Comparison of femtosecond laser-assisted corneal relaxing incisions and toric implantable collamer lens for low-to-moderate astigmatism: A retrospective study

Abstract

To compare the clinical efficacy of femtosecond laser-assisted corneal relaxing incisions (FS-CRI) with that of toric implantable collamer lens (TICL) for low-to-moderate astigmatism. This Retrospective study included patients with regular astigmatism ranging from 0.75 D to 2.25 D who underwent FS-CRI combined with implantable collamer lens (ICL) implantation or TICL implantation alone at Beijing Aier-Intech Eye Hospital between March 2020 and December 2021. FS-CRI were made using the LenSX platform (Alcon Laboratories, Inc). Study parameters included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, refractive astigmatism, total wavefront aberration and retinal image quality parameters, and any surgery-related complications. Vector analysis of astigmatism was performed using the Alpins method. The FS-CRI and TICL group included 35 (56 eyes) and 36 (55 eyes) patients, respectively. There was no significant between-group in the proportion of UDVA reaching 20/20 at 3 months postoperatively (FS-CRI group: 98% and vs. TICL group: 100%). Both groups achieved comparable postoperative residual refractive astigmatism, and the mean correction index was 0.80 in FS-CRI group and 0.82 in TICL group. The total spherical aberration, coma, and high-order aberration were comparable between the two groups, but the postoperative total trefoil was significantly higher in the FS-CRI group (P = 0.022). There was also no significant between-group difference in retinal image quality parameters. FS-CRI combined with ICL implantation can achieve similar astigmatism correction efficacy and postoperative visual quality to TICL implantation.

Background

The implantable collamer lens (ICL V4c; STAAR Surgical, Monrovia, CA, USA) is a type of posterior chamber phakic intraocular lens for the treatment of ametropia that has the advantages of excellent accuracy, and long-term stability [1–4]. ICL implantationis gradually becoming one of the mainstream surgeries for the treatment of refractive errors [5, 6]. Postoperative residual astigmatism is an important factor affecting the success of refractive surgery. Residual astigmatism > 0.75 D can cause symptoms such as glare, visual fatigue, and reduced contrast sensitivity, which may seriously damage visual quality [7]. Therefore, methods for correcting accurately astigmatism is a research interest in refractive surgery.

Toric ICL (TICL) is a treatment modality for astigmatism that has the benefits of good predictability and stability [8, 9]. However, some studies have shown that TICL tends to produce higher vaults than ICL after implantation, which may more likely to lead to complications such as pupillary block and elevated intraocular pressure [10, 11]. In particular, only four fixed TICL sizes are available; therefore, the lenses may not match properly the ciliary sulcus-to-sulcus diameter of different patients. Consequently, due to the built-in cylinder, unlike ICL implantation, TICL can not adjust its position in the ciliary sulcus to improve vaults, it can only be replaced or removed through the second operation, which may cause more damage to the eyes.

Arcuate keratotomy is widely used for the treatment of low-to-moderate astigmatism in cataract surgery by making paired relaxing incisions on the steep meridian [12–14]. The application of femtosecond laser-assisted corneal relaxing incisions (FS-CRI) further improves the safety and accuracy of astigmatism correction [15–18]. Theoretically, for patients with ciliary sulcus-to-sulcus diameter not matching the TICL size, FS-CRI combined with ICL implantation can effectively solve this issue and provide a safer surgery. Moreover, the rotation after TICL implantation may affect the postoperative visual result, and the use of FS-CRI to correct astigmatism can avoid this occurrence. Thus, FS-CRI combined with ICL implantation may be an effective alternative for patients ineligible for TICL implantation.

In our clinical practice, we observed that FS-CRI with identical incision diameters and comparable nomogram parameters demonstrated reduced astigmatic correction efficacy compared to international reports [13]. This discrepancy likely stems from ethnic differences in corneal anatomy, particularly the significantly smaller mean corneal diameter in Asian populations (approximately 0.5 mm less than in White populations [19]). The reduced corneal diameter positions arcuate incisions closer to the limbus in Asian eyes, thereby attenuating the biomechanical response to incision creation and ultimately diminishing astigmatic correction effectiveness [20-22].Therefore, revising the nomogram with ethnic-specific adjustments is imperative to optimize astigmatic correction outcomes. To our knowledge, there is no study assessing the clinical efficacy of FS-CRI combined with ICL implantation in the treatment of low-to-moderate astigmatism. This study aimed to evaluate the efficacy of astigmatism correction, visual outcomes, and occurrence of postoperative complications in this new methods in comparison with those of TICL implantation alone.

