Effect of long-term rotation on astigmatism following EVO-toric intraocular collamer lens implantation

Objective To evaluate the effect of long-term rotation on astigmatism following Evolution-toric intraocular collamer lens (EVO-TICL) implantation. Methods Forty eyes of 22 patients were enrolled in this prospective study. Visual acuity, refractive parameters, and axial position of the EVO-TICL by OPD-Scan III aberrometer were measured preoperatively, 1 month and 3 years postoperatively. Results Last visit, the safety index was 1.32 ± 0.15 and the efficacy index was 1.01 ± 0.23. The best-fitting curve of the attempted versus achieved correction was y = 0.9751x + 0.001. The mean spherical equivalent (SE) decreased from −8.94 ± 2.72D preoperatively to 0.06 ± 0.24D and − 0.36 ± 0.46D 1 month and 3 years postoperatively, respectively. The mean target and surgical induced astigmatism were 1.55 ± 0.61D and 1.67 ± 0.94D 3 years postoperatively. The average expected axis of the TICL was-1.15 ± 9.07 (−21–19°). One month and 3 years postoperatively, the average actual axis was −0.70 ± 9.86 (−20–20°) and − 0.35 ± 11.72 (−25–30°), respectively. The absolute rotation of the TICL was 3.70 ± 4.42 (0–22°) and 6.00 ± 6.70 (0–32°) 1 month and 3 years postoperatively, respectively (p < 0.001). The expected astigmatism was −0.10 ± 0.12D, and the mean actual astigmatism was −0.21 ± 0.30D and − 0.44 ± 0.45D 1 month and 3 years postoperatively, respectively. The mean absolute rotation without postoperative astigmatism was 3.73 ± 2.69 (0–9°) and 1.67 ± 1.66 (0–5°) for low (<2D) and high (≥2D) astigmatic TICL, respectively (p < 0.05). Conclusion EVO-TICL implantation is safe and effective, with good predictability and stability. OPD-Scan is a fast device to detect the axial position of the TICL without mydriasis, and the axial position is relatively stable in the long term postoperatively. A slight rotation of low-astigmatic TICL may not cause postoperative astigmatism, whereas rotation of the high-astigmatic TICL may cause it.


Introduction
Myopia is a global health problem (1). Several studies have shown that the prevalence of astigmatism in the population can reach >30% and that people with myopia are more likely to suffer from astigmatism (2,3). Even 0.75 D uncorrected astigmatism can cause significantly decreased vision (4); therefore, precise correction of astigmatism has always been the focus of attention.
Evolution-toric intraocular collamer lens (EVO-TICL; STAAR Surgical, Monrovia, CA), a posterior chamber phakic intraocular lens, has been widely used in recent years because of its wide range of correction of myopia and astigmatism, independent of corneal conditions. The safety, effectiveness, stability, predictability, and significant improvement in postoperative visual quality have been reported previously (5,6). Accurate operative alignment of the TICL axis and its stable postoperative position are crucial for achieving ideal refractive outcomes (7). Once EVO-TICL rotates, it may cause new astigmatism and visual impairment. To our knowledge, few studies have reported the short-term efficacy and safety of EVO-TICL implantation for myopic astigmatism correction (8,9), and our study is the first to prospectively investigate the long-term efficacy, safety, and rotational stability, and the effect of rotation on astigmatism of EVO-TICL.
The exclusion criteria were as follows: (1) eye inflammation, obvious refractive interstitial opacity, previous eye surgery, glaucoma, cataract, and other eye diseases, (2) systemic connective tissue and autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and diabetes, (3) patients with mental or psychological abnormalities and unrealistic expectations.

TICL axis position measurement
OPD-Scan III (Nidek Co., Ltd., Gamagori, Japan) was used to measure patients with TICL implantation preoperatively, 1 month postoperatively, and 3 years postoperatively, and to record the axial position of the TICL in the eye within serveral seconds without mydriasis. Using the image obtained by OPD-Scan III, the axis position was adjusted to be parallel to the TICL axis position, and the angle between the adjusted axis position and the calibration axis was calculated to determine the TICL axis position ( Figure 1). Each measurement was performed thrice by experienced technicians, and the average of the three measurements was used in the analysis. Rotation was defined as the difference between the expected and actual axes at each follow-up.

