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CEDARS\/ASPENS Debates<\/h3>\n View all
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Welcome to another edition of CEDARS\/ASPENS Debates. CEDARS\/ASPENS is a society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.<\/p>\n
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Kenneth A. Beckman<\/strong><\/p>\n<\/div>\nThis month, we are going to tackle the delicate and somewhat controversial issue of toric IOL planning, with a special focus on incision management. When dealing with astigmatism, nothing is ever easy and straightforward, and this explains the variety of approaches with regard to incision size and location, IOL selection, calculation methods, formulas and tools.<\/p>\n
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Two experienced specialists, Gary W\u00f6rtz, MD,<\/b> and Lisa K. Feulner, MD, PhD,<\/b> discuss the different options, practice variations and technical nuances of this surgery as well as the criteria that guide their preferences and choices.<\/p>\nKenneth A. Beckman, MD, FACS<\/h2>\n
OSN CEDARS\/ASPENS Debates Editor<\/p>\n
Incision size and location<\/h2>\n Surgically induced astigmatism (SIA) has been commonly overestimated in its impact by some of our colleagues, stemming back to the early days of extracapsular cataract extraction surgery. At the time, we performed large incisions, which led to 3 D or 4 D of astigmatism. As we moved to phacoemulsification, our incisions decreased from 7 mm or even 9 mm to 3 mm, 2.75 mm and then 2.4 mm, with a significant positive impact on SIA. In my hands, and I believe in the hands of most surgeons who are operating temporally on the horizontal axis, the amount of SIA is now negligible, likely between 0 D and 0.25 D.<\/p>\n
The incision size and location as well as the formulas we use to account for posterior corneal astigmatism all have an impact on the amount of SIA.<\/p>\n
I always place my incisions on the temporal horizontal axis, exactly at 180\u00b0. Many calculators do not take into account the posterior corneal astigmatism, which is typically against the rule. Some of this underestimated against-the-rule astigmatism can be neutralized by operating on the horizontal axis. Surgeons who place the incision superiorly, on the preoperative steep axis at 90\u00b0, are operating closer to the center of the cornea because the cornea is wider horizontally and narrower vertically. As a consequence, they amplify the against-the-rule astigmatism that is being underestimated and at the same time induce greater corneal astigmatic change because the incision is closer to the center. Some surgeons may operate at 20\u00b0, to be more comfortable, or at 200\u00b0, depending on the eye. However, my results are better when I operate exactly at 180\u00b0.<\/p>\n
I use the Lensar Ally femtosecond laser system. I mark the lens chops so they are exactly at 0\u00b0 and 90\u00b0, using the system\u2019s iris registration to make sure they are aligned with those axes. That works as an internal mark for my incision, which will be exactly on the horizontal meridian. Other surgeons have recommended operating around the clock of the eye, depending on where the steep axis is, but I have no experience with that method. However, I feel that operating on the steep axis makes a lot of sense in terms of maximizing the impact on astigmatism. Corneal astigmatism is not randomly assigned. Corneal biomechanics dictate the location of the steep axis, and by placing either arcuate incisions or your phaco incision on the steep axis, you have the greatest potential impact for reducing astigmatism because corneal hysteresis is different across that meridian.<\/p>\n
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Gary W\u00f6rtz<\/strong><\/p>\n<\/div>\nI use the Barrett toric calculator. I believe, and I think a lot of my colleagues would agree, that this is among the best toric calculators because it can also account for posterior corneal astigmatism. I also use the Zeiss IOLMaster 700 and the AI IOL calculator integrated in the Veracity Surgery Planner (Zeiss). With those tools together, I get an accurate picture of the corneal astigmatism and a consistent outcome in terms of my refractive results.<\/p>\n
Some of my colleagues use the Ocular Response Analyzer (ORA, Reichert Technologies) to make the final adjustments to their toric IOL power and location intraoperatively. For those surgeons who have learned how and when to trust it, ORA can be a fantastic tool, but I rely on my preoperative measurements. What has prevented me from using the ORA is that external factors, such as how much pressure has been inflated or warpage has been caused by the speculum, can lead to false results. It is a fantastic technology, but it is user dependent and requires a lot of experience to be used with confidence.<\/p>\n