Methods

Study design and patients

This retrospective study was approved by the institutional ethics committee of Beijing Aier-Intech Eye Hospital and was conducted according to the tenets of the Declaration of Helsinki. The need for informed consent was waived owing to the retrospective nature of the study.

Patients who underwent FS-CRI combined with ICL implantation and TICL implantation at Beijing Aier-Intech Eye Hospital between March 2021 and December 2022 were included in the study.

The inclusion criteria were as follows: (1) age ≥ 18 years; (2) stable refraction within 2 years; (3) regular low-to-moderate astigmatism ranging from 0.75 D to 2.25 D (Regular astigmatism is that refractive condition which is amenable to correction by cylinders. The axes of the principal meridians of the astigmatism are at right angles to each other.); [23] (4) endothelial cell density (ECD) ≥ 2000 cells/mm2; (5) anterior chamber depth (ACD) ≥ 2.8 mm. The exclusion criteria were corneal pathology (e.g., corneal opacity, leukoplakia, pterygium, abnormal topography, subclinical keratoconus and keratoconus), previous ocular surgery, severe dry eye, any systemic contraindications for surgery (e.g., autoimmune disorders) and nystagmus not indicated for femtosecond laser surgery.

Preoperative evaluation

All patients underwent a preoperative evaluation of uncorrected (UDVA) and corrected (CDVA) distance visual acuity, ultrasound biomicroscopy, slit-lamp biomicroscopy, ultrasound biomicroscopy, refraction, endothelial cell density, partial coherence interferometry (IOLMaster − 700, Carl Zeiss Meditec Inc., Dublin, CA, USA), Lenstar LS900 (Haag-Streit Inc., Köniz, Switzerland), and an autorefractor (ARK-510 A, Nidek Inc., San Jose, CA, USA). Scheimpflug pachymetry (Pentacam, Oculus Inc., Saint Louis, MO, USA) was used to examine the regularity of astigmatism. Total wavefront aberration and retinal image quality parameters were obtained at the 4.0-mm zone from OPD Scan III (Nidek Inc., San Jose, CA, USA). The power and size calculation of the ICL or TICL were performed using the STAAR surgical calculator (https://evo-ocos.staarag.ch/). The UDVA and CDVA were examined using standard logarithmic visual acuity charts and then converted to the logMAR scale for the statistical analysis.

Corneal relaxing incisions

The epithelium- and Bowman-penetrating CRIs were designed by the Donnenfeld nomogram using the online calculator (https://www.lricalculator.com/), which already built in adjustment for with-the-rule/against-the-rule astigmatism and age. This nomogram was originally designed for manual LRI; therefore, we modified the diameter and depth of the nomogram based on our previous clinical observations [22, 24].

The data including steep keratometry (K), flat K, and steep meridian, were entered into the online calculator and were determined by the surgeon according to the automated phoropter (RT-5100, Nidek Inc., San Jose, CA, USA) and Scheimpflug pachymetry. For surgically induced astigmatism (SIA) of the primary incision, 0.31 D was entered. The meridian incision location was 150 degrees.

Surgical technique

All surgical procedures were performed by an experienced surgeon. Before docking, the patient’s corneal limbus was marked at the 0 degrees and 180 degrees positions using sterile skin markers (Medplus, Inc., Hyderabad, India) while the patient sat upright. The horizontal marks of the LenSX femtosecond laser platform were manually aligned with the limbal marks. Then, paired symmetrical CRIs were placed at a diameter of 8.7 mm, with a depth of 90% of corneal pachymetry, plus energy of 3.2 µJ, side cut angle of 90 degrees, and spot and layer separation of 4.0 μm for both. All CRIs were epithelium- and Bowman-penetrating. After finishing the FS-CRI, patients were transferred to another room for ICL implantation. A 3.0-mm corneoscleral limbal primary incision at 150 degrees and a 1.2 mm auxiliary incision at 30 degrees were created with a disposable steel keratome, and the ICL was implanted into the ciliary sulcus using a traditional two-step procedure. The CRIs were bluntly opened at the end of the surgery. In the TICL group, all the patients did not perform FS-CRI, and the position of the TICL was adjusted according to the horizontal marks. Conventional anti-inflammatory agents and topical antibiotic were administered for 1 month postoperatively.

