who have each reported improvements in the perception of visual details, including contrast, shape, and movement. Retina Implant AG in Germany has also developed a subretinal implant, which has undergone clinical testing in nine patients. Trial was put on hold due to repeated failures. The Retina Implant AG device contains 1500 microphotodiodes, allowing for increased spatial resolution, but requires an external power source. Retina implant AG reported 12 months results on the Alpha IMS study in February 2013 showing that six out of nine patients had a device failure in the nine months post implant Proceedings of the royal society B, and that five of the eight subjects reported various implant-mediated visual perceptions in daily life. One had optic nerve damage and did not perceive stimulation. The Boston Subretinal Implant Project has also developed several iterations of a functional subretinal implant, and focused on short term analysis of implant function. Results from all clinical trials to date indicate that patients receiving subretinal implants report perception of phosphenes, with some gaining the ability to perform basic visual tasks, such as shape recognition and motion detection. Spatial resolution 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. "State-of-the-art" retinal implants incorporate 60-100 channels, 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; in reality the expected spatial resolution is 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 naïve 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