Interim Results of a Multicenter Trial with the New Electronic Subretinal Implant Alpha AMS in 15 Patients Blind from Inherited Retinal Degenerations

Abstract

Purpose: We assessed the safety and efficacy of a technically advanced subretinal electronic implant, RETINA IMPLANT Alpha AMS, in end stage retinal degeneration in an interim analysis of two ongoing prospective clinical trials. The purpose of this article is to describe the interim functional results (efficacy).Methods: The subretinal visual prosthesis RETINA IMPLANT Alpha AMS (Retina Implant AG, Reutlingen, Germany) was implanted in 15 blind patients with hereditary retinal degenerations at four study sites with a follow-up period of 12 months (www.clinicaltrials.gov NCT01024803 and NCT02720640). Functional outcome measures included (1) screen-based standardized 2- or 4-alternative forced-choice (AFC) tests of light perception, light localization, grating detection (basic grating acuity (BaGA) test), and Landolt C-rings; (2) gray level discrimination; (3) performance during activities of daily living (ADL-table tasks).Results: Implant-mediated light perception was observed in 13/15 patients. During the observation period implant mediated localization of visual targets was possible in 13/15 patients. Correct grating detection was achieved for spatial frequencies of 0.1 cpd (cycles per degree) in 4/15; 0.33 cpd in 3/15; 0.66 cpd in 2/15; 1.0 cpd in 2/15 and 3.3 cpd in 1/15 patients. In two patients visual acuity (VA) assessed with Landolt C- rings was 20/546 and 20/1111. Of 6 possible gray levels on average 4.6 ± 0.8 (mean ± SD, n = 10) were discerned. Improvements (power ON vs. OFF) of ADL table tasks were measured in 13/15 patients. Overall, results were stable during the observation period. Serious adverse events (SAEs) were reported in 4 patients: 2 movements of the implant, readjusted in a second surgery; 4 conjunctival erosion/dehiscence, successfully treated; 1 pain event around the coil, successfully treated; 1 partial reduction of silicone oil tamponade leading to distorted vision (silicon oil successfully refilled). The majority of adverse events (AEs) were transient and mostly of mild to moderate intensity.Conclusions: Psychophysical and subjective data show that RETINA IMPLANT Alpha AMS is reliable, well tolerated and can restore limited visual functions in blind patients with degenerations of the outer retina. Compared with the previous implant Alpha IMS, longevity of the new implant Alpha AMS has been considerably improved. Alpha AMS has meanwhile been certified as a commercially available medical device, reimbursed in Germany by the public health system.

Functionality and Performance of the Subretinal Implant Chip Alpha AMS

“…(20) The stimulation strength can be adjusted to match the necessary stimulating current to the individual patient's needs, depending on the degradation level of the patient's retina. Several material and design changes (7) led to a significant improvement of the durability of the current implant Alpha AMS compared with the predecessor Alpha IMS. From the KaplanMeier plot, which shows the current status of the functionality of all implants in clinical use (Fig.…”

“…(7) Two patients were able to distinguish Landolt C-rings of 20/1111 and 20/546. Twelve patients could achieve a basic grating acuity between 0.1 and 3.3 cpd.…”

“…Study details and interim functional outcomes of the first 15 patients were described by Stingl et al (7) All of these patients had end-stage hereditary retinal degeneration with impaired light localization or worse. Fourteen of the patients had RP and one had cone-rod dystrophy.…”

“…(15) Improvements in the chip encapsulation and voltage management led to a more robust implant. (7) So far, none of the technical failures of the Alpha AMS implant have been related to a failure of the conformal coating.…”

Interfacing with the nervous system: a review of current bioelectric technologies

“…Retinal implants have also made their way into the clinical realm, with three retinal implant approaches in clinical trials: epiretinal, subretinal, and suprachoroidal implants, all of which relay visual input to the retina to stimulate surviving retinal neurons [99,146]. Retinal implants are meant to treat degenerative disorders such as retinitis pigmentosa and agerelated macular degeneration, which destroy photoreceptors in the retina.…”