gms | German Medical Science

Background: The VLARS (very large array retina stimulator) was designed for the purpose of epiretinal stimulation. Due to its unique composition of materials and good surgical feasibility this study aims to determine the feasibility of suprachoroidal-transretinal stimulation of the VLARS device as a second approach for its use.

Methods: An active VLARS device was partially implanted suprachoroidally into scleral pockets in a cat. The position of the array was reassured with an OCT (optical coherence tomography). In order to detect retinal stimulation a chiasm electrode was placed. Also, an optical imaging fundus camera came into use. Out of the 25 active electrodes on the VLARS device single electrodes and groups of four were stimulated with the threshold biphasic current of 90uA at 500ms pulse duration in trains of 100 at 1Hz at different suprachoroidal positions.

Results: While the optical imaging fundus camera did not show significant stimulation, the chiasm response electrodes showed fast responses clearly related to the suprachoroidal stimulation performed at various implantation sites. A cluster stimulation of four electrodes simultaneously shows superior results in comparison to single electrode stimulation. Aside from that the surgical feasibility of the acute suprachoroidal implantation in the cat was demonstrated succesfully for the first time.

Conclusion: Even though the VLARS device is intended for epiretinal stimulation its flexibility and thin crafting are useful attributes in suprachoroidal stimulation. The single electrodes of the VLARS are rather small compared to those used in suprachoroidal stimulation, thus current thresholds are lower making it difficult to elicit retinal responses. Also the distance to the Fovea centralis seems to affect the results. Overall this study demonstrated the possibility of using the electronical engineering and experience obtained for epiretinal stimulation and translating that on suprachoroidal stimulation.