Consider all available technology when using a toric calculator
February 16, 2021
8 min read
Source/Disclosures
Published by:
Disclosures:
Jackson reports he is a consultant with Lensar, Alcon, Oculus and i-Optics. Stephenson reports she is a key opinion leader for Cassini, Zeiss, Lensar, Bausch + Lomb and Alcon.
Welcome to another edition of CEDARS/ASPENS Debates. CEDARS/ASPENS is a joint society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.
Surgeons’ ability to manage astigmatism at the time of cataract surgery continues to advance. With the latest technology available, astigmatism may be calculated both preoperatively and intraoperatively. Then, with the development of sophisticated formulas and calculators, even greater precision may be attained. Yet, with all of this information, it may also lead to confusion. This month, I am presenting a case requiring astigmatism management at the time of cataract surgery, but the information does not agree and may lead to more confusion.
In this case, a patient desires a PanOptix trifocal IOL (Alcon). Preoperatively, corneal measurements were obtained using the IOLMaster (Zeiss), the Pentacam (Oculus) and a manual keratometer. All three devices identified 1.5 D of with-the-rule astigmatism. This would be too much to leave untreated at the time of surgery with a multifocal IOL, so a decision needs to be made. In this case, both the Pentacam and IOLMaster measure total corneal astigmatism, identifying the contribution of the posterior surface. They both measured about 1.2 D of total astigmatism, meaning the posterior surface only contributed about 0.3 D against-the-rule. Because 0.3 D was used as the surgically induced astigmatism, operating on the steep axis superiorly would estimate leaving 0.9 D to be corrected during surgery.
Source: Kenneth A. Beckman, MD, FACS
The data were entered into the Alcon toric calculator to help select the proper IOL. One unique feature of this calculator is that it incorporates a nomogram to estimate the effect of the posterior surface to calculate the total astigmatism. Unfortunately, this nomogram estimates significantly more posterior astigmatism than what was actually measured by the Pentacam or IOLMaster. If operating on the steep superior axis, the IOL calculator recommends not using a toric lens, but calculates only 0.5 D of residual astigmatism, rather than 0.9 D, which was calculated by using the measured astigmatism. This leads to the dilemma of which measurement to trust. Relying on the nomogram estimate may lead to significant uncorrected astigmatism and an unhappy patient. Ignoring the nomogram and relying on the actual measurements may lead to the flipping of the cylinder axis to against-the-rule and may also lead to an unhappy patient.
Mitchell A. Jackson, MD, and P. Dee G. Stephenson, MD, FACS, will discuss their approaches to this situation in which the data are inconsistent. We hope you enjoy the discussion.
Kenneth A. Beckman, MD, FACS
OSN CEDARS/ASPENS Debates Editor
Use all available technology
This is an interesting case. This is a PanOptix (Alcon) toric case in a patient who has 1.5 D of corneal astigmatism at 90°. The controversy at hand is with the PanOptix toric IOL calculator.
Based on what you put in as your surgically induced astigmatism or your incision location, the calculator only accounts for anterior astigmatism and only uses a theoretical posterior astigmatism based on the Baylor nomogram, not the actual posterior astigmatism measured for that specific patient. You want to always leave your patient slightly with-the-rule and not against-the-rule if any residual astigmatism is to occur.
The problem in this case is if the surgeon went with the online toric calculator, the patient would have been left with theoretically too much with-the-rule astigmatism, or it might have flipped the axis so it was against-the-rule. The calculator was relying on the Baylor nomogram theory vs. the actual measurement for the patient.
What I do in this case is I use the PanOptix toric calculator to acquire a reading. Then I look at my IOLMaster 700 (Zeiss) with the total keratometry upgrade, and I use my Pentacam HR (Oculus) and the Cassini (i-Optics) to acquire anterior and total keratometry readings. If all three of these total keratometry readings are slightly different from the theoretic calculation online, then I will fudge going up or down one level of toric IOL correction to make sure the patient is left slightly with-the-rule as a result.
I am lucky that I have these three devices to give me the actual readings of the patient. I will compare the readings with the online calculator, and if everything matches, I will go with it. If they do not match, I will fudge it up or down to leave the patient slightly with-the-rule.
Then I use my Lensar, and I streamline from one of those devices to account and adjust for cyclorotation error. I get the PanOptix toric IOL aligned properly to avoid cyclorotation error. I use all of my devices to get as close as possible to the real reading for the patient, compare it with the theoretic reading with the online calculator, and then I use my femtosecond from one of these devices to streamline and adjust for cyclorotation error to put in the right axis. Then, when I use ORA (Alcon) intraoperatively, I confirm aphakic power only for these patients but not for the pseudophakic axis.
I use a great deal of technology, and with my technique, it is why I probably have less than a 1% enhancement rate for these advanced lenses currently.
