Suprachoroidal Retinal prostheses, longterm stability and safety results

ABSTRACT

Purpose: To report the longterm safety and stability of two suprachoroidal retinal prosthesis trials (NCT01603576, NCT03406416), comprising of seven patients, with followup ranging from two to nine years. Methods: Three patients with retinitis pigmentosa were implanted with our prototype 24 channel suprachoroidal retinal prosthesis in May-August 2012. One patient had the entire device removed following the trial in 2014 for a medical reason unrelated to the device. The other two patients had the intraocular array left in situ and the percutaneous connector removed, as planned. Ocular followup has continued since that time, albeit interrupted due to the Covid 19 pandemic. Four patients with retinitis pigmentosa were implanted with our second generation 44 channel fully implantable device in February to August 2018. They continue to use the device in the home enviroment. Ocular assessments including clinical examination, colour fundus photographs and optical coherence tomography (OCT) have been used to assess stability of the devices and retinal health longitudinally in patients (P) 1-7. Results: Electrode to retina distance OCT measurements over two to nine years, calculated by comparing group means, showed an increase over time. (Wilcoxon, p=0.03) In the prototype trial, the increase appeared linked to fibrosis and stimulation, with no progression once devices were inactivated, in the second generation trial, it seemed primarily due to passive fibrosis. Retinal thickness OCT measurements showed a slow reduction in central retinal thickness, as expected, due to progression of dystrophic disease. (Wilcoxon, p=0.11) Device position compared to the optic nerve head (ONH) was calculated and three patients demonstrated some temporal movement. P1 position returned to baseline over seven years, P2 stabilised over three months and P6 had a temporary choroidal effusion event which settled spontaneously. Function of the four Generation two fully implantable devices remains stable. Conclusions: Using fundus photography and OCT measurements we demonstrate that retinal prostheses implanted in the suprachoroidal space for up to nine years are overall stable in position and cause mild progressive fibrosis in the suprachoroidal space. Longterm assessment of the changes in the retina are all consistent with the underlying retinal dystrophy. This provides further evidence of the safety of the suprachoroidal surgical approach for retinal prostheses.