Retinal Implants and Visual Psychophysics

Several research groups are currently working at the development of visual prosthesis for different sites of the visual system (visual cortex, optic nerve, or retina); the aim being to restore some vision in blind patients. The most advanced of these prostheses are in clinical evaluation or even on market.

At the ophthalmology division of HUG, we are studying the psychophysical aspects associated to visual prosthesis and we collaborate with Second Sight Medical Products Inc. to evaluate in  a clinical trial their retinal implant Argus II® .

The first objective was to determine minimum requirements for retinal prosthesis to restore useful vision in blind patients with external retinal degeneration. For that purpose, the group used simulations of artificial vision for daily living tasks, such as reading, visuo-motor coordination and orientation as well as mobility tasks. These results provided important clues regarding visual recovery that could be expected considering current technology limits. This knowledge is mandatory for the design of visual prostheses and it is of main interest for research groups involved in this field. These Results also provide essential information on the mechanisms that modulate visual function.

Afterwards, the team continued their psychophysical testing with patients carrying a retinal implant. We wanted to determine the usefulness of such systems for blind patients and evaluate various stimulation parameters in order to improve present systems. The knowledge acquired with our simulation studies was and is of great help for such clinical studies.

The epi-retinal implant Argus II from Second Sight has been evaluated in an international clinical study. Thirty patients have been enrolled (http://clinicaltrials.gov/show/NCT00407602), of which two have been implanted at the HUG. The system works as follows: the patient wears glasses incorporating a micro-camera. Images from the camera are transferred to a small processor that communicates with the implanted simulator through a coil fixed on the glasses (wireless induction). The simulator is fixed on the ocular surface and connected to the retinal electrodes to inject stimulation currents into conserved retinal cells, in order to induce visual sensations. A series of psychophysics tests, as well as regular follow-ups, were conducted with the implanted patients. Our patient, who received in beginning of 2008 the first implant in Switzerland, is still pursuing measurements in the context of this study.

We mainly worked with the Geneva patients. For the collection of some specific data, however, we also travelled to see patients of other centers in Europe participating at the study.

Summarised, the outcomes of the study are:

  • The Argus II implants are well tolerated (with few medical complications)
  • There are almost no technical problems. Most implants are still functional after 6-9 years
  • The functional results are patient-dependent. Some patients take good advantage of the system, others little. Overall, outcomes for visual performance tests are better with system on than system off, but this does not really prove a real benefit for all patients.
  • Most of the patients do not regret their participation in the study.

For the future, the challenge will be to improve visual prosthesis in a way to reach functional results that are comparable to those obtained with cochlear implants for audition.

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Last update : 29/01/2019