PhD Defenses


Date Range
Thu July 27th 2023, 3:00 - 4:00pm
PAB 102/103

Ph.D. Candidate:  Bingyi Wang

Research Advisor: 
Daniel Palanker

Date: Thu July 27th, 2023
Time: 3:00 pm

Location: Physics and Astrophysics Building (PAB) room 102-103

Zoom Link:

Zoom Password: email nickswan@stanford for password

Photovoltaic subretinal prosthesis for high visual acuity: design, fabrication, and in vivo assessment

Retinal degenerative diseases, such as atrophic age-related macular degeneration (AMD), cause the loss of photoreceptors and remain the primary cause of untreatable blindness. Photovoltaic subretinal prosthesis has shown promise in restoring vision by electrically stimulating the second-order retinal neurons: the bipolar cells. Clinical trials in AMD patients demonstrated prosthetic vision with an acuity up to 20/438, closely matching the 100m pixel size of the implant. Further improvement and wider adoption of this technology require smaller pixels, at least below 50m, to exceed the US legal blindness level of 20/200. However, scaling down pixels of the current geometry is not feasible below 75m, since the local return electrodes overly confine the electric field, precluding stimulation of the bipolar cells within the safe range of charge injection. 

I will present two alternative pixel design strategies for shaping the electric field with smaller pixels, in order to enable effective stimulation of retinal neurons without compromising safety, contrast, and resolution. One strategy involves a monopolar pixel array with current steering, where the circumferential local return electrodes in each pixel are replaced with a return path through neighboring dark pixels. This allows for deeper field penetration while maintaining high spatial contrast. Another strategy relies on 3-dimensional electrodes to vertically shape the electric field. Anatomical and electrophysiological studies of these 3D arrays in vivo show feasibility and long-term biocompatibility of this approach. Grating acuity measured with these new implants in blind rats matches the sensor pitch with 40m pixels, while with 20m pixels, acuity reaches the 28m limit of natural resolution in rats. Unlike the bipolar cell-mediated retinal stimulation, direct activation of the third-order neurons, the ganglion cells, do not provide high spatial resolution. Therefore, carefully optimized electric field for effective and selective stimulation of bipolar cells is required for achieving visual acuity of 20/100 in AMD patients.