Passive safety outcomes of a preclinical 44-channel suprachoroidal retinal prosthesis

Abstract

Purpose : Following successful clinical outcomes of the prototype 24-channel suprachoroidal retinal prosthesis (SRP), an upgraded fully-implantable 44-channel SRP has recently been developed by Bionic Vision Australia. Our aim was to evaluate the surgical implantation safety and long-term conformability and stability of the 44-channel suprachoroidal electrode array in a large-eye model.

Methods : Eight normal-sighted felines were unilaterally implanted with an array containing platinum electrodes (44 stimulating and 2 returns) in a medical-grade silicone base. Assessments were conducted under anesthesia at baseline, then at 2-, 4-, 8-, 12- and 16-weeks post-surgery, including retinal trauma and implant position from color fundus photography, retinal structure, electrode-retina (ER) distance and conformability from spectral-domain optical coherence tomography, and retinal function from full-field electroretinograms.

Results : The array was positioned near the area centralis in all animals. Most animals showed no surgical trauma to the retina (5/8), no increase in ER distance over time (6/8; p>0.05, ANOVA), minimal (<1 disc diameter (DD)) lateral array movement (6/8), and good array conformability to the retinal curvature (7/8). There was minor surgical trauma in two animals with localized, mild retinal folds and tapetum thinning at the implant edge. One animal showed minor axial (100±32µm increase, p=0.0002, ANOVA) and lateral (1.7DD) array movement at 12-weeks that subsequently stabilized. There was major surgical trauma in one animal (device buckling due to a bulged choroid) with many overlying retinal folds and a large increase in ER distance (451±177μm, p<0.0001, ANOVA) from 2- to 8-weeks resulting in poor conformability. One animal had an infection at the implant anchor site (due to overlying conjunctival erosion) associated with a large lateral (3.7DD) movement at 4-weeks. All animals showed no further changes (than that seen due to surgery) in retinal structure between 2- and 16-weeks. There was no change in retinal function either over time or to control eyes (a-wave amplitude, p>0.05, ANOVA).

Conclusions : The array has an acceptable surgical safety, conformability and stability profile to proceed to clinical trial. The two major complications (due to bulged choroid and infection) are more likely in feline surgery than human due to choroidal and scleral anatomical differences.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.