Calculation for contact lens testing for mini-monovision
Posted , 3 users are following.
I feel sure I've seen posts on how to calculate what strength contact lens to use to achieve different test ranges to experiment what would be the best target for the 2d eye in a mini-monovision setup. Maybe my foggy senior memory is wrong because I've searched and can't find such a thing anywhere.
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My first surgery is 3/7. Toric Clareon monofocals. I told the surgeon I wanted near and intermediate, but I think my giving him specific distances in inches may have resulted in his target for the second eye landing me more with what Bookwoman has (near-near) than what I had in mind. It's true I use a computer close. My back won't take sitting in a desk chair and I use a laptop actually in my lap sitting in a recliner.
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Laptop = 18-22"
Book = 13-14"
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However, shoving the laptop out farther would be easy enough, although how far is limited.
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So the near target is -2.5, which since I really want to be able to comfortably read books for hours, seems good. But he mentioned -1.8 for the right eye target, which is the one I would like to test. I'd like to be able to try everything from -1.0 through -1.75 with contacts after the first surgery is done. My last glasses prescription from 11/1/23 is:
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OD -2.00 -1.00 020
OS -2.00 -1.50 175
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I read without glasses now and the left eye is noticeably less clear than the right, which could be, I guess, because the cataract is worse in that eye. The extra astigmitism in the left should make it better for near, right?
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Anyway, I'd appreciate any help anyone can give with how I come up with what I'd need in contacts to test the right eye. If I'm remembering wrong and the way to do it is a trip to an optometrist for a prescription at one of the distances I'll do that.
0 likes, 10 replies
RonAKA maura04015
Posted
Let me get your situation clear. Am I correct in that your left eye will be done first for distance with a toric lens? And what you are asking about is your right eye which will be done for near?
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If so the best method is to do the distance eye first to -0.25 D on a spherical equivalent basis - sphere plus 50% of the cylinder. Then the first eye is allowed to heal for 5-6 weeks to see what the final outcome is. At that point get an eyeglass refraction to see where it ended up, and determine if any adjustments are needed to target the second eye.
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Assuming the right eye is the one you want to test for distance then you would first calculate the power of contact required to bring it to plano. Google CooperVision Contact Lens Prescription calculator. This seems to come out as follows:
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Right Eye: -2.0 sphere, -0.75 D sphere, 20 deg axis (toric contact)
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Now to simulate the various amounts of myopia you would just subtract that from the sphere. So -0.25 D sphere top simulate -1.75 D of myopia, -0.50 D sphere for -1.50 D of myopia, and so on. The cylinder would remain at the -0.75 D for each case.
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Once you have the left eye done for distance then you can also simulate what these amounts of of myopia look like through a IOL eye. For example if you end up at -0.25 D sphere, 0.0 cylinder, then you could put on some +1.25 D readers and that would simulate -1.50 D of myopia. The plus values of readers make you that value more myopic. This is a more accurate simulation as your IOL eye will have no accommodation to help with near vision.
maura04015
Edited
Thanks for your reply.
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Yes, both eyes will have toric iol lenses. However, no, neither eye will have an iol for distance. The left eye will be done first for reading at -2.5. But the math remains the same, so I think I can figure things out now, thank you.
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I won't be doing this until after the left eye is done and stable. The surgeon mentioned -1.8 as the target for the right eye. That sounds to me very close to BookWoman's near/near setup instead of near/intermediate. I'd like to be sure something like -1.5 wouldn't be better, and it seems, depending on results for the left eye, a target of -1.0 wouldn't be unreasonable if that works better for me.
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Right now I have computer glasses that suit all my needs except driving, which is usually no more than a couple hours a week anyway. I hope to achieve something like that or close to it after surgery.
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The first surgery is scheduled for 3/7, and the second 5 weeks later. If I have to put off the second surgery further in order to feel confident about the target, I will.
RonAKA maura04015
Posted
This is not really mini-monovision then, as you certainly will not have distance vision. A target of -2.5 D is the standard add for reading vision, and should be just fine for reading if they hit it. However, it will give you virtually no distance or even intermediate vision. So, I guess you are trying to get some intermediate with the right eye. The consensus is that you should not exceed 1.5 D differential between the eyes, so if the target in the left is met, then you would be limited to -1.0 D in your right eye. But, yes you can simulate that with contacts and it should give you a good idea what things will be like. You can't simulate the vision in your IOL eye though as this would require negative power correction, not the positive powers of OTC readers.
phil09 RonAKA
Posted
"You can't simulate the vision in your IOL eye though as this would require negative power correction, not the positive powers of OTC readers."
No, not with OTC readers. But you can get OTC distance glasses at -1.0 D, -2.0 D, etc. for 10 bucks or so on the internet. Just search on myopia glasses, or nearsighted glasses for distance.
maura04015 phil09
Edited
Amazon has the minus glasses. My surgeon told me to order some so I can drive after my second eye is done and before I'm ready to get a refraction and expensive prescription glass. Most of them run between $15 and $30.
phil09 maura04015
Posted
eBay is another source. Prices are lower, but quality and shipping times may be less reliable.
maura04015
Edited
Darn it. I wish this forum allowed for editing.
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That's should be "expensive prescription glasses."
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And for the test I'd like to do I think a contact would be better than glasses.
RonAKA maura04015
Posted
Actually if you do it in the first hour or so after posting a message you can edit them. On a PC just press F5 to refresh the screen and a pencil edit icon should show up.
phil09 RonAKA
Posted
There is a reply that I posted 10 days ago that I can edit right now. I've had others where the edit pencil became unavailable minutes after I posted. Sometimes it seems to matter whether someone has replied to your post or not.
RonAKA phil09
Edited
Yes, there are some strange things in the way this forum works.