Power of IOL
Posted , 5 users are following.
can someone tell me what numbers should I be looking for in my records to make sure I get the correct power of my IOL. I was told to see a few doctors to compare but not sure what I am comparing. Is it the refraction? Also I found in my records target -0.25. what is that number for. What is visual acuity and manifest refraction? What does Plano mean? All these terms are very new to me and just trying to be very proactive for the best outcome.
thank you!
0 likes, 16 replies
RonAKA Songirl
Edited
It is very difficult to use your eyeglass prescription to predict what you need for an IOL power. The problem is that refractive error that is corrected by eyeglasses is the result of error in your eye natural lens plus error in your cornea. The two errors (both spherical and cylinder) can be additive or subtractive. Your eyeglasses corrects for the net result. However when you have cataract surgery the lens is removed, so any error in your lens is gone too. The only error that the IOL has to correct for is the cornea error.
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The bottom line is that you depend on the skill of the surgeon to measure the topography of your cornea and shape of your eye to determine what power you need. They will usually use more than one method to measure and a computer program to determine the lens power needed.
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Visual acuity is just your quality of vision, like 20/20. Correcting to plano usually means they are correcting for distance 20/20 vision and would need not eyeglass correction for distance vision.
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What you really need to think about is what vision do you want without glasses. The large majority of people get a lens to correct to 20/20 distance or plano. With a monofocal type lens you will then need reading glasses to read. Another choice that not many make is to get corrected for reading without glasses. In other words you would be myopic or near sighted. Then you would need glasses for distance and driving for sure. Another option is to correct the dominant eye for distance plano, and under correct the non dominant eye slightly by leaving you at -1.25 D for example. This will allow you to read with one eye, and see distance with the other eye. It is called mini-monovision. Some like it, and some don't.
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There there are other lenses that try to let you see both near and far. They can be very expensive, and often have optical side effects, especially at night -- like halos, or flare, or spiderwebs around lights. Some adapt to it, and others do not.
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There are lots of options and it is well worthwhile to understand it all before you jump in. If you cannot take the time to get to the bottom of it all, I would stick with the most traditional and safest choice. That is to get a monofocal lens set for 20/20 at distance, and accept that you will need reading glasses for close vision. It is also the least expensive way to go.
Songirl RonAKA
Posted
thank you so much for your reply. I have researched alot already on the different types of IOL's. I am seriously considering the Panoptix as I do not drive much at night.
My main goal now is to avoid the doctor putting in the wrong power. I am actually glad you tell me they do not use the refraction to determine the power because it is my understanding those numbers can vary between doctors. My doctor has had wonderful reviews and over 35 years of experience. However I am still thinking about going to another opthamologist to compare numbers. Do you know the exact names of the methods of measurements I should be looking for? Also what does it mean in my report that says target -0.25?
thanks again
Night-Hawk Songirl
Edited
The -0.25D target is common with a goal of distance focus. Thats very slightly nearsighted but can still achieve 20/20 distance vision.
The reason that is the usual target is because the IOLs come in 0.5D steps, so even if all measurements are perfect there will still be a +/- 0.25D error. Also the healing of the incision is unpredictable and that can induce further refraction error especially astigmatism.
So they would rather be off with a slight nearsighted result rather than farsighted that reduces any intermediate/near focus vision.
If you are especially concerned about losing intermediate vision, you may want to go for an even more slightly nearsighted target like -0.5D for more margin for error. Also with a multifocal like Panoptix IOL if error ends up resulting in a slightly farsighted target you may lose the near focus making the high extra cost of the multifocal wasted.
RonAKA Songirl
Posted
For more detail (perhaps too much) on the measurement methods used google this article:
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EyeWiki Biometry for Intra-Ocular Lens (IOL) Power Calculation
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As @Night-Hawk has said, if the -0.25 D is a target for the IOL, this just means they are targeting to under correct the distance vision by that much. This is a very small amount, and since the IOLs come in steps of 0.5 D power the next step up would be a +0.25 D. Ending up at a +0.25 D will give you the same 20/20 vision at distance, but it will be a significant hit in ability to see closer. You will have lost 0.5 D in close vision. It is standard practice to target -0.25 D.
