Retinal implant

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Retina implants are visual prostheses for severely visually impaired or blind people whose receptor cells in the retina have lost their function due to illness, but whose optic nerve still forms an intact connection to the brain, as occurs above all in advanced retinitis pigmentosa (RP) .

Working principle

There are various approaches to artificially replace the function of degenerated receptor cells in the retina. The functional principle is essentially the same: images of the environment are converted into electrical impulses and passed on to the nerves.

In the last few years two promising systems have been developed, the subretinal implant and the epiretinal implant . The subretinal implant is placed in the eye under the retina, while the epiretinal implant is implanted on the retina. Recent studies on the epiretinal implant show that patients are able to recognize and grasp objects. It has also been shown that patients can read letters up to 0.9 cm in size.

The subretinal implant

The subretinal retinal implant consists essentially of

The implant lies between the retina and the choroid and is only fixed by intraocular pressure.

To put it simply, the photodiode array converts the image that hits the retina into a two-dimensional distribution of electrical impulses. Each diode element delivers a pulse according to the intensity of the incident light. The spatial resolution of the image on the retina depends primarily on the spatial density of the diode array. Diode arrays with approx. 1500 diodes on an area of ​​approx. 3 × 3 mm² are used. This corresponds to a field of view of 10 ° to 12 °. So far, a maximum visual acuity of 0.037 could be achieved.

The electrical signals of the array are then amplified by the circuit integrated in the microchip and passed on to the intact nerve cells of the retina by the stimulation electrodes. The energy required for the reinforcement process is coupled into the system from outside by infrared radiation or inductively. Since the photodiodes and the stimulation electrodes are placed next to each other on the microchip, no further processing of the signals is necessary.

The development of the subretinal implant has advanced and in the meantime the research team led by Professor Eberhart Zrenner (Tübingen / Reutlingen) has developed the subretinal chips to such an extent that shape vision is possible. Miikka T. was able to distinguish an apple from a banana in Tübingen and read his name from giant letters (and discovered a spelling mistake in it). On December 18, 2009, Professor Eberhart Zrenner received the Karl Heinz Beckurts Prize in Munich for his research and development work on these subretinal chips.

In July 2013, Retina Implant AG, Reutlingen, successfully completed the conformity assessment procedure for the Retina Implant Alpha IMS and has since been able to mark the implant with the CE mark.

The epiretinal implant

The epiretinal implant consists of

  • Video camera (usually integrated into glasses)
  • Microchip
  • Transmission unit for the transmission of processed camera data to the implant
  • Stimulation electrode array
  • Power supply unit

The implant rests on the retina. Since the vitreous is routinely removed during implantation, the implant must be fixed to the retina. The operation for the epiretinal implants is simple and safer than the subretinal approach.

With the epiretinal implant, the image is recorded by an external video camera and converted into electrical signals. These are then transmitted wirelessly to an implanted electrode array, which stimulates the nerves in the retina accordingly. The main disadvantage of the epiretinal implant is that the image is not recorded in the eye, but by an external camera. As a result, the natural mobility of the eye cannot be used to capture the environment. The camera must be rotated in order to change the direction of view. In addition, with the epiretinal implant, the signal processing takes place externally before the signals are transmitted to the electrode array, while with the subretinal implant, the "signal processing" is carried out by the eye itself. This leads to an increased complexity of the system.

The first epiretinal implant, the ARGUS device, consists of a platinum array with 16 electrodes. The clinical phase I study with ARGUS began in 2002 with the implantation of six patients with the device. The ARGUS II device contains 60 electrodes. Preliminary results in 30 patients were published in 2012.

literature

  • Michael Javaheri, David S. Hahn, Rohit R. Lakhanpal, James D. Weiland, Mark S. Humayun: Retinal prostheses for the blind. In: Annals of the Academy of Medicine, Singapore. Vol. 35, No. 3, 2006, ISSN  0304-4602 , pp. 137-144, Review, PMID 16625261 , online (PDF; 167.5 KB) ( Memento from June 15, 2006 in the Internet Archive ).
  • JD Loudin, DM Simanovskii, K. Vijayraghavan, CK Sramek, AF Butterwick, P. Huie, GY McLean, DV Palanker: Optoelectronic retinal prosthesis: system design and performance. In: Journal of Neural Engineering. Vol. 4, No. 1, 2007, ISSN  1741-2560 , S72-S84, doi : 10.1088 / 1741-2560 / 4/1 / S09 .

Web links

Individual evidence

  1. ↑ Aachal Kotecha, Joe Zhong, David Stewart and Lyndon da Cruz: The Argus II prosthesis facilitates reaching and grasping tasks: a case series. In: BMC Ophthalmology 2014, 14:71, doi : 10.1186 / 1471-2415-14-71 (free full text).
  2. ↑ Lyndon da Cruz, Brian F Coley, Jessy Dorn, Francesco Merlini, Eugene Filley, Punita Christopher, Fred K Chen, Varalakshmi Wuyyuru, Jose Sahel, Paulo Stanga, Mark Humayun, Robert J Greenberg, Gislin Dagnelie: The Argus II epiretinal prosthesis system allows letter and word reading and long-term function in patients with profound vision loss. In: British Journal of Ophthalmology, doi : 10.1136 / bjophthalmol-2012-301525 (free full text).
  3. ↑ Stingl et al., Artificial vision with wirelessly powered subretinal electronic implant alpha-IMS. Proc R Soc B 280: 20130077.
  4. ↑ Norbert Lossau: Microchips can turn blind people into sighted people. DIE WELT, December 5, 2011, accessed December 8, 2017 .
  5. ↑ Mark S. Humayun, Jessy D. Dorn, Lyndon da Cruz, Gislin Dagnelie, José-Alain Sahel, Paulo E. Stanga, Artur V. Cideciyan, Jacque L. Duncan, Dean Eliott, Eugene Filley, Allen C. Ho, Arturo Santos, Avinoam B. Safran, Aries Arditi, Lucian V. Del Priore, Robert J. Greenberg: Interim results from the international trial of Second Sight's visual prosthesis. In: Ophthalmology. Volume 119, number 4, April 2012, ISSN  1549-4713 , pp. 779-788, doi : 10.1016 / j.ophtha.2011.09.028 , PMID 22244176 , PMC 3319859 (free full text).