Postoperative follow-up measurements at 1 day, 1 week, 1 month, and 3 months included UDVA, CDVA, manifest refractions, OPD Scan III, and anterior segment OCT were uesd to measure the vault. Any surgery-related complications, such as postoperative infection, glaucoma, cataract, epithelial implantation, and excessive or insufficient vault, were documented. The vault was defined as normal when measuring 250–750 μm, low when < 250 μm, and high if > 750 μm [25]. Refractive astigmatism values were measured using an autorefractor.

Vector analysis of astigmatic correction

The Alpins vector analysis method analyzes the changes in astigmatism by converting them into horizontal (X) and vertical (Y) coordinates in a rectangular coordinate system [26, 27]. There are three basic vectors: target induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector (DV). TIA indicated the astigmatic correction aimed to achieve with the arcuate incisions (AIs). Meanwhile, SIA indicated the astigmatic correction truly achieved by the AIs. DV indicated the further astigmatism required to achieve the intended outcome. Other indicators were calculated from these three vectors. The correction index (CI) is the ratio of SIA to TIA, with an ideal value of 1.0. The index of success (IOS) is the ratio of DV to TIA. The flattening index (FI) is a measure of SIA on the astigmatic change at its intended axis. The angle of error (AE) is the difference in the angle between the axis of SIA and TIA. The magnitude of error (ME) is the arithmetic difference between SIA and TIA.

Statistical analysis

Sample size calculation formula was employed to determine the required sample size for the study. Statistical analyses were performed using SPSS software (version 22.0, IBM Corp.). Continuous variables were expressed as the mean ± standard deviation, while categorical variables were expressed as frequency and percentage. Shapiro Wilk and P-P plots were used to check the normality of the data distribution. Normally distributed preoperative and postoperative data were compared using a paired t-test, while non-normally distributed data were compared using a Wilcoxon signed-rank test. Between-group comparisons of age and of sex differences were performed using Student’s t-test and the chi-square test, respectively. Linear mixed models were used to compare ocular biometric parameters, refractive astigmatism, vector parameters, total wavefront aberration and retinal image quality parameters among groups while accounting for correlations between the records from the two eyes of the same patients (i.e. a random intercept) [9]. A P-value < 0.05 was considered statistically significant.

Results

According to the sample size formula , a margin of error (δ) of 0.07 was selected (not exceeding 0.10). Based on a pilot survey indicating an estimated proportion (P) of 15%, and setting the significance level at = 0.05 (corresponding to = 1.96), the required sample size was calculated to be approximately 100. To further minimize sampling error, the sample size was increased by 10%, resulting in a final study sample of 111 participants.

In total, 111 eyes of 71 patients were included in this study. Among them, 56 eyes of 35 patients were treated with FS-CRI combined with ICL implantation and 55 eyes of 36 patients were treated with TICL implantation. Overall, 3 patients in the FS-CRI group were not followed up at postoperative week 1 and month 1 postoperatively. Further, 4 patients in the TICL group were not followed up at week 1 postoperatively, and 1 patient was not followed up at week 1 and month 1 postoperatively. The demographics and ocular biometric parameters are compared between the two groups in Table 1.

Table 1.

Comparison of preoperative baseline characteristics between groups (n = 111 eyes)

Parameter	FS-CRI group	TICL group	Pvalue	Cohen’s d
Number of eyes	56	55	-	-
Female sex (%)	71.4	69.4	0.86	-
Right eye (%)	50	56.4	0.50	-
Age (y)	26.23 ± 5.21	26.44 ± 5.72	0.87	-
Anterior chamber depth (mm)	3.13 ± 0.23(3.07-3.19)	3.21 ± 0.26(3.14-3.28)	0.11	0.31
Endothelial cell density (cell/mm²)	2878 ± 221(2819-2937)	2829 ± 185(2779-2879)	0.21	0.24
White to white(mm)	11.64 ± 0.31(11.56-11.73)	11.54 ± 0.35(11.44-11.63)	0.09	0.32
Corneal astigmatism (D)	1.65 ± 0.41(1.54-1.76)	1.73 ± 0.52(1.59-1.87)	0.37	0.17
UDVA	1.48 ± 0.24(1.41-1.54)	1.44 ± 0.33(1.35-1.53)	0.53	0.12
CDVA	0.01 ± 0.03(0.003-0.020)	0.02 ± 0.05(0.006-0.034)	0.31	0.20

