gms | German Medical Science

Purpose: Retinal prostheses are susceptible to damage by body fluids over time. Long-term reliability of retinal prostheses requires hermetic packaging to protect the electronic circuitry of the implant from the harsh environment of the human body and a robust high-density electrode array for safe chronic stimulation. In addition to lifetime testing under normal use conditions, accelerated lifetime testing has been widely used to predict the implants’ life and to better understand their failure modes.

Methods: Lifetime testing of the Argus II implant has been conducted at the component, subsystem and final device levels. Long-term stability of the implants is assessed in vitro through active soak tests under constant pulse stimulation. The implants are tested in buffered saline at body temperature, or elevated temperatures for accelerated tests. The implants are attached to a silicone eye model to simulate the actual implanted condition. In some tests, a motor moves the entire eye model to simulate micromotion of a human eye. The device functionality, visual appearance, and material changes are monitored through the course of the lifetime test.

Results: Electrode material lifetime has reached 7 years in real-time testing under constant pulse stimulation and predicted equivalent of over 50 years of use in accelerated testing. Thin-film polymer electrode array insulation has reached 7 years in real-time testing and an equivalent lifetime of over 26 years in accelerated testing. Finished implants have reached more than 10 year lifetime in accelerated testing. These bench-test results are supported by clinical trial data: 30 subjects have been implanted an average of 4.2 years (range 3.3 to 5.5, excluding one explant at 18 months). Cumulatively, this represents 125 patient-years with only one device failure at 4 years post-implant.

Conclusions: The Argus II Retinal Implant has been tested at the component and system levels for long-term reliability. Thin-film electrode arrays withstood aggressive constant pulse stimulation and provided long-term safe stimulation without corrosion or material degradation. The hermetic package demonstrated the functional lifetime of the implant by preventing the moisture level accumulated inside the device. Lifetime tests support long-term reliability of Argus II Retinal Implants. Such long-term reliability is of paramount concern with respect to regulatory approval, and clinical utility, safety, and adoption.