Visualisation of active subretinal implants with external connections by high-resolution CT.

Two patients carrying an active subretinal implant with extra-ocular parts were examined by high-resolution CT. Cranial scans were acquired in the primary position and in eight additional directions of gaze with eyes open and closed to demonstrate the mobility of the eyeball and the implant within the orbital cavity. Three-dimensional images were constructed to visualise the path of the implant from the retro-auricular space around the lateral orbital rim through the orbit and within the subretinal space up to the device's final para-foveal position. Images were obtainable in high quality, resulting in three-dimensional models illustrating all parts of the implant including the micro-photodiode array at the tip in the subretinal space. The implant followed eye movements in all directions of gaze; eye movements were only minimally restricted as described in previous publications. Since all, except intra-ocular, parts of the implant evade direct examination, CT can be useful to assess the technical integrity and the biocompatibility and biostability of retinal implants.