Surgical methods
All surgeries were performed with standard practice by the same surgeon (XW). The implanted intraocular lens was EVO-TICL, the optical area was 4.9-5.8 mm, the spherical lens power range was −0.5 to −18.0 D, and the cylindrical lens power range was +0.5 to +6 D. Four sizes were available: 12.1, 12.6, 13.2 and 13.7 mm.
Anti-inflammatory eyedrops were administered 3 days preoperatively. The mydriasis was started 30 min before ICL implantation, surface anesthesia was given to the operative eye, the cloth was disinfected routinely, the eyelid opener was used to open the eyelid, and a 3.0 mm corneal incision was made at the temporal corneoscleral margin. The special injector implanted the ICL in the crystal chamber into the eye. After the ICL unfolded naturally, a special positioning hook was used to adjust the haptics to the back of Frontiers in Medicine 03 frontiersin.org the iris. Postoperatively, the patients were administered the steroid drug brigitte (1% prednisolone acetate, Elgin, Ireland) qid * 3 days; antibacterial drugs (levofloxacin, Towering, Japan) qid * 1 week; non-steroidal anti-inflammatory drugs (Prauprofen, Ginseng, Japan) qid * 2 weeks; and artificial tear, qid * 1 month.

Statistical analysis
SPSS 26.0 (SPSS Inc., IBM, United States) was used to analyze the data. The Kolmogorov-Smirnov test was used to test the normal distribution of data and repeated-measures analysis of variance was used to compare the data at various time points pre-and postoperatively. Also, a paired t-test was used to compare the parameters in the early and long postoperative period, and an independent sample t-test was used to compare low-and high-astigmatic TICL. Continuous variables were expressed as mean ± standard deviation. p < 0.05 was considered statistically significant.

Study population
Forty eyes of 22 patients with preoperative manifest spherical equivalent (SE) and cylinder of −8.94 ± 2.72 and − 1.60 ± 0.61 D were included. Their mean age was 24.82 ± 4.32 (18-33) years. The preoperative data for the two groups are listed in Table 1.

Safety
Three years postoperatively, CDVA was −0.13 ± 0.06 logMAR (range: −0.18-0.10 logMAR) and the safety index (postoperative CDVA/preoperative CDVA) was 1.32 ± 0.15. A significant increase was observed from the preoperative to the postoperative CDVA (p < 0.001). Figure 2C shows the changes in the CDVA Snellen line. No eye lost CDVA, 55.00% gained one line, 40.00% gained two or more lines, and 5.00% exhiubited no change compared to the baseline.

Predictability
A scatter plot with the best-fit line of the attempted versus the achieved SE correction is shown in Figure 2D. Three years postoperatively, the best mimic curve was y = 0.9751x + 0.001. Three years postoperatively, 78.00% of the eyes showed a manifest SE within ±0.50 D of the target; 95.00% were within ±1.00 D of the target ( Figure 2E).

