What's "good enough" visual acuity?
Posted , 7 users are following.
Some of you may recall the late 'hard' science fiction author Jerry Pournelle. From about 1982 to 2008, he wrote a regular computer column (Chaos Manner) for Byte magazine in which he championed "good enough" computer performance, based on the idea, as I recall, that most people should seek equipment and performance good enough for their needs rather than the best and most expensive.
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In this spirit, as I have contemplated my choice of IOL and vision strategy, the question has occurred to me, what's good enough vision? For me, being too risk averse to choose a multi-focal IOL, this question has at least two aspects. One is entirely subjective: what range of vision do I want to prioritize? Some choose distance vision; a few choose near or intermediate. This is not the subject of this inquiry. (Nor is contrast sensitivity, which goes to vision quality.)
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The other aspect I think has more of an objective component, namely: what counts as good enough vision so that, at any distance within its, one can see comfortably without glasses? For these purposes, I assume that wearing glasses can correct any deficiency.
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Having no clear idea about the answer, when I looked at defocus curves for the Eyhance IOL—my surgeon’s recommendation and my current choice—I arbitrarily differentiated different ranges, e.g., 20/20–25; 20/26–32 (logMAR 0.2); 20/33–40 (driving cut-off); etc. Yesterday, however, I ran across a blog post at For Eyes, that, citing the American Optometric Association, lumped together 20/30–60 saying: “This means you may have a small vision issue, but your vision is almost normal. It’s unlikely you’ll need to wear glasses all the time.” See Starting At What Level of Prescription Should I Wear Glasses All the Time? (Note that the linked AOA webpage doesn’t quite say this.)
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Accordingly, I’d appreciate your thoughts regarding what counts as “good enough” vision. To explain how I want to use the concept, averaging three binocular Eyhance defocus curves that I’ve found on-line suggests that, if my surgeon’s preferred target of -0.50 D is achieved, the mean uncorrected distance visual acuity for subjects in the three studies was 20/22 (logMAR 0.0467), which I’m inclined to think would be more than good enough vision. They also suggest that, at 40 cm (15.75”), the mean visual acuity was 20/38 (0.273 logMAR), about which I’m doubtful. In contrast, and momentarily assuming no degradation in visual acuities from 0.75 D mini-monovision, mean visual acuity with -0.50 and -1.25 D eyes indicatively would be 20/28 (0.153 logMAR) at 36.36 cm (14.31”) and 20/32 (0.2 logMAR) at 33.33 cm (13.12”), about which I’ve no clear idea.
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For anyone interested, the three binocular Eyhance defocus curves mentioned above can be found on-line at the following sources:
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Gerd U. Auffarth, et al., Clinical evaluation of a new monofocal IOL with enhanced intermediate function in patients with cataract, J Cataract Refract Surg 2021; 47:184–191.
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Mayank A. Nanavaty, et al., Visual Acuity, Wavefront Aberrations, and Defocus Curves With an Enhanced Monofocal and a Monofocal Intraocular Lens: A Prospective, Randomized Study, J Refract Surg. 2022;38(1):10-20.
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Ella SeoYeon Park, et al., Visual outcomes, spectacle independence, and patient satisfaction of pseudophakic mini‑monovision using a new monofocal intraocular lens, Nature Scientific Reports (2022) 12:21716.
1 like, 18 replies
Bookwoman RebDovid
Edited
Interesting question. From a purely subjective standpoint, my version of 'good enough' vision is the ability to do most things around the house without glasses. For reading books and using the computer I wanted completely crisp, clear vision, and for TV watching, driving, etc. I expected to (and do) have to wear glasses. For those reasons, I got -2 monofocal IOLs.
Someone who spends a lot of time outdoors, or doing sports, etc., is probably going to feel exactly the opposite.
jr3791 Bookwoman
Posted
With -2 monofocals are you able to read books without glasses? What about using a computer?
Bookwoman jr3791
Posted
Yes to both, perfectly. My left eye wound up at -2.5, which no doubt helps, and is also a reminder that what you target may not be what you wind up with. In my case, it has worked out really well.
RebDovid Bookwoman
Posted
Thank you for your thoughtful response. Among other things, it tells me that I may not have have framed my question to get at my real interest for this thread.
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What I'm trying to get at is information regarding what uncorrected visual acuity counts as "good enough" at different distances. I then can look at defocus curves, and see, for example, that the mean average of the three binocular Eyhance curves I've found is 20/32 (0.2 logMAR) in the better eye at -0.50/-1.25 D and 33.33 cm (13.12"). Comparing these judgments for all the near-vision points on the curve at this and other potential IOL combinations, I then can proceed with determining whether -0.50/-1.25 D are the targets I want my surgeon to try to achieve.
