How to Make a Bionic Eye: Try a Little Engineering Vision

PHILADELPHIA, June 18--Whether you're planning to market a pacemaker, an artificial hip or knee, or a cochlear implant, design considerations are of the utmost importance from the ground up. This was the takeaway message from the MD&M East MedTech Innovate Seminar focusing on the design of implantable devices. Speaking on "Retinal implant: Designing the World's First Bionic Eye--A Fully Implantable Retinal Prosthesis," Robert Greenberg, president and CEO of Second Sight Medical Products Inc., noted that a series of design iterations were required before the company was able to successfully develop an eye implant capable of helping patients to achieve some vision.

Internally, the Argus device incorporates a 4 x 4 electrode array containing 60 independently controlled electrodes, electronics, and a radio-frequency receiver. Externally, it consists of a small wearable computer and a pair of glasses with a small video camera similar to a normal cellphone camera. However, early versions of the implant were not surgeon friendly, requiring surgery time of eight hours. After incorporating an array of design modifications, the company was able to produce a device that can be surgically implanted in just two hours.

The electrodes, Greenberg explained, are made from platinum. "However, even noble metals like platinum can corrode under extensive neural stimulation," he added. Platinum oxidation, in turn, can cause surface expansion and result in cracks. In addition, it can cause greater impedance. To prevent metal corrosion, the company decided to fabricate the device's electrodes from platinum gray, a more robust type of platinum than either shiny platinum or platinum black. In addition to these materials challenges, the company had to consider that the electronics can injure sensitive retinal tissue, while incorporating a battery small enough to fit in a miniature form factor.

Determining the efficacy of the device was complicated by the fact that there was no existing measurement for determining levels of vision impairment. However, through a series of tests, the company--and eventually FDA--determined that the implant helped to improve quality of life by enabling patients to perform such functions as following straight lines while walking, reading characters, and identifying colors. One patient, according to Greenberg, quipped after gaining the ability to sort socks by color, "Unfortunately, now I have to do the laundry."

For future versions of the device, the company intends to improve the design of both the software and hardware, incorporating advanced image-processing capability, enhanced acuity, color vision, and human factors. At the same time, it is also considering increasing the number of electrodes. "However, there's probably a biological limit to how many electrodes will make a difference," Greenberg commented. "The theoretical limit is probably around 200."

Bob Michaels is managing editor of Medical Product Manufacturing News.