Measurements...How reliable are they?

Hi Soks,

Thanks. Interesting that you had 4 measurements done at different places. And I thought I was being cautious! : ) But seriously, good on you for taking the time and not letting any self-pressure (or for that matter external pressure) affect your process. I, myself, feel I'm putting a bit of pressure on myself...thinking I need to just "go for it." At the same time, I feel I'm not entirely convinced that what I've been told at two clinics so far makes complete sense. One rather well respected clinic's surgeon recommended 1.0 diopter difference in my near eye to my plano distance lens already implanted. Another doc at another clinic recommended 2.0 diopters (which I felt was too large a difference. We've since agreed 1.50 would suffice for my needs.).The second clinic took detailed measurements whilst the first gave me a very general look-over and will only take the detailed measurements when I book the surgery.To the second clinic's credit, the surgeon did send me details and data showing how several formulas (Barrett, SRK/T, and Holliday I) dovetail well with each other whilst one, the Haigis, was an outlier.

Your strategy to get several measurements is one I'll likely take on board. Thanks.

IndyG

The IOL formulas have their strengths and weaknesses while some are more universal. Some require adjustments for certain eye conditions, and some allow for a "surgeon factor" which is a way the surgeon can tweak the formula based on their own personal surgical experience with each lens type. If you google this you should find an article which talks about the application ranges of a few different formulas.

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Zeiss IOL power calculation formulas

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The Hill RBF formula is not included, and I believe is the one my surgeon used on my last lens. As I understand it this formula is based on artificial intelligence processed data collected from surgeons.

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I think at the end of the day you depend heavily on the surgeon's experience in selecting the best formula considering their own experience and the specifics of your eye. If I was picking I would choose the Barrett Universal II or the Hill RBF V2. My eyes are mildly myopic so I assume mildly longer than average.

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For my first eye my surgeon ended up about 3/8 D more hyperopic than he expected. And on the second eye he was 1/4 D more hyperopic. I recall my wife's outcome was similar.

i also did the intra operative ORA. they actually brought me to my senses and as i had requested showed me the ORA screen and asked me for and asked me what IOL inwanted to choose. after choosing i my memory is faint again.

i think under normal circumstances -1.5 should give you good intermediate and functional near. -2.## will make near better but will distort far and intermediate significantly. the reason for this is that higher diopters are needed for near so you would have good vision for a smaller range of near vision.

Thanks Soks,

Sorry for the late reply. I've been away. Yes, initially the doc suggested 2.0 for the near eye, but I felt that was on the high side. I'd be pretty happy if I had my near vision set to just a few inches in from what I'm currently seeing with my "far" eye. I seem to have quite good intermediate range with my far eye and can read at a bit closer than arms length. I've read 1.5 is near the ideal for most people. I've sent an email to the doc's secretary to book the surgery. He assures me that the measurements are good and taken with some kind of Zeiss machine that he says is the "gold standard" by which all modern machines are compared. I'm going to trust him on that. He did say it's rare for him to encounter a patient with as much knowledge as I have about cataract surgery. This, of course, I attribute to this forum and people like you and RonAKA and others.So thanks to everyone here for that. I'm probably looking out to June sometime for the procedure.

IndyG

I think the best machine is an Zeiss IOLMaster 700. The other common machine used is the Haig-Streit Lenstar LS900. I think the IOLMaster 700 may be able to measure through a more dense cataract. And the IOLMaster 700 is much faster. I have had my eyes done with the IOLMaster 700, 500, and most recently the LS900 for a Lasik evaluation. If found it very difficult to keep my eyes still long enough with the LS900.

I have seen some claims about LAL being able to achieve an extended range of focus, but I would be very skeptical about that. LAL however would be well suited to doing monovision which can give you an extended range of vision. Monovision requires accuracy in the correction power and because the power can be adjusted after the lens is in your eye, the LAL is well suited to do that. Also because you are highly myopic power prediction for a standard lens is more difficult. LAL solves that problem too.

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I am not so sure that LAL can correct astigmatism though, and you should ask about that. Astigmatism before surgery is a hint that it may be a problem. But, astigmatism can get better or worse after surgery because the lens is removed. When the measurements are taken of your eye for an IOL you need to ask what the residual astigmatism will be after surgery. They can give you an estimate. If it is over 1.0 D then it can be a problem. Usually more than 0.75 D of astigmatism is corrected with a toric lens, and I am not sure an LAL is available in toric versions. If you will have high astigmatism after surgery, it is probably best to go with a standard toric lens.