FS-CRI group = femtosecond laser-assisted corneal relaxing incisions with implantable collamer lens implantation; TICL group = toric implantable collamer lens implantation; UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity.Cohen’s d is the standardized mean difference between two independent groups, calculated as mean difference divided by the pooled SD   

Efficacy

The vision outcomes were similar between the two groups. The 3-month postoperative UDVA was − 0.09 ± 0.06 and − 0.11 ± 0.05 in the FS-CRI group and TICL group, respectively (P = 0.102). In the FS-CRI group, the UDVA was 20/25 or better in all eyes (100%) and 20/20 or better in 55/56 eyes (98%). In the TICL group, it was 20/20 or better in all eyes (100%). The efficacy indices were 1.27 ± 0.19 and 1.36 ± 0.23 in the two groups, respectively. The outcomes of refractive surgery are shown in Fig. 1.

Fig. 1.

Standard nine graphs comparing the refractive results between the two study groups. (A) Postop uncorrected distance visual acuity (UDVA) versus preop corrected distance visual acuity (CDVA), (B) difference between postop UDVA and preop CDVA, (C) change in CDVA, (D) attempted spherical equivalent (SE) refraction change versus the achieved SE refraction change at 3 months postoperatively, (E) spherical equivalent refractive accuracy, (F) stability of mean SE refraction, (G) distribution of refractive astigmatism, (H) target induced astigmatism versus surgically induced astigmatism, (I) refractive astigmatism angle of error

D = diopters; Preop = preoperative; Postop = postoperative; group 1 = femtosecond laser-corneal relaxing incisions with implantable collamer lens implantation group; group 2 = toric implantable collamer lens group

Refractive astigmatism outcome analysis

In this study, the Linear Mixed-effect Model was used to analyze the data on an individual basis, and the correlation between the binocular data was fully considered. In each group, the refractive astigmatism was significantly lower at 3 months postoperatively than that preoperatively. It was reduced from 1.55 ± 0.38 D to 0.38 ± 0.27 D in the FS-CRI group and from 1.67 ± 0.33 D to 0.37 ± 0.24 D in the TICL group (P < 0.05 for both groups). The mean astigmatism correction magnitude was 1.17 ± 0.43 D and 1.30 ± 0.38 D, respectively. Although the TICL group showed relatively smaller residual astigmatism and greater correction, there was no significant difference between the two groups (all P > 0.05) (Table 2). At 3 months postoperatively, residual astigmatism ≤ 0.50 D was observed in 84% and 89% of the eyes in the FS-CRI and TICL groups, respectively, and ≤ 1.0 D was observed in 98% and 100%, respectively.

Table 2.

Change in refractive astigmatism between groups using the linear mixed model

Parameter	FS-CRI group	TICL group	Pb value	Cohen’s d
Preop refractive astigmatism (D)	1.55 ± 0.38 (1.45–1.66)	1.67 ± 0.33 (1.58–1.76)	0.10	0.32
Postop residual refractive astigmatism (D)	0.38 ± 0.27 (0.31–0.46)	0.37 ± 0.24 (0.31–0.44)	0.82	0.04
Astigmatism correction magnitude (D)	1.17 ± 0.43 (1.06–1.28)	1.30 ± 0.38 (1.19–1.40)
Pa value	< 0.001	< 0.001
Cohen’s dz	0.994	0.999

FS-CRI group = femtosecond laser-assisted corneal relaxing incisions with implantable collamer lens implantation; TICL group = toric implantable collamer lens implantation; Astigmatism correction magnitude = Preoperative refractive astigmatism - Postoperative residual refractive astigmatism.Cohen’s d is the standardized mean difference between two independent groups, calculated as mean difference divided by the pooled SD .Cohen’s d_z is the effect size for paired comparisons, calculated as the mean difference divided by the standard deviation of the difference scores ( d_z = M_diff / SD_diff).^aComparison between the preoperative and postoperative refractive astigmatism values.^bComparison between the FS-CRI group and the TICL group.

