Monofocal lens set for near vision
Posted , 11 users are following.
hi guys. im curious as to why i never hear of people getting a monofocal vision set for near instead of for far. for myopes, the pleasure of not needing glasses to drive etc would perhaps be outweighed by having less of an adjustment to just put glasses on to see for intermediate and far, as we all have been doing that for as long as we had myopia. is there a down side to getting a close monofocal lens? thoughts?
also, for those who have gotten monofocal implants set for far distance, at about what distance from your eyes does your vision begin to get blurry as you get nearer something?
thanx much. trying to amass info for the future
dan
1 like, 86 replies
Bookwoman Dapperdan7
Posted
soks, yes, perfect vision is in that range, but usable vision extends much further. It's not like everything is suddenly completely blurry after 2 feet, it's just a bit fuzzier.
soks Bookwoman
Posted
with +2.5 glasses on my symfony eye it is suddenly blurry after a foot. so with iol it nay be differenr than glasses.
Dapperdan7 soks
Posted
can you explain what you put in your last message?
a little confusing it is
soks Dapperdan7
Posted
which message exactly?
Lynda111 Dapperdan7
Edited
dapper
There are many posts on this site about near/ intermediate vision. In my case, I specifically said I wanted intermediate or computer vision in both eyes and it worked out better than I or my cataract surgeon expected. I have 20/20 distant vision, excellent intermediate vision, and I can read my cellphone and depending on the light and font size, can read fairly well. I do sometimes use readers. And I see this well despite having 2D of astigmatism prior to surgery that was not corrected by a toric iol or limbal relaxing incisions. My surgeon said that because of the axis, targeting both eyes for intermediate reduced my astigmatism. But remember, all eyes are different. What worked for me may not work for others.
Dapperdan7 Lynda111
Posted
hi lynda. so did you get multifocal IOLs to achieve that good vision at far, intermediate and near?
thx for any input
Lynda111 Dapperdan7
Posted
Dapper
No multifocal. I had a standard Tecnis 1 piece monofocal IOL in both eyes
Dapperdan7 Lynda111
Posted
why did you not get the toric or incisions? did the doctor already know
the axis would improve things? thx
Lynda111 Dapperdan7
Edited
I should add that many patients and cataract surgeons think only about near or distance vision. They forget the third option: intermediate vision.
Dapperdan7 Lynda111
Posted
linda, what would be the advantage of intermediate correction?
thx
dan
jimluck Dapperdan7
Posted
Intermediate is what you need for computer.
jimluck Dapperdan7
Edited
Such an important topic!
DapperDan: You say you "see this well despite 2D of astigmatism." It might be that you see that well BECAUSE of 2d of astigmatism (and perhaps higher-order aberrations in your cornea). Uncorrected astigmatism and higher order aberrations gives one greater depth of focus, albeit a softer focus.
Here is a quote from one scholarly article I found online: "It is known that the MTF of an unaberrated eye shows greater sensitivity to defocus than an optical system with aberrations. Although, these aberrations compromise the MTF at best-focus, they increase its relative measure with defocus and, therefore, result in a higher DoF.5 "
You can pull up the article by using a snippet of that paragraph in your search string.
One of the ways that you can get extended depth of focus in an IOL is through manipulation of spherical aberrations introduced into the lens on purpose. They do this with the light adjusting lens, for example, if you request it.
I am a high myope with extreme astigmatism and other aberrations in my cornea. My right glassis lens has 8.25 cylinder. I discovered that reducing my glasses prescription by 0.75 diopter (absolute value) on the sphere in both lenses gives me an incredibly versatile pair of glasses. I can read my phone, use my computer and drive, all with one set of monofocal glasses. And yet I am 73 and have cataracts, so almost certainly hardly any accomodation left.
This versatility is apparently a result of the corneal aberrations. I recently got scleral contacts in order to do experiments to see what targets I wanted for my cataract surgery. Sclerals are a hard contact lens that eliminate the effect of all aberations. I was thrilled by the sharp vision, and shocked by the loss of depth of focus. I got the contacts set for reading distance. I need glasses to do ANYTHING other than read normal-size print at about a foot, once I put the contacts in. Worse, I need 3 sets of glasses -- one to read tiny print, another to work on the computer, and a third set to see the TV or drive.
This is one big reason why people's experience with the same IOL varies so greatly. They have different corneas! You can't base your expectations for depth of focus on anyone else's experience unless you know your corneas are shaped like theirs!
I had asked for my contacts to be set to -2.75, which I had determined to be the value I need for reading tiny print. I believe they missed that target and I am at -2.00. I have glasses with -2.75 lenses and another set with -2.00 lenses. Distance vision is better with the -2.00 pair. In fact, vision is better at all distances with the -2.00 pair than with the -2.75 pair. To read tiny print with the contacts, I need +0.75 lenses.