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Of course, there are other factors, such as contrast sensitivity, binocular vision, etc. But visual acuities at the distances that are important for me is one of the key ones. (One thing I think I've learned from my nearly three-week experiment with contact lenses and mini-monovision is that, despite having worn glasses since third grade--I'm now 73--and being perfectly comfortable with them--so that I wouldn't contemplate eye surgery if I didn't need it--I don't like frequently putting them on and taking them off, as I have to do with the contact lenses and readers. Accordingly, if forced to choose, I think I'd choose to compromise distance vision, as in needing glasses to drive at night, or to drive at all, rather than needing to put on and take off readers when working at my computer and wanting to read papers on my desk or turn to talk with someone. But maybe with mini-monovision I don't have to choose. That's what I'm trying to determine.)
Bookwoman RebDovid
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if forced to choose, I think I'd choose to compromise distance vision, as in needing glasses to drive at night, or to drive at all, rather than needing to put on and take off readers when working at my computer and wanting to read papers on my desk or turn to talk with someone.
This was exactly my thinking, since I spend much of my day either reading or on the computer, and also what I was used to visually. I was highly myopic before surgery (-8 in both eyes), so the vision I have now is not only suited to my life, but also far, far better in all respects than it has been since I was a teenager. (I've also worn glasses since 3rd grade.)
But maybe with mini-monovision I don't have to choose. That's what I'm trying to determine.
This is indeed the big question! So, how good do you want your close vision to be? Do you want to be able to vaguely make out what the words say on a page or your phone, or do you want really crisp, perfect reading vision? If it's the latter, I don't know that -1.25 is going to be enough to get you there. If you're ok with "I can read it, even though it's blurry", then you might be fine.
Lynda111 RebDovid
Posted
With my Tecnis 1 piece iol set for both eyes at intermediate, I have 20/ 20 distance minus a few letters. Intermediate is good; can see computer easily. Need readers only for sustained close reading of print material. My case may unusual owning to my uncorrected astigmtism.
RebDovid
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Thank you for responding. And I'm glad for you. What I'm trying to get at, however, is what visual acuity less than 20/20 is "good enough" at various distances.
soks RebDovid
Posted
20/40 for distance
and j4 for near.
RebDovid soks
Posted
In what respects are 20/40 distance and j4 near, which a conversion chart attributed to Dr. Jack Holladay equates with 20/32 and logMAR .2, good enough or not good enough for your purposes? And, if you're willing to answer, what are those purposes?
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To the extent the defocus curves I've found are useful, averaging all seven (three binocular and four monocular), it looks like, all going well, mini-monovision with the Eyhance has the potential of meeting your criteria. Here are some examples of average mean visual acuities:
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Of course, I also some idea of the combined results at each distance. Are the differences between the two eyes small enough so that the monocular results would be closer to the biocular defocus curves because of binocular summation?
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Making possibly heroic assumptions about the validity, at least indicatively, of averaging together the visual acuities from different binocular and monocular defocus curves, and recognizing that even if the data are right they're all subject to significant deviations around the means, and recognizing further that surgeons seems to regard coming within 0.5 D of their target as a good result, these data suggest to me that I well might be pleased.
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And given the various uncertainties, I'd still have to decide how much distance vision I'm prepared to risk to guard against my surgeon falling short of the target for my near eye.
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It's all complicated enough to drive one to distraction.
karbonbee RebDovid
Posted
I don't know if you can get a proper answer based upon those terms, because the results seem to vary amongst the users of the same IOL. Just because someone else got good results, it unfortunately might not happen the same for you -- which I know you already know. It's all pretty much of a crap shoot isn't it, to a certain extent. Ultimately, even if 20/20, or more or less either way, works for someone else, it still might not work for you as your standards will be different.
RebDovid karbonbee
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Because of all the uncertainties, I'm probably over-thinking it. But then again, all going well, it's a once-and-for-all decision.
karbonbee RebDovid
Posted
I hear you. Having to stop myself from doing that also. I won't read any posts about problems post surgery (other than the basic warnings) cos I was freaking myself out. If something goes wrong, then I'll look.
karbonbee RebDovid
Edited
It's been three weeks since having both eyes done (Eyhance) -- I go to my optometrist in about two weeks time. Two days post surgery on the "near" eye, targeted to -1.25D (according to surgeon, achieved -1.21 D), the cataract clinic tested that eye at 20/25 (which I thought was a bit optimistic), the next day it came out at 20/35 (which seemed more realistic). I'm extremely happy with the near and intermediate -- clear reading, etc from about 28.5cm (11") in the near eye. I can easily read J1 from about 11" to about 26" (measuring from the eye, not the body). Intermediate in this eye is astounding, can read small print on pill bottles, etc at about 28" to 40" (arm's length). The distance I can live with -- even if it drops to 20/40. I can see well enough what I want to see further away. If both eyes were the same prescription, I'd say I'd be relatively capable of say, playing baseball -- might be some guessing involved, but I think I could do it. In current life though, I can see the bird feeders well enough at about 25' - 30' (the small birds are kinda blurry, tho I could figure out which is which, but that's what binoculars are for anyway), the name on the street sign is pretty clear at about 40' -- it's all about size of the item you're looking at, isn't it? The larger items in the distance (say 200' away or more) like the windows on a house, etc, are clear enough to determine what they are, even if missing the finer points. I can see the top branches of a tall tree and could see movement (ie a squirrel or a bird) in them even if I'm not sure what it is causing the movement. I could drive my car (already have) well enough, even if there was a delay in reading street signs -- everything else is clear enough to not cause mistakes. If both eyes were like this (say 20/35), I probably would just get a pair of glasses, or contacts, for driving, but everything like walking around, fixing stuff, watching TV (42") at about 8' are more than manageable.
