Near vision after cataract

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If near vision is requested in a cataract operation, would there be a greater depth of focus for near vision (without using spectacles) than with the far vision option + reading spectacles ?? 

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    I have a lens replacement fittet set for near vision. I can read at about 23 - 25 cm away without my glasses.. any closer i need a magnifying glass any further I need prescription glasses. 

    In other words you will have only 1 set focal point as deteremined by the fitted lens.

    Hope this helps

    P.

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  • Posted

    The question is a little ambigous. I'm uncertain if you are talking about "depth of focus" in its optical sense where it means the range of vision that things are in focus, or if you are talking about simply how near you'd be able to set your eyes to focus (since some people pick up jargon but don't using it quite right).

    You can set an IOL for near to focus at the same distance as reading spectacles are set to focus for, and then if you wish to see even closer in then you can wear reading spectcales on top of a  near IOL for even nearer vision. 

    If you are talking about the actual optical phrase "depth of focus", the range of good visoin, If you are talking about setting both eyes for near vision (rather than monovision, where only one is set near),  the depth of focus would be essentially the same since in both cases the same model of lens would be used, merely at a different power. The point of best focus is the only difference between an IOL set for near vs. far, and reading spectacles would just change a far-focused IOL's  best focus to be where the near one would have been focused. 

    In theory the need for reading spectacles with a far vision set IOL might   have a very tiny reduction in  the depth of focus, but I'm not sure if anyone would ever notice the slight difference in practical terms. The only trivial difference is the light is passing through 2 lenses rather than 1 so the image quality might be reduced a minuscule amount. Even the highest quality optical glass isn't perfect.

    If you want more of a range of focus, you can set each eye to focus at a slightly different near point, which is a variation of the more usual use  of monovision. Alternatively there are premium IOLs that people pay for out of pocket which can give a larger range of focus, but I'm guessing you are just talking about the standard monofocal lens included with surgery. 

    Your eye's range of focus would vary depending on the model of IOL. Its  measured in units of lens power, i.e. your eye would have some range of diopters X where it has a decent range of vision.  Unfortunately it is hard to get much of a range of focus at near in terms of physical distance since each added diopter of power makes less and less of a difference the closer in you get. Lets say it was 1 diopter. A range of focus from 0 diopters to -1 diopter converts to infinity down to 1 meter, whereas a range of focus from -2 to -3 diopters would be from 50cm to 33.3 cm, and  a range of -3 to -4 diopters would be from 33.3 cm to 25 cm.  The formula is distance_in_cm = - (100/ refraction_in_diopters), or to reverse it refraction_in_diopters = -(100/ distance_in_cm).

     

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    • Posted

      Thank you for your reply and this very helpful information.  I meant the range of distance within which things are in focus.    It doesn't sound as if setting iols for near would increase this.  

      (I need a range of distance: eg smartphone and reading 40 cm, laptop 45 cm, playing the organ c.45-60 cm, teaching reading distance as above and 80-116 cm to follow the student's score).    I was advised not to go for premium iols as the quality of vision is less clear, and they can cause halos and glare.  My concern with fixed focus iols set on mini-monovision is that, if I didn't get used to them, they couldn't subsequently be changed to non-mini monovision without a further operation.

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    • Posted

      re: "couldn't be subsequently be changed to non-mini monovision without  a further  operation"

      Of course you can always wear correction, glasses/contacts, that correct for it. In terms of an "operation", usually a minor tweak like that they'd do using laser correction, which is technically surgery, but its done on the surface of the eye and doesn't involve the sort of risk of entering the eye that cataract or lens exchange surgery does (though those are both overall low risk procedures despite that).  I never got LASIK/PRK back when I was a high myope before cataract surgery partly since I'd based my impression of it on its early days, these days, especially for low correction, its fairly accurate and not a big deal. I'd checked on it a bit before my surgery, knowing I might need a laser tweak. (my vision is good enough that I haven't needed it, though one eye wound up slightly hyperopic so I might tweak it someday, it just hasn't been a high priority since my other eye makes up for it, even if it could be even better).