Discussion
In this prospective study, we analyzed the visual and refractive outcomes after implantation of a EVO-TICL in 40 eyes of 22 patients.
We demonstrated that the EVO-TICL is predictable, safe, and effective for correcting low and high levels of astigmatism. Furthermore, EVO-TICL showed promising results in terms of postoperative rotational stability. Although several articles (12)(13)(14) have reported the efficacy and safety of toric ICL implantation for myopic astigmatism correction, our study is the first to prospectively investigate the longterm efficacy, safety, and rotational stability and the effect of rotation on astigmatism of the EVO-TICL.
The present study's safety and efficacy indices were 1.32 and 1.01, respectively, which indicates that TICL implantations offer excellent safety and efficacy in the long term postoperatively. Previous research FIGURE 3 The standard display of polar graphs for surgically induced astigmatism vector (A), target induced astigmatism vector (B), difference vector (C), and correction index (D).   (18) demonstrated that patients with higher myopia and longer AL were more likely to experience continuous axis elongation and progression of myopia. In some cases, the residual SE is up to −1.13 D and patients are unsatisfied with the UDVA, a laser touch-up may be effective and safe after ICL implantation.
The rotational stability of the toric ICL is a crucial factor for achieving high efficacy in the correction of astigmatism. In our study, the absolute degree of rotation at 1 month postoperatively was 3.70 ± 4.42°, which is comparable to that obtained in recent studies evaluating the EVO-TICL (3.75 ± 2.93° and 3.87 ± 3.07° at 3 and 6 months postoperatively, respectively) (8). However, the absolute degree of rotation 3 years postoperatively was 6.00 ± 6.70° in our study. Thus, rotation of the TICL may occur in the early postoperative period or in the long term, and a longer postoperative period correlates with a greater angular variability of TICL rotation.
In our study, we measured postoperative rotation by determining the angle between the adjusted and alignment axes using an image obtained from the OPD-Scan III. Compared with the traditional method of observing the TICL axial position with a slit lamp after mydriasis, measuring the TICL axial position with OPD-Scan III did not require mydriasis and could quickly locate the TICL axial position. The patient did not experience photophobia or discomfort of mydriasis (19).
In this study, clockwise rotation occurred in 35.0 and 42.5% and counterclockwise rotation occurred in 42.5 and 47.5% of eyes at 1 month and 3 years, respectively. Both clockwise and counterclockwise rotations were possible and random. Furthermore, if the TICL rotated 1 month postoperatively, it continued to rotate in the distant 3 years. At 3 years postoperatively, only four eyes did not rotate compared with the preoperative design axes, and 90% of eyes had TICL rotation. In summary, rotations after TICL implantation were within a small range, with individual cases rotating up to 32°. Low astigmatic TICL rotation within 10° did not generate residual astigmatism and UDVA loss. However, high astigmatic TICL rotation outside 5° might cause unwanted astigmatism and UDVA loss. Clearly, rotation in TICL with higher astigmatism had a greater influence on UDVA.
Three years postoperatively, three eyes had a rotation of >15°. Based on the patient's preoperative white-to-white, sulcus-to-sulcus, and ACD parameters, the slightly smaller ICL size might have caused the significant rotation. The postoperative astigmatism of three eyes was −1.00, −1.50, −2.00 D, respectively, and the patients' UDVA was 20/30-20/25. The patients experienced UDVA loss, but they thought this had no impact on their daily lives. After fully informed of the pros and cons of the realignment operation, the patients chosed to undergo close monitoring instead of a second operation.
This study had some limitations. First, due to the epidemic's impact, the 3-year loss to follow-up was high, resulting in an inadequate sample size; we can conduct future studies with a larger sample size over a longer follow-up period. Second, we did not measure the immediate postoperative TICL axis; therefore, perioperative TICL misalignment might have caused the postoperative axis deviation from the expected axis. The surgeon in this study was one of the most experienced surgeons worldwide, so we assumed that all TICLs were placed in the expected axial position.
In conclusion, EVO-TICL implantation is safe and effective, with good predictability and stability. OPD-Scan is a fast device to detect the axial position of the TICL without mydriasis, and the axial position is relatively stable in the long term postoperatively. A slight rotation of low-astigmatic TICL may not cause postoperative astigmatism, whereas rotation of the high-astigmatic TICL may cause it.

Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement
This study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethical Committee Review Board of Fudan

Author contributions
XC, HM, MC, I-CL, BL, YJ, YL, XW, and XZ involved in the conception or design of the work, the acquisition, analysis or interpretation of data for the work and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. XC and HM drafted the work or revising it critically for important intellectual content. XW and XZ final approval of the version to be published. All authors contributed to the article and approved the submitted version.