00:01
So this question is dealing with the difference between far -sided vision and near -sided vision when looking at something underwater.
00:09
In order to answer the question, we have to talk a little bit about what is the difference in far -sighted and near -sided vision.
00:16
I've got two little sketches drawn here.
00:19
The top one shows a far -sided eye, which is a basic sketch of it.
00:24
You notice that a close -in object here that's relatively close to the eye.
00:28
The rays of light coming from that object do not meet anywhere in the eye.
00:33
They don't come together quickly enough.
00:35
So the problem is they converge too slowly.
00:38
If they would meet, they would actually meet behind the eye, which of course is impossible.
00:44
And so instead of meeting at the retina, they are just a little bit blurry when they get to the retina.
00:51
On other hand, a near -sighted person has the opposite problem.
00:55
Near -sided person, the rays of light from, say, a distant object.
00:58
Shown here, if i have two almost parallel lines, those rays of light converge too quickly.
01:06
So we want a situation, if you want to correct the vision, we either got to have something that is going to make the raise of light converge a little bit faster or the rays of light converge a little bit slower.
01:18
And that is where we need to look at what the air or water outside the eye versus the intraocular fluids inside the eye have to do with anything here.
01:29
Here you see a refraction diagram showing what's happened when light goes from either the outside medium, which could either be air or water, into the inside medium, which is the interocular fluid.
01:43
This is say when it's passing the corneum.
01:45
The cornea is one of the principal refracting surfaces of the eye.
01:51
Now, we know from snell's law that the index refraction of the incident medium times the sign of theta i equals the index refraction of refracting medium times the sign of theta r.
02:11
So if the incident medium is air, the index refraction of air is about one, and the intraocular fluid is index refraction is somewhere along with water...