If you do not have all the devices, you can simply use what you have to look at the one device and its real reading compared with the theoretic readings. It will help you fudge it one way or the other to keep astigmatism neutral in the end or slightly with-the-rule at a minimum.
- For more information:
- Mitchell A. Jackson, MD, can be reached at Jacksoneye, 300 N. Milwaukee Ave., Suite L, Lake Villa, IL 60046; email: mjlaserdoc@msn.com.
Not all IOL calculators are created equal
When evaluating a patient for cataract surgery today, it is important that the ocular surface is addressed. This is an important factor in all preop measurements, and if not corrected before surgery, it may cause you to miss your targeted refractive outcome, resulting in an unhappy patient. Preop testing may have to be repeated several times to get reliable, repeatable testing. I place all my surgical patients on a dry eye regimen inclusive of lid hygiene and preservative-free tears, and if it is severe, I may postpone their surgery for several months until they have significant improvement.
When I work up a patient for cataract surgery, it is important to also identify any comorbidities such as corneal dystrophy, macular pathology and glaucoma, as well as systemic diseases such as diabetes and thyroid disease. The diagnostic workup for my cataract surgery patients consists of Cassini topography (for magnitude and axis of astigmatism), iTrace (Tracey Technologies) (which helps show the patient the components as to why their vision has decreased and how the cornea and the lens contribute to this), IOLMaster 700 (Zeiss) (for axis and total astigmatism) and macular OCT (to rule out macular pathology). After looking at all the preop measurements and reviewing the patient’s needs and wants, my suggestions are discussed. Then, the surgical counselor will help the patient choose the type of lens that best fits their lifestyle.
When choosing the IOL that the patient requires, I will use the appropriate toric calculator that each company provides. Some calculators use the Barrett formula, others do not, and some only use the anterior cornea, not the posterior cornea, so not all calculators are created the same. Make sure you know which ones include which things, or you again may find that your outcomes may be off.
I always use the total corneal from Cassini that is Bluetoothed over to my Lensar at the surgery center. I look at all the numbers and see what matches and what does not match. I also look at the quality of the tests performed. Your keratotomy readings on the IOLMaster and the toric calculator and topography all should be within 5° of the axis and within 0.5 D or less of astigmatism. Again, if these vary or do not match, make sure that the quality of these measurements was good and that dry eye is not the culprit.
I am fortunate in my practice that I have the same technician who does all of my preoperative testing. What she does is built into my equation, and that is what I base my surgery on. It is not a variable, but more of a constant.
If you are way off, many times the IOL calculator tends to undercorrect and will say not to correct anything with-the-rule, and we all know that we treat less when it is with-the-rule, and we treat more when it is against-the-rule.
In this situation, if I did not feel comfortable, if I had all the information and did not have ORA (Alcon), I would probably tell the patient I am a little stumped because I have half of the diagnostics telling me one thing and the other half telling me another. I would have a game plan in place to tell the patient that I may have to do an enhancement to give them the best outcome.
In many offices, the premium package allows for an enhancement, either limbal relaxing incisions (LRI), PRK or LASIK. For me, I am a little different. I am a cataract refractive surgeon. I do not do touchups. I need to get it right the first time. So, my go-to tool is ORA, and I was the first commercial owner of an ORA in the U.S. 11 years ago. So, that has been my go-to. In this particular case, I want a confirmation from ORA.
If I have a case like this, I will ask a colleague for advice. This is a great learning case for us all.
We need to always account for our variables and remember that toric calculators are only a tool, like all things we use. I do not use them 100% of the time to make my decision. It is a moving target because every time something new is developed we have to think it through. We do not have vast experience with these calculators because they have all been refined many times.
My advice and my take-home message are that everything is not created equal. Make sure ocular surface disease is controlled in your patients. If you are uncomfortable with your preoperative testing and it does not match up, although in this patient it was fairly close, and your ringer is your toric calculator, you need to reassess and maybe not rely on the toric calculator. Maybe you need to rely on what you would think based on your observations and other testing.
If you are lucky enough that you have an ORA, you can always check it one more time, in the aphakic state, and then line up the toricity magnitude and axis using ORA guidance. If you were going to do a small LRI and you did not do it with your femto, you can do it with the ORA’s toric program that actually lines it up on the appropriate axis and shows how long the arc is.
There is nothing you can trust 100%. A good portion of what you do is based on your own experience and your outcomes.
If all things are created equal and you are just having trouble with a toric calculator, make sure the patient knows you had to scratch your head a few times. They will appreciate your honesty and they will respect you. I am in between with this case. Do you put a toric lens in, or do you do an AI? Or do you just put a monofocal lens in and find out how they like their vision? If you are honest and say I will do my best to make you happy, it just might take another trip to the operating room to do it.
- For more information:
- P. Dee G. Stephenson, MD, FACS, can be reached at Stephenson Eye Associates, 200 Palermo Place, Venice, FL 34285; email: eyedrdee@aol.com.