My idea is a test for the eyes. The procedure is to set the smallest font, on the computer/phone that you can read with the test eye. You move your eyes fore and aft to find where you see the font best.
This is different from focus. The best view of the font will be closer than the focus point, because the characters will cover a bigger angle (subtends a bigger angle). If your near prescription is at -1.5D, that corresponds to a focal distance of 26.25 inches. That may be longer than arms length. Yet the distance to best read ingredients on a package will be closer.
This is where EDOF should help. I expect brightness will have a big effect. The effect will still be there with a pure single focus lens. Any thoughts on this topic? I don’t know that this really gets discussed.
First, props for subtending an angle. It's been a while since I saw that word!
Second, how would the test results be used? Suppose in your -1.5 D example the best reading distance turns out to be 18 inches. What would you do with that number?
Not sure. I was thinking that this could serve as an indicator of the degree of EDOF a lens has. So a wider defocus curve would result in a lower distance.
It would be interesting to see that distance vs focus distance graphed for various people.
What confounds that is the degree that brightness would pay.
For me, if I got the near eye set to -1.5 vs -1.75, how far out would I need to read a small font label.
When I was doing testing I concluded that the simplest way was to use the Jaeger test at 14" in sunlight. Acceptable vision (20/32) with -1.5 D of myopia extends from just over 1 foot to 5-6 feet. That is quite a wide range and it probably would be hard to determine where the peak vision really is. And, I think the reality if the purpose is to figure out what is needed for mini-monovision, is that one is not looking for the peak visual acuity, but more the limit of acceptable visual acuity.
I thought of this topic as I began testing my brand new LAL eye with reading glasses of various powers. The idea as suggested by RonAKA is to try out different focal lengths for what will be my near-vision eye, so as to plan for the upcoming light adjustments.
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My LAL eye seems to be in the general vicinity of plano. I am so far liking the -2.0 D glasses, and they give me sharpest reading at a distance of 12" for the LAL eye. Before surgery, I was very nearsighted and read the tiniest type most clearly at around 5". With the -1.50 D glasses, best reading distance is somewhere between 16" and 18". It gets harder to measure this distance as the refraction gets closer to plano.
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I do find myself considering this issue as I think about my refraction target for the new eye. It feels fairly normal to bring fine print to 12" for reading, whereas 16" or 18" just feels wrong and uncomfortable and very presbyopic. No doubt this feeling is partly a function of what I've been accustomed to, and there are other considerations. But it will be something I consider as I work through my lens adjustments over the next few weeks.
What you may want to test for is binocular 3D vision at 2-3 feet. There may be a loss with the -2.0 D as the near eye, compared to -1.50 D. But if it is at a distance that is not important to you, then it may be a good option. Is there a loss in adjustment ability if you jump all the way from plano to -2.0 D in one light adjustment. Will you be able to fine tune from there? Or would it be better to jump to -1.75 D and then count on one or possibly 2 more steps to go up and down from there?
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The other aspect that will be hard to simulate at this point will be the eventual total loss of accommodation in the distance eye once you go to an IOL, which would seem inevitable. However, if you are at plano now with the LAL eye, this would be the time to estimate what it will be like.
Yes, intermediate vision is definitely the main tradeoff for more near vision. My computer screen is at ~30"-32", and I am comforted by the fact that I can read it pretty well already with the LAL eye near plano. Hard to test binocular vision with one eye remaining natural, but monocular intermediate vision is clearly worse at -2.0 than at -1.5. Hopefully intermediate will still be ok either way when I eventually get a new distance lens, and perhaps this is where the apocryphal EDOF cabability of the LAL will help.
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I was not able to discuss the adjustment strategy in any depth with the surgeon - he said it's too early to figure it out now, and much will depend on the measurements three weeks out. My biggest question right now is the amount of astigmatism they'll need to correct, and whether there'll be enough room within the available 4.00 D to cover both astigmatism and desired myopia. You raise some good questions, and I suspect it may be better to target -1.5 or so at first to avoid overshooting the mark. My doctor and others have mentioned the idea of 'creeping' toward the final goal with the near-vision eye.
