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Re: IOL: what is meant by near, intermediate, and distance vision....?

Hi All;

What is the distance in inches or feet that constitute near, intermediate, and distance vision?

My right eye has pretty bad macula pucker due to residual ERM from a botched 2013 vitrectomy/ERM peel.  An ILM peel is recommended.  Cataract surgery is needed before the ILM peel (my natural lens is too cloudy for surgeon to see through well enough to do ILM).

After 3 years of retinal traction due to residual ERM, my retina will never fully unwrinkle, even after the ILM peel.  The retina and cataract surgeons each said I'm not a candidate for multi-focal IOL's.  Both said mono-vision is the only real option.  The cataract surgeon said he'd use an Alcon IOL set for distance vision.  Lens measurement is scheduled for early October.

The cataract surgeon said he'll target a post-op contact lens prescription of -0.50.  That's the prescription I wear in my good (left) eye.  It gives me BCVA of 20/20.  Uncorrected VA in my good (left) eye is 20/40.  The surgeon said using an IOL that will allow me to then wear a contact close to the -0.50 I use in my good eye is the best choice.

Is he correct, and if so, why?

Would mini-monovision be better and if so, why?

I've hesitated to ask these questions.  But I've become overwhelmed and burned out trying to learn about post-refractive targeting, mini-monovision, etc.  And the posts where people use lots of prescription numbers (I guess they're post refractive diopter measurements) has my head spinning.

Hoping to gain some knowledge in layman's terms and appreciate all anwers.
10 Responses
177275 tn?1511755244
177275 tn?1511755244
There is no universally agreed to definition of near, intermediate and distance.  These are guidelines. You must understand that a monofocal IOL or a monofocal toric IOL inserted correctly in an eye with a corresponding amount of astigmatism there is a precise distance that the IOL will be focused  anything closer or further away will be somewhat blurred. Due to the pupil changing size there is a "depth of focus" where within that range things will be pretty clear.

Distance:  This means 20 feet (6 meter) or further
Near: Generally this means about 12 to 18 inches which is where most people read.
Intermediate: this is the most imprecise.  Generally it means 2-5 feet away. Within this distance are using a computer, seeing a dashboard on a car, seeing shelves at a store.

This leaves a distance of 5-20 feet that falls between the gaps.  This often includes 8-18 feet away which is the distance that many people watch television and without glasses on there can be problems reading the news/weather scroll and scores of ball games.

Avatar universal
Thank you for your answer.  This is how I understand that answer.  Is my understanding correct?

Say I got an IOL for distance.  Say this IOL gave me perfect vision at 30 feet; clear, sharp, focused, I could read a newspaper.

Without contacts or glasses, items closer than 30 feet will be out of focus, and items farther than 30 feet will be out of focus.

Wearing contacts or glasses will bring into focus items that are closer than/farther than the 30 feet "in focus" distance.

Thank you again.
Avatar universal
Forgot to ask.

1.  Is the cataract surgeon's plan to make my bad eye equal to my good eye a good or not so good idea?

2. Why or why not?

3. Before the cataract surgery, can I try a contact lens in the bad eye that will approximate what the prescribed IOL will give me vision wise?

4. I already wear the strongest Alcon contact available in my bad eye (-10.0).  How is or is not a contact that approximates the prescribed IOL power work different from my current -10.0 Alcon contact?
Avatar universal
One other thing that is hard for people to think about is what a 20/X figure means in terms of how well they can see. This page:

http://www.teachingvisuallyimpaired.com/print-comparisons.html

gives a description of the sorts of print sizes you can see with different 20/X visual acuities like newsprint and books. Unfortunately your situation is complicated by the fact that the other eye issues may lead your vision to be worse than the typical results quoted for an IOL for different distances.

