In this particular episode of Ask an Eye Doc, you will learn:
- What is the cornea
- How to look at your cornea
- How the cornea survives without a blood supply
- What is aqueous humor
- Why corneal scratches are so painful
- How the cornea relates to early detection of diabetes
This episode will make more sense if you have already listened to the following episodes:
- episode 1 – what is astigmatism
- episode 7 – what is the retina
- episode 8 – how does diabetes affect the eye
- episode 19 – what is the iris
For you readers out there, here’s the answer in written form:
Today’s question is a simple anatomy question regarding the cornea. Anatomy is the structure of the body, and the cornea is a basic structure of the front part of the eye.
The cornea is the clear dome that sits in front of the iris (see episode 19). It’s the part of the eye that a contact lens sits on. In fact, that’s why it’s called a contact lens, because it makes contact with the cornea, as compared to glasses which don’t touch the eye at all (at least not normally – you may need to see your optician for an adjustment if this is the case).
The cornea is a fixed focusing lens and is clear like a window. It has a specific focal length associated with how curved it is and helps converge light to the retina. (Check out episode 7 to learn more about the retina and how the eye is like a movie theater).
You can get a good look at someone’s cornea by having them look straight ahead and shining a light from the side. You should note that the light passes through one side of the cornea and out the other, lighting up the iris along the way.
No blood supply
An interesting fact about the cornea: it is the only part of the body that has living cells that do not receive oxygen and nutrients from a blood supply. The cornea wouldn’t really work too well if it had blood vessels since it needs to be clear in order to transmit light. The oxygen and nutrients instead come from the tears on the front surface of your eye and the fluid behind the cornea, called the aqueous humor.
Corneal nerves & diabetes
Another cool fact about the cornea is that it has one of the highest concentration of nerve endings in the body. This is a good thing because you want to know right away when something is stuck in your eye. This is why a scratched cornea is so painful. If you’ve never experienced this before, be grateful!
An interesting thing that is being researched is early detection of diabetes. Diabetics tend to have neuropathy, a disease of the nerves. New research suggests that we can detect diabetic neuropathy earlier by measuring the concentration of corneal nerves with high magnification imaging.