I was wondering where you draw the line between monovision and mini-monovision (1.5 may be it)

Suppose my distance eye is tuned for 0.5 D nearsighted (a common target). I would then think that if using 1.5 D monovision, that the other eye would be tuned for 2 D nearsighted. Your thinking, I think, is that the near eye would be tuned to 1.5 D nearsighted.

I am thinking that for the brain to accommodate the change, it would be the difference that matters.

So this was a point that I wanted to explore. I don't know where this is defined.

I break it down to three different issues you are trying to manage. First you want to get as near as you can to plano (0.0 D) in your distance eye without going to the plus region. The normal target is about -0.25 D. Yes, you can get unlucky and end up at -0.50, but I would not go that far intentionally. The second issue is that you are trying to get good reading vision (not excellent) in your near eye while maintaining some intermediate and distance vision. That has nothing to do with your distance eye. Your near vision will be determined by your myopia in that eye. The normal amount to achieve a balance trade off is -1.5 D. The third issue is the differential between the eyes. If the differential exceeds 1.5 to 1.75 D there can be issues with the eyes working well together. That means you don't want to exceed that value, but you do not have to make it that much either. If you want a bias to near vision you could go to -2.0 D in your near eye without violating the differential rule, but do you really want to do that? It will limit your distance and intermediate vision in this eye. It is a personal preference and you certainly could do it. Being -0.5 D in the distance eye and -2.0 D in the near eye is likely to be tolerable, but will not be ideal for distance vision.

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I meant to mention in my last post that all of these targets I am quoting are spherical equivalent numbers. This means they are the sphere in diopters plus 50% of the cylinder in diopters. This compensates for any residual astigmatism. You can't base your targets on sphere alone and need to consider astigmatism too.

Thanks for your post.

I have been thinking that they should make astigmatism (cylinder) test lenses that are not plus or minus, but symmetric. I understand there is a convention, but if I were designing the system, that would be the norm.

A semantics question is is " -0.5 D in the distance eye and -2.0 D in the near eye" an instance of 1.5 D monovision? I would think so, but you may be disagreeing on that point.

Looking at Defocus Curves, I think I have not found one for a monofocal lens that has no extended aspect. I only recently came across that term on this forum. I like the ones that include numbers such as 20/15, 20/20, 20/30 etc on the vertical axis. The ones with just VA(LogMAR) seem more cryptic to me.

Anyway, the defocus curves make me think somebody getting the LAL tuned might opt for 0.5 or 0.25 nearsighted on purpose, rather than just being a way to keep from getting into farsighted.

The lenses are symmetric and are not really plus or minus as they are both. It is just a convention as to how it is expressed. Optometrists do it one way (negative cylinder) and Ophthalmologists do it the other way (positive cylinder). The same lens would be used regardless of which way it is expressed. It is just a confusing convention.

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"A semantics question is is " -0.5 D in the distance eye and -2.0 D in the near eye" an instance of 1.5 D monovision? I would think so, but you may be disagreeing on that point."

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In my opinion that is 2.0 D monovision with a poor -0.5 D result in the distance eye, not 1.5 D monovision. I say that because near vision is determined by the spherical equivalent of the near eye, and not by the anisometropia which is 1.5 D in this case. But that is my opinion only. There are no hard and fast rules on the types of monovision and even the terminology, just like there are no hard an fast rules on near, intermediate, and far. That is why it is always preferable to discuss targets in diopters with the ophthalmologist and in spherical equivalent, not just sphere, so there is no misunderstanding.

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It certainly is a judgement call as to how close to come to plano in the distance eye. My understanding is that the eye correction is very stable over time once the natural lens is removed. It is where most of the year to year variation comes from, and especially after cataracts start to develop. My first eye done is coming up to 3 years and it has perhaps drifted slightly more myopic, by 0.5 D SE, or a little less. It would be a good question to ask the LAL surgeon. How stable will the eye be after the power is locked in? The other thing to remember is that if you go to +0.25 D that is not the end of the world if you have mini-monovision as it is the near eye that is giving you the near vision, and the +0.25 D is almost insignificant on distance vision. My brother is in that situation with +0.25 D sphere and -0.50 cylinder for a spherical equivalent of 0.0 D. He is happy with his vision.

I bought one of those test lens kits. It has both plus and minus versions of each amount of cylinder.

