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Thread: Advice on vision distortion

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    I had cataract surgery on both eyes about a month ago. I had IOL’s implanted, 0.5 diopter in the right eye and 2.0 diopter in the left. Since then I have gotten two glasses proscriptions filled. The first prescription was
    Right eye: +1.25 sphere, -.75 cyl, 060 axis
    Left eye: +1.00 sphere, -.50 cyl, 155 axis
    Add +2.25 in each eye for reading.
    With this prescription (and with non-prescription 2.75D readers) I had double vision at reading distances. My left eye alone seems to see the letters distinctly smaller than my right eye alone (maybe 10% smaller, maybe more). It also looks like the line of print slopes upward from left to right with my left eye (perhaps 5 degrees). When I read with both eyes the left side of the image comes from my right eye and right side comes from my left eye, and the images overlap meaning the middle of the word in the center of my vision is missing. I usually cover my left eye if I have to read very much.
    For the second prescription, I asked my optometrist to magnify the image on in my left lens. She ended up changing the base curve on the left lens to three instead of six (six what?, she didn’t know), which she said would magnify the image, but she admitted she was just taking a stab in the dark and didn’t know how much it would change the magnification. The new glasses don’t seem to have changed the picture as far as I can tell.

    I have several questions:
    Is it normal to have some distortion after cataract surgery and how is the distortion usually handled? (I complained to my surgeon about seeing double a week after surgery and he said my vision would change. I’ve considered going back to him but first I want to get my facts straight. Plus, if glasses can fix the problem, I want an optometrist to do it, not an MD.)

    Can glasses correct this type of distortion? I’ve tried magnifying the left image with the lens from a pair of reading glasses (which I have to hold several inched from my eye) and I imagine that then the images fuse. However I may be deceiving myself.

    Would most optometrists be able to diagnose and prescribe glasses for such a problem (apparently the mine couldn’t) or do I have to look for a specialist? How would I find such a specialist?

    How much should the second prescription have magnified the image for the left lens?

    What units is base curve expressed in?

    Thanks for any info you can give me.


  2. #2
    Master OptiBoarder Jeff Trail's Avatar
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    No, you do not have to go to a specialist. BUT I would find an OD or MD with a little more experience in "fitting optics".. changing the base curve of the lens would have ZERO effect on your problem. :)
    With you description of the problem one of two ways to go about correcting it, you can have two different additions, say one would be +2.25 add and the other would be a +2.50 (just an example).. the second option is having prism in the reading only. where you would "move" the object through prism to get fusion, but since you say the image appears "different sizes" I would think the better option would be having separate addition powers.
    It would be a very simple procedure to check and see if it helps you by putting either a trial frame on you or having a trial lens handy and just "hold" it in front of your existing frame and lens to get a rough idea if it would work or improve your acuity. The fine tune it if it is working to get the exact mixture of powers.
    She was a little off "base" (nice pun huh?) by thinking that changing the base curve would do much with the problem you have, in would make it worse if anything because by making the base curve to flat you would not have as much sharpness.
    You get base curve by taking the corrective power and then figure which amount of front curve in combination with back curve would give you the widest degree of distortion free zone. To much base curve or two little then you get peripheral distortion and your "target" zone of clear visual field looking through the lens is decreased. A good example is take a clear piece of glass.. has no power right?.. now tilt that piece of glass and see how it distorts objects. same thing happens to your visual field.. you get the clearest vision looking straight ahead and as your eye travels across the lens surface you get more and more distortion, by using proper base curve and surface designs (spherical, aspherical, atoric) we can make that "sweet" spot larger and more distortion free.
    Maybe someone else will have another option, but I vote for having unlike adds myself. And checking to see if having prism in the reading only as the second option or something to maybe check into.

    Jeff "grind'em if ya got'em" Trail

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    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    The bit about the images being displaced nasally sounds like strabismus or esophoria, but I don't know how that might be caused by cataract surgery, other than, I believe it is the case that hyperopia (uncorrected far-sightedness) can exacerbate esophoria - in effect, it can trigger double vision for which your eyes would accomodate were your refractive error properly corrected.

    Please note that this is NOT my area of expertise.

    In any case:

    1) the numbers for the IOL's sound odd - don't these have to have refractive powers on the order of +20D? I don't know how these are labeled, now I'm curious - someone on the board must know...

    2) Lowering the base curve on one of the lenses will decrease the magnification produced by that lens, not increase it.

    3) The sloping effect is probably caused by uncorrected astigmatism.

    4) The perceived difference in image size MAY be the result of your spectacle RX simply being incorrect (which, given (3), it may be). The significant image displacement you describe sounds like the more significant problem to me.

    My advice: go back to your MD. The problem MAY have to do with your IOL's, and he's best equipped to deal with that.


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    I would suggest you consult an optometrist whose expertise is in binocular vision.

