Approach aids toric IOL alignment, IOL centration, wound/astigmatic keratotomy placement
The drive to perfection in cataract surgery is enhanced by intraoperative real-time appreciation of the status of individual patients.
Reviewed by Zaina N. Al-Mohtaseb, MD
Patient expectations for cataract surgery are at an all-time high. As a result, to reach excellent refractive outcomes, great emphasis is placed on the preoperative steps taken in preparation for cataract surgery, such as keratometry, biometry, and IOL power calculations. With technologic advances, that list has lengthened to include intraoperative considerations.
Newer technologies that provide intraoperative imaging are continuously improving to aid surgeons with toric IOL alignment, IOL centration, and wound and astigmatic keratotomy placement to lessen errors as much as possible, according to Zaina Al-Mohtaseb, MD.
“Greater importance is being placed specifically on capsulorhexis and IOL centration, astigmatic keratotomy placement, and toric IOL alignment with the introduction of presbyopia-correcting IOLs that include both a multifocal and a toric component,” said Dr. AlMohtaseb, assistant professor of ophthalmology, Cullen Eye Institute, Baylor College of Medicine, Houston. “Their optimization is definitely important to get excellent refractive outcomes.”
The impact of alignment errors is great and demonstrates the need for precision, and the degree of alignment errors increases exponentially in the more complex commercially available lenses. If the alignment is off-axis by about 10°, the result is a 34% error, and when an IOL is off-axis by 30°, this results in an error of 100% with almost no effective astigmatic correction but a resultant change in the axis, she said.
Errors can occur in a few key areas when placing a toric IOL, i.e., in determining the initial reference axis when the eye is marked for example at the 3, 6, and 12 o’clock positions, when marking the axis intraoperatively, and then aligning the lens to that axis.
Dr. Al-Mohtaseb provided a brief overview for some of the newer instrumentation technologies (including the Zeiss Callisto, Alcon Verion, and TrueVision) that aid in aligning toric IOLs with the goal of lessening potential errors. ZEISS CALLISTO. A reference image is acquired during routine biometry with the IOLMaster 700. This reference image is then viewed intraoperatively to center the capsulorhexis and multifocal IOLs, place incisions, and align toric IOLs.
She cited a study (Mayer et al. J Cataract Refract Surg. 2017;43:1281–1286) in which the accuracy and outcomes were compared between the Callisto (n = 28 eyes) and manual markings (n = 28 eyes). The study showed less degrees of postoperative IOL misalignment were in favor of Callisto digital marking, i.e., 2.0° for digital marking compared with 3.40° for manual marking, a difference that reached significance (p = 0.026).
Another finding was that the time required to perform IOL alignment was significantly shorter with the digital approach compared with manually, i.e., 37.2 seconds versus 59.4 seconds, respectively; p< 0.001). Titiyal et al. (Clinical Ophthalmology. 2018;12:747-753) compared toric IOL alignment assisted by image-guided technology (Callisto) vs. manual marking methods and its impact on visual quality and reported a significant (p = 0.003) difference with lower refractive cylinder postoperatively, –0.89 D versus –0.64 D, respectively.
The study also found less deviation from the target axis with the Callisto both on postoperative days 1 and 30 (p = 0.005 for both comparisons).
Zaina N. Al-Mohtaseb, MD
This article was adapted from Dr. Al-Mohtaseb’s presentation during Cornea Subspecialty Day at the 2018 meeting of the American Academy of Ophthalmology. Dr. Al-Mohtaseb is a consultant to Alcon Laboratories, Bausch + Lomb, Carl Zeiss Meditec, and Johnson & Johnson.