University of Southern California Department of Biomedical Engineering The USC Andrew and Erna Viterbi School of Engineering USC


Research Overview

Threshold Maps of Electrically Stimulated Retina 

The main goal of this project is to understand the spatial properties of the retinal response to electrical  stimulation, both in the normal and degenerate retina. This is accomplished by imaging retinal ganglion cell activity evoked by pattern stimulation in the isolated retina. The goal is to only stimulate cells near the site of stimulation and to selectively activate cell bodies over axons.


Graduate Student: Andrew Weitz
Collaborator: Dr. James Weiland
Funding: National Science Foundation (NSF)

Intracellular Response of Retinal Ganglion Cells in Degenerate Mouse Retina

The aim of this project is to understand how retinal ganglion cell physiology is affected during retinal degeneration. Despite loss of photoreceptors due to degenerative diseases, the inner retina remains largely intact and functionally viable. While the cells in the inner retina appear structually preserved, the same cannot be assumed about their physiological behaviour.

This specific project utilizes whole cell patch clamp recordings to measure the intracellular response of retinal ganglion cells to extracellular electrical stimulation. This technique can be used to observe the single-cell response in more detail and allows for physiological manipulations that may not be as feasible in other setups.


Graduate Students: Alice K. Cho
Collaborator: Dr. James Weiland, Dr. Alapakkam P. Sampath
Funding: National Science Foundation (NSF)

Functional MRI Analysis of Visual Cortex Activity in ARGUS 2 Retinal Prosthesis Subjects

Functional magneic resonance imaging (fMRI) will be used to assess the long-term effects of an active retinal prosthesis on the processing of visual and non-visual stimuli in the occipital cortex. Consequently, this project also aims to ensure that the ARGUS 2 retinal prosthesis is functional within a 3.0 Tesla MRI scanner.


Graduate Students: Samantha Cunningham
Collaborators: Dr. James Weiland, Dr. Bosco Tjan
Funding: National Science Foundation (NSF)

The Effect of Electrical Stimulation of Crystallin Expression and Distribution in the Retina

The purpose of this project is the evaluate the role of retinal alpha-crystallins, members of the heat shock family of proteins, on the safety and effectiveness of acute electrical retinal stimulation in mice.

Alpha-crystallins are small heat shock proteins that are upregulated during retinal injury and play a role in response to injury  and cell survival. They serve the dual function of protecting other proteins from misfolding and as anti-apoptotic agents.


Graduate Students: Samuel Lee
Collaborator: Dr. David Hinton, Dr. James Weiland, Dr. Gerald Chader
Funding: National Science Foundation (NSF)

Nanoindentation of Porcine Sclera

Nanoindentation was used to characterize both the quasi-static and dynamic properties of agar samples since agar has mechanical properties similar to soft tissue. Quasi-static indents recorded reduced modulus and maximum load and depth related effects. Ramp load functions using a dynamic oscillation of constant frequency were used to evaluate the depth-dependent effects.


Graduate Student: V Timothy Nayar
Collaborator: Dr. Dr. Andrea Hodge, Dr. James Weiland, Dr. Mark Humayun
Funding: USC Eye Institute, Department of Energy (DOE)

Bioelectronic Research Lab: Chronic Implantation of a 240 Electrode Active Retinal Prosthesis

The DOE's Artificial Retinal project has worked towards the goal of a retinal prosthesis with 200-300 electrodes. A major milestone was reached with the implantation of an electrically active array in a canine. The electronics have been modified to expand the 60 output channels of the ARGUS 2 up to 240 channels while occupying the same space. This device has been implanted and operational for 6 months, with 228 electrodes functional.  

Post Doc: Rodrigo Brant 
Collaborator: Dr. Mark Humayun, Dr. James Weiland
Funding: Department of Energy (DOE)

Wearable Low-Vision Mobility Aid

The overall goal of this project is to develop a wearable, low-vision aid that provides assistance to patients with impaired vision. Different algorithms will run for navigational assistance and object recognition. The navigation function consists of a head-mounted stereo camera, a computer system and a vest that holds vibration motors. The stereo camera provides visual sensory input in the form of a 3D map. The computer system then implements an algorithm for path planning and navigation based on this input, while the vest provides tactile feedback depending on the path the user takes and the cues of the computer algorithm. The drawback of the system is that it cannot be used in low contrast environments based on the limitations of the stereo camera, therefore further research is being done integrating cameras into the current system that may be used in a variety of indoor and outdoor environments. This has led to the evaluation of Primesense, which interpolates a pattern of dots using an infrared laser, while a CMOS image sensor detects reflected segments of the infrared dot pattern and maps the intensity of each segment to a corresponding distance from the sensor. Additionally, RGB input from a second CMOS image sensor is pixel aligned to add colour to the acquired data. Object recognition algorithm will use a neutrally inspired algorithms to detect important regions of a scene and then top-down information from the user to perform recognition in a confined search space.
Graduate Student: Aminat Adebiyi, Nii Mante, Young-hoon Kim, Ben McIntosh
Collaborator: Dr. James Weiland, Dr. Laurent Itti, Dr. Gerard Medioni, Dr. Armand Tanguay
Funding: Department of Defense, Telemedicine, and Advanced Technology Research Center (TATRC)

Wide Field Electrode Array Implantation



Graduate Student: Alejandra Gonzalez Calle
Post Doc: Rodrigo Brant Fernandes
Collaborator: Dr. James Weiland, Dr. Mark Humayun
Funding: National Eye Institute

Metabolic Prosthesis


Graduate Student: Karthik Murali
Post Doc: Ramiro Ribeiro
Collaborator: Dr. Mark Humayun, Dr James Weiland

Hyperspectral Imaging

This project aims to use hyperspectral imaging to study several processes in the eye. Other machines use just a few wavelengths, but our novel system uses wavelengths across the EM spectrum to capture information from the retina. One of the main areas being studied right now is the oxygen saturation in the retinal vasculature in diseased retinas.
Graduate Student: Karthik Murali
Post Doc: Gilberto Raul Lopez, Sally Saati
Collaborator: Dr Amir Kashani, Dr. Mark Humayun


Characterizing Percepts in Retinal Prosthesis Subjects

Psychophysical experiments in the past 6 months have been performed involving selective adaptation of the retina using electrical stimulation. The experiments examined how perceptual threshold resulting from electrical stimulation are affected by an adapting/preconditioning pulse train. Psychophysical experiments with 16 electrode epiretinal array determine the efficacy of the device for future developments of the electrode array, stimulation protocols, and image processing strategies.
Graduate Student: Devyani Nanduri
Collaborator: Dr. James Weiland, Dr. Mark Humayun
Funding: National Science Foundation (NSF)