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    By increasing the bc on one lens and decreasing the bc on the other you can minimize magnification. There is a formula for calculating, although I have not seen it for quite some time. If I can locate it I'll pass it along

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    Master OptiBoarder Jeff Trail's Avatar
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    I take it that you are talking about spectacle lens magnification? You can figure it as SM=1/1-(t/n)D1 X 1/1-hD (shape factor x power factor) t=thickness n=index of ref.
    D1=front curve D=actual power h=vertex plus3mm

    Then you can figure the difference %SM=(SM-1)100

    I thought about it, but with some of the problems that were listed, especially the one about "things seemed to be curved" I started to think about the basic pricinples of prism. What are the things that show excessive or unwanted prism? BD flat surfaces seem concave, base up they seem convex base in or out horizontal objects tables or floors seem to SLOPE, one of the things he mentioned.
    Oh well just one lab rats opinion. I still think that you could either get correction by mixing add powers or possibly seg types. I don't think changing the curve from a 6 to a 4 base in one eye would do much in this case.

    Jeff "optics is fun..but trying to post formuli stinks on the internet" Trail

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    What was your pre-op refractive status? do you remember having longstanding image size difference problem prior to cataract surgery?

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    Master OptiBoarder Jeff Trail's Avatar
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    Shabbir,

    Welcome to the board by the way :) Usually when it occurs naturally and over a period of time one does not even notice a problem (accomendation)I would think since his RX is almost the same OU the problem lies in the IOL more then likely a slight shift in the IOL and it may correct itself in time.. wonder if he was placed on any type of steriod? hmm...
    Good question though..so now we wait for the answer :)

    Jeff "TGIF" Trail

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    Master OptiBoarder OptiBoard Gold Supporter Judy Canty's Avatar
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    My thought is that you're just a month post-op and still in the healing process. Call your Ophthalmologist and let her or him know about your visual problems. Then schedule your next follow-up as soon as possible. I have had post-op Rx's change as long as 6 months after the surgery.

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    Thanks everybody for your help.
    In answer to several questions – the IOL numbers are odd because I’m (or was) very near sighted – my prescription before surgery was about –14 diopters so that’s why minimal IOL correction was needed.
    Also, I didn’t have the image size discrepancy before the surgery that I’m aware of.
    I’ve been taking Accular, 4 times a day for 4 weeks and then twice a day for one week.
    Theoretically, I should go back to my ophthalmologist but several things bothered me about him. Although he has an in-house optometrist, they computed my prescription using one of those automatic prescription reading machines (whatever they’re called) which I’ve been lead to believe is not really accurate enough. Another thing that bothered me was that even though I complained one week post-op of double vision, he told me to make a follow-up appointment for six months. I didn’t feel he took my problem seriously so I’m reluctant to go back. But then, maybe it takes six months for the eyes to stabilize (if that was the case, I wish he would have said so).

    I’m seeing my original optometrist one more time this afternoon (she’s giving me free follow-ups) and I’m going to ask her to try the unequal add and/or prism correction. I’m hoping she can try these things in her office so I won’t have to get a bunch of new lenses made. In her defense, she did try a different add in my left eye by placing different lenses in front of my eye. But when I complained that the image was blurry, she tried the changing the base curve on advice from her favorite optician.

    If she can’t help I’ll then probably go see my ophthalmologist or maybe she’ll be able to recommend a more experienced optometrist.

    Thank you again.

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    JEFF TRAIL,
    When you come across post-op problems always first check the patients pre-op records.
    Steriods are harmful medication if wrongly administered-think of drug-drug inter actions too.
    Please advice them to consult an optometrist or an ophthalmologist.
    This is not an area of dispensers(opticians)who does not even know effects of base curve on visual optics of the eye.
    Shabbir

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    Master OptiBoarder Jeff Trail's Avatar
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    "When you come across post-op problems always first check the patients pre-op records."

    Since the OD did try some things to try to correct the problem and could not, as was posted that tells me it was not an existing problem or the answer would have already been there. Be it prism, spectacle magnification or a mixture of seg with different seg oc depth.



    "Steriods are harmful medication if wrongly administered-think of drug-drug inter actions too."

    I was just thinking that he could have been on a possible combination since he was "refracted" so soon after going post-op.


    "Please advice them to consult an optometrist or an ophthalmologist.
    This is not an area of dispensers(opticians)who does not even know effects of base curve on visual optics of the eye."

    The "dispenser(optician)" in this case was the ONE who understood spectacle magnification NOT the OD who was prescribing the lens RX, as the original poster posted in the beginning.
    I don't know about you and where you are located but the "dispenser(optician)" knows far more about theoretical optics in lens fabrication then most OD's and MD's I know.
    If it was aimed at me, I think I have a very good understanding about spectacle magnification. I do understand as well
    "does not even know effects of base curve on visual optics of the eye." I deal with those type problems daily.
    I think you have it backwards, the vast majority of OD's and MD's I know should let the "dispenser(optician)" deal with these type problems because they have a deeper understanding of optical theory in lens fabrication. I wouldn't expect an OD or MD to poke around in this end of the field.. why would they? Go to med school and then spend time in optical theory instead of pathology and anatomy..doesn't make since to me....
    Oh well to each his own, with your low opinion of opticians I would hate to think what you think of us lowly "labrats" :)

    Jeff "whatever..isn't it Friday yet?" Trail

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    Dear Jeff Trail,
    Please do not misunderstand me." I HAVE VERY HIGH REGARD FOR DISPENSING OPTICIANS" I know opticians are best when it comes to optics of eye.
    Please accept my apology,my noisy friend.
    Regards,
    Shabbir

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