Deep brain stimulation for visuomotor function in Parkinson's disease

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The sufferers of a prevalent condition called Parkinson's disease have tremors, rigidity, and slow movements. In addition to its effects on body movements, Parkinson's disease affects many other brain functions. Visual impairments are common in Parkinson's patients who have difficulties holding their eyes steady at a given location, seamlessly look around and read, and refocus their eyes from one image to the other placed at different depths. About two thirds of Parkinson's disease patients have problems coordinating two eyes' movements necessary to refocusing at different depths, i.e., abnormal vergence causing disabling double vision and abnormal depth perception. Most treatment options available to Parkinson's disease patients are limited to their effects on tremor, rigidity, and slowness – their impact on visual function is poorly understood. Orbital muscle surgeries are not ideal treatments given the brain's continually changing state due to the disease's degenerative nature. Presently available strategies of deep brain stimulation have variable effects on eye movements and vergence function. Our research program aims to identify the best possible therapeutic approach using deep brain stimulation to improve vergence eye movements in Parkinson's disease while continuing to offer its other benefits. Our multidisciplinary program has two aspects. One part of the study will examine the effects of deep brain stimulation on vergence abnormalities affecting their ability to focus at various depths. Using state-of-the-art, high-resolution, research-grade ophthalmic equipment, we will examine how deep brain stimulation can improve the patients' ability to refocus and treat vergence abnormalities affecting depth perception. Once we identify these favorable changes, we will correlate them with the stimulated anatomical location within the same patient's brain. To do so, we will combine novel computer simulations of deep brain stimulation-induced electrical field overlaid upon the patient's magnetic resonance images. The knowledge gained will allow us to find the most beneficial stimulation locations to improve vision while offering improvement in tremors, rigidity, and slow movements.