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In the Western world, the two most common degenerative diseases of the eye are Retinitis Pigmentosa (RP) and Age-Related Macular Degeneration (AMD). These can be very debilitating and in their worst forms can cause the sufferer to gradually go blind. These diseases target the super-fine layer of cells at the back of our eyes which help us to see, the retinal ganglion cells (RGC) of the retina.
A person with either of these conditions gradually loses the use of these RGCs and without them, slowly goes blind. But recently, scientists and ophthalmologists across the globe believe that they have cracked the retinal code and, with the use of some nifty neuroengineering and ophthalmic genetics, are on the way to restoring the sight to tens of millions of people who have lost their vision in this way.
How Does the Eye Work?
Our eyes see by using a complex pathway of different types of cells which fire off nerve signals to each other in rapid succession. To demonstrate how fast these signals fire, imagine that you switch on a light bulb. How quickly do you see the light? It is the time taken for the light to reach your eye, and for that signal to travel along cells in the retina, optic nerve, into the brain and then to the back of your head where the visual system is found. That’s fast!
The retina is made up of around 15 million RGCs and other types of cells which all feed in to the optic nerve. This is a long insulated pipe of about a million cells sending the signals from all the different types of cells which are responsible for vision. Think of it as a big electricity cable which is insulated. Inside, the copper wires conducting the electricity are like the long axons of the optic nerve fibres, except that there are about a million in each eye.
Now think about the different types of information about our environment that these cells send to our brains. Look around for a second, you take in information about:
- Visual Textures
- Hues and Shades
This is just the beginning of the story. A visual scientist could list many more.
AMD and RP
The area of the macula in the retina is where we see fine detail. When we focus our vision on something, we are using the macula and this has the highest number of retinal cells. With AMD, degeneration of these cells can occur with age and it means that we can no longer focus on things, but retain our peripheral vision. Some scientists believe that this may be due to ‘light toxicity’, and many types of medicines are available to slow down this change.
RP is the name given to a collection of inherited diseases of the retina which begin with the loss of peripheral vision and night blindness, but can end with a loss of even central vision. Inherited genetic defects affect at least 40 different genes which are responsible for making sure that the cells in the eye and retina function properly.