Alejandra Gonzalez Calle

Effect of Stimulation parameters on percept color and percept shape in Argus II retinal prosthesis patients | mentored by Jack Whalen, Ph.D.

Alejandra Gonzalez-Calle, PhD. received her B.S. from La Escuela de Ingenieria de Antioquia (Medellin – Colombia) in 2010. After two years working as a research intern in the ophthalmology field, she joined the University of Southern California for graduate school, earning degrees in biomedical engineering (M.S. 2012, Ph.D. 2017). During the master’s program she received a full tuition Master’s BMES researcher award. The award is one of the highest awards Viterbi School offered to incoming master’s students in biomedical engineering. Currently, Dr. Gonzalez-Calle is a postdoctoral research associate at USC Dr. Allen and Charlotte Ginsburg Institute for Biomedical Therapeutics with an overall interest in the conservation and preservation of vision.

Dr. Gonzalez-Calle’s current project studies the effect of stimulation parameters on percept color and percept shape in Argus II retinal prosthesis patients. Loss of photoreceptors due to retinal degenerative diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), is a major cause of blindness, for which there is no cure and few ameliorative treatments. The FDA-approved Argus II epiretinal microchip, co-developed by Dr. Mark Humayun at USC, stimulates the surviving inner retinal neurons, restoring light perception and rudimentary object recognition in human RP patients. Implanted patients show improvement in object localization and discrimination, mobility, and in some patients, letter reading. Although subjects are capable of reading large letters only, and at a rate slower than normal reading, these results are remarkable considering that there RP patients prior to treatment demonstrated bare or no light perception. To date, more than 100 patients in the U.S. have been implanted with the Argus II and the number is growing rapidly.

Some technical issues remain unresolved. Images created by the retinal prosthesis are downsampled due to the limited number of electrodes. Compared with the multi-million pixel resolution of a healthy eye, electrical prostheses at present time merely offer a reduced resolution of 20 to 2000 pixels. The image downsampling essentially acts as a low pass filter that abandons high frequency spatial information of the view. Under the circumstances, color and percept shape, becomes particularly valuable. Color could carry an additional cue that could to some extent compensate for the reduced acuity, and precise activation of retinal cells could help elicit small visual phosphenes that can serve as a building block for a shape. Our proposed research will be tremendously valuable as it will not only advance our understanding of the highly novel prosthetic vision, but also make a direct impact on the day-to-day life of the otherwise blind patients, significantly improving their quality of life.

The overarching goal of the proposed study is to leverage new, second-generation retinal prosthesis technologies to (1) advance our understanding of the electrically-evoked color perception based on the Argus II platform and (2) to study and develop new stimulation paradigms in Argus II patients to produce smaller, rounder percepts, with the goal of providing higher resolution prosthetic vision to enable patient independence and improved quality of life.