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Thread: Near Vision Prism Question

  1. #1
    ABO-AC, NCLE-AC, LDO-NV bob_f_aboc's Avatar
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    Near Vision Prism Question

    Had a pt just pick up today. LASIK 7 years ago, monovision correction no longer working like it used to. Ordered FT28 Trivex, Rx: OD -.25 DS, OS -1.75 DS, Add +2.25 OU. Frame B=27 seg=12 OC=15.

    When she put them on the distance was great, but she was complaining of double vision at near. I think I figured the prism at near correctly at ~1^ imbalance (OC 3mm above seg, allowing for 7mm drop to read). Is this normally an adaptable amount of imbalance at near?

  2. #2
    What's up? drk's Avatar
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    I don't get freaked until 2.0^ imbalance, but you're at 1.50 to 1.0^.

    One negative factor is that her iatrogenic anisometropia was sudden onset vs. natural.

    Believe me, offsetting surgical monvision is a biyatch. I universally undercorrect to leave no more than 1D imbalance, and patients generally see the glass half-full.

    If she can't dig her specs in 1 week, to save a two lens remake consider remaking OS to about -1.00 /+2.25 add.
    Last edited by drk; 09-09-2008 at 03:52 PM.

  3. #3
    ABO-AC, NCLE-AC, LDO-NV bob_f_aboc's Avatar
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    She had the LASIK done in sunny California about 7 years ago and doesn't remember the name of the surgeon who did it. We were trying to get some records before LASIK but couldn't. I guess I don't have anywhere to send the thank you card. :angry:

    Thanks Doc.

    Bob

  4. #4
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    I am not a fan of monivision LASIK or post-cataract. You usually end up with glasses anyway and then you frequently need different base curves.
    My sister-in-law got monovision LASIK eight years ago and one of the first things I had to do was make her a pair of reading glasses with largely different powers amd she complained of image size differential.

    Boy, if she could see through my glasses now.:D
    Is there a way to calculate image size say, relative to a -1.50 -1.00 and a -14.75-2.00?;)
    My own estimate is image size is about 35% smaller through the higher minus.
    DragonlensmanWV N.A.O.L.
    "There is nothing patriotic about hating your government or pretending you can hate your government but love your country."

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    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by DragonLensmanWV View Post
    .

    Boy, if she could see through my glasses now.:D
    Is there a way to calculate image size say, relative to a -1.50 -1.00 and a -14.75-2.00?;)
    My own estimate is image size is about 35% smaller through the higher minus.

    Assuming you have an OU axis of 180, with 2.2mm c.t.'s, 4 base OD 1 base OS 1.6 index and 13.5 vertex you've got a 15% difference in minification.

    Now if you made yourself some iseikonics....
    OD 1.5 ct (mm)
    OS 30.0 (mm)

    OD 2 base
    OS 10 base

    1.6 index OU

    and 13.5 vertex , You could cut it down to 4.43% difference.


    * note; that would be one funky lookin' pair of glasses!

    :cheers:

  6. #6
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Quote Originally Posted by optical24/7 View Post
    Assuming you have an OU axis of 180, with 2.2mm c.t.'s, 4 base OD 1 base OS 1.6 index and 13.5 vertex you've got a 15% difference in minification.

    Now if you made yourself some iseikonics....
    OD 1.5 ct (mm)
    OS 30.0 (mm)

    OD 2 base
    OS 10 base

    1.6 index OU

    and 13.5 vertex , You could cut it down to 4.43% difference.


    * note; that would be one funky lookin' pair of glasses!

    :cheers:
    They're already funky.
    OD -14.75 -2.00 X 20 1.70 index 1.5 CT
    OS -1.50 -1.00 X 150 1.557 index CT 2.0

    Tried using a plano in the OD today, as with my patching of the OS, I'm starting to see the OS get a bit lazy and getting hard to fuse. The OD is so blurry with the plano, I can hardly tell there's an eye there and switch easily to the non-dominant eye to see. Otherwise if I patch the dominant OD, I get headaches after a busy day using only the OS. Not mention (oh, wait I just did!) the damaged area left of center in the OS due to optic neuritis.
    DragonlensmanWV N.A.O.L.
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  7. #7
    Master OptiBoarder optical24/7's Avatar
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    When's the right eye getting surgery?

  8. #8
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Quote Originally Posted by optical24/7 View Post
    When's the right eye getting surgery?
    Should be in around 5 weeks. The OMD wanted to wait a bit longer than normal to do the OD because there are some structural differences between my eyes and he wants the left one to be mostly stabilized so he can calculate the lens to get about the same power OU.

    Meanwhile.. sheesh!
    DragonlensmanWV N.A.O.L.
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