Crystalens Diopter rating vs Glasses?

[Lackosleep]

Does anyone know what the difference between the Crystalens HD500 diopter rating scale and that used for eyeglass prescriptions? I have the HD500s implanted beginning of March 2009 (L=24 R=25 according to the cards). The numbers just seem so extraordinarily high compared to the multifocal contacts (+2.5,+2.25) I wore before surgery.
Is there a "conversion scale" so I can get an idea of how much correction really was applied? I have [too?] great reading, mediocre near and poor distance that may have to be adjusted with lasik and would like to be able to understand better what the doctor is doing with numbers that make sense :)
Thanks in advance!

Lackosleep

*For more post op info, see my other posts RE: crystalens

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

1. You NEVER know ahead of time the outcome of surgery. All surgery carries risk. Worse risk is loss of eye (1 in 15,000 cases). You can do your own homework about various combinations of monovision and mini-monovision and ideal target refractive errors. With crystalens HD most surgeons are now shooting for 0.00 and -0.50 to -0.75 in the other.  If the eye is too myopic lasik can be done without removing the IOL. If you're not sure and can't work it would with your surgeon get a secon opinion.

JCH MD

[Lackosleep]

Thanks. I think that will help a few people here who wanted to know.

So are you saying that with the Crystalens HD500s that I have, and have poor distance but good mid-reading with, I should try to correct for best distance, and let the ciliary muscles make these IOLs work for mid & reading? Shouldn't I be able to simulate the outcome of LASIK or PRK with corrective lens now? ie, "try before I buy"? I don't like the idea of more eye surgery without fully understanding what the outcome should be.

Thanks again
Lackosleep.

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

A diopter is a unit that never varies whether talking about glasses, contacts, IOL or camera lens:

A measure of the power of a lens or a prism. The diopter (also called dioptrie) is usually abbreviated D. Its dimension is a reciprocal length, and its unit is the reciprocal of 1 m (3.28 ft). See also Focal length; Lens (optics).

The dioptric power of a prism is defined as the measure of the deviation of a ray going through a prism measured at the distance of 1 m. A prism that deviates a ray by 1 cm in a distance of 1 m is said to have a power of one prism diopte

You cannot look at a glasses RX or contact lens RX and determine what IOL is needed. That's why people having cataract surgery have to have special measurements that are not done on glasses or contacts. These include: axial length of eye, cornea radius, anterior chamber depth and an A constant that varies with IOL.

When looking at distance ( greater than 20 feet at that distance all light rays enters eye parallel no matter how far away they are, the focus muscle (ciliary body) is relaxed.  

After cataract surgery with a standard monofocal IOL the eye cannot truly accommodate. There is some pseudo or false focus due to pupil constriction, residual corneal astigmastis and depth of focus of the IOL.   With a multifocal IOL there is no true focus as the diffractive patter of the IOL creates multiple focus rings (example ReStor and the TERRIBLE ReZoom)  only a true accommodating IOL like Crystalens allows focusing by the focus muscle.

This latter proves that the reason we need reading glasses and bifocals as we age is not that the ciliary body gets weak its that the lens gets too stiff and rigid to change shape and allow focus to occur.

JCH MD

[Lackosleep]

Do the eye muscles relax or contract to see distance?

ie, does the eye start out in a relaxed state and then actively contract to see closer as needed, or the reverse?
I am trying to understand so I can get my eyes corrected with lasik with best overall results with the Crystalens HD500s already implanted and currently having bad far vision, med near, good reading 2 1/2 mos post op.

ie, If the eyes start off relaxed for distance, and the CHDs can accomodate with the contraction of eye, would it be best for me to try to achieve BEST distance with lasik, then the muscles should work to focus near over time (?)

Or if reverse, should I attempt best near/reading and hope for distance over time?

Thanks again!
Lackosleep

*For more post op info, see my other posts RE: crystalens