      If you use monofocals you'll obviously need correction for some distances, so the issue is to figure out what you'd like to be able to do without correction. It sounds like those are the tasks you'd prefer not to need to wear correction for.   One issue with targeting exact visual ranges is that the lens power they insert isn't based on an exact formula, but is based on statistics regarding eye measurements of past patients. You don't mention what your vision is like now, how myopic or hyperopic you are. The results tend to be fairly accurate for those with low prescriptions before surgery, with more risk of the power being off for those with high prescriptions. If you are willing to spend some out of pocket then a laser tweak after the surgery can fine tune the correction. The small adjustments made via laser tend to be fairly accurate (moreso than the large corrections usually done by laser for people with high prescriptions).  Most IOLs only come in power steps of +0.5D, though for some people in the most common normal range there are somethat come in power steps of +0.25D, so vision can't be as precisely targeted via a standard IOL as it can with a laser.

      There is also a light adjustable lens which is a lens whose power they can adjust after it is implanted via a special UV light, until they make it permanent. For the first few days you need to wear special UV blocking spectacles until they finalized the power, so its less convenient, but allows more precise power setting.  Its not available in the US, but your use of the word "spectacles" suggests the odds are you aren't in the US (since although I'll use that when someone else starts with it, usually we use "glasses" by default). 

      So the diopters those correspond to are "smartphone and reading -2.5, laptop -2.2, playing the organ c.-2.2 to - 1.67, teaching reading distance as above and -1.25 to -0.86 to follow the student's score".  

      If you average to follow the students score is about -1D, and the aveerage of the others is about -2D. Most people adapt to small levels of monovision in the range of 1 diopter, its fairly low risk and it doesn't impair stereo vision too much, and for those tasks stereovision doesn't seem too critical. The visual quality of an IOL tends to drop a bit faster going outwards from the best focal point than inwards, so IOLs erring on the side of being a little less myopic in each eye than those averages would make sense. I mention that since as I noted unfortunately the lenses only come in +0.5D steps to there may not be one to give you precisely what they target (in addition to the power not being predicted precisely beforehand).

       

      The -1 might give you enough vision to walk around the house a bit without correction, even if you might want correction still for some household tasks and social distance. 

      In terms of premium IOLs, they provide benefits but with some low risk of problems like halos or adaptation issues, but  the vast majority of patients are happy with the results. Unfortunately some surgeons would rather not deal with those who have any problem and conservatively steer people to monfocals where the risk of complaints is lower, even if a patient might have been happier with a premium IOL. The issue is that someone needs to be willing to take the very low risk that if there were problems that they'd need to get a 2nd operation for a lens exchange. In my case I decided I was atypically young and it was worth the potential for more convenient vision without correction  for decades to take the risk. I had also tried multifocal contacts beforehand and knew I adapted well and preferred that over monofocals.  Its useful for people to do a contact lens trial of such things if possible, but unfortunately most people who are ready for surgery have vision too degraded from a cataract to make that as good a test.

      In terms of the quality of vision being "less clear", thats mostly a concern for those who have other eye problems that degrade their visual quality already and so even a slight change from the IOL is a concern. With the Symfony lens I have at least 20/15 vision at distance (they didn't have a line below that, and that one was easy to see). A trifocal might be slightly less clear at distance, but likely not noticeably (the tradeoff is that the Symfony may provide noticeably better intermediate, while the trifocal has more really close near, which may be a better bet for some people who use more near, and the trifocal has likely somewhat more risk of halos and reduced low light vision).

      Those who had great distance vision without correction before cataracts, or perfectionists may be sensitive to slight changes in visual quality that might be a concern with premium IOLs, but for most people its not usually an issue. 

      It partly depends on your tolerance for risk, and how much you like the thought of not wearing correction. I'd worn contacts for decades, disliking glasses (especially progressives/varifocals) and liked the thought of not needing correction the rest of my life, not worrying about some accident or fire or emergency leaving me without correction when I could use it. 

