Comparison of 3 Surgical Implantation Techniques Regarding Mechanical Stress for Power Supply Cables of Active Subretinal Electronic Implants

Abstract

 

Purpose:

 

Due to eye movements, power supply cables of retinal implants are exposed to considerable mechanical stress over time. Three different cable routing techniques are compared regarding mechanical stress.

 

Methods:

 

A subretinal chip (Alpha IMS, Retina Implant AG Reutlingen Germany) was implanted with a power supply cable running from an equatorial connection point at the sclera in the upper temporal quadrant to the superior orbital rim and further in the Fossa temporalis to a retroauricular subdermal coil in 9 patients. Three different surgical techniques for intraorbital cable routing were used: 1. straight route (3 patients), 2. parabulbar loop (3 patients), 3. encirclement of the eye bulb by cerclage (3 patients) [see Figure]. Analysis was performed as described previously (Kernstock et al, ARVO poster 2011). Briefly, bending angles of the cable were compared in 4 diagonal directions of eye movements for each patient using Computer Tomography. Standard deviation of the bending radius in these 4 positions was expressed relative to the mean bending radius (in %) as a marker for mechanical movement.

 

Results:

 

Comparison of the three implantation techniques showed 87% (5.9 ± 4.8 mm) change in bending radius for straight route, 16% (4.1 ± 0.7 mm) for encirclement and 11% (2.5 ± 0.4 mm) for parabulbar loop.

 

Conclusions:

 

Parabulbar loop and encirclement were comparable regarding mechanical stress on the power supply cable as measured by maximal and minimal bending angles during intentional eye movements. Both techniques have advantages and disadvantages in other aspects. In contrast, the straight implantation technique leads to considerably more mechanical stress in comparison to the other both techniques, leading to decreased long term integrity of the power supply cable and potential failure of the system. Hence, either the parabulbar loop or encirclement should be the preferred surgical techniques.  

 

Clinical Trial:

 

http://www.clinicaltrials.gov NCT01024803

 

Keywords: retina • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal degenerations: hereditary