Vector analysis of astigmatism

Table 3 showed the vector analysis outcomes. There was no significant difference in SIA, DV, AE, ME, IOS, and FI between the two groups (all P > 0.05) (Table 4). The absolute AE was similar between the two groups (FS-CRI group: 4.45° ± 4.53° vs. TICL group: 3.55° ± 3.50°, P = 0.444). Figure 2 showed the single-angle polar plots of the correction index in each group, and the geometric CIs were 0.80 and 0.82, respectively. There were 7 eyes (12.5%) in the FS-CRI group and 4 eyes in the TICL group that showed overcorrection.

Table 3.

Vector analysis of astigmatic correction

Parameter	FS-CRI group	TICL group	P value	Cohen’s d
Target Induced Astigmatism Arithmetic mean ± SD (D)	1.55 ± 0.38 (1.45–1.66)	1.67 ± 0.33 (1.58–1.76)	0.10	0.32
Surgically Induced Astigmatism Arithmetic mean ± SD (D)	1.31 ± 0.44 (1.19–1.42)	1.40 ± 0.40 (1.29–1.51)	0.25	0.22
Difference Vector Arithmetic mean ± SD (D)	0.38 ± 0.27 (0.31–0.46)	0.37 ± 0.24 (0.31–0.44)	0.82	0.04
Angle Of Error Arithmetic mean ± SD (°)	0.84 ± 6.32 (-0.85-0.91)	0.12 ± 5.01 (-1.24-1.47)	0.50	0.13
Absolute Angle Of Error Arithmetic mean ± SD (°)	4.45 ± 4.53 (3.23–5.66)	3.55 ± 3.50 (2.60–4.49)	0.25	0.22
Magnitude of error Arithmetic mean ± SD (D)	-0.25 ± 0.29 (-0.32~-0.17)	-0.27 ± 0.24 (-0.33~-0.20)	0.65	0.09
Index Of Success Arithmetic mean ± SD	0.26 ± 0.19 (0.21–0.31)	0.23 ± 0.15 (0.19–0.27)	0.40	0.16
Flatting index Arithmetic mean ± SD	0.82 ± 0.21 (0.76–0.87)	0.82 ± 0.16 (0.78–0.87)	0.88	0.03
Correction Index Geometric mean	0.80	0.82	-	-

FS-CRI group = femtosecond laser-assisted corneal relaxing incisions with implantable collamer lens implantation; TICL group = toric implantable collamer lens implantation.Cohen’s d is the standardized mean difference between two independent groups, calculated as mean difference divided by the pooled SD .

Table 4.

Change in total wavefront aberration and retinal image quality parameters by groups

Parameter	FS-CRI group		Pa value	Cohen’s dz	TICL group		Pa value	Cohen’s dz
	Preoperative	Postoperative			Preoperative	Postoperative
T. Spherical aberration (µm)	0.023 ± 0.018 (0.018–0.028)	0.041 ± 0.034 (0.032–0.050)	< 0.001	0.498	0.023 ± 0.019 (0.018–0.028)	0.033 ± 0.026 (0.026–0.040)	0.003	0.42
T. Coma (µm)	0.062 ± 0.033 (0.053–0.071)	0.093 ± 0.066 (0.076–0.111)	0.003	0.521	0.053 ± 0.036 (0.044–0.063)	0.073 ± 0.051 (0.059–0.087)	0.018	0.33
T. Trefoil (µm)	0.095 ± 0.046 (0.083–0.107)	0.193 ± 0.121 (0.161–0.226)	< 0.001	0.840	0.108 ± 0.056 (0.093–0.123)	0.155 ± 0.076* (0.134–0.176)	< 0.001	0.656
T. HOA (µm)	0.142 ± 0.045 (0.130–0.154)	0.258 ± 0.111 (0.228–0.288)	< 0.001	0.966	0.149 ± 0.056 (0.133–0.164)	0.208 ± 0.082 (0.185–0.230)	< 0.001	0.695
Strehl ratio	0.000 ± 0.000 (0.000–0.000)	0.037 ± 0.024 (0.031–0.044)	< 0.001	1.539	0.000 ± 0.000 (0.000–0.000)	0.052 ± 0.039 (0.041–0.063)	< 0.001	1.323
Area ratio (%)	10.48 ± 0.11 (10.45–10.51)	33.66 ± 9.73 (31.05–36.22)	< 0.001	2.382	10.55 ± 0.26 (10.48–10.62)	38.91 ± 11.34 (35.85–41.98)	< 0.001	2.516

