Posted , 10 users are following.
so lets use an example of two people who have cataracts, one has perfect vision and one has myopia due to axial length. how do these two different scenarios affect lens choice, and all other things being the same (good outcome, no astigmatism etc) the vision limitations they will be left with after surgery? i have always wondered. no difference?
0 likes, 18 replies
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Guest Dapperdan7
Edited
I don't think being myopic or not makes any difference on lens choice.
RonAKA Guest
Edited
In the extremes it may make a difference. An extreme myope for example may need a negative power IOL. There are not may lenses available in that power range and they are quite specialized.
RonAKA Dapperdan7
Edited
The short answer would be no difference given a good surgeon and good power selection for the IOL. There is some research which suggests that the patients with myopia prior to surgery may have better near vision when targeted for distance, but that is about it. More recently I have become aware that the lower the IOL power the less sensitive it is to position in the eye. If eye measurements are done well, high myopia is no excuse for missing the IOL power targets. Those that are far sighted or hyperopes are more prone to errors do to the effective lens position in the eye.
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This said there are some surgeons who make the assumption that if one is near sighted before surgery, somehow we myopes will be happier being myopic after surgery. I think that is condescending and a bit of a cop out. It is easier to hit a myopic target than a plano target. "You know what it is like to be myopic, so I can do that for you, and you will be happy!"
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That comes from someone who has been myopic since I was a child. Yes, there are some advantages in having a bit of super vision up close with your glasses off, but after that all the rest is negative in my view.
pershoot RonAKA
Edited
Agreed! Quite a bit of negatives in being highly myopic, in my opinion. Perhaps I would feel differently, if my particular level wasn't a bit off the charts. I 'think' I would rather be a hyperope, for potentially a bit less of a burden. Grass greener; maybe in another life!; hehe.
ka76787 RonAKA
Posted
Where are you getting the data on accuracy of IOL power prediction for high myopia? I've heard again and again that in very high myopia there is less accuracy than in regular eyes.
It is true that effective lens position plays no role when IOL powers are very low, but the axial length measurement can be too long if staphyloma affect the length of the eye.
RonAKA ka76787
Posted
I got it from an article on the Hill RBF 3.0 IOL power calculation method.
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Prediction Accuracy +/- 0.5 D:
All Eyes (AL 20.97 - 29.10 mm) - 91%
Short Eyes (AL <22.5 mm) - 84.5%
Normal Eyes (AL 22.5 - 25.0 mm) - 92.2%
Long Eyes (AL >25 mm) - 98.4%
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A quote:
"In a retrospective multicenter study of 459 consecutive patients of IOL power calculation performed with Hill-RBF, a ±0.50 D accuracy was achieved in 91% of all eyes (AL, 20.97–29.10 mm), 92.2% of normal eyes (AL, >22.5 mm and <25.0 mm), 98.4% in eyes with axial myopia (AL, >25.0 mm), and 84.5% in eyes with axial hyperopia (AL, <22.5 mm)."
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Hill-RBF Calculator: More Data to Further Refine Outcomes
A new approach to optimum IOL prediction in any patient.
Warren E. Hill, MD and Adi Abulafia, MD
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I also have seen somewhere that measurement error is lower on long eyes on a %error basis. A 0.01 mm error on a 27 mm eye is a lower % than the same 0.01 error on a 21 mm eye. Makes mathematical sense, but not so sure how significant the difference is on outcomes.
ka76787 RonAKA
Posted
Thank you, I'll look that up.
ka76787 RonAKA
Posted
Thank you very much. The source looks very good and I was wondering how I could have gotten it so wrong up to this point and then I realized that study only includes eyes with axial length up to 29.10mm. My eyes are 31-32mm long. So I don't even fall into their category of "all eyes." No wonder I'm so scared of this surgery. I wish that missing the refractive target was all I had to worry about.
RonAKA ka76787
Posted
I find the trend of accuracy interesting. The shortest eyes have the lowest accuracy, while the longest eyes have the highest. I would have expected that normal length eyes would have had the highest accuracy.
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I suspect with long eyes and low power IOLs the uncertainly in predicting powers shifts from issues with the lens position to inaccuracy in measuring the eye dimensions.
ka76787 RonAKA
Posted
Yes, if there is a staphyloma then you can get an overly long measurement. The other problem is getting the pupil to fixate properly so that you are measuring the distance to the correct part of the macula. Very long eyes can have other problems that make pupil fixation more difficult.
When they measure my eyes they tell me to look at the dot but I see three dots. I don't know which one to look at so I try to look at the brightest one.
With short eyes they can get a refractive miss of several diopters-- due to variability in effective lens position as you already pointed out.
And let's not forget that the machines used to measure eyes have been developed and optimized using standard eyes, not extremes. So they can't be expected to perfectly measure extreme eyes. Even if the formulas are optimized for long eyes, the results are only as good as the raw measurements used to calculate the IOL power.
RonAKA ka76787
Posted
I believe the issues of measuring an eye with staphyloma are minimized when an optical instrument like the Lenstar LS900 or IOLMaster 700 is used instead of an ultrasonic A-scan. I believe the IOLMaster is much faster at 45 seconds vs 170 seconds for the Lenstar. Not sure where the Alcon Argos compares to these two.
aly38331 Dapperdan7
Posted
Does anyone have blurry vision post cataract surgery two years ago left eye is uncomfortable despite using drops and warm compresses
RonAKA aly38331
Posted
A common cause of blurry vision post cataract surgery is posterior capsule opacification (PCO). You should ask your doctor if that is a possibility.
aly38331 RonAKA
Posted
I'll do that. Thank you for your help
jo61855 Dapperdan7
Posted
What type of vision do you have?
aly38331 jo61855
Posted
Hi Jo
My right eye is always blurry and has a floater which is in line with my vision my left eye feels uncomfortable (gritty) .
jo61855 aly38331
Posted
The deleted post referenced an article which described problems by time periods after cataract surgery. Too much for me to paraphrase.
phil09 jo61855
Edited
I would have found that kind of article helpful.