1. 70 – 90% of input to the brain is from vision. Vision activates 32-36 areas of the cortex.
2. There are six eye muscles that move the eyeball about. Four of them are controlled by one nerve, the oculomotor nerve. This nerve also innervates the muscle that contracts the pupil, that contracts the lens of the eye and controls the eyelid.
3. The oculomotor nerve has a connection to our guts. It’s one busy nerve; among other things relating vision to nausea and repulsion.
4. This same nerve plus cranial nerve 4 (responsible for the eye muscle that pulls our eyes in and down, so we can look at the the cicada on the tip of our nose) lives in part of the brain stem called the mid brain. They are the only two cranial nerves with their roots here. The other ten cranial nerves have their roots in the other parts of the brain stem.
Part of the mid brain is called the tectum and this area has primary processing of vision and hearing along with co-ordination with the body and as such, acts like a second cerebellum. The cerebellum’s primary job is accuracy of movement, balance and co-ordination. The tectum directs the us to look at things – either with the head and eyes or the eyes only and to co-ordinate hands, arms and eyes when we reach out to grab something, why it is called the second cerebellum.
Which also means that people who are naturally clumsy may get great benefit from working on their vision.
So step on a christmas tree decoration and we automatically look down at it. I think the swearing originates somewhere else in the brain.
5. Since so much of vision and movement depends upon this part of the brain stem, it can get over worked. This leads to hypersensitivity; for example, bright lights can be very annoying; sounds can be irritatingly distracting or a sudden loud sound makes us jump more than others; crowds are overwhelming.
6. Overload of the mid brain, with its connections to the membranes that surround the brain and spinal cord can cause headaches and migraines.
7. Only about 6% of vision is foveal – the centre of vision, where things are clearest, making roughly 94% of the visual field periferal. Foveal vision is largely made up of cones, the photoreceptors that pick up colour, fine detail and changes in images. Cones work best in bright light. Rods are the photoreceptors that work better in dim light and they are very good at picking up motion. They don’t see colours well, which is why we can’t see colours so clearly in the dark. We use rods in our periferal vision and at night. So weak rods leads to problems with night driving.
8. Apart from rods and cones, there are other cells on the back of the eyes which are sensitive to light and these cells trigger the whole sleep/wake cycle. They are very sensitive to the colour blue, which is why it is a good idea to have apps on the phone and the computer that turn down the colour blue when it’s dark outside. On the other hand, blue light is very stimulating to the brain. You can do what you like with that bit of information!
9. If the brain does not believe that an eye can see well, it will stop trying very quickly. However, if the brain thinks it can see, it will try its very best to improve vision.
10. Vision can be improved. All of vision can be improved: distance vision, periferal vision, night driving vision, close up vision, suppression.
Vision is far more complicated than needing glasses to pass a driving test. And the brain likes two eyes of equal strength to see with.
11. Final astonishing bonus fact: I can help. This astonishes me too; but it is the result of much study.