in patients with Parkinson's disease.

Blindsight is observed in people who are blind as a result of a lesion in the visual cortexof their brain. Although these individuals are blind, they maintain the ability to sense accurately a light source or a rapid movement without being aware of it. Strangely, blindsighted patients even can respond appropriately to emotional facial expressions, especially those expressing fear or danger. It is believed that these visual stimuli can be turned directly into actions (e.g., movement of the eyes) by passing through lower areas of the brain. Thus, these retained visual functions operate as unconscious responses to visual stimulation even when there is extensive damage to the visual cortex. .

Conversely, patients with Parkinson's disease, who do not have a problem with their general vision, are unable to do these tasks: they display slowness and reduced accuracy of pursuit eye movements. They often have difficulties grasping a moving object, and show decreased sensitivity to low contrast and impaired ability to read "right away" other people's facial expressions.

Taken together, these Parkinson's disease symptoms represent major impairments in blindsight – hence, "blind to blindsight." Based on this new concept, the researchers could now propose a new concept how to comprehensively understand within one visual system—blindsight—numerous visual signs and symptoms of patients with Parkinson's disease. Impairment of the evolutionary old networks in the brain operating within the blindsight visual system form the basis of the visual problems in Parkinson's disease.