In-vivo Test of Visual Prosthetic

A few years, a group of researchers from such institutions as Cornell University and MIT tested the second-generation version of their Boston visual prosthesis (concept drawing shown at right). This device includes a 15-channel stimulator chip inside a hermetic titanium case and secondary data/power receiving coils that surround one’s cornea upon implantation. The idea for this prosthetic came after this and other groups around the world demonstrated that focal electrical stimulation of the retinal ganglion cells in patients with degenerative retinal diseases can yield responses from the cells, which hints at the possibility of one regaining their sight if enough electrical stimulation is applied. However, it soon became apparent that a chronic implantable device was necessary to return a patient’s eyesight.

The second-generation version of this prosthetic improves on the first-generation model in three important ways. First, the second-generation is designed with larger receiver coils to make data and power telemetry easier; the team hoped to minimize the impact of adding volume on to their existing device by having the coils conform to the patient’s eye. Also, a hermetic titanium case to house the circuitry was designed to allow the prosthetic to be viable for years of usage. Finally, the second-generation model was designed with an electrode array extending from the titanium case to the superior-temporal quadrant, which allows for an easier implantation surgery when compared with the first-generation version.

One of the primary purposes of the test was to determine if long-term electrode pulsing was a possibility with the new design. To assess this possibility, the electrodes used for the device were subjected to long-term in vitro pulsing. Additionally, the entire prosthetic system was tested dry on the bench, in a phosphate buffered saline solution, and in vivo inside a Yucatan mini-pig.

The device worked reliably for over three months; however, tension on the conjunctiva as a result of the coils forced the experiment to end early. In response, the researchers redesigned both the coil forming process and the connection between the coils and the titanium case so as to ease the tension. They remain hopeful that this technology can someday be used to help people afflicted by degenerative retinal diseases.

I found this article interesting enough to create a blog about it partly because I did not know the current status of visual prostheses. The primary reason remains that I am fascinated by prostheses in general, and especially by prostheses that affect prominent body parts/functions. I do not think that I am alone in this viewpoint.

http://dspace.mit.edu/handle/1721.1/58563