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    • Posted

      Thank you again.  Yes, I'm in the UK.   The prescription for the left (non-dominant) eye that has had the cataract op came out +0.5 sphere, -0.50 prism, 10 axis - slightly over-corrected. It is good for night driving, but the over-correction is apparent for most other tasks, and I would prefer it to be at 0 or even slightly under-corrected. Perhaps best to request the other eye at 0, then have a laser touch-up to the left eye or both depending how on the prescription of the right iol.  Presumably your readings for the tasks I do should be adjusted -0.5 to compensate for the current over-correction ? The quality of vision in the left eye is 20/20 and I believe the quality might be slightly less good after a laser adjustment ?

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    • Posted

      PS My right eye is currently -14.50 sphere, 0.25 cyl and 175 axis - so extremely myopic !

       

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    • Posted

      Oh, you hadn't mentioned you'd already done one eye. So you are already familiar with the concern over the lens power not being exactly right in high myopes. In that case the issue is to decide first if you don't mind correcting that via laser before deciding where to set the 2nd eye.

      In terms of "the quality might be slightly less good after a laser correction", that partly depends on the person and the laser technology they use, e.g. if you get the latest "topographically guided" laser,  its likely not a noticeable change using modern technology when just doing a small tweak. I was surprised to discover that a small fraction of people actually see an improvement in their best corrected vision after lasik, while most see best corrected vision staying the same (and a minuscule fraction may see a slight decline, but it sounds like that is very rare with a minor tweak).The  refraction only measures vision  to a precision of 0.25 diopter steps, so you might have say -0.1D of astigmatism its not picking up in the current eye (you don't mention any cyl) and the other eye might have say 0.35 cyl rather than 0.25. A refraction also doesn't measure other higher order aberrations, i.e. other ways the cornea isn't a perfect sphere and any irregularities in its shape. The newest laser techniques map the cornea exactly and can correct such minor irregularities fairly precisely. Unfortunately most of the data out there on laser correction is based on large several diopter corrections,  or older data.  

      My hyperopic eye is also +0.5D (with 0 cylinder), so I'd partly hestitated about laser correction for fear there might be any reduction which would undermine the benefit of a tiny tweak, but my impression is that a modern technique is safe enough not to be a concern, but its best before doing so to get the doctor to exlicitly talk about there results (or go to a surgeon who does, some clinics with good results have started to put theirs online). 

      Since I have the Symfony, even with +0.5D I still get good distance and intermediate out of that eye. I don't tend to notice its diminished near due to the other eye. The other eye initially was 0 sphere and -0.5 cylinder, the most recent check shows -0.25D sphere and -0.25 cylinder. Combined i get 20/15 (at least) at distance, 20/20 (plus a bit) at 80 cm, and at least 20/30 at 40cm (they didn't have a 20/25 line and I saw some off the 20/20, and in the past they'd measured at best near rather than 40cm and it was 20/25 so it may now be that at 40cm).

      In terms of "adjusted by -0.5 to compensate for", if you were talking about say ordering spectacles, then yes that is what you'd do to get the prescription you'd want to focus at those distances for the eye you already had done. 

      You could try to target all your near tasks with the 2nd eye.  Unfortunately the range of tasks you listed covers a range of -0.86 to -2.5 diopters, which is about -1.68 on average. Though as I noted, the vision out from the eye drops off faster than going inward, so it depends on how important the further out vision for the student's score is, whether to err on the side of being less myopic than that.  Unfortunately you need to factor in the possibility the lens power could be  off in either direction, but if you were willing to get laser correction that is less of a concern, or a light adjustable lens.

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    • Posted

      Also, in terms of preferring your hyperopic eye to be 0 or undercorrected, obviously it does seem a waste even if you do want good distance vision in that eye since its reducing near&intermediate. If I tweak my +0.5D eye I'd likely shoot for -0.25 or -0.5. My other eye gives me good near though so I rarely notice it, but occasionally when something is in front of the good near eye I'll notice the near drop out. So I don't need the tweak, but it'd be nice, just not high enough priority yet to research details or spring for it. 

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    • Posted

      I should note, I'd referred to topographic guided laser correction, but there are other kinds like various technologies out there like wavefront methods that analyze how the light passes through your eyes rather than the shape of the cornea,  it depends on the person what is best.  I just happened to check on it the other day, "window shopping" for the possibility of  getting a tweak, and wavefront methods might be a problem with the sort of IOL I have, but they might not be for someone with a monofocal, I hadn't checked.