What astigmatism did your far eye have pre-surgery?
Regarding "whether there'll be enough room within the available 4.00 D to cover both astigmatism and desired myopia." remember that the lens at implant already has a target that could be aimed at where you want to end up. So the needed adjustment could go either way to hit your target.
Now if that LAL Plus changes the plan, we will see.
Yes, I am much less concerned about the far eye, for the reason you suggest. I expect to need very little adjustment from the plano target, and hopefully will have plenty of adjustment available for any astigmatism. Also, I don't plan to get the far eye surgery any time soon. I will not be using LAL+. My surgeon advises against it because of my previous LASIK, and also I think it makes sense to avoid EDOF and go for the best achievable distance vision with that eye.
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It's the near eye I just got operated that I am concerned about. Pre-op astigmatism on that eye was small, just -0.25 D. But that was including lens and cornea. With the lens gone, residual astigmatism could be substantially greater. I had a 'corneal wavefront' scan that reported 1.30 D of "total" corneal astigmatism, but it was unclear just what that meant - there are correctable astigmatisms, with the rule, against the rule, and other astigmatisms like 'oblique' and 'second' order astigmatisms that may not be correctable, at least not with LAL.
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So the math I'm doing now is:
+0.25 D post-op hyperopia (guesstimate)
+1.30 D of astigmatism to be corrected, maybe
+2.00 D of myopia to get my preferred reading vision
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That's already 3.55 D of the available 4.00 D adjustments. And I've heard sometimes the adjustments produce fewer diopters than expected and you may not get the full 4.00 D. So, I'm a little concerned. But I am encouraged by my pretty good vision right now - close to 20/20 when tested the day after surgery. I figure even if they don't correct any astigmatism and just get me a couple diopters of myopia, the outcome should be pretty good. So, I'm not too worried, but I do want to try for the sharpest near vision I can get.
" I had a 'corneal wavefront' scan that reported 1.30 D of "total" corneal astigmatism, but it was unclear just what that meant - there are correctable astigmatisms, with the rule, against the rule, and other astigmatisms like 'oblique' and 'second' order astigmatisms that may not be correctable, at least not with LAL."
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Normally corneal astigmatism regardless as to whether it is with the rule, against the rule, or oblique can be well corrected with a toric or I assume with the LAL. It is just a matter of orienting the correction with the specific axis of the astigmatism. Now if the astigmatism is irregular that starts to become a bit of an issue. If you have been given the opportunity to see the topographical scan of the cornea it should give you a good idea how regular you astigmatism is. You should see a symmetrical hourglass or bow tie shape or similar at an oblique angle. But if the steep area is offset then the surgeon will have to make an estimate as to the best way to correct it, or perhaps that may be built into the computer system that maps out what the correction should be. You may have some higher order astigmatism due to the prior refractive surgery that cannot be corrected.
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On the total range of adjustment possible you will want to hope that they can go as far as you want. But with your commitment to monovision, I think I would have started at -1.0 D to -1.25 D, and adjusted from there. But that ship has sailed now!
"Normally corneal astigmatism regardless as to whether it is with the rule, aainst the rule, or oblique can be well corrected with a toric or I assume with the LAL."
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My scan showed significant amounts of both WTR/ATR and oblique astigmatism. I would not expect that both types can be corrected well with a standard toric lens. I could be mistaken about that, but it seems like it would be difficult to correct both with a single, standard toric lens. Perhaps it could be done with LAL, though. I guess I will find out!
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Yes, I agree that a more myopic initial lens target may have been better. My hindsight has been measured at 20/12...
