Subretinal electronic chips allow blind patients to read letters and combine them to words. Technology and the transchoroidal implantation procedure

for the German Subretinal Implant Project (Retina Implant)
  
  Light sensitive external powered microchips were surgically implanted subretinally in the macular region of volunteers blind from hereditary retinal dystrophy. The implant consists of a foil bound array of 1500 micro photodiodes (chip) each with its own amplifier and local stimulation electrode. The size of subretinal active film bound visual prostheses and their necessary connection to extraocular structures for energy supply requires a transchoroidal surgical implantation procedure. A safe surgical transchoroidal subretinal access is mandatory for a successful chronic implantation in humans. The visual scenes are projected naturally (without the need of a camera) in the physiological way through the eye onto the chip under the transparent retina. The chip generates a corresponding pattern of about 1500 pixels each of them stimulating the retina with light intensity dependent electric pulses.
  Eleven volunteer legally blind patients were implanted with a transdermal cable bound device in a first series. A transchoroidal subretinal implantation of the stimulation device (active implant) was carried out. The implant consisted of a stimulation chip on a polyimide film and additional stimulation electrode array with16 TiN electrodes. The energy which was required for the stimulation was delivered via a retro auricular plug transdermal by a cable and transchoroidal by a polyimide film with supply lines. Thus subretinal stimulation experiments could be carried out successfully in chronic subretinal implanted patients for the first time. According to schedule the implants in the first series had to be removed after 30 days and after 3 month for the last 3 patients. The following patients kept the implants. Careful radiodiathermy with precise adjusted parameters allowed penetrating the choroid without bleeding. A specially designed guide film was used as an implantation instrument. Silicone oil served as a tamponade.
  Implantation was successfully performed in all patients. No surgically induced adverse events (choroidal bleeding, retinal detachment, inflammation etc.) were observed during the procedure or the follow up period of up to 3 years. The implants remained stable in all cases.
  The new developed transchoroidal implantation and explantation procedure was successfully established in humans. This procedure enables a safe chronic stable subretinal implantation and explantation of large scale electronic prostheses which are necessary to create a usable visual percept. With these results a variety of experiments was carried out. Visual percepts were monitored starting with the first implanted patient. Subsequently three previously blind patients could locate objects on a table. One out of these first eleven patients was able to correctly describe and name this objects like knife and fork was able to discern fruits and shades of grey. Without training the regained function enabled him to localize and approach persons in a room and to read large letters and complete words after years of blindness. These results demonstrate for the first time that a subretinal chip with 1500 micro photodiodes can create detailed meaningful visual percepts in previously blind patients.
  The transchoroidal subretinal implantation surgery which was previously regarded as not manageable is a challenging complex surgical procedure which proved to be a safe strategy and led to these unique visual results. Good surgical results determine the basis for a successful electrical stimulation and are of prime importance for the whole procedure. Technical problems with the chip and the system in the early phase of the project were solved but potential for technical development is obvious.