FS-CRI group = femtosecond laser-assisted corneal relaxing incisions with implantable collamer lens implantation; TICL group = toric implantable collamer lens implantation; T = Total; HOA = high-order aberration.^aComparison between the preoperative and postoperative values.*P<0.05, significantly different between the FS-CRI group and the TICL group.Cohen’s d_z is the effect size for paired comparisons, calculated as the mean difference divided by the standard deviation of the difference scores ( d_z = M_diff / SD_diff).

Fig. 2.

Single-angle polar plots of correction index in the FS-CRI group (A) and the TICL group (B)

FS-CRI group = femtosecond laser-assisted corneal relaxing incisions with implantable collamer lens implantation group; TICL group = toric implantable collamer lens group

Aberration and retinal image quality

The postoperative total wavefront aberration and retinal image quality parameters were significantly increased postoperatively in both groups (all P < 0.01). The total spherical aberration, coma, and high-order aberration at 3 months postoperatively were not significantly different between the two groups (FS-CRI group vs. TICL group: P = 0.93, 0.95, 0.79, respectively). Meanwhile, the total trefoil in the FS-CRI group was relatively higher (P = 0.022). In addition, both groups achieved an approximate postoperative strehl ratio (SR) and area ratio (AR) (P = 0.33 and 0.083, respectively).

Safety

Both groups showed a good safety index (1.27 ± 0.19 in the FS-CRI group and 1.36 ± 0.23 in the TICL group). The postoperative vault was 571 ± 136 μm and 590 ± 209 μm, respectively (P = 0.507). During follow-up, no patient had a postoperative infection, glaucoma, cataract, epithelial implantation, etc. Figure 3 shows the distribution of the postoperative vaults in the two groups. No low vaults were noted in either group; however, the FS-CRI group had a higher proportion of normal vaults (89.3% vs. 80.0%) and thus lower of high vaults (10.7% vs. 20.0%) than the TICL group. Besides, 2 patients in the FS-CRI group underwent ICL position adjustment owing to excessive vault, and in the TICL group, 2 patients each underwent TICL replacement owing to excessive vault and insufficient vault. After receiving corresponding treatment, the vault of these 6 patients returned to normal. Figure 4 showed the postoperative anterior segment images in the patients who underwent FS-CRI, showing well-placed incisions.

Fig. 3.

Postoperative normal ophthalmic photograph showing paired corneal relaxing incisions at an optical zone of 8.7 mm. Arrows indicate the relaxing incisions

Fig. 4.

Postoperative normal ophthalmic photograph showing paired FS-CRI at an optical zone of 8.7 mm. Arrows indicate the relaxing incisions (FS-CRI = femtosecond laser-assisted corneal relaxing incisions)

Discussion

Several studies have reported the efficacy and safety of FS-CRI in the treatment of low-to-moderate astigmatism in cataract surgery, and the corresponding nomograms have been developed [12–14, 28–30]. However, as discussed above, these nomograms may not be applicable to Chinese patients, and there is currently insufficient research on the application of FS-CRI in refractive surgery. In this study, the Donnenfeld nomogram was used to guide the design of FS-CRI, and we adopted a diameter of 8.7 mm and a depth of 90% corneal pachymetry, based on our previous clinical experience [22, 24]. The results suggested that the FS-CRI and TICL methods can achieve similar magnitudes of astigmatism correction, postoperative residual refractive astigmatism, vector parameters, and visual quality, indicating that the preliminarily modified nomogram can effectively correct astigmatism in Chinese patients, and also highlight the potential for developing personalized nomograms in future research.

