Low duty cycle inter-implant communication of the Artificial Accommodation System

The Artificial Accommodation System is an autonomous mechatronic implant aiming at restoring accommodation after cataract treatment or in the case of presbyopia. The employed sensor concept requires a continuous wireless data exchange between the two systems implanted in the left and in the right eye, respectively. In this paper, we present three strategies for establishing this inter-implant communication link and evaluate them with regard to their lowest achievable duty cycle. We also describe a two-way synchronisation method for efficient computation of the relative timer offset between both systems. The method accounts for relative clock drift, which significantly increases accuracy when using clocks with large relative drift. The proposed communication strategies are currently being implemented in the industrial, scientific and medical (ISM) band at 433 MHz using off-the-shelf transceivers and microcontrollers. First measurements of synchronisation accuracy and relative clock drift predict duty cycles in the range of 0.6% - 1.0 %.