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The value of intraoperative imagining remains unclear
HIGH-TECH cataract surgery
Clinical value of current intraoperative digital technologies for toric IOLs remains unclear. Roibeard Ó hÉineacháin reports
Many new digital imaging technologies designed for intraoperative use in cataract and corneal surgery have become available in recent years, although the increased precision they provide does not always provide the same increase in outcomes, reported Rudy Nuijts MD, PhD, Maastricht University Medical Center (MUMC), Maastricht, The Netherlands.
Two areas where image-guided surgery has made inroads in recent years are digital marking for toric intraocular lens (IOL) rotation and intraoperative aberrometry to increase the accuracy of IOL surgery, said Prof Nuijts at a clinical symposium during 24th ESCRS Winter Meeting in Marrakech.
Dr Nuijts noted that accurate marking of the astigmatic axis is essential to the functionality of a toric IOL. Misalignment by 10 degrees results in 33% reduction in astigmatic correction. The incidence of misalignment greater than 10 degrees in the MUMC cohort is 4%.
Digital marking has the advantages of automatically accounting for cyclorotation and eliminating the need for manual toric eye markings, he said. The first digital marking device to be introduced was the Verion (Alcon). The device is connected to the surgical microscope and provides real-time registration and tracking overlay during surgery. It also receives phaco status information from the phaco machine.
Research suggests that digital marking systems for toric IOLs results in significantly less misalignment of the lens compared to manual marking, although its clinical value remains questionable.
He cited a prospective randomised clinical trial that he and his associates conducted involving 24 patients undergoing toric IOL implantation who were assigned to image-guided or manual marking. That study showed that one hour postoperatively there was significantly less misalignment in the digital marking group compared to manual marking technique (1.2 degrees vs 2.8 degrees, p=.02).
However, there was no statistically significant difference between the two groups
in terms of residual refractive astigmatism, which was less than 0.5D in 82% of the digital group and in 72% of the manual group(p>.05) (Webers, ESCRS 2017, Lisbon) (See also: Webers VSC, Bauer NJC, Visser N, Berendschot TTJM, van den Biggelaar FJHM, Nuijts RMMA. Image-guided system versus manual marking for toric intraocular lens alignment in cataract surgery. JCRS. 2017;43(6):781-788. doi:10.1016/j. jcrs.2017.03.041).
“The improved accuracy does not translate to significantly better uncorrected distance visual acuity,” Prof Nuijts said
Another study indicated that the Callisto digital iris-marking system can also improve the predictability of toric IOL postoperative orientation. However, it indicated that some of the predictability could be lost through IOL rotation during the first postoperative hour.
The study involved 50 patients. Immediately after surgery the deviation from the aimed IOL axis was 0.52 degrees. However, between the immediate postoperative period and one hour postoperatively, the IOLs rotated by a mean of 5.11 degrees with a range of 0.28 degrees to 18.77 degrees (Varsits et al, JCRS 2019;45:1234-1238).
Another imaging approach used in cataract surgery is intraoperative wavefront aberrometry. The technology provides the surgeon with real-time data, enabling the intraoperative refinement of surgical planning. For example, it allows the surgeon to measure aphakic refraction, so that the spherical and cylindrical power of the lens and orientation of the cylinder axis may be adjusted to more accurately match the refraction of the cornea.
At present the only intraoperative wavefront aberrometry system available is the Optiwave® Refractive Analysis (ORA). The aberrometer is mounted to a surgical microscope cart with touch screen monitor and CPU Secure web-based system. It stores patient clinical data and provides data analysis.
Research suggests that intraoperative aberrometry improves accuracy of spherical power estimation in post-refractive surgery patients compared to older IOL calculation formulas, but performs roughly equally with more modern IOL calculation formulas in astigmatic eyes.
In a retrospective consecutive cases series of 215 patients who had previously undergone LASIK, postoperative refraction was less than 0.5D off target in 67% with the ORA, compared to 46-50% with conventional preoperative methods such as the Haigis formula (Lanchulev et al, Ophthalmol 2014;121:56).
Prof Nuijts reported another study from his centre involving 151 patients, where spherical equivalent refraction was less than 0.5D off target in 89% with the ORA system compared to 74% with SRK-T formula (Webers, JCRS 2017, 43:781-788).
Regarding toric IOLs, in a study involving 50 eyes of 38 patients, the overall prediction error and residual astigmatism did not differ significantly between the ORA aberrometry and the Alcon Barrett Toric calculation, which was 0.49 D with both.
However, among a subgroup of eyes where the ORA suggested different power calculations or astigmatic axis for the toric IOL, the prediction error for the implanted IOL was significantly less with the ORA than with the Barret toric IOL calculator (0.44D vs 0.73D).
“When considering new technology, it is important to keep in mind that results can be quite variable. Different studies have yielded different results with the same devices,” Prof Nuijts cautioned.
