*Letís learn about eyes!*
By: Red Dog
28 February 2004

When you look at a persons eyes, you see the cornea, which is the front clear part of the eye. Behind the cornea is some clear fluid and then the iris, which is the part that gets smaller in bright light and bigger in dim light. Behind the iris is the lens.

The lens is usually a clear body that somewhat changes shape as you focus on different things at varying distances. This allows you to focus on items both near and far away.

Sometimes, the lens starts to become cloudy, which is known as a cataract. This may be due to chemical changes inside the eye from diabetes or other reasons, such as exposure to radiation (even radio frequency radiation!) or from trauma. Once the lens starts to become cloudy, light can not pass through it as easily, and vision becomes harder and harder. Eventually, this lens will become completely opaque, but can be replaced during cataract surgery, where an acrylic lens is inserted into the eye, behind the iris where it will now work as the lens.

Behind the lens, is a membrane called the posterior capsule. This is what holds the lens in place, so it does not fall back into the posterior chamber, which is the large round part of the eye.

The posterior chamber is filled with vitreous fluid, which maintains the round shape of the eye. As we get older, this vitreous can get thinner, but may start to form fibrous bands. These bands may even be able to be seen as moving shadows in our visions. When that happens, it's called floaters.

The back of the eye is covered with a thin membrane called the retina. This retina is the multi-layered membrane that holds the rods and cones that you probably remember from high school. It is very important that the retina remains intact and in place. Think of it as wallpaper inside a room. When this wallpaper stays in place, everything is good, but should that wallpaper start to peel off the wall and fall out into the room, it doesn't work well then. When the retina starts to peel away, or detach as it's called, the detached area loses its ability to allow images to focus there anymore. That may not be too bad if its way off in your peripheral vision, but another possibility is that the detached portion may also actually flip up enough to block the vision in a non-detached area. Think of this as trying to see past your hand held in front of your eye.

There are several very important structures inside the eye. If you've ever seen pictures of the inside of an eye, you may remember the whitish spot where the optic nerve comes into the eye. This is also where the eye's central arteries and veins enter and exit the eye, giving the retina its circulation. Diseases such as diabetes, can cause these vessels to become very fragile, or may even simply clot off. When that happens, the part of the eye that that artery feeds simply dies and you will lose the vision in that part. The eye wants to still see, so it will start to form new vessels, but the new ones are very fragile and will easily break, causing bleeding inside the eye, which will block your vision from the cloud of blood.

The point inside your eye that you actually focus on, when you look down the street at something is called the macula. This is the most important area of vision. If you damage your macula, when you look at something, you would only see a blank spot at what you look directly at, surrounded by visual areas. Think about how this would be, trying to drive. YIKES, not good!

When the retina starts to detach, it gets fluid behind the retina. This may be caused by membranes forming scar tissue and pulling against the retina, lifting it up from the wall of the eye. When that happens, we must go in and do surgery to remove the traction and allow the retina to again lie flat in place. Then, it is treated either with laser burns, or by freezing which is still a burn, but caused by cold instead of hot. This forms its own type of scar, but it holds down the retina in place where the burns are placed. We do NOT laser or freeze anywhere near the macula.

Sometimes there can be a small hole in the macula that is caused by a membrane forming there. It pulls against the macular tissue, until it causes that small hole to form. This is bad. We have to go in and very carefully remove that membrane from the macula and allow it to heal. Macular holes can do well, IF the membrane peeling is successful.

Many times, when the eye has either detached and was repaired, or when a macular hole has been peeled and repaired, we must fill the eye with either air or a medical gas and the patient then must remain face down for several weeks. The reason for the face down is to allow the fluid that had gotten behind the retina to come out from behind the retina and to allow the retina time to heal, so the fluid won't simply run back behind it. In extreme cases, we may even have to fill the eye with silicone oil to push the retina flat against the walls of the eye.

If you have had air, medical gas or silicone oil instilled into your eye, you must not fly or even drive through the mountains because of the pressure changes. Think about how your ears pop. The same thing (pressure changes) occurs in your eyes, but with the gasses or oil, they react differently to the changes than your normal eyes do. If the intra-ocular pressure increases too much, you lose all circulation inside your eye on the retina, kind of like putting a tourniquet on your arm.

Those of us, me included, with diabetes, have a greater chance of having eye problems, but EVERYONE can have these same problems as we get older. There is not much we can do to prevent retinal detachments, but getting regular eye examinations with a retinal exam is very important every year once you hit around 40 or so. This won't prevent problems, but it might catch them early so you can have the easier, non-surgical repairs done in the office.

If you have ANY sudden, un-explained partial or complete loss of vision, or start seeing the flashing lights that do not go away in more than 30 minutes, then go see an eye doctor right away. There are flashing lights that you can get, called migraine experiences, but these should go away in about 20 minutes or so. If they last longer, go see the docs.

One thing we can do to protect our eyes, is to get and wear a good set of protective glasses or goggles when doing anything even remotely risky to your eyes. Cutting the grass, working in the woodshop, going to the gun range, playing paintball, etc... could all be safer wearing eye protective equipment.

You've only got two eyes. Protect them so they'll be there to help you down the road when you need them.
Red Dog

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