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Stupid question about numbers (but I really am confused).

Posted , 7 users are following.

david32346
david32346

I'm looking at an old glasses prescription of mine and it says R: -1.50, L: -2.00

I have been near-sighted my entire life so I know that the prescription was to correct my near-sightedness and allow me to do things like drive and catch footballs.

But my question is this, which do the numbers mean, A or B?

A: This person's eyes are at a +1.50 and +2.00 when uncorrected, so please make corrective lenses with offsetting -1.50 curvature in the right corrective lens and -2.00 curvature in the left corrective lens.

B: This person's eyes are at a -1.50 and -2.00 when uncorrected, so please make corrective lenses with an offsetting +1.50 curvature in the right corrective lens and a +2.00 curvature in the left corrective lens.

On Monday I am telling my cataract surgeon that I want -0.5 Left eye, -1.70 right eye, aiming for near-perfect distance vision in my left eye and intermediate vision in the right eye.

Am I correct on Monday if I give negative numbers and not positive numbers?

Thanks in advance for any help with this.

0 likes, 8 replies

8 Replies

  • soks
    soks david32346

    Posted

    you can say that you want to be myopic after the cataract surgery by -0.5 in the left eye and by -1.5 in the right eye.

  • Night-Hawk
    Night-Hawk david32346

    Posted

    The Rx indicates what the eyeglasses lenses would be, so a negative number in the lens corrects for nearsightness.

    If you say what your targets for cataract surgery in the eye are, it would be specifying what your target would be for an eyeglasses Rx for the eye after the surgery. So yes, you would specify those negative values you listed.

    However, the results will not be exact. First the IOLs come in steps of 0.5D, so they will pick the closest IOL available for your target. That could end up being +/-0.25D off. Also due to unpredictable things like the effect of the incision in the cornea of the eye and how it heals (varies with each person) that can add more error and/or introduce some astigmatism (cylinder in the Rx) as well. So some will target a bit more to the negative side so that any error would make it more nearsighted rather than farsighted.

    Note that there is the new type of IOL available with some eye doctors that can be adjusted after surgery via ultraviolet light treatments - so that type of IOL can overcome the errors after surgery that can't be corrected with other standard types of IOL.

    • Guest
      Guest Night-Hawk

      Posted

      Point of clarity, the margin of error for cataract surgery is plus or minus half diopter on EITHER side of the target, not plus or minus a quarter. For a long time I thought the latter was the case when people say it can be off by a half but my surgeon corrected me on that.

    • RonAKA
      RonAKA Guest

      Posted

      A recent article found the very best IOL Calculation formula, the Hill-RBF 3.0, was found to be +/- 0.5 D in 95% of patients. Other top formulas were closer to 90%. I suspect however, that surgeons can do better on the second eye, than the first, if they look at the 5-6 week post surgery results and compare them to what was expected. If the eyes are similar they can use that information to refine the formula for the second eye.

  • RonAKA
    RonAKA david32346

    Edited

    Targets are set based on the eyeglass prescription required to correct the eye to plano. So your targets of -0.5 D and -1.70 D are mild and moderate myopia respectively. You are correct in giving negative numbers. The IOL Power calculation will likely not even accept a + number. Nobody wants to be far sighted (+ number).

    .

    I would not really call -1.70 D intermediate vision. You should be able to read a phone, computer and most text on paper with that target. I am not sure I would target -0.50 D with the distance eye though. You put 20/20 vision at risk with that target, and will probably need eyeglasses for the best distance vision.

    .

    Also don't forget about potential astigmatism. Be sure to ask if any is anticipated. Targets are normally set on sphere plus 50% of the expected astigmatism (cylinder).

    .

    And keep in mind that you cannot really pick specific diopters as targets. Once your eyes are measured the IOL Calculation sheet will show you what targets are possible with your specific eyes. It is always worthwhile to ask what the options are. They will be displayed on the IOL sheet.

  • Guest
    Guest david32346

    Edited

    "A". In effect myopes have eyes that are "too powerful" at rest… like we have reading glasses built in.

  • RonAKA
    RonAKA david32346

    Posted

    I also think it makes the most sense to do your distance eye first, and then wait 5-6 weeks to get an accurate refraction of what the outcome is. Then you can experiment using reading glasses with this eye to determine how much reading vision you want/need. And, then you will know what you have in the first eye, so you will further know how much myopia you can risk in the near eye.

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