Virtual reality validation of naturalistic modulation strategies to counteract fading in retinal stimulation.

Objective. Temporal resolution is a key challenge in artificial vision. Several prosthetic approaches are limited by the perceptual fading of evoked phosphenes upon repeated stimulation from the same electrode. Therefore, implanted patients are forced to perform active scanning, via head movements, to refresh the visual field viewed by the camera. However, active scanning is a draining task, and it is crucial to find compensatory strategies to reduce it.Approach. To address this question, we implemented perceptual fading in simulated prosthetic vision using virtual reality. Then, we quantified the effect of fading on two indicators: the time to complete a reading task and the head rotation during the task. We also tested if stimulation strategies previously proposed to increase the persistence of responses in retinal ganglion cells to electrical stimulation could improve these indicators.Main results. This study shows that stimulation strategies based on interrupted pulse trains and randomisation of the pulse duration allows significant reduction of both the time to complete the task and the head rotation during the task.Significance. The stimulation strategy used in retinal implants is crucial to counteract perceptual fading and to reduce active head scanning during prosthetic vision. In turn, less active scanning might improve the patient's comfort in artificial vision.

Virtual reality simulation of epiretinal stimulation highlights the relevance of the visual angle in prosthetic vision.

OBJECTIVE: Retinal prostheses hold the potential for artificial vision in blind patients suffering from outer retinal dystrophies. The optimal number, density and coverage of the electrodes that a retinal prosthesis should have to provide adequate artificial vision in daily activities is still an open question and an important design parameter needed to develop better implants. APPROACH: To address this question, we investigated the interaction between the visual angle, the pixel number and the pixel density without being limited by a small electrode count. We implemented prosthetic vision in a virtual reality environment in order to simulate the real-life experience of using a retinal prosthesis. We designed four different tasks simulating: object recognition, word reading, perception of a descending step and crossing a street. MAIN RESULTS: The results of our study showed that in all the tasks the visual angle played the most significant role in improving the performance of the participant. SIGNIFICANCE: The design of new retinal prostheses should take into account the relevance of the restored visual angle to provide a helpful and valuable visual aid to profoundly or totally blind patients.