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The "distance" eye targeted at -0.5D (surgeon thinks -0.36D) was tested the day after surgery at 20/20 and I would agree with that, and even better, it doesn't seem to have shifted from that. It has amazing clarity and sharpness for distant viewing -- what is missing from distance clarity with the "near" eye is more than made up for with this eye. Near vision with this eye, not so great (as anticipated). I can make out parts of J4 and J5 at about 28" but J6 is a lot easier at that distance, or a little closer. and intermediate is pretty good for most things on the closer end (once again size of object) and that keeps improving as things move away -- moving around the house, doing chores or washing dishes are quite doable -- depth perception is a bit wonky, but I haven't broken anything yet. Would need reading glasses of about +1.75 when reading, using my phone, or computer use, for any length of time.
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Both eyes individually, I'm very happy with, but it's when using them together that things really start to pop! If the surgeon's calculations are correct, then there's a difference of about 0.85D between both eyes. I am not aware at all of what eye is doing what, but what the "near" eye does best seems to be even sharper when using both eyes (even though I know the distance eye isn't really seeing as well), and vice versa. The overlap between the strengths of each eye is filling in any gaps nicely. Contrast in dim light is good, can discern shades other than greys in near darkness. No problems driving down dark roads, I can distinguish what's on the sides of the roads. Can see the new moon clearly (and the line around the rest of it) and the stars and the night clouds in the sky, whether in town or out in the middle of nowhere.
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Overall, I'm very happy with the visual acuity I have now, and probably will pick up a pair of glasses for driving, though not sure if I'd actually have to use them, though in general, I'm pretty much glasses free for anything I try to do, whether changing the battery in my car, or the button battery in my little 2" long LED flashlight. Is that the kind of feedback that you're looking for?
Lynda111 RebDovid
Edited
Well, I guess "good enough" is pretty subjective. My younger brother is a very outdoors person who regularly hikes through thick brush. He doesn't want to be bothered with eyeglasses. He said he has 20/40 distance vision and that he is fine with that.
maura04015 RebDovid
Edited
Hi - I've been lurking here a long time. Recent discussions, including this one, have finally provoked me to register.
The question really is very individual. For instance, distance vision is the one of the 3 distances I feel the least concerned about. Not that I don't need it, but I need it pretty much only to drive, which means a couple hours a week at this time in my life (I'm 77). Having to wear glasses to do it is no burden, and 20/40, required for a license, is maybe not what I'd hope for but as it's the best that can be achieved now, I know it does allow safe driving, albeit with an aggravating difficulty is seeing street signs. I use distance contacts for driving and that's about all I put them in for.
Around the house I wear computer glasses, which serve me fine, even for outdoors when doing things like walking my dogs, and even doing that at night. It's not great distance vision, but it gets me by and I have no problem with that. I can still read with naked eyes and prefer it, even though I'm at the point readers make things a little more clear.
I'm another risk-adverse person, and I had an loved monovision until about 10 years ago when the difference between my eyes meant so much difference it no longer served, so it will be mini-mono for me, and I need to get my cataracts fixed before my driving vision deteriorates more.
What I believe would be best for me and hope can be achieved is glasses-free intermediate and reading vision. While I might wish for more, I expect that means glasses for distance. If I were to need glasses for one of those two distances, my choice would be intermediate. I don't even hope for near vision that enables reading small print, but really want to be able to read books comfortably without glasses. That doesn't even mean paperbacks, but hard covers and on my Kindle.
I'm a writer, intermediate and near are where I spend the majority of my time, and not having to take glasses on and off, remember what I did with them, be careful with them, etc., would be a boon. For distance, I wear sunglasses when driving most of the time anyway, glasses are no burden there. I try to avoid driving at night but have to do it sometimes and do need that ability. Again, glasses wouldn't be the burden there they are for intermediate and would be for near.
So - very individual. Just reading this forum I've seen a really broad spectrum of want, need, and hope for post-surgery result.
Lynda111 maura04015
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Maura
Bookwoman is our resident intermediate vision person.
Bookwoman Lynda111
Edited
Well that depends on your definition of intermediate. I think of myself as the close vision person. 😉