That some prescriptions are written one way vs the other confused me for a good while.

There are no hard and fast rules on the types of monovision and even the terminology, just like there are no hard an fast rules on near, intermediate, and far.

Be aware that I do not agree with most of RebDovid's conclusions. He tends to over analyze things to the point of confusing himself. He reads much more precision into the defocus curves than what they really contain. Don't be misled.

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The best defocus curves that I have found are the generic monofocal IOL curves that you can find by googling the article below. They use the Snellen visual acuity numbers you prefer, and express the distance in meters, instead of diopters which makes it much easier to read. There is a graph of what individual offset diopters do in addition to a plano target, and there is another graph which shows the combination of a plano eye and a nearer power monovision eye. The conclusion of this article which unfortunately no longer has the text portion on line, is that -1.5 D is the best compromise target for the near eye. However if you click on each graph more text will show and pretty much all of the article content is still there.

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Optimal amount of anisometropia for pseudophakic monovision Ken Hayashi, Motoaki Yoshida, +1 author H. Hayashi Published 1 May 2011 Medicine Journal of refractive surgery

Sorry, but I have no idea what these test lens kits are like. The angle of an astigmatism correction is extremely critical. How would you get an accurate angle with a test lens kit? And what would you learn beyond just getting an eyeglass prescription from your optometrist?

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Also it is rather meaningless to do such a test before surgery. The astigmatism you have now is a sum of the astigmatism in the natural lens, plus the impact the cataract is having on it, plus the astigmatism in the cornea. After cataract surgery the astigmatism in the lens and cataract are gone. You only have to deal with the astigmatism in the cornea. The only way I know that this astigmatism can be measured is by using the IOLMaster and Pentacam instruments which measure the topography of your cornea. In practical terms you have to ask the surgeon what your residual astigmatism is likely to be after they have taken these measurements. Ideally you want to ask for a printout of the IOLMaster measurements and the predictions for IOL power needed.

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You can find an online calculator to convert positive cylinder prescriptions to negative cylinder prescriptions.

I have had symfony lenses for 3 years, the left eye is sph 0.50 cyl +0.50 and the right is sph 0.50 without astigmatism.

I can see very well up close and I haven't worn glasses for near vision for 3 years. I've been without 20/25 glasses for a long time and I only wear glasses for night driving and rarely on TV.

I had asked the doctor to do everything I could to have good intermediate and distant vision,

He told me that because I had done lasik years ago, he could not guarantee the result.

I really like the way it turned out, although he suggested that he could make me the remote with PRK.

However, I am so happy with the final result that I don't want to take a risk, what is your opinion please

You rotate the test lens. The test glasses mount the test lenses, and have a rotary knob. However the cheap test frames are giving me poor repeatablity. But one good thing is they can let you turn with a blind test (you don't know what the reading is indicating while you adjust. The lens can be mounted at a wide range of positions. The knob then turns the lens in the frame. There are little lines on the lenses that you use to point to a degree scale.

If you search for "test lens kit" on an auction site or a big online retailer, you will see such kits. This is not a recommendation to buy one, but mainly it explains what it is.

My hope is that the reading axis would be more repeatable, and that I could see if the number changes during the day. However it is not really turning out to be that useful. Maybe I will figure out how to make it more useful. Maybe it will be a toy.

I have done that positive/ negative transformation in a spreadsheet.

I was thinking the test could be useful after surgery and before adjustment.

From the article abstract I get this:

Conclusions: Pseudophakic monovision with anisometropia of 1.50 or 2.00 D provides useful binocular visual acuity from far to near. However, because stereopsis with 2.00 D of monovision is substantially impaired, approximately 1.50 D of anisometropia is thought to be optimal for successful monovision.

The defocus curves are on the semanticscholar version. Nicely graphical and enlightening.

In optometrist convention your left eye is at:

+1.00 D sphere, -0.50 D cylinder for a spherical equivalent of +0.75 D

The right converts to:

+0.50 D sphere

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This would indicate you are far sighted for distance. My experience in checking into Lasik and PRK is that it is difficult to make the eye more myopic. They can reduce myopia easily, but increasing it is no predictable and may not hold up over time even if they can do it.

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You may want to ask about a piggyback lens to make the correction to get closer to plano for distance if that is the objective.

