Restriction of eye motility in patients with RETINA IMPLANT
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Eye motility was determined in eight gaze directions in ten blind retinitis pigmentosa patients, who had received the RETINA IMPLANT Alpha AMS, before implantation of the subretinal implant and at six time‐points up to one year after. The analysis of eye motility showed a restriction in the upgaze and gaze to the temporal side directly after surgery in eight of the nine patients included. The degree of motility restriction decreased continuously with recovery during the observation time. One year after surgery, eye motility was still restricted in the majority of patients, especially in the upgaze to the temporal side at 20°.

The electronic subretinal implant was implanted according to the procedure as published earlier. First, a retroauricular opening is provided for the fixation of the power supply and control signal system housed in a ceramic box compartment in the periost. Secondly, a tunnel beneath the temporal muscle is generated to lead the extra orbital cable anterior to the orbital rim. Thirdly, intraocular surgery is performed. From a temporal superior scleral flap, the tip of a polyimide foil with the active microchip is pushed in the subretinal space along a leading foil towards the fovea, resulting in a preferably subfoveal position of the microchip. The polyamide foil leads in the subretinal space in anterior temporal direction and leaves the eye penetrating choroid and sclera at the equatorial region.

In a next step, the ceramic adapter plate that connects the intraorbital polyimide foil with the extraorbital silicon cable is sutured to the sclera. To provide a stable cable connection even during eye movements, the silicone cable forms a parabulbar loop beneath the eye bulb. This technique enables the distribution of the occurring forces during eye movements on a longer cable segment and reduces the cable breakage. The surgical procedure with a parabulbar loop was the consequence of cable breaks in cases with a short intraorbital cable.

An example of the gaze restrictions encountered is shown in Fig. 2. Nine patients were included in the final analysis. Eight of nine patients showed eye motility restriction at days 1–21 postsurgery, six of seven patients at month 1, six of eight patients at month 3, five of five patients at month 6, six of six patients at month 9 and four of six patients at month 12 after surgery. Eye motility was evaluated in the nine viewing directions (straight, upgaze straight, upgaze temporal, upgaze nasal, gaze to the temporal side, gaze to the nasal side, downgaze nasal, downgaze and downgaze temporal) at seven time‐points.

In conclusion, retinal implants with intraorbital parts (e.g. connecting cables) caused a restriction in the temporal and superior viewing directions in the majority of patients. Although this restriction might be cosmetically visible, this limitation in eye motility has no effects on the monocular vision and the implant’s efficacy for daily use.