I had thought I would want my IOLs targeted to something like -2.00 or -2.75. But now each time I put in my contacts, I am so thrilled to see the table I am sitting at so clearly without glasses -- and so disappointed when I look up from the table at something across the room. I am coming around to thinking I want to target -0.75 and get glasses-free vision for my most frequently used distances. I will gudgingly get readers for tiny print and close work in my workshop.
An interesting byproduct of all my research with glasses of different powers and contact lenses is I discovered I can put off cataract surgery. I still CAN get 20/20 vision -- or close to it . I just have to use different glasses than I was prescribed. My complaints about vision with glasses were entirely based on not being able to use my computer comfortably with progressives. Once I threw away the progressives and started ordering monofocal glasses with different sphere powers, my problem was solved. My optometrist and ophthalmologist had told me I needed cataract surgery. But I have concluded I don't. Not yet.
I highly recommend experiments with contacts and cheap on-line prescription glasses as a way to determine what IOL targets you want. It's not a perfect method, because the contacts counteract your cornea's spherical aberrations and reduce your depth of focus. What you see with your natural lens and your corneas plus contacts is going to be different from what you will see with IOLs and just your corneas at the corneal plane. The depth of focus and the sharpness will both be different. But still, it's educational to experience different glasses-free vision, and mini monovision, and different strategies with glasses. I now have many pairs of glasses of different powers ordered at $20 - $25 each from Zenni Optical, that I can only use with contacts.
Soft contacts don't work for me (they make my vision worse, not better) but most people can use cheap dispoable soft contacts for experimentation. Just get your eye doc to give you prescriptions for the different targets you want to try. Sclerals are great, but they cost thousands of dollars. For me, they are covered by insurance because of my weird corneas (keratoconus).
Dapperdan7 jimluck
Posted
great info and advice jim!
so im assuming you are still experimenting and have not gotten the surgery yet correct?
im having a more difficult time driving at night because of the glares, halos etc. but not sure that is a good enough reason to proceed. outside of floaters and all the normal age related stuff like presbyopia, i still see ok. i worry that all the people who are extremely happy and relieved after surgery had such bad vision that ANYTHING would be an improvement. im certainly not there. i need to understand more of what you are explaining about experimenting before i dive in. i cant afford scleral contacts but seems like a good idea to do more research.thanks. ill likely ask more questions very soon.dan
Dapperdan7 jimluck
Posted
jim, can you (or anyone else) explain "depth of focus" as well as the "defocus curve"? are the two different concepts?
thx
dan
jimluck Dapperdan7
Edited
Depth of focus - range of distances over which the image remains reasonably sharp.
Defocus curve - graph showing how much the image goes out of focus at various distances. Farther is shown to the left and nearer to the right.
If you had infinite depth of focus, the defocus curve would be flat -- meaning your vision was just as sharp at all distances. If you had zero depth of focus, the defocus curve would be a spike at just one distance.
They don't actually generate defocus curves by moving the eyechart closer and farther. Instead, the eyechart and the patient are in fixed positions and they simulate changing distance by putting spherical lenses of different powers in front of the patient's eye.
From an article on the web which you can find by googling a snippet from this quote:
"Defocus curves are created by presenting a series of positive- and negative-powered lenses in front of a patient’s eye and measuring the degree of “defocus” that is induced. The zero reference on the x-axis is controlled across patients by correcting for the best possible distance acuity. Using 0.50-D increments, the defocus curve measures a patient’s binocular visual acuity often from +1.00 D to -4.00 D. In doing so, the resulting acuity that is measured can be used to simulate what the patient’s visual acuity would be at different distances. To understand this concept, we have to remember the most basic formula in optics, the formula for focal length: f = 1/D. For example, when an emmetropic patient views a logMAR chart through a plano lens, the image is at infinity representing distance vision. Place a -2.00 D lens in front of the eyes, and this would essentially equate to viewing the chart at 50 cm (20 inches). When looking through a -4.00 D lens, it would be the visual acuity equivalent at 25 cm (10 inches). Thus, the defocus curve can be created in a more controlled means for evaluating visual acuity at various distances."
Remember, you can shift the defocus curve left or right with glasses. So you might get an IOL that gave you sharpest vision at 3 feet, and let's say your vision that got blurry fast as the eye chart was moved farther from you, but got blurry only slowly as the chart was moved closer than 3 feet. To depict this, the defocus curve would be steep to the left and gradual to the right of its peak at 3 feet.
Putting on a pair of glasses with minus correction would move the peak to the left (sharpest vision at a greater distance). You might have sharpest vision then at 5 feet instead of 3 feet once you put the minus glasses on.
How bad would the glasses make your vision at 3 feet? Since we said the curve is relatively gradual to the right, we would predict your vision at 3 feet would remain fairly sharp.
How much better would the glasses make your vision at 5 feet? Since the graph is steep to the left of its peak, we would expect that the gain in sharpness for objects 5 feet away would be rather dramatic when you put on the minus lenses.
