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Different approaches available to determine axis of astigmatism for toric implants
Four experts share their preferred approaches to align toric IOLs.
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Correcting astigmatism at the time of cataract surgery provides patients with improved vision; toric IOLs are an excellent option for patients with greater than 1 D of symmetric astigmatism. However, the implant must be properly aligned to provide the desired outcome. As cataract surgeons, we measure our patients in a myriad of ways — manual keratometry, optical biometry, intraoperative aberrometry, wavefront topography — but which measurement do we use as our final pick to align the toric implant? Below are comments from multiple surgeons describing their preferred approaches.
Cynthia A. Matossian, MD, FACS: I pretreat the ocular surface with a customized plan depending on the severity of the ocular surface disease I note at the time of the cataract consultation. When the patient returns for pre-surgical measurements approximately 2 weeks later (or longer depending on ocular surface disease severity), we start with manual keratometry readings with a keratometer that is calibrated weekly. These manual readings are only performed by our most senior technicians. We then use our OPD III topographer/wavefront aberrometer (Nidek). Next, our technicians proceed with the IOLMaster (Carl Zeiss Meditec) and finish with the Cassini topography measurements (i-Optics) with the three-color LED light technology for posterior corneal measurements and precise axis determination.
I look for consistency among all of these pieces of equipment. The magnitude between the flat and steep corneal measurements between the various diagnostic tools should not be greater than 0.5 D. Because each piece of equipment measures keratometry readings at a different diameter, the readings will not be identical. The key is to look for consistency of less than 0.5 D difference in the keratometry delta. I also look for the axis of the keratometry readings to demonstrate a less than 10° discrepancy between the various diagnostic machines. Then, I plug these data into various IOL formulas such as the Barrett Universal II, Hill-RBF and/or Holladay II. Based on recommendations by Warren Hill, MD, I currently use a surgically induced astigmatism of 0.12 for all of my patients. We are fortunate to have good optical biometry technology, accurate keratometry and incredibly good IOL formulas. The key is knowing which ones to trust and which to throw out. Validation criteria are now available on Dr. Hill’s website for both the IOLMaster and Lenstar (Haag-Streit) technology. “The data that fit, we keep; the data that do not fit, we need to toss out. We need to look at our data with a critical eye instead of at face value,” Dr. Hill said.
I use the ORA (Alcon) for patients who have had previous refractive surgery such as LASIK, are high myopes or high hyperopes, or have selected a toric IOL. Because being off axis by 1° decreases the cylinder effect by 3.3%, I use the ORA to determine the best orientation for my toric IOLs whether monofocal toric, extended depth of focus toric, multifocal toric or accommodating toric.
Alice T. Epitropoulos, MD, FACS: Toric IOLs provide the potential for optimal uncorrected quality visual acuity in cataract patients with regular astigmatism. Once the ocular surface is optimized, I bring the patient back for final biometry, which allows for more consistent and reliable measurements. I measure my patients with both the IOLMaster (Carl Zeiss Meditec) and topography and compare the keratometry readings. If there is a discrepancy, I look at manual keratometry and often use the ORA intraoperative aberrometer (Alcon) for a tiebreaker. Intraoperative aberrometry provides real-time refractive information including spherical and cylindrical power along with the axis placement of my toric IOLs. It also takes into account the contribution of both anterior and posterior astigmatism. In addition, I often use the Callisto surgical guidance system (Carl Zeiss Meditec), which allows me to accurately and reliably align the toric lens on the steep axis. One of the advantages with the Callisto eye and Z Align function is marking the patient preoperatively is no longer required. This device collects data from the IOLMaster and matches images of the limbus, scleral and conjunctival vessels intraoperatively, providing a “fingerprint” of the eye.
Sheri Rowen, MD, FACS: My current client base is predominantly post-refractive, and in many cases you have to add dry eye syndrome to the mix. Thus, I never rely on a single measurement. I have access to the iTrace wavefront aberrometer (Tracey Technologies) and the Cassini total corneal astigmatism (i-Optics) and generally have compared up to five devices, including the Pentacam (Oculus), Galilei (Ziemer), Orbscan (Bausch + Lomb) and Atlas (Carl Zeiss Meditec). If I get three to match, I am thrilled. Without a doubt, treating the ocular surface first will enhance consistency in our measurements, so I do take the time to normalize the surface as best I can. Obtaining the best guesstimate of the axis and magnitude is still an art.
Most of the time I am using the Cassini and trying to get it to match ORA (Alcon) in the OR. Having used the Stellaris vision enhancement system (Bausch + Lomb) with a 2-mm incision for many years, I have had no measurable surgically induced astigmatism. However, with the new femtosecond lasers it is difficult to know (but it appears the same). Therefore, I factor no more than 0.1 D into my surgically induced astigmatism and usually enter a zero. Operating temporally induces less astigmatism than operating superiorly due to the longer distance to the visual axis, and I have found that entering as close to the limbus as possible also helps conquer the challenge of astigmatism management.
I am currently hand-marking the 3, 6, 9 and 12 o’clock positions before I get to the laser, and I know this makes us less reliable for arcuate incisions when we do not have iris registration due to cyclotorsion. (Iris registration will eventually be the norm in all lasers, I would predict.) Operating and implanting 80% to 90% premium lenses in a largely post-refractive market has truly been a challenging dilemma, but with good preop measurements, treating the ocular surface, ORA and great new lens calculations, I feel I have been obtaining a much higher percentage of successful outcomes not requiring laser enhancement.
Kenneth A. Beckman, MD, FACS: I measure my patients using manual keratometry, IOLMaster (Carl Zeiss Meditec) and Pentacam (Oculus). I do not have the Cassini (i-Optics), so I also look at the Pentacam for posterior and total astigmatism. I pick which of the keratometry measurements I want to use, which is usually a hybrid of the measurements. I typically look for which ones match and discard the outliers.
Astute attention to astigmatism correction using the availability of a wide range of toric IOLs can provide outstanding outcomes for patients with symmetric astigmatism.
- For more information:
- Kenneth A. Beckman, MD, FACS, can be reached at Comprehensive Eye Care of Central Ohio, 450 Alkyre Run Drive, No. 100, Westerville, OH 43209; email: kenbeckman22@aol.com.
- Alice T. Epitropoulos, MD, FACS, can be reached at The Eye Center, 262 Neil Ave. #430, Columbus, OH 43215; email: eyesmd33@gmail.com.
- Cynthia A. Matossian, MD, FACS, is the founder of Matossian Eye Associates, with offices in Doylestown, PA, Hopewell, NJ, and Hamilton, NJ. She can be reached at email: cmatossian@matossianeye.com.
- Sheri Rowen, MD, FACS, can be reached at NVISION Eye Centers, 4220 Von Karman, #100, Newport Beach, CA 92660; email: srowen10@gmail.com.
Disclosures: Beckman reports no relevant financial disclosures. Epitropoulos reports she has a financial interest in Alcon and Carl Zeiss Meditec. Matossian reports she is a consultant or a speaker for Nidek, Alcon, Zeiss and i-Optics. Rowen reports financial disclosures with Ziemer, Johnson & Johnson, Alcon and Bausch + Lomb.