Towards a high resolution retinal implant

2018-02-15Several incurable diseases result in blindness for hundreds of thousands of individuals each year. Aged related macular degeneration (AMD) and Retinitis pigmentosa (RP) are two degenerative diseases that affect the photoreceptor cells causing the retina to lose its ability to translate light into electrical signals. RP is caused by mutations in over 100 genes that result in the degeneration of rod and cone receptors and the retinal pigmented epithelium (RPE). Patients will lose their night vision due to the degeneration of the rods, and their central vision in the later stages of the disease when macular cones start to degenerate. The overall incidence of retinitis pigmentosa is 1 in 4000 live births worldwide. AMD causes loss of vision in the center of the visual field. AMD is the most common cause of irreversible blindness in elderly individuals worldwide. Studies have shown that 30 percent of the ganglion cells and 78 percent of the inner nuclear layer cells remain largely intact in retinas with severe RP and AMD, thus allowing the retina to be electrically stimulated to restore a sense of vision. ❧ Retinal prostheses are being studied as a method to restore vision. They have demonstrated the capability to elicit the sensation of light and to give subjects more independence in their day to day activities. The results are remarkable because RP patients before implantation had bare or no light perception. Patients implanted with the Argus II system, in their 5 year follow up are able to perform tasks such as following a white line on the floor and finding a door in a room and walking towards it. ❧ Some technical issues remain unresolved, clinical studies of epiretinal implants reveal limitations in the ability of patients to determine the orientation of grating (used to measure visual acuity), and those who can recognize letters take more than 40 s to do so. High resolution retinal prostheses will require close proximity between the electrode array and the retina to maintain low stimulus thresholds and to minimize the power required by the system, smaller electrodes to accomplish precise activation of retinal cells to elicit a small visual phosphenes that can serve as a building block for the pattern, and new stimulation paradigms that will provide better control over the spatial patterns of activation. ❧ Currently a custom tack is used to attach the electrode array to the retina making it a challenge to control the electrode-retina distance overtime. During this report we study and present a novel attachment method based on disintegrin-integrin binding for retinal tissue. We developed a reliable technique to lase and produce an active area on the silicone surface, we found a reliable sterilization method for bioactive materials and we developed a new and reversible method of attachment to retinal tissue. ❧ Human subject testing has shown patients often see large, elongated phosphenes due to stimulation of RGC axon bundles. Smaller electrodes will allow more focal stimulation but will also require higher charge densities to have the same neural activation. It is unclear if these new high charge densities are safe for the tissue and this is why we developed a new method that allowed us to study the effects of electrical stimulation on the retina in an in vivo model during the stimulation period. This is important because it allowed us to study the retinal response in its natural conditions. In addition, this technique allowed us to study the long-term effects of retinal stimulation during survival experiments. We tested the safety of high charge density stimulation in the retina, which is a main factor that will need to be used in the future during the design of a high-resolution retinal prosthesis