Implants of cells from the human retina improved motor symptoms in patients with Parkinson disease, and they appear to be safe and well tolerated, a new study published in the December issue of Archives of Neurology said.

Parkinson disease is a neurodegenerative disorder characterized by tremor, rigidity, postural instability, and slowed ability to start and continue movements.

Most patients with PD require therapy with the medication levodopa to control symptoms three to five years after a diagnosis of PD. However, disease progression and long-term oral treatment with levodopa may lead to the development of motor fluctuations and dyskinesias (difficulty or distortion in performing voluntary movements).

Human retinal pigment epithelial (RPE) cells produce levodopa and can be isolated from post mortem human eye tissue, grown in culture, and implanted into the brain attached to microcarriers.

These implants have ameliorated the motor deficits in animal models of Parkinson disease, according to background information in the article.

In a study conducted by Natividad P. Stover of the University of Alabama, six patients with advanced Parkinson disease received cell implants, which were inserted into the brain tissue.

"The implants were well tolerated," the authors report. "We observed an average improvement of 48 percent at 12 months after implantation in the Unified Parkinson's Disease Rating Scale motor subscore with the patient in the off state, which was sustained through 24 months," the researcher said.