Dapperdan7 jimluck
Posted
thanks jim. lots of info and confusion too.
questions: i did not know contacts reduce depth of focus. if true, why is that?
how does an astigmatism help with depth of focus?
you never mentioned what your sphere numbers are in each eye? what are they if you dont mind..?
thx
dan
jimluck Dapperdan7
Edited
I wouldn't phrase it that contacts reduce depth of focus, (though that's not wrong in my case). It's that my corneas have lots of astigmatism and higher order aberrations, and the the aberrations in my cornea made them multifocal. The contacts take that away. When I put the contacts in, the multifocality is gone. I see more sharply that I ever have, but only over a narrow band of distances.
I am juggling 3 different pairs of glasses with the contacts. The contacts with no glasses give me good vision at 12 inches. For really tiny tiny print where I need to get closer, I put on +2 reading glasses. For computer at about 20 inches, I put on -0.75 glasses. For TV and driving, I put on -2.00 glasses.
I was supposed to need -2.75 for full distance but something didn't go according to plan. I feel they missed the target, because -2.75 does not give me better distance vision than -2 glasses. I think it's a little worse.
Astigmatism gives one mutiple focal points. That translates to greater depth of focus, but softer focus at the optimal distance.
My glasses prescription without contacts is -5 sph -2.25 cyl left; -3 sph -8.25 cyl right (not a typo, repeat: - 8.25). My contact lens prescription that leaves me -2 myopic is -5.5 left -6 right. So a full prescription would be -7.5 and -8.0. The left contact has just a tiny bit of cyl (0.5) for lenticular astigmatism and my right has none. Amazingly, 100% of the -8.25 astigmatism in the right is corneal, and just disappears when I put in the scleral contact, and it is not a toric. Poof! What was my worse eye all my adult life becomes my better eye, just like that.
Dapperdan7 jimluck
Posted
thx jim.
so you have contacts at this point, not IOLs?
another question. can a doctor tell you where your astigmatism is, the cornea or lens? seems like it would be useful information
RonAKA Dapperdan7
Posted
When you get your initial consult with the cataract surgeon they will measure your eyes to determine how much astigmatism is in the cornea and at that point will be able to tell you what the predicted residual astigmatism will be after the lens is removed.
Dapperdan7 RonAKA
Posted
thx sir
jimluck Dapperdan7
Edited
I have contacts not IOLs. They told me I needed cataract surgery, so I started do experiments with different power lenses in glasses, including buying my own trial lens set (couple hundred on Amazon) and many pairs of glasses of different powers, in order to help decide on IOL choice and targeting. There are limits to what you can do with glasses along those lines, so I wanted to do contact lens trials. Logically, I should have been able to try different sphere powers with contact lenses, which relying on glasses with sphere undercorrected and astigmatism fully corrected to complete the experimental setup. But, soft contacts would not work in my eyes. They made my vision worse, not better. So, that's what led me to sclerals. The bottom line from all the experiments was (a) I don't think I want to target near when I get surgery (b) I am a long way from needing surgery. Item (b) is surprising. But I found with sclerals I could still get to 20 - 20. I very much want to postpone surgery until Fixoflex PCR comes to market (google it) so I don't have the risk of PCO, don't have the risk of capsule wrinkles, and do have the option for future IOL exchange. Might be a few years and might have to travel to Europe for it.
Why am I turning away from targeting near? Not sure. I just know my contacts are targeted for near and I wish they were for distance. I can learn to use reading glasses like most of the rest of the world.
Dapperdan7
Posted
ron, how long did it take you to adjust to mini monovision?
so you are basically ignoring the eye that does not contribute to clarity depending on where you are looking? of the three distances, would you say intermediate is where the two different prescriptions are at their most equal?
thx much
dan
RonAKA Dapperdan7
Posted
I really didn't need any significant time to adapt to monovision. When I first tried it with contacts it pretty much worked well from the time I put contacts in. My only issue was with the comfort of the contacts. The second time I tried it was after the first eye cataract surgery was done, and I was only using a contact in the non operated eye. There really was no adaptation period, and since I had found a much better contact I went that way for well over a year. Then when I had the second eye done and I had IOL mini-monovison there was no adaptation needed. I will post a couple of graphs to answer your question about where the best vision is. Since it will get delayed in moderation I will make another post. Check back for it tomorrow.
RonAKA Dapperdan7
Edited
Here is a graph from a trial done to determine the optimum amount of difference between the eyes for mini-monovision. This first graph shows the vision from the distance dominant eye (dashed line), as well as individual graphs for three different amounts of myopia for the close eye, 1, 1.5, and 2 D differential.
.
.
This graph shows the combined binocular vision with both eyes for the three levels of differential between the eyes. This study concluded that the -1.5 D differential was the optimum amount. The binocular vision with this amount is the dark line with the triangular markers. As you can see that there is a slight dip in visual acuity at the 1 meter position or about 3 feet. However this dip does not go below about 20/22 or so, which is pretty good. Peak vision is better than 20/20 at 0.7 meters, or about 2 feet. And at distance vision is 20/20.
.
Dapperdan7 jimluck
Posted
why not get the sclerals targeted for distance? is it cost?