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    • Posted

      Thank you.  Correction: the left eye that has had the operation is Sphere: +0.50, Cyl: -0.50, Axis 10.  Another optician got a slightly different result: Sphere +0.75, Cyl -0.50, Axis 15, Base 6/6+  The first appt was early morning, the second late afternoon, which might account for the small difference.     

      I suppose the main decision is whether to tweak the left eye with laser before the right eye is operated on, or whether to wait and see how the right eye comes out?

      If my left eye is reduced to -0.5, I guess it would be fine for everything except reading, laptop, playing and teaching, for which I would need (?progressive) glasses, but I might need to keep a pair of -0.5 glasses in the car for night driving?

       

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    • Posted

      There is no way to be sure what vision you'd get with -0.5D, whether it'd be good enough for driving, since that depends on the person  (e.g. if their vision is reduced even when best corrected), but since you say it has 20/20 visual quality despite some refractive error now it seems   very  likely. There are charts around the net that attempt to convert between diopters and visual acuity, but those are just statistical estimates, not guarantees (and usually based on a natural lens), different ones seem to suggest a guestimate of 20/27 to 20/32 for a -0.5D eye, but again the depth of focus is different with an IOL.

      That could be conservative. My better eye that is at -0.25D and -0.25 cyl gets 20/15 distance, which is why in my case I figured it'd be safe to target the other eye for -0.5D since I'd have good distance vision regardless of how that eye came out.  The Symfony has extended depth of focus in the near direction, inwards from the best focal point, but for further out its about the same as the Tecnis monofocal.

        Obviously its best to have the highest quality vision possible for driving so it makes sense to at least consider a cheap pair of glasses for driving (or two, sunglasses), especially if you have monovision,  even if technically you can get away without them. Its  surprising how cheap you can get them online from reputable vendors. I wanted some new sunglasses anyway with a lighter tint, so even though I don't need prescription glasses for distance with a trivial prescription, I finally   ordered a cheap pair of prescription sunglasses I'm waiting for now   to see what slightly  higher quality vision is like. I never had distance vision this good before surgery so I'm curious what even slightly better might be like  (high myopes sometimes see their vision improved after cataract surgery when most of the correction is done at the IOL plane rather than spectacle/contact plane).

      Though if you are going to have monofocals in both eyes, I guess you might go not quite as cheap for driving to consider varifocals/progressives or bifocals to deal with things inside the car, unless you undercorrect one eye to leave a slight bit of monovision. Some of the latest, more expensive, photochromic lenses will darken even inside cars.  

      The first decision is merely whether you wish to get a laser treatment. If you didn't, then you'd need to target the 2nd eye based on that.  If you are willing to consider laser treatment at some point,  it does as you say make sense to still get the other eye's cataract surgery done first to be sure where it ends up, in case you wish to rethink things afterwards. Since there is a chance of error, its also likely you might wish laser tweaks for both so you may as well wait. I'm guessing its cheaper to do 2 at once rather than at different times. 

      The difference between the opticians refractions may be a result of time of day, our eyes do change slightly. I don't know if you have any dry eye issues, that can especially lead to some fluctuations. If you are on the border between two 0.25D notches it might fluctuate, even  perhaps merely with  different equipment and slightly different methods used.

       

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    • Posted

      oops, I see I  accidentally deleted part of that. The defocus curve shown for the Symfony includes the Tecnis monofocal as a comparison, and that shows setting the eye to  -0.5D as being in the range of 20/25 for distance (if the focal point is at -0.5D then distance at 0 is +0.5D  compared to the the best focal point which is the value on a defocus curve or table). I didn't know what IOL you were getting so I out of curiosity I checked   the estimate based off of the typical -0.5 to 20/X conversion charts for another data point of how well that worked out with the natural lens to see that even that is also in the same range, so I'm not sure how much IOLs would vary or how much the visual acuity going outward is based on the eye rather than the IOL. IOLs tend to be designed to be more concerned with improving depth of focus from the 0 point inward.  