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As the surgeon who did my eye said "Nobody ever thanks me for going over to the + side". And, they have a hard time being within 0.25 of the target. I recall that the surgeon was expecting -0.35 for my eye, and it came out at 0.0 D - perfect plano. The cylinder (astigmatism) was not so good. He was expecting -0.0 to -0.4 D, but it came out at -0.75 D. He either measured incorrectly or the incision induced more astigmatism than he was expecting. It may have been a bit of a blessing in disguise. Some astigmatism can help with the reading end of the range of vision. I can read down to about 18" with my monofocal IOL.
Songirl Night-Hawk
Posted
So if I go with the -0.5 would that be best to not loose and close and mid distance vision?
RonAKA Songirl
Edited
You have to think of the target as a range, not a single number. It is best to have the discussion with the surgeon that has your eye measurements and ask what the power choice options are, keeping in mind they are in 0.5 D steps. It is almost certain there will be two powers to choose from. It is better to have a little more than -0.25 than a little less. Also keep in mind an experienced surgeon knows all the issues and will not steer you wrong. You can probably only get into trouble if you push the surgeon to give you exactly plano. Then you could end up in the + zone.
Have you had any vision correction with laser surgery? That can make the power you need more difficult to calculate.
Songirl RonAKA
Posted
no, never had laser and now so glad I have not.
RonAKA Songirl
Edited
That is one complicating factor out of the way.
lucy24197 Songirl
Posted
That was my thought--my target was -0.5 (surgery was a little more than 2 weeks ago--Tecnis monofocal lens.) When I talked to the scheduler, I asked them about ranges, and they told me the surgeon would pick whatever lens put me closest to -0.5 per the calculations--basically +/- 0.25. Then when I talked to the surgeon a couple days before the surgery, he told me I needed to pick between -0.5 and -1.0, or -0.5 and plano. It was spur of the moment and he had to get off the phone, I had to decide immediately, so I said -0.5 to -1.0 (he said it would probably end up around -0.75.) One week after the surgery, I was between -0.5 and -0.25. Not sure where I am today; I have some issues with blurriness that are affecting things so I'm not sure where I'll end up. It's better today, and I can read the 20/25 line just fine on a Snellen chart, and make out some characters on the 20/20 line. Near vision is not great compared to results other people have had. Looking at a Jaeger chart, nothing is sharp closer than 3'. At 3' things are sharp down to J9; finer print than that isn't really readable (some of it's just too small.) At 14" where you're supposed to read the Jaeger chart, everything is pretty blurry. The near vision seems to be coming in more slowly than the distance vision, so I'm hoping it will get a little better. That said, it is MUCH easier to make out text on the computer than on a paper chart. I can read what I'm typing at 13" or farther out. It's blurry, but I can read it. The font on my computer right now is about the same size as a J11 on the Jaeger chart. I can still make it out from a few inches away, although it is blurred.
RonAKA lucy24197
Posted
Black text on a bright white computer screen is easier to read than text on paper. I find with the Jaeger chart it is very light sensitive with my IOL eye. If I have it in bright sunlight I can read much smaller than in dim light. I suspect both of these effects are due to the pupil "stopping" down in bright light and increasing the depth of focus. There probably is some specified brightness that you are to be tested at, but I have no idea what it is.
Songirl Night-Hawk
Edited
If the target is off, is this something that can be fixed besides changing the lens? Like with lasik?
Sue.An2 Songirl
Posted
yes corrections can be made with lasik and some premium lens packages offer tjose touch ups depending on private clinic. Others will charge you for the treatments
Songirl Sue.An2
Posted
so I was wondering if lasik can be done after cataract suegery, is it possible to do mono focal and then do lasik to correct the vision to 20/20 at all distances?
RonAKA Songirl
Posted
The short answer is no. I think some Lasik methods try to replicate the MF effect, but of course there will be issues just like with a MF IOL. Lasik would be mainly used when the power of the IOL is off target.
Songirl RonAKA
Posted
Thank You, figured not or everyone will do that. Wishful thinking.
Sue.An2 Songirl
Posted
is it possible - yes but i would tend to think anyone going with monofocals accept glasses for at least one distance (if doing a bit of monovision) 2 distances if targeting same distance so why would one opt for lasik if wearing glasses anyways. Tend to think those with MF would opt for lasik touchups as they wanted glasses free