Subretinal Implants

Research that led to the subretinal implant began in 1995. The device has now reached the stage of clinical testing after 10 years of research. Measuring 3 x 3 x 0.1 mm, the chip contains 1,500 photodiodes, amplifiers and electrodes. The external energy supply is a power line implanted subdermally. The implant depends on the light reaching the retina. This becomes a stimulus to the photodiodes of the implant. Because the implant is placed directly on the retina, it can communicate through the electrodes to the nerves in the eye.

Eberhart Zrenner, MD, presented the results of the first trials. After 30 days, the seven patients with implants did not experience any complications during or after the procedure. Some visual perception was restored in six out of the seven patients. Despite the lengthy implantation process (5 hours), improvements were recorded. Recognition of vertical and horizontal orientation pixels showed improvement along with differentiation of angles and movement. A wide range of brightness was perceived. The brightness and size of the dots viewed correlated with the voltage of the stimulation.

Even though results differed among the patients, all the patients were happy with the outcome. Just to see light again was a great experience. The next trials will include the effects of a long term implantation of 3 – 6 months. For now, the researchers are working on ways to improve the spatial resolution and the energy supply with the stimulation. The first trial producing positive feedback is encouraging. However, the subretinal implant is far from perfect but shows signs of potential vision for the blind.

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