gms | German Medical Science

Objective: To engineer a highly reliable, light-detecting chip with a high-density electrode array for subretinal stimulation.

Materials and Methods: The light-detecting CMOS chip of the CE-marked device RETINA IMPLANT Alpha AMS comprises 1600 pixels. Each pixel has a dimension of 70 µm x 70 μm and includes a photodiode, an amplifier and a stimulation electrode. It stimulates the overlying retinal tissue with biphasic current pulses, whose amplitudes are related to the locally measured light intensity. The sensitivity and the maximum stimulation current of the chip can be adjusted by the patient to suit the ambient light intensity and the individual retinal response behavior. Since hermetic housing of the chip with 1600 microelectrodes and light-sensing elements is not applicable, the chip is protected from corrosion by a conformal coating. Lifetime estimation for the implant components are obtained from accelerated laboratory tests and statistical analysis.

Results: The median lifetime of the chip Alpha AMS in laboratory tests is about 6 years. Based on accelerated component tests and a model validated with clinical data, we expect a median functional lifetime of the implanted system of 5 years. So far, no failure of implanted chips due to corrosion has been observed within the maximum observation period of 40 month.

Discussion: The conformally coated retina chip Alpha AMS with ist 1600 pixels is a non-standard and novel neurotechnological system for neural prostheses, which withstands the wet subretinal environment with high reliability.