Giving Vision to the Blind

Neuroengineering

Once some of these diseases become completely understood, then it is possible to start to work on developing a cure. Another key to begin to explain this process is the miniaturization of technology. We could not have done this twenty years ago, even though scientists (and sci-fi writers) were dreaming of the advent of the sort of technology which could make it possible.

A Californian company called Second Sight has developed an external visual system which enhances the eyesight of retinally damaged patients.

It consists of a pair of glasses wired up to detect visual stimuli which send impulses to an array of receptors which are surgically attached to the retina. These receptors only consist of a 6 by 10 array right now, but no doubt as this technology is enhanced, the number of receptors can grow into the millions of cells they replace.

The receptors then send signals in the usual way along the optic nerve to reach the brain. Such signals at present allow a legally blind person to be able to detect changes in light and dark or large movements in front of them and even be able to count objects placed in front of them, and it is a good start.

Optogenetics

Sheila Nirenberg, a neuroscience professor in Cornell University and one of her students, Chethan Pandarinath, have recently demonstrated breakthroughs in the field of optogenetics.

Optogenetics can be used to target single populations of cells in the retina. For example, Nirenberg has been experimenting with a group of retinal cells which only express a certain type of chemical, in this case channelrhodopsin-2 (ChR2). They are able to do this because the different types of visual stimulus that we discussed earlier are all decoded by a certain type of cell in the retina. So, for example, a group of cells respond when a light is switched on – and only on. Another group responds when a light is switched off. And so on. We have Nobel Prize winning scientists Hubel and Wiesel to thank for these painstaking discoveries.

Nirenberg and Pandarinath infect only a certain type of retinal cell with a mutated version of ChR2 which is a chemical which responds to blue light. A prosthetic device attached to the retina is then able to stimulate this group of cells into producing action potential (nerve transmission) in the same way that undamaged cells do. Amazingly, because of the advances in understanding the retinal code, it does this reliably and efficiently, so a person can not only see rough movements, but also landscapes, animals, and even recognise faces.

These amazing advances can only get better as our technology improves and shrinks. Watch this space!