Near vs. intermediate setting for IOLs

I think we need to be more circumspect in saying what particular choices would provide. First, we don't know how close our surgeon will come to hitting the targets. Second, we don't know whether our individual visual acuity will be better or worse than the mean visual acuities reported in defocus curves. Third, although defocus curves provide information that we hope is more-or-less reliable, and the alternative would seem to be simply relying on our surgeon's judgment alone, we don't know how reliable they are in terms of methodology and implementation. Also, their sample sizes are often fairly small. So, we don't know how representative the results actually are. (That's why I have tried to gather and average together as many Eyhance defocus curves as possible.)

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What we can say, for example, is that, with the Eyhance, if you end up with one IOL at -1.00 D and the other IOL at -2.50 D, and if your visual acuities correspond to the average of the mean results in the ten defocus Eyhance defocus curves I've so far found, then, absent any other factor degrading your vision and subject to the other caveats in the first paragraph, you would have 20/30 vision at -4.00 D defocus (9.85") and 20/25 at -3.50 D defocus (11.25"). You'd also have 20/32 vision at infinity.

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And if these results could be guaranteed, I'd probably take them myself. Although because I can't be 100% sure that the favorable results of trying 1.50 D of monovision with contact lenses over a few weeks guarantees longterm success, I instead might take -1.25 D in my distance eye (20/35 at infinity, which still would make driving without glasses legal in a pinch).

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But, of course, these results cannot be guaranteed. For myself, therefore, I think, for example, about IOL targets as ranges. If I were to tell my surgeon I want him to target -2.50 D in my near eye, then I'd think of it as accepting that the result most likely will end up somewhere between -2.00 D and -3.00 D, with the actual result constraining the range I could choose for my second (distance) eye. So for me, it's not the end result I'd like to achieve that's the problem. It's thinking through how happy I'd be with possible other end results.

Doing any form of monovision should be a process rather than a single decision up front. In the example I gave above the process I would suggest to do the further distance eye first at -1.0 D. If it comes out at -0.75 D, then the surgeon should learn something and not miss on the second eye. And instead of a target of -2.5 D on the near eye, one could reduce it to -2.25 D to maintain the 1.5 D of anisometropia. Or if it missed to -1.25 instead, then I would expect the surgeon to adjust the calculation and still target -2.5 D. I wouldn't think there would be much value in targeting -2.75 D but that could be done too. And last if the surgeon really misses, and hits -2.0 D instead of -1.0 D, then one could switch eyes and make the -2.0 D eye the close eye, and with a readjusted formula then target -1.0 in the other eye. There really is no big deal with switching from the more standard dominant eye being the distance eye to the reverse. Some believe it is better. My monovision is reversed.

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This is the value of scheduling to have eyes done at least 6 weeks apart so you can get a final refraction on the first eye to help with the decision on the second eye refinement. It short it is a plan rather than a one time decision.

Hi RonAKA,

It sounds like I should ask that the first eye be set for -2.0 and if the target is reached, I would stick with -2.0 for the second eye. Alternatively, if the result of the first eye is -2.5 I may need to ask for the second eye to be set at -1.5? I'm not sure about the second eye calculation...

I would say no, you would not need to target -1.5 D for the second eye if the first one turns out at -2.5 and you wanted 2.0 in both. I would just ask the surgeon to sharpen their pencil and hit 2.0 in the second eye.

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Within reasonable limits, you do not see with a blend of the targets in both eyes. In other words one eye at -2.5 and the other at -1.5 does not average out to be effectively -2.0 D. What really happens is that each eye sees a different focus image. The -2.5 D eye will see closer and your brain will select that image over the eye seeing -1.5 when the object you are looking at is close. And at some point as the object is further away then the -1.5 D eye will take over and provide the image that your brain will select.

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The net effect is that with one eye at -2.5 and the other at -1.5 you will see a wider range of distances. With both eyes at -2 you will probably see relatively well from 10" or so to 2 feet. With the -2.5 and -1.5 combination good vision would likely extend from 6" out to 5 feet or so.

Hi Ron I will be getting -1.50 EMV in bad eye. Second eye not for long time as this surgeon says not ready and will not touch it till it is. Has to balance bad eye with good eye which is -3.25 little astig -under one but forgot exact He says think of it as -3.50 so if hit target that is 2 between eyes. Never had monovision contact lens to experience such a differenec between eye. He Says glasses will balance if having problem ,

I am concerned with this between eyes. And guess no one can say if will even settle at target of -1.50 I live at computer right now so good intermediate important at about 26 inches where comfortable. . I want to maintain most of near but also be able to go as much distance when time for second eye. If my eyes (brain) adjusts to the -2 between eyes and who knows how long could be really long time till second eye done and then will do less than 2 when time comes is that going to be a strange readjustment again. If the emv does what is says and gives enough near with 150 target so not readers on and off, I can use other eye to go out. If can tolerate would aim for -50 or -.75 or if other eye stays on -1.50 target. If eye refracts to --1.75 that means 20"? or 22"? clear vision and if do second eye - 75 or -1 would that pick up more interemediate to see computer without needing glasses at 24-26 more or less. I understand none of this is exact math. thanks

If you get -1.50 D in the near eye with an EMV lens, and the objective is to be glasses free, then I would target -0.25 D in the second eye when it comes time to do that. If the second eye is good then you could could use a contact in it to bring it to -0.25 D to see if you like it ahead of time.

FWIW, I think of -2 as near, but perhaps that's a matter of individual semantics. I told my surgeon that I wanted to be able to read a book with crystal clear vision without glasses. That was pretty much all that mattered to me, since I was perfectly happy wearing progressive glasses for anything else. But in the end it turned out that I only need glasses for TV and driving.

So much depends on what you're used to. For someone like me, who had fairly high myopia, being able to see -2 instead of -8 was (and continues to be) a revelation. Someone with really good vision to begin with will have a different experience.

2.0 D - 10" minimum to 30", Peak vision at about 1.5 feet

1.5 D - 1 foot minimum to about 3.5 feet, Peak vision at about 2 feet

1.0 D - 16" to about 9 feet, Peak vision at about 2.5 feet

Thanks RonAKA. The this information is very helpful! My cataract surgeon said he could aim for a compromise of 1.75 since I'm debating between near and intermediate, and I feel good about that.

Yes, you could do that. However, I think the much better way to compromise is to make a split in the two eyes like 2.0 D in one and 1.0 D in the other. This is a low differential and gives you a much wider range of vision. There is nothing to be gained by making both eyes exactly the same, and they most likely will not end up exactly the same in any case.

Thanks Ron! My concern is that I may not like the difference and it could end up being a larger spread than anticipated. I do plan to let the first eye heal and get the result and depending on that select either the same or different target for the second eye. I don't mind wearing glasses.

That is a good plan. You will find out where the vision lands for you and will be able to more accurately determine what you want - closer or further. Also with the result your surgeon should learn something and be more accurate on the second eye, reducing your risk of a surprise.

Yes, I meant to say -2.0 D and -1.0 D. You would never want to be +2.0 D. That would give you very poor hyperopic distance vision and near vision would be even worse.