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Since it sounds like your cataracts are not too advanced and your corrected vision must be good, now would be a good time to simulate monovision with contact lenses to see if you like it. The idea is is to use a contact in your dominant eye which fully corrects for distance vision. And, in the non dominant eye use a contact that under corrects your myopia to leave you myopic by about -1.5 D. For example if your full correction requires a -9.5 D lens then you go with a -8.0 D lens. This arrangement with contact lenses will give you a good idea what vision is like with monovision. You should be able to see in the distance clearly and also read. You may in fact find this a good option to be glasses free before you do cataract surgery. I did it and liked it, so now I have selected IOL lenses which give me the same effect and am glasses free except for really find print. For that I use some +1.25 D readers. I perhaps use the readers once a week or so, and never bother to take them when leaving the house. An optometrist should be able to help you select contacts which will give you monovision. Costco optical was helpful in doing this for me.

Songirl,

I know what you mean. And as you can see, RonAKA is The Man. I think I've learned more from him than just about anyone. He's been very helpful to me because a) he's knowledgeable, and b) his situation was much the same as mine. I've got my final surgery scheduled for 3rd June on my remaining eye (I had my other eye done a few years ago) and I'm going for a mono-vision strategy much like he has now. I'm aiming for around 1.5 diopter difference between the eyes although it looks like the various models put me around 1.4 if I'm not mistaken.

I've recently learned something rather interesting from my research from various sources...that being that if one has some degree of positive spherical aberration that can be a good thing as it can provide a bit of additional range of focus, albeit at some very minor cost to sharpness. My doc told me I have some of this spherical aberration that might help my range a bit. We'll see I guess. Theory doesn't always translate into the actual outcome but I'm hopeful.

By the way, are you into music or writing songs? Your profile name makes me wonder.

Cheers,

IndyG

I was told I have very minor astigmatism and I would not require a toric lens. I really like the fact LAL lets the doc cater to the patients desires. I do remember trying monovision several years ago and hated it but I will give it another shot with contacs. You said you only need readers for very small print, would that usually be the case for someone who is as nearsighted as I am? I believe I am like -1100. I had asked one doc about mini mono and he said I will definately need readers. I did not as about Mono itself.

It should not matter what your starting point is for mini-monovision. An under correction to -1.5 D should give you good reading down to about 12" away. It is not going to give you ultra close vision like you have now with -11.0 D myopia of course.

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I have astigmatism complications, but my equivalent refraction in my near eye is about -1.5 D. I can read 10 point text on paper, and also my iPhone. I would have difficulty reading 6 point text or less. That is when I have to drag out my +1.25 readers. There is a Jaeger reading test at the All About Vision website. I can read J1 fairly easily in bright sunlight. In typical indoor light I am more like J3. Compared to reading with a natural eye lens an IOL tends to be more light dependent.

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On the astigmatism I would be insistent on them telling me what my astigmatism is predicted to be after the surgery. They will have the number. I wouldn't let them brush me off by saying it is minor or not worth worrying about. The LAL people may want to understate it as I don't believe they have any way of correcting it.

ok, I will be sure to ask.

Thank You

One thing I have learned lately about IOL power is that it is better to be left too myopic after surgery than without enough myopia, if you plan to do any fine tuning of the power with Lasik. It seem it is much easier to reduce myopia than it is to increase it with Lasik. In other words if you are left at -2.0 they can bring you down to -1.5 D. However, if you end up at -1.0, it appears difficult to increase myopia to -1.5 D. It has to do with where the incisions have to be made with Lasik to change the curvature of the cornea.

Reinforcing what you said, in recent studies, LASIK for correction of residual error after cataract surgery, showed that 92.85% of eyes reached a final spherical equivalent (SE) within +0.50D and -0.50D and 100% of eyes within +1.00D and -1.00D, so no surgeon will use LASIK to correct something that is less than +/- 1.00D, as this would already be within the "acceptable" error range.

