Incidence and Risk Factors of Repositioning Surgery to Correct Misalignment of Toric Intraocular Lenses after Cataract Surgery: A Single-Center Retrospective Observational Study

Toric intraocular lenses (IOLs) are considered a safe, effective, and predictable technique for correcting corneal astigmatism during cataract surgery [1, 2]. Nonetheless, some patients have not achieved adequate visual acuity after toric IOL implantation, leading to patient dissatisfaction. Previous studies have described that unsatisfactory visual acuity following toric IOL implantation is mainly caused by residual astigmatism resulting from incorrect preoperative measurement of the anterior and posterior corneal astigmatism and IOL misalignment [3‒5].

It was reported that a 30-degree rotation of the toric IOL from the intended alignment axis could lead to a 50% loss of cylindrical power and a 45.85% reduction in image quality, while a 45-degree rotation might lead to a complete failure of astigmatism correction [6, 7]. Therefore, accurate intended alignment axis and rotational stability after toric IOL implantation are crucial during cataract surgery. Furthermore, a misalignment above 10 degrees is generally considered an indication for repositioning surgery [3, 5].

Based on previous large-scale studies in other countries, the incidence of misalignment requiring repositioning surgery after cataract surgery ranged from 0.065% to 3.23% [8‒12]. In China, investigations about repositioning surgery following cataract surgery have not been conducted. Thus, the present study aimed to comprehensively analyze the clinical characteristics of repositioning surgery with several toric IOL models to provide clinical guidance for future cataract treatment.

This single-center retrospective observational study was conducted at Qingdao Eye Hospital of Shandong First Medical University, Qingdao, China. This study adhered to the principles of the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Qingdao Eye Hospital of Shandong First Medical University. Written informed consent was routinely obtained from each patient. The medical records of patients who underwent repositioning surgery with toric IOLs following cataract surgery between January 2019 and December 2021 were screened and collected from our hospital. Afterward, analysis was performed on variables such as age, gender, preoperative axial length (AL), corneal astigmatism, astigmatism axis, IOL models, intended IOL axis, misalignment axis, uncorrected distance visual acuity (UDVA), residual refraction, time of repositioning surgery, and postoperative outcomes including UDVA, residual refraction, and IOL axis. The characteristics of the IOLs used in this study are shown in Table 1.

IOL alignment was measured by a slit lamp with the pupil fully dilated at each postoperative visit. Misalignment was defined as the difference between the intended alignment axis and the postoperative IOL axis.

A greater than 10-degree misalignment was regarded as an indication for surgical repositioning [3, 5]. Repositioning surgery was carried out if the misalignment degree was greater than 10 degrees and the patient consented to secondary surgical intervention. During repositioning surgery, an adjustment hook was used to dial the IOL axis to the intended IOL axis through the main incision, while a balanced salt solution was injected through the side incision to maintain the anterior chamber. In order to prevent the overfilling of the capsular bag from impairing the attachment of the IOL to the capsular bag, a small amount of balanced salt solution was slowly injected to create a marginally lower intraocular pressure after operation.

All statistical analyses were performed with SPSS Statistics (version 22.0, IBM Corp., NY, USA). Continuous variables were presented as mean ± SD. A paired t test was used to compare the mean UDVA and residual astigmatism before and after repositioning surgery. The incidence and related factors of repositioning surgery were assessed using univariate (χ² test or Fisher’s exact test) and multivariate analyses (logistic regression analysis). A p value less than 0.05 was considered statistically significant.

Among the 1,135 eyes implanted with toric IOLs at the Qingdao Eye Hospital of Shandong First Medical University, 23 eyes (2.026%, 23/1,135) underwent repositioning surgery. The repositioning surgery was performed at an average of 8.22 ± 12.87 days (range, 1–60 days) after the primary cataract surgery. The last follow-up after repositioning surgery was at 4.17 ± 3.64 weeks (range, 2–9 weeks). Patients’ characteristics are summarized in Table 2. Preoperative AL, corneal astigmatism, and IOL misalignment degrees were 24.73 ± 1.87 mm (range 22.73–30.36 mm), 2.56 ± 0.68 D (range 1.13–3.58 D), and 32.65 ± 18.23 degrees (range 14–86 degrees), respectively.

Univariate analysis revealed that the incidence of repositioning surgery was significantly lower with AcrySof (0.636%, 5/786) than with ZEISS (2.959%, 5/169) and TECNIS (7.222%, 13/180) toric IOLs (p < 0.001) (Figure 1). Furthermore, the incidence of repositioning surgery was significantly lower with monofocal toric IOLs (1.169%, 11/941) compared to multifocal toric IOLs (6.186%, 12/194) (p < 0.001) (Figure 2). However, there was no significant difference in gender, AL, IOL type (hydrophilic vs. hydrophobic), and alignment method (p > 0.05) (Table 3).

Multivariate logistic regression analysis determined that IOL platform (p = 0.004) and multifocal toric IOLs (p = 0.006) were risk factors for repositioning surgery. Relative to the AcrySof IOL platform, the TECNIS IOL platform had an odds ratio (OR) of 8.373 (p = 0.001) and the ZEISS IOL platform had 3.875 (p = 0.047). Relative to age ≤50 years, OR of repositioning surgery in age 51–60 years, age 61–70 years, and age ≥71 years were 0.166, 0.154, and 0.239, respectively (p < 0.05), indicating that younger age was a risk factor of repositioning surgery (Table 4).

