Visual psychophysics is the study of the perceptual characteristics (such as brightness, size, perceived position, shape, colour, etc) seen by people when physical stimuli are applied to the retina (such as electrical pulses applied to electrodes in a predetermined pattern).
Three blind patients with retinitis pigmentosa received the prototype bionic eye in Melbourne as part of the research conducted by Bionic Vision Australia (2010-2014). The Bionics Institute worked with the Centre for Eye Research Australia (CERA) to develop a plan and tools for the collection of psychophysical data for clinical and research purposes.
A NHMRC project grant awarded to researchers from CERA, the Bionics Institute, the University of Melbourne and Data 61 (CSIRO), and support from Bionic Vision Technologies Ltd, has supported the continuing development and clinical trial of the next generation bionic eye.
Electrical stimulator design and construction
We designed and constructed a very flexible stimulator capable of applying safe electrical stimuli to an array of electrodes implanted in the suprachoroidal space behind the retina of a blind patient.
The stimulator uses principles and designs similar to a cochlear implant stimulator but was capable of stimulating a larger number of electrodes, and at a higher voltage.
We continue to advance this stimulator so that it is lightweight, compact and can run for days on battery power as well as provide flexibility in the types of stimulation that can be used.
Our visual psychophysics laboratory contains a suite of tests to record how visual percepts produced by bionic eye devices can be controlled by varying the parameters of electrical stimulation.
The prototype bionic eye recipients in the first clinical trial showed variations in threshold, dynamic range, and other characteristics of the visual percepts produced by electrical stimulation. These variations were measured in detail so that the bionic eye vision processor could be programmed for individual use.
The Institute developed special software and hardware for this purpose, with the goal of providing patients with a vision processor as soon as possible after the implant operation.
Three main research questions must be answered in order to build, control, and understand the function of the bionic eye at the psychophysical level.
How are the percepts produced by electrical stimuli from a single electrode perceived by patients, and how can they be optimised?
How can the percepts produced by stimulation from multiple electrodes be controlled to accurately convey size, brightness and location cues?
How are the dynamic properties of electrically generated visual stimuli perceived?