Is a prescription of -0.25 (distance) the best result you could get the 0.5 jumps in IOL?
Posted , 4 users are following.
Hello there. This is just to make sure that I am understanding things correctly.
It's been three weeks since my second IOL implant (Vivity.) We agreed to aim for plano.
At my followup visit today, I asked the Dr for a prescription and he gave me one for Sphere -0.25 Cyl 0.50.
My understanding (thank you @RonAKA) is that since IOLs come in 0.5dpt steps, if the Dr. had chosen a different lens power, I would have ended up with hyperopia—which is not a good thing.
So, given the choice between -0.25 and +0.25 (the only possibilities given the 0.5 steps in IOLs) I got the best possible results.
Am I understanding the math correctly?
0 likes, 10 replies
RonAKA RandallG
Posted
Yes, that is basically correct. A sphere outcome of -0.25 is pretty good, and close to perfect. Cylinder of 0.5 D is not that much. Did you get this prescription from an ophthalmologist? They typically write the cylinder correction as a plus value with an axis. Optometrists and optical dispensaries typically use negative cylinder with an axis.
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For example if this is an ophthalmologist prescription it would convert to:
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Sphere +0.25 D, Cylinder -0.50 D. This combines to give a spherical equivalent of 0.0 D which is perfect on a spherical equivalent basis. But it does mean you would be slightly far sighted with the astigmatism offsetting it to zero total. If this is the case it is possible a 0.5 D step change might have given a slightly better outcome. You could be targeted to be slightly myopic. But it would be a toss up as to whether that would be better or not. It may have given you slightly better near vision but possibly slightly worse distance vision.
RandallG RonAKA
Posted
Thank you for the reply Ron. I still get a bit confused with the two different standards for writing prescriptions.
Mine is from the Ophthalmologist who did my operation. Here's what it reads:
OD: Sphere -0.25, Cylinder +0.50, Axis 045, Add +1.75
OS: Sphere -0.50, Cylinder +0.50, Axis 115, Add +1.75
... so the Sphere and Cylinder should offset, right and result in 0.0D ... but that would mean 20/20 correct, and I don't think I am seeing THAT well.
RonAKA RandallG
Edited
"OD: Sphere -0.25, Cylinder +0.50, Axis 045, Add +1.75
OS: Sphere -0.50, Cylinder +0.50, Axis 115, Add +1.75"
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That converts to the following in Optometrist format.
OD: Sphere +0.25, Cylinder -0.50, Axis 135, Spherical Equivalent 0.0 D
OS: Sphere 0.00, Cylinder -0.50, Axis 25, Spherical Equivalent -0.25 D
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The Add is just to help with reading. Your left eye probably has the better correction, and you may have a bit better nearer vision with it. But in the scheme of things these are very good outcomes.
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If you google this you should find a calculator that does this conversion:
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ACLens Eyeglass Prescription Positive Cylinder Conversion
soks RandallG
Posted
u need a +1.75 reader with vivity??? how good is your intermediate and near without glasses and what was your pre cataract prescription?
RandallG RonAKA
Posted
Thank you, Ron.
RandallG soks
Edited
Hi @soks,
Pre-cataract, I was myopic (I had a myopic shift: from far sighted to near sighted over a few years) so that does not apply.
My intermediate (from arm length of a few feet) is excellent, my distance is good to very good ... it still varies through the day.
As for near, in good light I can operate/read a smart phone (but I use a bold/larger font) and see my smart watch. I too was a bit surprised by the +1.75 ... I guess it has to do with how close I want to read because at ~14-26" in the dr's office I was able to read J3 without glasses.
RonAKA soks
Posted
Vivity when set for distance like Randall's are are not going to give good reading vision. They only promise to give about 0.5 D extra depth of focus, so improved intermediate. Normally the add is 2.5 D, so they are giving the Vivity credit for about 0.75 D.
soks RonAKA
Posted
the pan optix add is +2.17 and +3.25. the symfony add i think is +1.66. so its nothing but a low add bifocal. if vivity is providing as much near as symfony, shouldnt the vivity have atleast a 1.66D extra depth?
RonAKA soks
Posted
The defocus curves I have seen from Alcon for the Vivity show that it adds about 0.6 D extension at the 20/32 visual acuity line compared to a monofocal. I have seen some defocus curves which show the Vivity to be similar to the Symfony. Not sure how accurate the Symfony curves are. You have to be careful with how the extension is measured. Is it in comparison to a monofocal, or is it the total depth of focus at the 20/32 visual acuity line.
RebDovid RandallG
Posted
Implicit in your observation that IOLs progress, or regress, in advertised power in 0.5 D steps is the assumption that this 0.5 D difference in power results in a 0.5 D refractive difference in the eye. But this is not so, as plugging your optical biometry into an online IOL calculator will show.
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In my own case, for example, my surgeon and I chose a 14.0 D Eyhance IOL for my first (left, nondominant) eye, which was done last Tuesday. Based on my most recent optical biometry and the surgeon's personal a constant, this meant a refractive target of -1.97 D. Had we chosen the 14.5 D IOL, the target would have been -2.31 D (a 0.34 D difference), and a 13.5 D IOL would have meant a -1.64 D target (a 0.33 D difference). Similarly, as I'm planning on mini-monovision, the choices for my right eye include targets of -1.01 D and -0.68 D.
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In your case, assuming -0.25 D was the surgical target as well as the result, and assuming equal accuracy had a 0.5 D less myopic IOL power been chosen, the result would have been in the very close vicinity of +0.08/0.09 D, which is not the end of the world.