Lens?

I was doing some research on the human lens and would like a bit of clarification on some points as my logical reasoning skills seem to be lacking.

First here are some facts that I have gathered (please correct me if I am wrong):
     1. The lens is 100%  responsible for accommodation.
     2. The lens provides +20D of power to the eye.
     3. The +20D of power the lens provides inside the eye equals +10D in the form of  a corrective/spectacle lens.

So, taking the facts above into consideration, if a person has no refractive error prior to a lensectomy, then once the lens is removed (and no IOL is implanted), the person would lose the ability to see clearly. S/he would have lost the ability to accommodate, so the person would need bifocals. Also the person’s distance vision would be able to be corrected with a +10D pair of glasses.

Now, due to point #3, the following would result from lens removal (again no IOL implant): If a person is highly myopic, after lens removal he/she would still remain myopic, but to a lesser degree. If a person were only mildly myopic before then afterwards he/she would become hyperopic. Lastly, if a person was a hyperope before surgery, then the result would be a greater degree of hyperopia.

Is any of the above correct? What about near vision?

Sorry for the long post. Thanks for the clarification.

[John C Hagan III, MD, FACS, FAAO]

Virtually everything you said is wrong. Most of the bending power of the eye comes from the cornea. The power to correct an eye will depend on many things among them the position in the eye, the length of an eye, the radius of curvature of the cornea, an A constant based on the properties of the IOL.

Most myopic eyes that have an lens removed and an IOL not put in will be hyperopic after the surgery.

You will need to work through this on your own.

JCH MD

[berrywoo]

"Most myopic eyes that have an lens removed and an  IOL not put in will be hyperopic after the surgery."

Why?

[John C Hagan III, MD, FACS, FAAO]

Because the eye is bereft of the focusing power of the human lens which is almost always greater than the amount of divergence caused by their pre-existing myopia.

Before IOLs when cataracts were removed and NO IOL put in almost everyone including myopes wore strong plust hyperopic cataract glasses (think George Burns glasses).

JCH MD

[battleax]

Berrywo, are you trying to figure out what someone's vision would be like after surgery?

What accomodations in your life style you would have to make with cataract surgery?  

What situation you face have after choosing an option?

[John C Hagan III, MD, FACS, FAAO]

-

[berrywoo]

I just wanted to know why the myopic eye becomes farsighted w/o a lens. I think I was just trying to get a more in-depth answer to the question when there really isn't one, other than the simple fact that w/o a lens you're left w/o a focusing/accomodating mechanism. I was really hoping that there was some sort of mathematical explanation, after all surgeons use measurements of the eye to calculate IOL strength.

FYI, I have only the use of one eye. It is currently aphakic and in time, when/if my retina stabilizes, I hope to be able to get an IOL.

[Harold14370]

According to this:
http://www.wiskit.com/marilyn/contactlenses.html
"an eye with no crystalline lens will require a glasses lens of about +12.00 diopters to correct the vision. "

I think the doc misunderstood your statement # 1. I believe it is true that the crystalline lens is responsible for all the accommodation (but only about a third of the focusing power.)

[John C Hagan III, MD, FACS, FAAO]

By definition in a farsighted eye light rays entering for distance (> 20 feet = parralel) are not bent enough in a farsighted eye to focus on the retina and in myopia they are focused too much. Since the lens is the second most important focusing part of the eye (the cornea is first) with the lens gone all eyes are myopic.

HOWEVER a long myopic eye will require a lower power IOL. If the eye is long enough it might not require any power at all while a short farsighted eye will need a large power IOL .    Remember that because the IOL is closer to the retina it will require a larger power than a cataract glass which is much farther from the retina.

JCH MD

[AnnaE]

I am rooting for your having the best vision possible, no matter what it takes,

[battleax]

In the July 28 post, you stated

"Most myopic eyes that have an lens removed and an IOL not put in will be hyperopic after the surgery."

In the Oct. 31, post, you stated:

Since the lens is the second most important focusing part of the eye (the cornea is first) with the lens gone all eyes are myopic.

Can you please clarify your statements?   They seem to contradict..

[AnnaE]

With no lens, myopic eyes become hyperopic.
With no lens non-myopic eyes become myopic.

That is some name you've got.

[Harold14370]

You got half of that  almost right, Anna :)
Myopes like me wear concave corrective lenses. A convex lens corrects for hyperopia, i.e., it makes one more moypic. Therefore loss of the convex crystalline lens makes one more hyperopic. With no crystalline lens, non-myopic eyes become hyperopic.

[battleax]

The name is crazy and doesn't fit, but I got tired of getting the message the other names I wanted were taken.

I really want to hear from Dr. Hagan on my question, but he hasn't answered yet.  

I'm getting that not having a lens in one's eye means there is no ability to change focus for the eye.   That the cornea provides some focus, but it would be stationary.   That there is a difference in the strength of the lense implanted, and the state of the eye, whether myopic, normal or hyperopic before surgery.   That myopic eyes need a lens that will focus light on the retina, and the correction is normally less than one of a person with a short eyeball (farsighted).

[AnnaE]

Post your question again--new post. Sorry for my bad answer. "Battleax" is humorous to me; my mother used to call women she was angry at "battleax." I thought it was funny back then.

[AnnaE]

50% right is an "F."  Sorry for my sloppy answer.