WTR only means that it is a more common orientation of the axis angle. It is when the angle is close to 0 deg or 180 degrees or essentially horizontal. Astigmatism in children or younger adults is generally with the rule. ATR is more common in older adults and develops later in life. The axis of the cylinder is closer to 90 degrees. Both types are equally well corrected with the same standard toric lens. The only difference is the angle that the surgeon implants them at. Oblique is just an angle in between like 45 degrees. Again equally well corrected with a standard toric.
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To see the difference between regular and irregular astigmatism google this. Irregular astigmatism is often associated with keratoconus. The images in this article are probably from a Pentacam. I have one eye that has irregular astigmatism and the Pentacam image looks much like the one on the right. This is much harder to correct and a standard toric may or may not help. I recall from a previous discussion that the LAL is not capable of programmed custom lens configuration to handle irregular astigmatism.
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vision and eye health keratoconus What is it
Those search terms do not seem to work. Here is a clip of the image I am talking about.
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Once the astigmatism is corrected, I believe your surgeon is correct - take smaller steps. Some EDOF will be created on the first adjustment. My surgeon told me as well as the optometrist, people are amazed at how well they see with -1.25 diopters in the near eye. If you had chosen a more myopic LAL Target such as -1.0 diopters, you would not benefit from as much EDOF. That is my understanding. I wish somebody else would chime in. Also, the ophthalmologist that performs the LDD treatments just had LAL's implanted in both of her eyes. She chose -1.5 diopters for her near eye.
This is my dilemia: I would like to be intermediate/near in both eyes and wear glasses for distance. Should I Target the LALs -0.25 diopters to take advantage of EDOF? Or should I Target the LALs -0.75 to be certain I don't run out of macromers. Should I consider the LAL + and Target -0.75? I have given up on having it all: far - intermediate - near, like Deanna81707.
I have made an appointment Thursday afternoon with yet another ophthalmologist. This will be my fourth ophthalmologist! I will be sure to ask him how much EDOF both the LAL and the LAL Plus have.
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I believe @JDvision and @trilemma both had astigmatism corrected.
@JDvision has much experience on light treatments and using diopters. trilemma has much experience on lens trials after getting her LAL in her distant eye.
RonAKA it's just Amazing about everything!
When I was doing testing I concluded that the simplest way was to use the Jaeger test at 14" in sunlight.
Sunlight for the Jaeger test seems too strong for a more-useful test. Normal room lighting would be informative to me. Or in-between would be average store lighting.
Full noon sunlight would be more repeatable, because normal room lighting, without a light meter, would vary a lot.
I often make a pinhole with my fingers to read stuff in stores.
I use a reading lamp over my shoulder in a room with window blinds closed. There's also phone apps, but I couldn't be bothered to figure out the impact of variations in screen size and how to make sure the brightness setting is the same every time.
I like sunlight because it is a known fixed light level without having to measure it. F16 @ 1/60 second is the nominal camera setting for a good sunlight exposure in the old days of film!
https://en.wikipedia.org/wiki/Sunny_16_rule
"On a sunny day set aperture to f/16 and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting] for a subject in direct sunlight."
Maybe you were using Kodacolor-X or Kodachrome-X, which were ASA 64.
I guess that would make another interesting graph-- typical acuity vs lux.
I have thought that the chart an optometrist places at a short distance was too-greatly illuminated when they turned on the associated lamp.
Those search terms do not seem to work. Here is a clip of the image I am talking about.
After looking at your images, I had suspected that the colors mapped the prescription/focus at each point. Instead I see it is mapping thickness, but that will relate to prescription.
I expect there will come a time where they map many points and adjust the RxLAL accordingly-- as they now do with LASIK.
"Oblique is just an angle in between like 45 degrees. Again equally well corrected with a standard toric."
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Yes, I get that. My question is, what if you have both WTR astigmatism AND oblique astigmatism in the same eye? That's what my wavefront scan shows. I'm thinking that a toric lens can correct either one of those two just fine, but it cannot correct both. Is that right?