Your eye has a range of focus around where it is targeted, with the visual quality going down the further in or out you go from that. Usually targeting a tiny bit of myopia, like -0.5D, still leaves fairly decent distance vision. Choosing a lens power isn't an exact formula, so there is some chance the lens power might be off (even if for most people with low prescriptions its  fairly accurate). If you target 0D then there is a chance the IOL power might wind up being off in the farsighted direction, e.g. +0.5D, which could  noticeably reduces your closer in vision without a real benefit. If you target -0.5D and its off by +0.5D that merely leaves your eye target at distance, 0D. If its off in the other direction by -0.5D that leaves you at -1D which reduces distance vision a little bit in that one eye, while giving you more near, and is  still a rather small amount of monovision in the range almost every one adapts to well.

The higher the level of mononvision, the more impact there is on stereopsis (3D perception), though most people don't notice it or get used to it, and the more monovision the more near you get.

When they talk about focusing an eye at a certain diopter measure, e.g. -0.5D, the diopter units can be converted to a distance. If your eye is focused at X diopters then its focused at (100 / -X) centimeters. So a -0.5D focus is targeted at (100 / 0.5) = 200 cm = 2 meters = 6.6 feet. How much further in you see than that depends on the IOL you get (and the person, the results of studies are only averages).

Also your vision is coming from both eyes, so the visual acuity at a certain distance can sometimes be better than either eye individually (though it is sometimes only as good as one of the eyes, usually the best but sometimes the worst) so its hard to guess what you'll get with monovision if there isn't a study with that IOL, and I hadn't hunted for one.

Most IOLs have information online someplace giving a "defocus curve" which indicates the visual acuity (on average) you get going further in or out from the best focal point. Often monofocals don't have that on their own web page, but multifocals from the same manufacturer often show the monofocal comparison. This third party study uses an Alcon monofocal as a control:

http://www.healio.com/ophthalmology/journals/jrs/2015-5-31-5/%7B9bb0a5a1-2929-44c4-ae67-6309d303309e%7D/correlating-optical-bench-performance-with-clinical-defocus-curves-in-varifocal-and-trifocal-intraocular-lenses

Although the figures are behind a paywall, Google search turned up their graph of the defocus curves:

http://m1.wyanokecdn.com/23b034618d0c76aae89279e8fc5b08cf.jpg

Which seems to show the Alcon hits around 20/40 at -1D focus. That would indicate that if your eye were focused at -0.5D that at -1.5D  = 66.7 cm = 26.2 inches you'd still have 20/40 vision (if your eyes were average, your other eye issues make that less likely).

I haven't hunted for various sources to see what to trust regarding their defocus curves since the manufacturer itself uses a study that is much more optimistic.  Alcon shows their monofocal in a comparison on this page:

https://www.myalcon.com/products/surgical/acrysof-iq-restor-multifocal-iol/performance-comparison.shtml

which claims that even 2 diopters in from the target you'll get 20/40 vision (though that seems optimistic based on other data to my recollection, but   I hadn't checked). That would mean if you hit the target of -0.5D that at -2.5D you'd still have 20/40 vision (were your eye like average eyes), which would be (100 / 2.5) = 40cm or 15.7 inches. With premium lenses there tend to be multiple studies to check to compare their visual acuity results, but I hadn't looked at the Alcon monofocal data to know whether the studies tend to be usually closer to the manufacture's figures or the other study above.

Some defocus charts like one I used above use a different visual acuity measure like LogMar rather than 20/X, this page has a conversion chart:

https://www.wikiwand.com/en/LogMAR_chart
Avatar universal
I posted that before reloading the page to see   the other questions. I need to get to other things, but I'll note that of course a contact lens test now would be impaired by the cataract reducing your visual quality, but might still be of use.
177275 tn?1511755244
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177275 tn?1511755244
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Avatar universal
SoftwareDeveloper;

Thank you so very much for your reply.  I've read some of your previous posts and I've been hoping to hear from you.

