This article was written for physicians. Patients should talk to their Eye M.D. if they have questions about the content.

Background

Artificial vision describes a set of techniques designed to restore some vision to those with severe vision loss by replacing a defect or missing link along the visual pathway. Several models have been proposed, including a sub-retinal prostheses (designed to replace photoreceptors in the retina), epi-retinal prostheses (designed to communicate directly with the ganglion and bipolar cells), optic nerve stimulation, and cortical prostheses (designed to stimulate the visual cortex directly for patients without a viable optic nerve).

In 1929, electrical stimulation of the occipital lobe of the human cortex resulted in perception of a small point of light, called a phosphene. 1 Studies of electrical stimulation and the production of phosphenes led to research on cortical prostheses that used implanted electrodes. 2,3 Current investigations of cortical electrode arrays include the Dobelle artificial vision system and the Utah Intracortical Electrode Array.4 The Utah Intracortical Electrode Array has undergone several years of testing in animals for safety and efficacy.

Technology

A description of an implanted cortical prostheses and external electronic interface was reported by W.H. Dobelle.5 A sub-miniature television camera and ultrasonic distance sensor are mounted on a pair of eyeglasses worn by the patient. The sensors are connected to a miniature computer, which is worn on a belt-pack. The computer processes the video and distance signals, reduces the noise, and triggers a microcomputer to transmit pulses to a 68 platinum electrode array implanted on the surface of the visual cortex. Each electrode produces 1-4 closely spaced phosphenes. The external computer package is about the size of a dictionary and weighs ten pounds, with the computer battery lasting about 3 hours. It requires recalibration each day, and ongoing training of the user. The purpose of the Dobelle artificial vision system is to promote independent mobility, but not for reading. It is contraindicated in blind people with severe chronic infections and those blinded by stroke or cortical trauma.

Results

Results of implantation of this device were described for one 62-year old subject, who had the device implanted in 1972. The patient is described as having lost vision in one eye at age 22 and in the other eye because of trauma at the age of 36 years. No problems or infections were reported with the implantation. The patient could count fingers and achieved a 20/1200 visual acuity with tunnel vision. The patient could reportedly navigate by himself in unfamiliar environments. With the addition of a more powerful computer and further magnification, the patient’s visual acuity improved to 20/400. A second patient implanted with the cortical prosthesis at the same time has never seen phosphenes.

Questions Regarding Clinical Application

  • Does patterned electrical stimulation via implantation of electrodes lead to discernable pattern recognition?
  • What are the surgical risks, and risks of long-term implantation, i.e., infection, immune response, discomfort?
  • How do patients adapt to different aspects to the electrical stimulus, and how does that affect specifications and effectiveness of the technology?
  • How viable is the technology for long-term (lifetime) implantation?
  • Can this technology result in reproducible good image resolution, ultimately enabling performance of everyday tasks? For which patients can it be effective?

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