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Digital markerless system improves predictability for astigmatism correction
Patients had better refractive astigmatism results with the Callisto markerless system.
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A digital markerless method may be more accurate for toric IOL alignment than manual ink marking for astigmatism correction during cataract surgery, according to a presentation at the American Society of Cataract and Refractive Surgery annual meeting.
In a prospective non-randomized clinical trial, Daniel A. Black, MBBS, FRANZCO, FRACS, and colleagues compared the efficacy of aligning toric IOLs (Abbott Medical Optics) using corneal ink marks in 507 patients compared with using the Callisto markerless system (Carl Zeiss Meditec) in 161 patients in order to determine the proportion of patients with 0.5 D or less of refractive astigmatism after cataract surgery.
“It’s really about attention to detail,” Black said in a subsequent interview with Ocular Surgery News. “It’s the little things that are really important, and if you think about why people get really good results from toric IOLs, it’s about paying attention to all of the possible sources of error. And with toric IOLs, the critical thing is to get the lens correctly aligned inside the eye.”
Markerless system process
The “foundation” to getting quality measurements is to measure a patient’s keratometry using the IOLMaster (Carl Zeiss Meditec) as the first step at the initial office visit in order to prevent any disruption of the tear film throughout the visit, Black said.
After obtaining biometry with the Holladay IOL Consultant program, data are imported electronically using a USB, which helps to eliminate potential transcription errors, he said. A microscope then populates the biometrical data into the system, and registration is confirmed by matching the limbal blood vessel pattern. The Callisto system then gives an overlay in the microscope optics in order to perform the capsulorrhexis.
“It gives us sort of a capsulorrhexis template into the microscope optic, and that is really important because with any of these premium IOLs, centration and avoiding tilt is very important, and having a properly sized and centered capsulorrhexis are important in getting consistency with that aspect,” Black said.
Once the lens is placed, the digital overlay shows the correct axis to align the lens. A temporal bimanual phaco-chop is performed, with a 2.2-mm incision for IOL implantation. To conclude, a photograph is taken for final data entry.
Improved results
Mean postoperative refraction was 0.18 D in the ink marking group and 0.17 D in the markerless system group, with no significant difference in mean or standard deviation regarding residual astigmatic refractive error.
However, in the ink marking group, 94% of patients had no more than 0.5 D of refractive astigmatism and 98% had no more than 0.75 D of astigmatism. The Callisto markerless system improved predictability, in that 99.4% of patients had no more than 0.5 D of refractive astigmatism and 100% of patients had no more than 0.75 D of astigmatism.
“By acquiring an image of the limbal vessels at the time when the keratometry is captured and then registering that under the microscope and providing a digital overlay, we were able to improve our accuracy almost up to 99% within no more than 0.5 D of postop astigmatism,” Black said.
Additional benefits
Errors may occur while obtaining the correct alignment during keratometry, obtaining accurate measurements, transcribing calculations, marking the axis or aligning the IOL, but the markerless system assists in reducing these sources of error, Black said.
“As surgeons, for us to meet that challenge, also to realize that potential, we need to pay close attention to those little sources of error and do whatever we can to address those,” he said.
The markerless system saves time in the preoperative stage and in the operating room, and it reduces the potential for ocular surface complications caused from ink marking. In addition, Black considers the learning curve for surgeons to be short.
“It’s remarkably easy to use. So if you’re an experienced user of toric lenses using ink marks, your transition is very simple,” he said.
Black also said it is important for the markerless system to be integrated with medical technology to be successful.
“It’s sort of a standalone technology,” he said. “We see a lot of standalone technologies, and until they get integrated, they are not going to really take off. So I think that is the key to medical technology, to get that integration right.” – by Kristie L. Kahl
- For more information:
- Daniel A. Black, MBBS, FRANZCO, FRACS, can be reached at the Sunshine Eye Clinic, 2nd Floor, Suite 20, 5 Innovation Parkway, Birtinya, Queensland 4575, Australia; email: daniel.black@suneye.com.au.
Disclosure: Black reports he receives travel expenses from Abbott Medical Optics and Zeiss.