Optimising Results of Toric IOL Surgery

Both a scleral image-guided limbal-based registration system (Callisto) and a femtosecond laser-enabled capsular marking system using iris registration (Intelliaxis) are safe and effective tools for assisting precise alignment of toric IOLs, a recent prospective randomised study concludes.

“We conducted this study after noticing the target meridian identified by the two systems sometimes differed when both were used in the same case,” said Sheetal Brar MD. “We believe ours is the first study to directly compare the accuracy and clinical outcomes achieved using these two approaches.”

There were no acquisition failures with either system nor were there any cases requiring repeat capture or postoperative repositioning of the toric IOL due to significant misalignment. However, analyses of data collected after one week and three months showed residual postoperative astigmatism was slightly but significantly higher when the limbal registration system guided alignment compared with the iris-based system.

“Our findings suggest the iris registration tool may have a potential advantage for more precise characterisation of the target meridian. As another advantage, it results in permanent capsular marks that facilitate postoperative determination of toric IOL position,” said Sri Ganesh MD.

“However, there are some practical advantages associated with the limbal registration system: it is a non-contact, less expensive approach that can be used independently of femtosecond laser-assisted cataract surgery. In addition, the limbal registration system can be used in small pupils and does not reduce the strength of the capsulorhexis, which is important in situations where capsular hooks are needed to stretch the capsule.”

The study enrolled eyes with regular corneal topography and astigmatism ranging from 0.75 D to 4.00 D. Sixty eyes were randomised 1:1 to have toric IOL alignment guided intraoperatively by the limbal registration system or the iris registration system.

The two groups were well matched preoperatively in their biometric characteristics. All eyes underwent femtosecond laser-assisted cataract surgery using the same laser (Lensar) performed by a single surgeon (Dr Ganesh) with implantation of a monofocal toric IOL under BSS. A plano target was used for all cases, and all IOL power calculations were done using the same formula (Barrett TK toric). Follow-up visits were conducted at one day, one week, and three months and included a check of toric IOL alignment using the tool found on a raytracing system (iTrace).

At postoperative day one and month three, mean cylinder was -0.07 D and -0.04 D, respectively, in the iris registration group and -0.20 D and -0.18 D, respectively, in the limbal registration group (P ≤0.05 for both comparisons). There was also a statistically significant difference favouring the iris registration group in the analysis of mean logMAR uncorrected distance visual acuity at both day one (0.03 vs 0.08) and month three (0.00 vs 0.08; P ≤0.04 for both comparisons). There were no statistically significant differences between groups in mean sphere, spherical equivalent, corrected distance visual acuity, or deviation from intended axis at either follow-up.

Dr Brar presented the study at ASCRS 2024 in Boston, US.

Sheetal Brar MD is a senior consultant in the Cataract and Refractive Department of the Brar Eye Hospital, Bathinda, Punjab, India. brar_sheetal@yahoo.co.in

Sri Ganesh MD is chairman and managing director at Nethradhama Superspecialty Eye Hospital, Bangalore, India. phacomaverick@gmail.com