Would you please tell me if my understanding of what you said is correct?  Here's my stats for reference:
OS UCVA 20/40
OS BCVA 20/20 with -0.50 contact = good vision 10' and out
OD UCVA 20/400
OD BCVA 20/80 with -10.0 contact = blurry, distorted

1.   What does it mean when you say "....if you target -0.5D..."?  Does that mean the IOL chosen is one that will require a -0.5D contact lens to read 20/20 Snellen?

2.    My good eye uses a -0.5D contact lens.  It gives me 20/20 Snellen.  It also gives me clear and sharp vision from about 8 feet and beyond, but I need cheaters (+2.0) to read and use the computer.  I'm satisfied with these results.  With that in mind, and also considering my bad eye's current and poor UCVA and BCVA, is the cataract surgeon's plan to target a post-op contact lens of -0.50 in my bad eye (to match my good eye) a good idea?

3.  You said "The higher the level of mononvision, the more impact there is on stereopsis (3D perception)..."  Do you mean higher monovision = less depth perception?

4.   Regarding stereopsis and monovision, what do you mean by "....and the more monovision the more near you get."?

5.   Can you please explain monovision and mini-monovision, and the good and bad of each?  I've read up on them but can't quite understand the pros and cons of each, or when one is preferable over the other.

6.   The Alcon chart.  Is it showing that with an IOL targeted for 0.0 (meaning the IOL alone, with no glasses or contacts will give the patient 20/20 Snellen), but ends up being off -2.0, will produce uncorrected VA of 20/40?

1 Comments
Sorry I'm late noticing this to reply to.

1. yup, it means focusing the eye at -0.5D, 2 meters out, which would  require -0.5D glasses (and contacts, for that measurement they are about the same) to be focused to see best at distance. Depending on the lens it may still give you decent distance vision in that eye, perhaps 20/25.

2. It depends on whether you want that eye to have good distance vision, or a bit of myopia to give better intermediate vision, though without a premium lens it wouldn't likely give any useful near. So it could be targeted nearer in to give more near, or at distance. One advantage of having both eyes the same is that you can use off the shelf readers more easily, or if you are wearing contacts use the same prescription for both.

3. Yup, higher monovision, i.e. a larger difference in focal point between the eyes,  means less depth perception because there is more of a range where you are relying mostly on one eye. Thats mostly an issue for near/intermediate things where we rely more on using both eyes to determine depth (at far distance there are other cues that play a part).  Most people don't even notice it, or adapt to it quickly. I mostly noticed it since I wore contact lenses in monovision and hadn't really noticed the loss of depth perception (since the difference was gradually increased over time from a tiny amount with early presbyopia) , but then when I switched to multifocals I was using both eyes and I noticed things seemed subtly more 3D and I preferred that.  


4. The more monovision you have, the greater difference between the eyes, which means that the near eye is focused nearer in so you have more near vision.

5. Mini-monovision is merely a small amount of monovision, there are no strict figures for what constitutes full monovision or mini monovision.  e.g. 2 diopters difference would be in the range of full monovision, 1.25 would be an example likely  considered mini-monovision, 0.5D would be considered micro-monovision.

The tradeoff is how much near you get, and how much stereopsis you lose. Almost all people adapt to small levels of monovision, higher levels some people may have more issues with. There is also some reduction in contrast sensitivity, low light vision, because again you are using only 1 eye for more of the visual range. Using 2 eyes in lower light allows the results from each eye to be combined to make out dim things that one eye might not make out.

Unfortunately the ideal thing is for people to try monovision with contacts before they get cataracts that interfere with trying it, but most never do.

6. The alcon chart means that if you are targeted at distance, 0D, then at a near distance corresponding to -2D,  which would be 50cm, you would still have 20/40 vision. I suspect that result may be optimistic since I saw another chart recently from a study showing that with the alcon monofocal that vision is down to 20/40 by the -1D, 1 meter, mark and worse closer in. Usually its best to compare multiple studies since manufacturers do tend to be optimistic sometimes (though some seem to be good about picking a representative study).
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