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Thread: Oddity of a high minus, high index pal.

  1. #1
    OptiBoard Apprentice
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    I have a Zeiss Gradal Tops in 1.67 with -10.25 and -10.0, with an add of 1.0D. The lens has 18mm height. Very light astigmatism in the right eye.

    Is it possible, assuming proper grinding of the lenses, that the center of the intermediate column would be optically superior to the center of the distance portion of the lenses?

    In other words, the lab (apparently) cannot make the distance portion of the lenses such that the glasses will deliver the same or better distance acuity than does the intermediate column.

    Seemingly, this is because the distance portion of the lenses contains more distortion than does the intermediate column.

    Thus, we are left with the supposedly unavoidable oddity of having superior distance acuity through the intermediate column (the difference is slight but noticeable and the glasses have been carefully fit and adjusted by a top optician).

    Might a new lab be in order?

    Perhaps a different lens material?

    What about a different lens manufacturer?

    Any suggestions or explanations for this mystery would be greatly appreciated.

    Cameron Reddy
    creddy@cameronreddy.com

  2. #2
    Bad address email on file Darris Chambless's Avatar
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    Redhot Jumper

    Hello Cameron,

    Here's the straight poop on this subject. You are a -10.25 which basically means you will experience some off axis problems at least for a period of time if not indefinitely. High index will give you a thinner lens, but you will sacrifice some visual acuity. Then to compound the problem you are adding a progressive addition power which can and will cause some other aberrations and visual anomalies as well.

    You are working with good technology, but it is still the "limitations" of the technology available today. Your visual acuity being better at your intermediate zone has to do with the angle at which you have to look through the lens and where the optical center sits in accordance to that intermediate zone. The lab or the doctors office may be able to duplicate this but it would be a lot of hit or miss.

    The reason that this is not as cut and dry as it should be is due to the fact that with your script you have a very small fitting button to work with, especially in high index materials. -10.25 is not a very forgiving script.

    Now with all that said and before people start jumping in and saying they fit scripts that high all the time and never have any trouble fitting their patients, rarely does one run into the situation you have encountered. I fit high scripts too and can't say I have dealt with what you describe, but you never know when it will happen.

    Case in point I had a patient recently that wore a very low distance power (almost non-existent -0.25-0.50 with a low add power of +1.25) The patient wanted a wrap around type of metal sun glass which we found and made for her. To make a long story short, after remaking the lenses in different base curves and different designs five times we finally got her fixed up and she can see great. During this process the patient asked me if it was just a problem with the curve of the frame and should she switch to a different frame? I told her that I have never had a problem with high base lenses in a script like hers (because I haven't).

    So in a nutshell it just happens some times and without warning. It's your and your doctors turn ;-)

    Hope this sheds a little light on the subject for you.

    Darris C.


  3. #3
    Master OptiBoarder Texas Ranger's Avatar
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    Cameron, Since the vertex distance is likely slightly different from the phoropter to the glasses, and nobody probably measured it on either end of the process, you probably would be comfortable with a bit less minus in the distance rx,countered by a similar reduction in add to equal the same near. the Dr. could do this with a trial lens over the glasses. Just a thought, Al.

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