A virtual-reality simulation tested prosthetic visual acuity for both rectangular and hexagonal phosphene grids. Thirteen normally sighted, untrained subjects were required to identify the Landolt C optotype over ten sessions. Overall performance, performance by filter setting (image analysis), and performance by size and orientation of the Landolt C optotype are reported. The results indicated that the hexagonal grid had a slight (4.1%) but statistically significant (p < 0.0001) performance advantage over the rectangular grid for correct identification of the testing symbol. It was also observed that both the phosphene grids had distinct performance profiles relating to their respective spatial orientation. Over the course of the ten sessions, learning afforded subjects an averaged improved performance of 10%.

The key to successful, clinical application of therapeutic neurostimulators lies primarily with the safety and efficacy of their electrode-tissue interfaces. The authors posit that for electrical stimulation of the visual system, supra-choroidal electrode placement provides a safe, stable and readily-accessible site for implantation and the provision of electrical stimulation. The present paper explores the efficacy of supra-choroidal electrical stimulation of retinal neurons. Based upon recordings made with surface electrodes placed on the primary visual cortex, areas of activation in the cortex were shown to change when different areas on the supra-choroidal space were stimulated. Finally, the threshold to elicit a response from neurons in the visual cortex, was found to be 77.55 +/- 29.85 nC.

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Functional optical imaging of intrinsic signals (OIIS) measures very small changes in the absorption and reflectance of light from neural tissue during a physiological event. These small changes, usually less than 2% of the dc‐coupled signal, may be captured by a light‐sensitive device such as a CCD (charge‐coupled device) camera. These small signals are, by way of cerebral metabolism and hemodynamics, an indirect means of measuring neural activity. As a result of the small size of the signals, many aspects of the acquisition system are designed so as to minimize noise and nontrivial image processing is often required to extract the signals from the raw image sequence. The OIIS technique has been central to neuroscience research in the past two decades and is of increasing clinical relevance. It is frequently used to identify functional maps of cortical regions of interest, especially, but not limited to, the visual cortex, auditory cortex, somatosensory cortex, and olfactory bulb. Animal models studied include rats, cats, chinchillas, and monkeys. More recently, OIIS has been used intraoperatively in humans to further the understanding of the diseased brain, such as the brain in seizure. Optical imaging may resolve the spatial details of neural activity to within 50 μm, yet the temporal resolution of neural activity observed via intrinsic signals is limited because of the origin of the intrinsic signals in cerebral metabolism and hemodynamics. OIIS requires the tissue in question to be exposed to the light‐sensitive device. However, with respect to the target tissue, it is less invasive than traditional microelectrode recordings of single‐cell activity or fluorescent dye imaging techniques.