The quality of vision expected from a retinal implant is largely based on the maximum spatial resolution of the implant. Current prototypes of retinal implants are capable of providing low resolution, pixelated images.
The "state of the art" retinal implants incorporate 60-100 channels, which is sufficient for basic object discrimination and recognition tasks. However, simulations of the resultant pixelated images assume that all electrodes on the implant are in contact with the desired retinal cell. Therefore, the expected spatial resolution provided is even lower as a few of the electrodes may not function optimally. Tests of reading performance indicated that a 60 channel implant is sufficient to restore some reading ability, but only with significantly enlarged text. Similar experiments evaluating room navigation ability with pixelated images demonstrated that 60 channels were sufficient for experienced subjects, while naive subjects required 256 channels. This experiment, therefore, not only demonstrated the functionality provided by low resolution visual feedback, but also the ability for subjects to adapt and improve over time. However, these experiments are based merely on simulations of low resolution vision in normal subjects, rather than clinical testing of implanted subjects. The number of electrodes necessary for reading or room navigation may differ in implanted subjects, and further testing needs to be conducted within this clinical population to determine the required spatial resolution for specific visual tasks.
Simulation results indicate that 600-1000 electrodes would be required to enable subjects to perform a wide variety of tasks, including reading, face recognition, and navigating around rooms. Thus, the available spatial resolution of retinal implants needs to increase by a factor of 10, while remaining small enough to implant, to restore sufficient visual function for those tasks.
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