Patient selection critical for electronic retinal implants
Room for improvement with many research projects underway
Electronic retinal implants are already providing some visual rehabilitative benefits to patients with advanced retinal deterioration, but there is still room for improvement, reported Eberhart Zrenner MD, at the 16th EURETINA Congress in Copenhagen, Denmark.
“Research in artificial vision has been very intense and successful during the last decade. The current goals of these implants are light perception and improved mobility for patients with end-stage disease,” said Dr Zrenner, University of Tübingen, Germany, at an ESCRS/EURETINA Joint Symposium entitled “Cataract, AMD & Beyond”.
And who may benefit? “Patients with loss of outer retina structures, such as those with retinitis pigmentosa, choroideremia and Usher syndrome. Patient selection is critical. The optic nerve and inner retina must be functional, the patient must have once had vision up to reading capability earlier in life, and the inner retina may not be suffering from other destructive diseases,” he explained.
There are three anatomical approaches- epiretinal, subretinal and suprachoroidal. Each implant location has its own relative advantages and disadvantages, but only epiretinal and subretinal are currently commercially available to patients.
Currently, six major projects are ongoing worldwide. Most have an external camera, an external, battery-powered image-processing device and a stimulating retinal implant with an array of electrodes.
The Argus II, an epiretinal implant from Second Sight, Sylmar, USA, has received the CE mark for commercialization in Europe. FDA approval has been given for use in the United States.
Retina Implant Alpha IMS (1500 Pixel) subserving a visual field of 15 deg across corners in blind RP patients
The Retina Implant Alpha, a subretinal implant from Retina Implant AG, Tübingen, Germany, is the only one with the “camera chip” in the eye and moving with the eye, omitting bulky goggles covering the face. It which has also received the CE mark. The implant underwent a multi-centre study of 29 patients. Of these 29 patients, 25 reported light perception of whom 17 could localise the light. Several (4/29) could even identify Landolt C-rings.
X-Ray showing the subdermal receiver coil behind the ear with a cable running to the intraorbital space . A connection piece sutured onto the eye bulb forwards energy and control signals to the implant via a thin foil with the golden connection lines seen in the the left image in the upper right. The return electrode is positioned subdermally near the temporal bone above the orbit.
Dr Zrenner showed several videos of patients who had received implants. The patients could correctly identify white shapes on a dark background and could localize eating utensils (fork, spoon, plate, etc) in a useful manner. Others were shown navigating independently in an outdoor environment. This worked particularly well when there was a great degree of contrast due to good lighting.
“Electronic implants are presently the only possibility for patients blind from hereditary retinal diseases to regain some vision. Other approaches, such as stem cells and optogenetic approaches, will need many years of development before being available to patients,” he noted.