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    • Posted

      Many thanks.     I suppose the first decision is whether to just let the surgeon aim at 'distance' for the right eye (presumably 0), or whether to request -0.5 ?  It seems safer to request the former, given the margin is apparently 0.5 (is that 0.5 or 0.25 either side of the aimed prescription?).

       

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    • Posted

      There is no exact margin of error for everyone. There are statistical averages discussed  of results being  within particular margins, e.g. within +- 0.5D or +- 1D (or even +-0.25D now for people with average eyes)  that vary for  different lens formulas and for different levels of myopia, and some surgeons keep their own statistics on their results.  The better surgeons do shoot for within +-0.5D these days, but I don't know what the odds currently are based on the best formulas for someone as myopic as you are. I should have looked into this more before my surgery, but I was more focused on the lens choice and hadn't paid attention to details since then,  so I don't know offhand the distribution pattern of errors, e.g. whether the errors tend to skew myopic or hyperopic or if there is an even distribution within the +-0.5D range. 

      Again, most people do adapt to some level of monovision without issues, I don't know if you have  preference for which eye is better for near or distance. I would think since the current IOL eye is hyperopic that it'd be easiest to shoot for that to be the distance eye, which it is at the moment,  and optimize it with a laser tweak.  So I don't know if you wanted to shoot for this 2nd eye to be near. Or you could shoot for distance, and if it achieves it then tweak the eye with the IOL currently to be near, it just seems there is less correction required to correct your current IOL for distance than to correct it for near, and the smaller the tweak the more accurate it is and the less risk.

      Part of that may be a question for surgeons who do laser tweaks (either your current surgeon, or a clinic that does laser correction).   I discovered after I had my procedure that although correcting small levels of hyperopia seems to be no problem,  there are more laser techniques to correct myopia than hyperopia (the techniques differ since they are trying to reshape the eye in different ways, increasing or decreasing central thickness vs. peripheral thickness). I haven't researched it to know if there is any advantage in accuracy with the techniques or if it doesn't really matter.  I don't know if that is merely because there is more demand for myopia correction so there is more focus on it. So I don't know if from the perspective of a laser tweak afterwards if its better to err on the side of being myopic or hyperopic, but without further information that suggests

       

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    • Posted

      oops, conitinuing.. 

      the possibility that  number of options for myopia correction  indicates perhaps targeting slightly more myopic to increase the odds that any laser tweak would be in the direction of treating myopia. I suspect though its  likely best not to worry about that,   to just go ahead and shoot for exactly what you want, and then tweaking it if you don't get it. 

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    • Posted

      My right eye is dominant, which is usually the eye set for distance. So it might be difficult to get used to the right eye set more myopic than the left ?

      Perhaps best to just let the surgeon aim for the same prescription in the right eye as in the left, and ask him if it will be safe to have a laser touch up to when they have settled down aftewards to balance them and set them both a little under full distance correction - but how much ??  

      I am cautious about setting the iols for mini-monovision in case I don't get used to it, and it would also mean over the counter reading specs wouldn't work ?

       

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    • Posted

      Taking a quick glance, I'd guess that unfortunately I'd guess a sizeable minority that myopic still don't fall within +-0.5D of refraction, but again I hadn't hunted for the latest data, and it depends on the surgeon, ideally they'd be able to give you statistics if you asked.

      In terms of how much under full distance, it partly depends on which IOL you go with and what acceptible visual quality is.  Prior to laser correction a test with contacts or spectacles can be used. If you find out what brand/ model IOL you would be using ( if you are using the same model for your current eye you should have been given a card with the lens model, though many people don't notice or keep it) there is "defocus curve" graph data  (or tables) giving average study results for visual quality vs. distance, in units of diopters usually. .e.g if you set the eye for -0.5D, then on a defocus curve the reading for 0D would give you expected visual acuity at  (-0.5D + 0D = -0.5D = 2 meters), -1D on the chart would give you expected visual acuity at (-0.5D+-1D = -1.5D= 67cm). Going the other direction +0.5D would give you the visual acuity at (-0.5D +0.5D  = 0D = infinity,i.e. distance), or for -0.5D you'd look at +1D. Again these are just averages, but since you have 20/20 quality now, it seems likely a decent estimate.