The Light Adjustable Lens (LAL, RxSight) is the final step to eliminate variability in surgical planning. With other lenses, we try to forecast what will happen after the incisions are made and after the tissue knits itself back together. We are placing a bet on the final shape of the cornea, and we are not always right. The great advantage of the LAL is that, if our predictions happen to be wrong, we have the opportunity to adjust the power of the lens, both in sphere and cylinder, to make up for any errors in our calculations. I find it to be particularly useful in post-refractive surgery eyes but also in patients who want to maintain high-contrast vision and are interested in blended vision. It does require work from the surgeon and out-of-pocket payment from the patient, but there is no better lens on the market for precision of outcome. With other lenses, it is like trying to make a hole in one. If you are a golfer, this one is par 4 \u2014 you get your initial guess and three additional tries.<\/p>\n
For more information:<\/h2>\n Gary W\u00f6rtz, MD,<\/b> of Commonwealth Eye Surgery, Lexington, Kentucky, can be reached at 2020md@gmail.com.<\/p>\n <\/h2>\n <\/h2>\nIncision creation<\/h2>\n
Many years ago, I calculated surgically induced astigmatism using the Hill formula. At that time, our incisions were manual, much larger and placed more anteriorly. Today, as a standard, I use a femtosecond laser to create my incisions whenever I implant a toric lens. The laser controls the position, size and architecture of the incisions, which tend to be more posterior and as small as 2.4 mm or less, with significantly less impact on final astigmatic outcomes.<\/p>\n
When operating on a right eye, I position my incision temporally at 180\u00b0. In a left eye, because I am right-handed, it is more challenging, so I place the incision where I am comfortable, typically between 15\u00b0 and 25\u00b0. This does not affect my outcomes at all. Surgeon comfort and ergonomics are prerequisites for successful surgery. With the femtosecond laser, the impact on astigmatism is negligible, so I do not feel the need to alter my incision location. I pre-mark my toric patients at 180\u00b0 and 90\u00b0 in the upright sitting position before laser treatment because I don\u2019t have access to iris registration. The laser then marks these axes on the cornea. I subsequently recheck alignment in the operating room with an intraoperative toric marker to make sure that the femtosecond incisions align with my original reference. Access to a Callisto (Zeiss) or intraoperative aberrometry (ORA, Alcon) allows for additional improvements in accuracy of toric placement.<\/p>\n
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Lisa K. Feulner<\/strong><\/p>\n<\/div>\nI use the Veracity Surgery Planner (Zeiss), which provides me with a wide variety of formulas and allows easy comparison between them. Primarily, I use the Barrett toric calculator, but I do compare it with other formulas, and they generally show good agreement. Veracity gives me the opportunity to calculate astigmatism correction quickly, including in patients who have had prior refractive surgery. It allows me to see what happens if I model different lens powers, if I use different lenses or if I move my incision. It gives me flexibility to customize my toric calculations and figure out which power, which lens, how much toricity and optimal positioning.<\/p>\n
I use multiple devices for astigmatism measurement and account for posterior corneal astigmatism, which is critical in toric planning. I use the IOLMaster (Zeiss), the Lenstar 900 (Haag-Streit) and the iTrace (Tracey Technologies) with wavefront keratometry. I use the OPD-Scan III (Nidek) to evaluate topography and Placido rings, and Veracity allows me to integrate this data into a single platform.<\/p>\n
Before any measurements, I make sure that the ocular surface is in pristine condition before surgery because surface integrity is essential for accurate corneal astigmatism assessment.<\/p>\n
With the ability to correct lower degrees of astigmatism (as low as 0.75 D at the corneal plane; Bausch + Lomb enVista toric ETE), I now rarely use limbal relaxing incisions. I use toric lenses whenever I can. In patients who have less than 1.75 D of cylinder and have had previous refractive surgery with irregular astigmatism, I use the Apthera small aperture lens (Bausch + Lomb). It gives patients excellent quality of vision while mitigating the astigmatism that may not be correctable with a toric lens or limbal relaxing incisions. Apthera provides extended depth of focus and at the same time reduces the impact of higher-order aberrations and irregular astigmatism from prior refractive surgery. It is suitable for patients with irregular astigmatism if their central cornea is clear and in patients with peripheral scarring, peripheral anterior basement membrane dystrophy or other conditions that may limit accurate astigmatism correction. In patients with keratoconus or pellucid marginal degeneration who have good central clarity and central regular astigmatism, I again use the Apthera lens to minimize refractive error and reduce dependence on postoperative scleral or toric lenses.<\/p>\n
For more information:<\/h2>\n Lisa K. Feulner, MD, PhD,<\/b> of Advanced Eye Care & Aesthetics, Bel Air, Maryland, can be reached at lisafeulner@yahoo.com.<\/p>\n
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