If you are reading this, as Sherlock Holmes would say, I deduce that you can see! But that is not the case for many Australians, as the statistics reveal that in 2006 there were 292,700 with a sight impairment and this is anticipated to balloon out to 421,600 in the next 10 years. In fact each day, 22 Australians become sight impaired and when that vision is lost, it is mightily difficult to restore.
We rely on our eyes for so much information and also for so much pleasure each and every day. They are amazing “instruments” that enable us to see close up and distant in the mere twinkling of said eyes. They not only see what is in front of us but give us peripheral vision too and allow us to appreciate the world in all its 3D glory. And then there’s the colour!
Naturally the mechanism of vision is extraordinarily complicated, and is in fact formed from two separate areas during its embryological development. The front part of the eye comes from the facial area of the embryo, but the back of the eye develops from an out “pouching” of the brain itself – this will later form the retina, or seeing area at the back of the eye.
But it’s at the back of the brain where the really interesting stuff happens. Take one simple fact: when light travels through a convex lens, it is “bent”, and when you see an image through the lens of your eye the image at the back of the eye is actually “upside down and back to front”. This information is flashed to the back of your brain where the “Seeing” information is decoded and altered, so that the tweaked information that is forwarded to the conscious part of the brain shows the image correctly aligned having it back through 180 degrees so that what you see is… what you see! And this is done all the time with 2 eyes feeding information from the very instant that you open your eyes in the morning until you close them at night.
From the picture above you can see that there are certain obvious structure where things may go wrong:
So how do things go wrong? Obviously the subject is far too big for this article, but lets cover the “usual suspects”.
- The Cornea – the outer surface of the eye that is protected by the conjunctiva.
- The Lens
- The Fluid within the eye that maintains its shape, and which is under pressure, and is constantly circulating.
- The Retina – which is the light sensitive membrane where light, colour and images are detected, transformed into electrical impulses and sent via the Optic nerve to the back of the brain.
This is the interface between the eye and the outside world. It has to be crystal clear in order to allow all light through, and it needs to be smooth so that light is not distorted as it passes through. It also needs to be able to heal itself as it can be subject to daily trauma from bits of grit or insect in the eye, or high impact foreign objects from work related accidents. Interestingly, the cornea does not have a blood supply of its own as any blood vessels, however small, would interfere with vision! So the cornea is fed and protected by tears and blinking – simple, yet so effective.
The cornea can be damaged by trauma, by infections such as Shingles, and by congenital diseases.
The lens is not like the glass lenses of your spectacles, but has more of an “onion” layer structure. It is suspended by the iris which is a muscle that pulls on the lens to alter its shape so that it can go from being squat and fat to long and thin, thus accommodating light from both near and distant allowing us to have near and distant vision with just one lens. As we age the lens gets a bit stiff, and it becomes more resistant to stretch, hence the need for older people to have longer arms, or to wear corrective spectacles in order to read! Also, later in life, crystals can get laid down in the layers of the lens making it more opaque – a condition that is better known as Cataracts, and now easily corrected by lens implants.
The Aqueous fluid
This is the fluid that the eye produces and fills the front part of the orbit of the eye. It is always under pressure giving the eye its round appearance. This fluid is maintained under a constant pressure that allows the eye to function normally without putting too much pressure on the sensitive retina at the rear of the eye. However, if the pressure is raised – known as Ocular Hypertension – then the retina can be damaged. When damage occurs, this is known as Glaucoma and it affects over 300,000 Australians. Please note that Ocular Hypertension occurs before Glaucoma appears, and this gives hope to those who wish to preserve sight. If those with family members known to have Glaucoma have their eye pressures checked early, and it is found to be raised, then treatment can start and vision can be saved.
The back of the eye is covered in light receptors, and where they are most densely packed is in an area known as the Macular that does the vast majority of our “seeing”. Lose this area and you still have peripheral receptors, but that means that you cannot see anything in front of you, but you do maintain blurred peripheral vision – this is sometimes called Tunnel vision. If you lose vision in the Macular area, there is no way to replace it. The condition known as Macular Degeneration affects one in 7 people over the age of 50, and if you have a family member with MD, then you have a 50% chance of developing it yourself. This is a serious and growing Vision problem for all Australians.
The conclusion from all this is that our eyes are so very precious and should be protected. There are things that we should never do that can damage our eyes and the big one would be to never smoke. The second most important thing to remember is that most treatable eye disease is usually silent, and it’s only when vision is lost that people seek help. So get a regular eye check, and protect and nurture your vision because believe me you will be lost without it!