Application of microfabrication technology to retinal prosthesis development
 
DB Shire, Ph.D., JL Wyatt, Ph.D., and J.F. Rizzo III, M.D.
 
VA Center for Innovative Visual Rehabilitation, Jamaica Plains, Boston, MA
 
Objectives: The purpose of this effort is to develop a chronically implantable retinal prosthesis to restore useful vision to patients who are blind with retinal diseases such as age-related macular degeneration (AMD). AMD is the leading cause of degenerative vision loss in the veteran population and in the developed world. There is no known cure for this disease, and its progress can only be slowed using currently available treatments. We are applying state-of-the-art microfabrication technology in micro-electromechanical systems (MEMS) to develop a process for creating the structures necessary to interface with the delicate retinal tissue. Two examples of this effort are a model flexible, inflatable prosthesis which is insertable through a narrow incision and may be expanded inside the eye to assume its proper shape for implantation, and micromachined retinal tacks which serve as a means of attaching our device to the retinal surface with minimal trauma to nearby tissue.
 

 
Methods: In the case of the inflatable retinal prosthesis, a central silicon hub which will contain the CMOS stimulating circuitry is micromachined to create a nib for attachment of a flexible silicone tube carrying compressed air to the implant. An array of flexible polyimide 'tentacles' radiates outward from this central hub, and embedded in each is a microchannel to facilitate inflation after insertion through a small pars plana incision in the sclera. These structures also contain the array of iridium oxide stimulating electrodes. In the case of the retinal tacks, Bosch process silicon micromachining techniques have been applied to the problem of developing a suitable means for attaching the above prosthesis to the eye in a biocompatible manner. An SEM micrograph of a sample tack is shown in the figure. Advanced photolithography techniques have recently been used to develop sharper tack points to facilitate insertion, and these will be demonstrated at the meeting.
 
Results: A model inflatable retinal prosthesis has been developed which may be bent into a nearly arbitrary state to facilitate insertion of the device through a narrow incision (for safety), yet may be inflated once inside the eye to over 9 mm in diameter. This device thus may be used to stimulate an area of the retina covering over 30 degrees of the patient's former field of view. Its flexible design also allows the implant to conform to the spherical shape of the anterior surface of the eye. Custom designed micromachined retinal tacks have also been developed for the purpose of attaching this device to the retina.
 
Conclusions: The application of recent developments in microfabrication technology to retinal prosthesis development is ushering in an exciting new era in visual rehabilitation research. The present efforts represent but two examples of the potential of collaboration between the nanotechnology and rehabilitation R&D communities.
 
Funding acknowledgment: This work was funded by the VA Rehabilitation Research and Development Service.