Electrically stimulating the retina through retinal prosthetics has shown to be promising in restoring limited vision in patients with retinitis pigmentosa. However, this treatment is not effective for patients with acquired blindness through degeneration of their retinal ganglion cells or optic nerve, as is seen in glaucoma. The Orion visual cortical prosthesis electrically stimulates an alternative target along the visual pathway, the primary visual cortex. The present study investigates the efficacy and feasibility of the Orion visual cortical prosthetic in creating visual representations termed phosphenes to aid blind individuals with visual perception.
Our subject is a volunteer with a 6-year history of blindness and right anophthalmia due to trauma. He is one of 5 patients in our early feasibility study. The device consists of an electrode array with 60 possible electrode contacts that is surgically implanted in the left occipital lobe over the calcarine sulcus. This is connected to an external unit that is worn by the user, that consists of a video processing unit and a pair of sunglasses with an embedded camera. The camera on the glasses captures the visual field of the patient in real time and the image is processed by the visual processing unit and converted to stimulation patterns. During experimentation trials, single electrodes are stimulated to determine the threshold amplitude of stimulation that is required to create a meaningful phosphene. The phosphenes are mapped by orienting the patient toward a tactile target located on a touch screen and having the patient draw the phosphene location after stimulation. With the camera on the device turned on, the patient is asked to complete a series of visual function tasks that gauge the functionality of the device in restoring some visual perception.
Electrical stimulation of 60 of 60 contacts resulted in phosphene perception. Phosphenes were described as points of light in space that did not have much variation in shape and size. Stimulation of certain contacts located along the calcarine sulcus resulted in perception of two phosphenes. Individual thresholds for each contact were consistent through weeks of experimentation. Phosphenes were perceived throughout the patient’s right visual field, and in contrast to other subjects, this particular patient’s phosphenes did not move with voluntary eye movement. Using the device, the patient was able to detect directionality of a line that was moving in either a vertical or horizontal fashion.
The Orion device is successful in producing phosphenes in our patient, and its electrode composition may be modulated to produce meaningful visual perception. The constant thresholds of the individual contacts demonstrate stability of the device through time. Since our particular patient’s phosphenes did not move proportionately with voluntary eye movements, this introduces the need to better understand the relationship between eyeball position and phosphene perception. These findings suggest that the Orion visual cortical prosthesis shows promise in restoring aspects of visual perception and should be further evaluated in a clinical setting.