Yes, the test lens could be useful after surgery, but I would expect an optometrist test would be better.

I agree. The test lens thing would be more curiosity and hobby, but it seems to me that it could be useful to an extent that I have not figured out.

I can certainly see that different people would prioritize different things. Some would have no problem always using driving glasses, if that gives nice glasses-free binocular vision for close work.

I will do a form of testing.

I agree with @RonAKA that I place more weight on evidence-based information than he does. But sadly he forgets that when speaking of defocus curve information I (a) generally refer to them as indicative; (b) frequently note that they report mean (not, for example, median) results and are subject to deviations, with the standard deviations only sometimes being reported; (c) and have explained why I use the average of the mean results of as many defocus curves as I can find for the IOL in which I'm interested.

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If you're interested in peer-reviewed articles regarding degrees of monovision, an entry point I endorse for evidence-based information, the following are available on the web:

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Debora Goetz Goldberg, et al., Pseudophakic mini-monovision: high patient satisfaction, reduced spectacle dependence, and low cost, BMC Ophthalmology (open access) (2018) 18:293

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JianHe Xiao, et al., Pseudophakic monovision is an important surgical approach

to being spectacle-free, Indian J. Ophth. (2011) Vol. 59 No. 6

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Not peer-reviewed but also of some interest because it emanates from the American Academy of Ophthalmology is Cynthia Matossian, MD, FACS, Mini-monovision: Reducingspectacle dependence after cataract surgery, American Acad. of Ophth. (August 26, 2013)

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Dr. Matossian writes that "Historically, surgeons have aimed for 2.0 to 2.5 D of anisometropia. Based on the defocus test we perform in the office, I have found that most patients are unable to tolerate a difference this large. Moreover, commonly used items, such as cellphones, tablets and laptops fall in the intermediate zone. Traditional monovision does not provide clear vision for this intermediate range." After describing how she performs a defocus test, she reports that "For mini-monovision, I aim for the IOL power difference between the eyes to be no more than 0.75D. I target the dominant eye for emmetropia and the nondominant eye between -0.5D and -0.75D,with power adjustment made to the nondominant eye based on the result of the dominant eye." Plainly, this is a very conservative approach.

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According to Dr. Goldberg, et al., "Modified monovision or 'mini-monovision'" assumes targeting emmetropia in the distance eye and that "typical calculations of the near eye are anywhere between −.75 and − 1.75 diopters of myopia....Previous

research has found that IOLs implanted bilaterally using the mini-monovision approach result in few optical side effects and exceptional distance and intermediate visual outcomes. Concerns remain regarding near visual outcomes that require some patients to wear spectacles for reading fine print or computer

work." (citing Ito M, Shimizu K, Niida T, Amano R, Ishikawa H. Binocular function in patients with pseudophakic monovision. J Cataract Refract Surg. 2014;40(8):1349–54).

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In (what I'll call) the Goldberg study, "The target refraction for the distance eye was plano and the near eye was − 1.25 to − 1.50. Fifty-one patients (91%) were within ±.50 diopters of the intended spherical equivalent for the distance eye. Fifty-two patients (93%) were within ±.50 diopters of the target range for the near eye. There were no patient reports of meaningful glare or halos for near or distance functions."

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Focusing on patient reports of their satisfaction with the results, the Goldberg study says "Almost all patients in the study reported that cataract surgery with the mini-monovision technique met their expectations for decreasing dependence on spectacles, with most patients reporting little or no use of spectacles post-operatively. Patients reported low use of spectacles for computer work, distance viewing, and general activities throughout the day. The quality and levels of light and/or the distance from the object may be related to the need for a small number of patients to wear spectacles postoperatively for reading and driving at night."

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By a parity of reasoning, if one prioritizes near and intermediate vision (rather than distance and intermediate), one would aim for more myopia in the near eye and, depending on the result and one's risk averseness, anywhere from c. -0.50 D to c. -1.0 D in the more distant eye. @RonAKA tells us that -0.50 D in the distance eye is a "poor" result, but of course this judgment merely reflects his prioritizing distance. Further, while -0.50 D in the distance eye won't give most people Ted Williams-like vision, my wife's experience-- -0.50 D with the Eyhance IOL in both eyes -- is that the 20/25 distance vision she has is very good indeed. YMMV.

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