The residual cylinder significantly decreased from a preoperative value of 2.09 ± 0.99 D to a postoperative value of 0.62 ± 0.43D (p ˂ 0.001), and the UDVA improved from 0.50 ± 0.24 logMar to 0.28 ± 0.31 logMar (p = 0.001), postoperatively. All postoperative misalignments of the toric IOL axis were within 5 degrees. No complications were found during and after the repositioning surgery.

With the increasing use of toric IOLs to correct astigmatism with cataract surgery for a high incidence of spectacle independence, associated complications, especially misalignment, have become more and more prevalent. In order to analyze the incidence and risk factors of repositioning surgery among the Chinese population, we conducted a retrospective study of patients with toric IOL misalignment who underwent repositioning surgery after cataract surgery.

Multivariate analysis exposed that age and toric IOL platform were related to the occurrence of misalignment undergoing repositioning surgery after cataract surgery, which is consistent with previous studies [10, 13]. The likelihood of misalignment undergoing repositioning surgery was greater in the use of the TECNIS platform, ZEISS platform, multifocal IOLs, and younger patients.

The results of this study determined that the overall incidence of repositioning surgery to correct misalignment with toric IOLs was 2.026%. Other studies with a larger sample size in other countries reported that the repositioning rates of toric IOLs were 0.653% [8], 0.944% [9], 1.3% [10], 2.513% [11], and 3.23% [12]. The use of different IOL models in these studies might have contributed to the results being slightly inconsistent. Therefore, based on the IOL platform of toric IOLs, the rate of repositioning surgery between different IOL platforms was analyzed. The rate of repositioning after implantation of TECNIS toric IOLs was 7.222%, which was higher than that of AcrySof IOLs (0.636%) (OR = 8.373, p = 0.001). This observation is consistent with previous studies that compared repositioning incidence between AcrySof IOLs and TECNIS toric IOLs [9, 10, 13]. A retrospective study demonstrated that TECNIS toric IOLs had a higher rate of IOL axis misalignment ≥5° than AcrySof toric IOLs [14]. Hence, it can be speculated that AcrySof IOLs have superior rotational stability to TECNIS IOLs.

Herein, we also found that the rate of repositioning with ZEISS toric IOLs (2.959%) was higher than AcrySof toric IOLs (0.636%) (OR = 3.875, p = 0.047). ZEISS toric IOLs had a higher risk of repositioning rate than AcrySof IOLs. No relevant studies comparing the repositioning incidence between the two IOLs have been found yet. Nonetheless, a randomized, controlled study including 62 eyes demonstrated that the rotational stability of a plate-haptic toric IOL (ZEISS platform) was more stable than a C-loop haptic toric IOL (AcrySof platform) for myopic eyes [15]. Seth et al. [16] found no significant difference in IOL rotation degree between ZEISS and AcrySof IOLs at 3-month follow-up. However, these two studies did not report the incidence of misalignment for repositioning. The mechanism behind these differences among 3 toric IOLs platforms is not clear at present and needs further research and clarification.

In this study, we found that the incidence of repositioning surgery was significantly lower with monofocal (1.169%) than with multifocal (6.186%) toric IOLs. A prospective interventional study uncovered that UDVA was more likely to be influenced by IOL rotation in multifocal toric IOLs compared to monofocal ones [17]. Given that multifocal toric IOLs have a higher intolerance to residual astigmatism than monofocal toric IOLs, it is easier for surgeons to identify misalignment with multifocal toric IOLs and subsequently perform repositioning surgery. Likewise, Lee et al. [13] theorized that the adverse effect of residual astigmatism on visual function caused by IOL misalignment with multifocal toric IOLs persuaded surgeons or patients to offer or accept repositioning surgery.

The lower risk of repositioning with older age may be due to the greater visual demands in younger patients [10]. High compliance and acceptance of repositioning surgery in young patients may have contributed to the above results.

Outcomes after repositioning surgery have been investigated by previous studies, and repositioning surgery could effectively correct misalignment with toric IOLs [8, 12]. In our study, the residual cylinder significantly decreased from a preoperative value of 2.09 ± 0.99 D to a postoperative value of 0.62 ± 0.43 D and UDVA improved from 0.50 ± 0.24 logMar to 0.28 ± 0.31 logMar postoperatively. The residual cylinder was slightly lower in our study at 0.62 ± 0.43 D compared to the outcome of Oshika et al.’s study [8] at 1.1 ± 0.8 D and at 0.83 ± 0.81 D of Kassner et al.’s study [12]. The mean last follow-up time after repositioning surgery ranged from 2 to 9 weeks in this study. Therefore, inconsistencies in postoperative follow-up time may affect refractive outcomes. Moreover, a mean follow-up time of 4.17 weeks was fairly short to assess the patient’s long-term visual refractive outcomes after repositioning surgery.

To our knowledge, this was the first study to investigate the incidence and outcomes of repositioning surgery with several toric IOL models in China. For patients with factors including TECNIS IOL platform, multifocal toric IOLs or younger age, the possible occurrence of misalignment requiring repositioning surgery after toric IOL implantation should be noted before cataract surgery. Future multicenter studies with larger samples are needed to confirm these findings.

The study followed the principles of the Declaration of Helsinki and was approved by the Ethics Committee of Qingdao Eye Hospital of Shandong First Medical University, approval number QYLS 2022(23). Written informed consent was obtained from all patients for sample collection and subsequent analyses.

The authors have no proprietary or commercial interests in any of the materials discussed in this article and no other conflicts of interest to declare.

No funding was received for this article.

Honglei Li and Xiaoming Wu were the major contributors for the experimental design and drafting of the manuscript. Lin Leng and Huiran Bai analyzed and interpreted the collected data. Jiajun Sun and Yunhai Dai contributed to the study concept and design.

All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.