|A schematic diagram of a bionic eye placed inside the eyeball. This version is made from diamond, making it completely inert.|
The retina at the back of the eye contains light detecting cells called photoreceptors. These cells convert light energy into electrical energy, which is transmitted to the brain via several layers of retinal nerve cells. In several forms of blindness, such as age related macular degeneration and retinitis pigmentosa, the photoreceptors die but leave the other nerve cells in tact. While those nerve cells cannot detect light themselves, they can respond to electrical stimulation.
The NVRI is involved in research to develop prosthetic vision devices, often referred to as ‘bionic eyes’. A bionic eye is constructed from an array of stimulating electrodes. The array is placed onto the retina in the eye and fed signals from a digital camera. Digital cameras work by converting light at each pixel in their sensor arrays into electrical signals that report the brightness of the light. These signals are then used to generate an image on a display at the rear of the camera. Normally sighted people then observe that image using their eyes.
In a bionic eye, we bypass the visual display and send the electrical signals from each pixel in the camera to the array of stimulating electrodes positioned on the eye. When placed into the eye of a blind patient, the electrodes stimulate the nerve cells that would normally receive input from the absent photoreceptors. The nerve cells have no idea that the electrical stimulation they are experiencing is coming through a man-made electrode array: they interpret the signals as if they were coming from normal photoreceptors. As a result, they send the information to the brain, which in turn experiences a pattern of electrical signals that replicates those experienced via the normally functioning eye.
|A retinal ganglion cell filled with fluorescent dye. The axon, which sends information to the brain can be seen exiting the picture to the right. The axon originates from the cell body, which is the circular structure.|
Of course, this process is complex and development of bionic eyes is technically demanding. Importantly, it requires a large volume of knowledge about the retina and about how prosthetic devices interact with the retina. Most importantly, the research requires us to understand how the retina responds to injected electrical charge. Not surprisingly, in the last few decades vision scientists have been focused on understanding how photoreceptors and visual nerve cells respond to light: most research has been focused on understanding normal visual function. Only in recent years, with the prospect of developing bionic eyes, have the electrical properties of the retina become a topic of interest to scientists.
We are fortunate at the NVRI to have a great team with the experience and knowledge required for this work. With three sophisticated in vitro retinal recording systems the NVRI is a world-leading centre in retinal physiology, particularly in the field of electrical stimulation. The bionic work is strongly supported by Bionic Vision Australia, an organization set up in 2009 to develop an Australian designed bionic eye and funded by a special program from the Australian Research Council.
The Bionic Eye App has now been launched!!
This app simulates the sort of vision that a person might experience using a bionic eye. The bionic eye is a retinal implant, placed at the back of the eye to restore a sense of vision for people with profound vision loss due to degenerative conditions of the retina. An external camera captures the visual scene and sends data to the implant. Electrodes on the implant electrically stimulate the nerve cells in the retina, providing a sense of vision. In this app, each spot of light that appears represents the percept from one electrode.
The purpose of this app is to simulate what bionic vision might look like. This app is not able to exactly represent the kind of vision processing that will be deployed with the full bionic eye devices. Research and development of vision processing strategies for the actual bionic eye implant is being completed at the NICTA Computer Vision Research Group in Canberra. Further, each and every patient’s experience with a bionic eye will be different and hence the vision they experience might be different to what is represented in this app. This app is intended for education purposes only.