Posted , 12 users are following.
my surgeon suggessted the Alcon Clareon monofocals set for distance for my L eye. i am highly myopic with glasses Rx -11. How close will I see with this IOL? some people told me 6 ft and under will be blurry but some said 3 ft and under. i am confused! help!
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jo61855 sam36130
Posted
Monovision or mini-monovision with monofocals can add some depth of focus to one's vision. That doesn't mean you won't need eyeglasses to improve your vision in certain situations either for reading or for driving.
RonAKA sam36130
Edited
Here is a quote from a large retrospective study that determined that the Hill-RBF 3.0 was very accurate for average and longer eyes.
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"ACCURACY VALIDATION
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). The mean absolute error for each group was 0.29, 0.30, 0.20, and 0.32 D, respectively."
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CRST Global 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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Based on your pre surgery refraction your eyes are most likely in the 28 mm range. Accuracy of the Hill formula in achieving results within +/- 0.5 D was 98.4% for lengths greater than 25 mm. This is a very high level of accuracy, and does not merit going overly myopic in your target. I would suggest a target in the range of -0.5 D would be as conservative as you want to go if your objective is distance vision. A target of -0.3 probably is a reasonable risk using the Hill formula. Ending up at +0.2 is not a disaster and the risk of it being that far off is very low.
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Interestingly in other reading it seems that effective lens position in the eye after insertion is one of the factors that causes outcome prediction errors. Each surgeon may have techniques which cause the lens to sit in different positions and the formulas can't predict that. However, as the lens power reduces as it does in those with high myopia the impact of different positions is minimized, and at least in theory in ultra myopic individual requiring at power of 0.0 D IOLs the impact of lens position becomes zero. For that reason there is a case to be made for lens power prediction to be more accurate in individuals with higher myopia.
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This theory is validated in this study as those with AL > 25 mm had 98.4% accuracy compared to those with AL < 22.5 at 84.5%.
sam36130 RonAKA
Posted
i have always read that lens power calculation can be less accurate for high myopes and patients that have lasik before. i also read that with monofocals, the surgeon's placement and skills are important for accurate lens power. is that why the formula usually has a constant that each individual surgeon needs to put in based on their habit of lens placement?
i am not sure i will see the iol calculation sheet from the surgeon i like to go with.... wouid i be offending him to ask for it? i dont want him to feel like i dont trust his judgement!
RonAKA sam36130
Edited
I have read and assumed the same about high myopes having the potential for more error. But, as I learn more about it, I am thinking that is not necessarily true. High but possibly not extreme myopes may have the potential for lower error in power prediction, because the power of the IOL is lower and the position in the eye becomes less critical. For example I believe they have predicted a power in the range of +8.0 for you. My brother's power was +15.0 D or nearly twice as strong. Any from memory my lenses are in the order of +18.0 D. They are going to be much more sensitive to lens position than your +8.0 D power.
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Yes, some IOL calculations allow for a surgeon factor, although I didn't see that in my brother's IOL data sheet. There is a field called SIA which is surgical induced astigmatism that is filled in with the surgeon's experience. In my brother's case it was left blank. Some surgeon's will modify the A-Constant with the personal experience. This value was not noted on my brother's sheet so I am not sure if he modified it or not.
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I think it is quite reasonable to ask for the IOL calculation sheet. Courts have determined that medical data belongs to the patient not the doctor, so legally they have to give it to you. However, it is worth considering that many doctors have big egos and you don't want to get their back up over it. I would suggest being more diplomatic and say that you would be more comfortable if you had a record of what the calculations are and what the options are for different outcomes, so there is no misunderstanding of what the target really is. I would focus on the range of lens powers and what the predicted outcome of each is. You really should be part of that discussion especially if you want to be eyeglasses free with mini-monovision.
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If you have any thoughts about having the measurements done again there is something else you could consider. Another of my more recent learning is that there are surgeons who believe proper preparation of the eye before surgery helps with getting an accurate eye measurement with the IOLMaster or Lenstar. They recommend using OTC dry eye drops 4 times a day for two weeks before taking the measurements. Most surgeons do not do this. But, if you were considering getting the measurements done again, it is probably a good idea to improve the accuracy of the measurement.
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You mentioned prior Lasik being an issue with the potential for accuracy issues, and it certainly is, but is unrelated to being myopic. I assume you have not had Lasik or PRK if your current refraction is in the -11.0 range? If you have had no prior refractive surgery, then it is nothing to be concerned about.
Guest RonAKA
Edited
BTW Barrett True-K is supposedly better for post LASIK eyes. The "true k" means it measures the topography of both the front of the cornea AND back / posterior of the cornea to make better predictions for post-LASIK eyes.
RonAKA Guest
Posted
I agree. My brother did not have prior refractive surgery, and I think there are better choices than the Barrett TK for those that are free of any laser surgery damage to the cornea.
Guest RonAKA
Posted
Also FYI… there is Barrett TK and Barrett TK True K… 2 different formulas.
RonAKA Guest
Posted
What is the difference between them?
Guest RonAKA
Posted
I heard it discussed in a webinar years ago and don't really recall except that the "true k" version is the one that takes both sides of the cornea into account.
RonAKA Guest
Edited
About all I know about it is that I believe the IOLMaster 700 is the only instrument that actually measures both sides of the cornea and only a very limited number of IOL Formulas uses the data. Most ignore the extra data. Not sure what they call the formula that accepts the extra data. I find the terminology they use very confusing. Total Keratonomy, True Keratonomy, Total True Keratonomy.... I have never been interested enough to get to the bottom of it.
Guest RonAKA
Edited
If you Google this there's a video discussing it briefly. "Refractive outcomes in post-myopic LVC eyes – Barrett True K formula with Total Keratometry (TK)". For sure the naming is confusing!
RonAKA Guest
Edited
Perhaps TK refers to the instrument and True K refers to the formula that uses it.
Guest RonAKA
Edited
Yah in the video Barrett says "it's True K TK… so True K with TK, posterior cornea". So I take that to mean that TK refers to measuring the posterior cornea (for better accuracy with post LASIK eyes) and maybe True K is related to the formula used. In other words, True K (the formula) with TK (total keratotomy i.e. measuring both the anterior and posterior cornea)
sam36130 RonAKA
Posted
That's good to know placement of a 8.0D lens is more forgiving in terms of visual acuity later!
yes i haven't had any refraction procedure, only contact lens and glasses.
i have been using Restasis fir dry eyes, it is making my eyes feel wet most time so i havent been using OTC eye drops very much. I hope i will get good measurement on Tuesday Jan 2nd!
RonAKA sam36130
Edited
The +8.0 D lens will not be more forgiving in terms of visual acuity later. It is more forgiving to the lens position that the surgeon actually implants it to at the time of surgery. This is what makes it easier to predict the outcome accuracy.
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After implant it will be subject to the normal defocus curve of a the lens as the distance changes from your eye to the object you are looking at, and based on the target for the peak acuity of the lens.
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This assumes the lens stays put where it was implanted. But, if it did move the lower power would reduce the impact of it moving. Lens movement after the recovery period is not common though. They tend to stay put.