Hmmm, interesting. But let's say they target -2.0 and they miss and you wind up at -2.50? Then with Lasik, they what.. bring you back at most down to -2.0? I'm not sure that's where I want to be ultimately. Seems to me a 2.0 diopter difference is borderline max I would want to go.I'm hoping to still retain some binocular vision in that "blend zone" area. The more I talk about this stuff the more confused I get. From everything I've been reading, it seems -1.50 is the sweet spot. And isn't it the case, though, that Lasik can correct more than just a 1/2 a diopter? I read somewhere that it can correct for much more than that in either direction? Seems what you're saying is that this isn't the case. My surgery is scheduled for 3rd June. I just hope I've made the right decision. I'm going with another monofocal lens but set off 1.50 from my plano eye at the moment.

IndyG

You are correct in that there is error in using Lasik for sphere correction post surgery. However, from what I can see and what I have been told by one Lasik clinic to date is that this error is asymmetrical with respect to pre Lasik hyperopia and myopia. The outcomes seem to be more predictable with myopia than hyperopia.

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Here is one study that shows quite good accuracy with low amounts of myopia correction. The data number is small but with a 1.0 to 1.25 D reduction in myopia error is very low - well under +/- 0.5 D. With a reduction of 0.5 D I would expect it to be even less. Errors of over +/- 0.5 do not seem to occur until the attempted correction is more than 2.5 D. Unfortunately I have not found this type of data for hyperopia reduction. If you see anything, I would be very interested. In any case have a look at Figure 1 on Google page 4 of this document. This tells me that if Lasik touch up is planned, you want to be over myopic compared to your target, not under.

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The Open Ophthalmology Journal, 2018, 12, 84-93 Visual Outcomes and Higher Order Aberrations Following LASIK on Eyes with Low Myopia and Astigmatism

Smita Agarwal, Erin Thornell, Chris Hodge, Gerard Sutton and Paul Hughes PDF

Yes, Lasik can correct up to 10 D or more of myopia. Correcting hyperopia is different though. Some say 3 D and others up to 6 D. If you look at that graph in the report I posted the title of the horizontal axis is the attempted correction, and the vertical one is the actual they got. The important part of that graph in my view is that the the lower the attempted correction the lower the error. However that does not seem to be the case when attempting to correct hyperopia.

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Yes a -1.5 D is a very good target for monovision. The issues come in when they miss it.

Have you researched anything about "Conductive Keratoplasty"?

no, I am actually an Ultrasound Tech but SONOGIRL was taken.

Yes, I have done a little research on it. It is claimed to be able to correct mild hyperopia. But, from what I found it seems to be a temporary improvement. The process is to essentially burn spots around the periphery of the cornea. Sounds ugly, but it is claimed to be painless. But, I wonder to what extent it is really being used. My searches in our province have not turned up anyone offering the service, while there are all kinds of places doing Lasik and PRK. And, I think it does not address astigmatism, so I would still need Lasik for that. It is looking more and more like I am stuck with what I have now.

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I unfortunately think my ship sailed when I had the final discussion with the surgeon on what power to use. The +19 D IOL would have left me about -1.6 D myopic, but with -0.75 D cylinder. The surgeon convinced me that with the estimated astigmatism I should instead target -1.25 D sphere with the +18.5 D IOL. And that would leave me closer to my desired total -1.5 D.

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Now I find out I can get rid of the astigmatism with Lasik, but I can't increase the myopia back up to -1.5. If I only get rid of the astigmatism my reading would be further degraded.

So I had my consultation visit for the LAL. They did not do any of the extensive measurements but it certainly sounds like this is the way to go for me. The doctor said again my cataracts are not that bad and he really didn't think I need the surgery just yet. However he understood my desire to get out of glasses. He also understood the discomfort of wearing contacts. He is not opposed to doing the surgery but did tell me the risks again of Retina detachment. I will hopefully be able to try the mono with contacts when I go to my optometrist in a few weeks. I am so torn. I know with any surgery there are risks but I am so tired of glasses/contacts but I also have the retina detachment in my mind. I will be doing another followup for him to check my optic nerve which is another issue but I had this checked before in the past and it was all good. I will address more questions after trying the mono at my F/U. Also he did mentioned he uses the ORA machine which I know someone on this board said it was the best. I know I'm rambling on but just wanted to fill you in. Thanks for listening.

It seems to me that the use of ORA might be a bit of an overkill when used with a LAL lens. It is a method of calculating IOL power during the cataract surgery and possibly making a power change from what was planned. With LAL that seems unnecessary as the power of the lens can be changed after the surgery is completed.