Questions about the plus and minus on prescription

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I've spent a lot of time trying to figure this out and am still confused and quite frustrated with myself at the moment. I understand sphere, cylinder, and axis, but I get confused about what the plus and minus means, specifically with respect to the sphere.

After my cataract surgery, my RE is .5 .5 127 (I wrote this down). I had thought that this meant that I was slightly myopic, but the doctor yesterday said that my surgery left me .5 diopters farsighted. I asked to be .5 diopters myopic for my new surgery (lens exchange) and he said the IOL power he would use would be targeting .4 diopters myopic. I thought I would get a pair of readers to simulate what my sight would be and here is where I get more confused. Readers are labeled with a plus. If I'm going from .5 to -.4, isn't that -.9? Would a +.75 or +1.0 reader simulate the target for my vision after the exchange?

Thank you in advance!

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4 Replies

  • Posted

    Hopefully this helps:

    When you look at your prescription for eyeglasses, you will see numbers listed under the headings of OS and OD. They are Latin abbreviations: OS (oculus sinister) means the left eye and OD (oculus dextrus) means the right eye. Occasionally, you will see a notation for OU, which means something involving both eyes. In general, the further away from zero the number on your prescription, the worse your eyesight and the more vision correction (stronger prescription) you need. A “plus” (+) sign in front of the number means you are farsighted, and a “minus” (-) sign means you are nearsighted. These numbers represent diopters, the unit used to measure the correction, or focusing power, of the lens your eye requires. Diopter is often abbreviated "D."

    For example, if your prescription says -1.00, you have one diopter of nearsightedness. This is a fairly mild amount of nearsightedness. If you are -4.25, that means you have 4 and 1/4 diopters of nearsightedness. This is more nearsighted than -1.00, and requires stronger (thicker) lenses. Similarly, +1.00 would be a small amount of farsightedness and +5 would be more.

    • Posted

      Thank you! I guess I had it backwards. Since dr is targeting -.4 diopters (.9 difference from what I have), do you think .75 or 1 diopter readers provide me an estimate of what my vision will be like?

  • Posted

    So you want your left eye to go from current +.5 to future -.4. so yes that is a difference of minus .9 Diopter.

    I don't know how you would simulate that, do -1 glasses exist? I don't understand glasses fully anyway! Maybe visit an eye glass place.

    Btw does your right eye have cataract too? Was it already operated? What are the readings for the right eye?

    What if your Dr had actually tried hitting plano but overshot to +.5. What makes you sure that he can hit -.4?

    Are you doing lens exchange purely for changing it from +.5 to -.4 or are there other reasons?

    • Posted

      I am doing an IOL exchange for positive dysphotopsia. I do believe the first surgeon targeted plano and I ended up +.5. My new surgeon showed me the formulas with my current lens and my eye measurements and the result should have been close to plano. Note there are multiple formulas so that's why I say close to plano - different formulas give slightly different results.

      I am not at all sure that the new dr will hit -.4. As you know the IOL powers are increments of .5 so I picked -.4 over -.9. Depending on where I land, I'll ask him to adjust the second eye accordingly. I'm not that concerned about eye dominance since I'm only looking for slight differences in the two eyes.

      Both eyes were operated on already (May and June) and I have positive dysphotopsia in both eyes. My dominant LE is .25 so I am farsighted in both eyes.

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