      Many surgeons seem to not worry about which is the dominant eye since usually the brain uses whatever eye's vision is best for each distance, which is why monovision works to begin with since your brain uses whichever eye is best for the relevant distance.  Again most people have no trouble with a small level of monovision, and it can always be corrected via laser.

      With monovision, off the shelf readers won't place both eyes at the right focal distance, but they can be used to place at least 1 of the eyes at the right focal point. There are actually some adjustable reading glasses out there from at least a couple of companies where you can shift the power for each eye seperately, though I'd seen mixed reviews and hadn't seen them in person.

      Prescription readers can be used to place both eyes at  a particular focual distance. Low powered glasses can use the cheapest lens material, CR39,its not like the expensive lenses you need for high prescriptions so they aren't too think. If you aren't picky about frames, there are some places to get dirt cheap prescription glasses on the net, especially if you hunt for coupons and don't mind waiting (some ship from China, though SelectSpecs does some of theirs in the UK), especiallly since the coatings seem to be much less expensive than at most retailers and are sometimes included. There are even some places that sometimes offer "first pair free", though often you need to pay shipping and for anti-reflective coating. 

       

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    • Posted

      Sorry, I should proof before posting, this: "or for -0.5D you'd look at +1D. " should have been "or for -1D you'd look at +1D" to find the visual acuity at distance off a defocus graph.

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    • Posted

      btw, I just ran into this article from a year ago (google the title, since they moderate links):

      "Outcomes of excimer laser enhancements in pseudophakic patients with multifocal intraocular lens"

       which suggests laser enhancement may not be quite as precise as the impression I've gotten from doctors, though its only one study and the data isn't presented in the most convenient way (e.g. it graphs attempted end result vs. achieved, vs. the number of diopters being corrected to see how much difference there is between small corrections and large). 

      High myopes  considering a monofocal (outside the US at least), might look into the  light adjustable lens as perhaps a better way to fine tune refraction. I don't know how its other qualities compare to other monofocals (e.g. how its depth of focus and risk of halos&glare, etc), but there usually isn't too much variation between monofocals (though they aren't all created equal, some do have more depth of focus or less chromatic aberration, etc).

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    • Posted

      Thank you - I'll look up the link.   I know experienced opticians find myopic people usually prefer to be a little under-corrected, but wonder how much is the norm ?

      Presumably somewhere between -0.25 and -1. Presumably (bi focal or progressive) glasses would be required for day, and for night, driving, and to read the dashboard and a satnav ?

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    • Posted

      The level of undercorrection would vary with the person's preferences, how much they mind distance vision being reduced, though a little won't impact it too much. In the case of surgery, often even for distance they might target -0.25D so that if the lens power is off a bit it doesn't leave them hyperopic (reducing the already imited level fo nearer in vision someone gets) while not having much impact on distance.

      If you have monofocals and wear glasses for driving then the odds are you'd want bifocal or progressive(=varifocal) glasses for things inside the car.   

      Or if you don't mind contacts, you could try out multifocal contacts, which is an alternative to getting premium IOLs. There   is an extended depth of focus contact lens that I know has been FDA approved (from the Brien Holden Institute, though I don't know what commerical brand it would be issued under), but I don't think its on the market anyplace in the world yet, though I'm not positive.

      Alternatively, there are actually studies being done on combining implants for presbyopia like the Raindrop or Kamra on top of  a a monofocal IOl to give more of a range of vision. The implants are usually used for people with presbyopia who still have their natural lens, but they work for those with an IOL also. They are  usually used in only one eye, and  removable if someone doesn't like them.  I haven't examined the level of risk of things like halo&glare with them. 

       

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    • Posted

      I am trying a soft daily contact lens in my other (right eye), at strengths between -12 and -15 diopters, as an alternative to an iol, and also to try out mini-monovision.  Unfortunately there is fringing above or below text, making reading very difficult at any distance.   A monthly contact lens from a different practitioner had the same result. The practitioner said an early cataract might be causing this.  However, I don't get any fringing or double vision at all using specs for near or mid distance, although I do see some distortion of shape with eg traffic lights - perhaps because my spectacles are not set on full distance.    I asked whether a hard contact lens would give better vision, but she said it would be too pricey to try out.

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