The efficacy of TICL in the current study is close to that in a previous report [31]. Theoretically, corneal refractive surgery often causes an increase in high-order aberrations while treating low-order aberrations [1]. A previous study showed that FS-CRI can cause an increase in corneal higher-order aberrations, [17] while ICL implantation can cause an increase in internal higher-order aberrations [9]. To compare the total wavefront aberration and retinal image quality parameters between groups, the data at the 4.0-mm zone measured by OPD-ScanIII were analyzed in this study. A 4.0-mm zone is considered because it is a standard value for analyzing ocular aberration and visual quality [31, 32]. In our study, total wavefront aberration was significantly increased postoperatively in both groups. Although the total spherical aberration, coma, and high-order aberration were similar between groups, the FS-CRI group showed higher postoperative total trefoil. This may be because FS-CRI combined with ICL implantation changed both corneal and internal wavefront aberrations. In addition, both surgical methods significantly improved the retinal image quality parameters of patients, with no significant difference between these methods. This proves that FS-CRI combined with ICL implantation can also effectively treat astigmatism.

The postoperative vault is an important indicator to evaluate the surgery safety in patients with ICL or TICL implantation. [33] Complications such as pupillary block and elevated intraocular pressure are associated with an excessive vault, whereas an insufficient vault may cause cataracts. Zhao et al. [10] reported that the vault after TICL implantation is generally higher than that with ICL, possibly due to the larger spherical equivalent expected in toric lenses since adding the power of the cylinder to the sphere modifies the intrinsic lens vault. The difference in the postoperative vault between the two groups was not statistically significant in our study; however, the proportion of high vaults was relatively larger in the TICL group. This finding indicates that TICL implantation is more prone to complications. Furthermore, since the vault of TICL cannot be adjusted by rotation, secondary procedures involving the replacement or removal of the TICL may cause greater damage. By contrast, for patients with a mismatch between ocular dimensions and TICL size, the implantation of ICL following astigmatism correction with FS-CRI enables the attainment of a safe vault through simple secondary repositioning even if postoperative high vault occurs, thus achieving favorable clinical outcomes.

Overall, although the combination of FS-CRI with ICL implantation may incur additional costs compared to TICL implantation alone, the automated procedure enabled by preset laser parameters imposes minimal additional learning burden on refractive surgeons. Furthermore, FS-CRI demonstrates substantial clinical value by effectively correcting astigmatism in patients as described previously, while mitigating excessive reoperation risks associated with long-term phakic intraocular lens rotation.

The present study has some limitations. First, we did not perform cycloplegic refraction or conduct mydriatic observation of the rotation of the TICL during the follow-up period. The former may underestimate residual astigmatism, while the latter is more conducive to comparing the long-term stability of FS-CRI and TICL [34]. Second, the quality of vision (QoV) questionnaire [35] was not provided to the patients in this study, it may not comprehensively capture patients’ visual quality, and thus QoV and essential patient-reported indicators will be integrated into our follow-up studies. Third, short-term follow-up (3 months) may not fully capture the long-term durability of astigmatism correction efficacy and the long-term stability of vault, We will continue to follow up with this cohort of patients. Fourth, owing to the small sample size, no subgroup analysis stratified by astigmatic axis was performed in this article, we will incorporate this analysis in subsequent studies.

Conclusion

To the best of our knowledge, this study evaluating the application of FS-CRI in refractive surgery and compare its outcomes with those of TICL implantation. In conclusion, FS-CRI performed during ICL implantation is effective in correcting low-to-moderate astigmatism and yields visual quality comparable to that achieved with TICL implantation. Thus, this surgical approach represents a viable alternative for patients with low-to-moderate astigmatism.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Fan Zhang, Shaowei Li, Jihong Zhou, Wenjuan Wang and Nuan Peng. The first draft of the manuscript was written by Fan Zhang and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

This study was funded by research grant from Alcon (IIT73551345).

Data availability

The datasets use and/or analyse during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This retrospective study was approved by the institutional ethics committee of Beijing Aier-Intech Eye Hospital Co., Ltd (BJAIER2022IRB05) and was conducted according to the tenets of the Declaration of Helsinki. The need for informed consent was waived owing to the retrospective nature of the study.

Competing interests

The authors declare no competing interests.

Clinical trial number

The Clinical trianumber is not applicable.