In this systematic review and meta-analysis, one Chinese literature and 13 English articles were selected, of which 15 studies were included.

Combined with the study, no significant difference was found in the postoperative visual acuity (BCVA, CDVA and UCVA) between sutureless SF-IOL and suture SF-IOL. Meanwhile, the operation time of sutureless SF-IOL is shorter than that of suture SF-IOL.

The intraocular lens inclination (horizontal and vertical), absolute postoperative spherical equivalent, and astigmatism after sutureless SF-IOL were compared with those after suture SF-IOL. The difference was not statistically significant.

For the study of postoperative complications, the common postoperative complications, such as dislocation/subluxation of intraocular lens, iris clamping, pupil deformation, elevated pressure and decreased intraocular pressure were analyzed. No statistical difference was found in these comparisons.

In addition, a funnel chart and sensitivity map analysis were performed for the comparative studies with I2 ≥ 50% and the number of studies ≥ 5 after the merger. In accordance with the results, the relevant literature was reviewed to analyze the causes of heterogeneity. The causes of heterogeneity are described in Table 5. According to the analysis of funnel chart and sensitivity map, the main sources of heterogeneity in BCVA after sutureless SF-IOL and suture SF-IOL were the studies of Daniel.et al.2021(2) [16] and Zhang.et al.2021 [21]. After the studies of Daniel.et al.2021(2) [16] and Zhang.et al.2021 [21] were excluded, the heterogeneity decreased (WMD =  − 0.01, 95% CI = [− 0.04, 0.03], p = 0.07, I2 = 49%; Fig. 8A), which also proved the present work’s idea. In the comparison of absolute postoperative spherical equivalent between sutureless SF-IOL and suture SF-IOL, the main source of heterogeneity was the study of Yodpong.et al. 2018 [22] and Jae.et al.2020 [20]. After the study of Yodpong.et al. 2018 [22] and Jae.et al.2020 [20] was excluded, the heterogeneity decreased (WMD =  − 0.30, 95% CI = [-0.51, -0.09], p = 0.15, I2 = 34%; Fig. 8B). A significant difference was found in the refractive values between sutureless SF-IOL and suture SF-IOL, and the refractive value was lower after sutureless SF-IOL. In the comparison of the postoperative IOL-related astigmatism between sutureless SF-IOL and suture SF-IOL, the main sources of heterogeneity were the studies of Kyu.et al.2021 [18] and Yodpong.et al.2018 [22]. After the above two studies were excluded, a decrease in heterogeneity was found (WMD =  − 0.67, 95% CI = [− 1.01, − 0.33], p = 0.57, I2 = 0%; Fig. 8C), and A significant difference was observed between the two interventions. In the comparison of intraocular pressure reduction after sutureless SF-IOL and suture SF-IOL, the main source of heterogeneity was the study of Yu. etal.2018 [23]. After the study of Yu.et al.2018 [23] was excluded, a decrease in heterogeneity was found (OR = 1.97, 95% CI = [0.66, 5.94], p = 0.24, I2 = 29%; Fig. 8D).

Meta-analysis on best corrected visual acuity,absolute postoperative spherical equivalent, postoperative IOL-related astigmatism and postoperative intraocular pressure decreased after exclude some researches. A Comparison of sutureless SF-IOL and suture SF-IOL with the best corrected visual acuity. B Comparison of sutureless SF-IOL and suture SF-IOL with the absolute postoperative spherical equivalent. C Comparison of sutureless SF-IOL and suture SF-IOL with the postoperative IOL-related astigmatism. D Comparison of sutureless SF-IOL and suture SF-IOL with the postoperative intraocular pressure decreased

In addition, the types of sutureless SF-IOL were divided into Gabor, Agarwal, and Yamane techniques. A subgroup analysis of the three techniques was conducted to determine the sources of heterogeneity in some of the comparative studies. In accordance with the number of studies, the difference in BCVA between Gabor technique and suture SF-IOL was compared (WMD = 0.12, 95% CI = [− 0.13, 0.38], P = 0.41, I2 = 0%; Fig. 9A). Although no statistical difference was found between the two, the heterogeneity of the study was low. In addition, the difference in BCVA between Yamane technique and suture SF-IOL was compared (WMD = 0.08, 95% CI = [− 0.00, 0.17], P = 0.93, I2 = 0%; Fig. 9B). No statistical difference was observed between the two, and the heterogeneity of the study was low. Meanwhile, the difference in the absolute postoperative spherical equivalent between Gabor technique and suture SF-IOL was compared (WMD =  − 0.06, 95% CI = [− 0.61, 0.50], P = 0.11, I2 = 55%; Fig. 10A). No statistical difference was found between them, but the heterogeneity was high. After the study of Yodpong.et al. 2018 [22] was analyzed and excluded, the heterogeneity decreased (WMD =  − 0.19, 95% CI = [− 0.50, 0.12], p = 0.22, I2 = 34%; Fig. 10B), and the difference was not statistically significant. In accordance with the original analysis, the heterogeneity caused by the study of Yodpong.et al. (2018) [22] is due to unnecessary refractive errors caused by the forward movement of the optical part of the intraocular lens after the IOL haptic enters the scleral tunnel during IOL fixation. The difference in the absolute postoperative spherical equivalent between Yamane technique and suture SF-IOL was also compared (WMD =  − 0.24, 95% CI = [− 0.49, 0.01], P = 0.02, I2 = 62%; Fig. 10C). No statistical difference was observed between them, but the heterogeneity was high. The study of Jae.et al. (2020) [20] was analyzed and excluded to further study and analyze the effect of reducing heterogeneity. The heterogeneity of the study decreased, and a statistical difference was found between the two (WMD =  − 0.33, 95% CI = [− 0.51, − 0.15], P = 0.13, I2 = 42%; Fig. 10D), which proved that the absolute postoperative spherical equivalent after Yamane technique was lower than that after suture SF-IOL. In accordance with the original analysis, the reason for the heterogeneity in the study of Jae.et al. (2020) [20] is that the caliber of vitrectomy for Yamane technique was 25G and that of suture scleral IOL implantation was 23G.The difference in astigmatism between Gabor technique and suture SF-IOL was also compared (WMD =  − 0.02, 95% CI = [− 0.11, 0.07], P = 0.29, I2 = 21%; Fig. 10E), without statistical difference between them. Meanwhile, a statistically significant difference in astigmatism was found between Yamane and suture SF-IOL (WMD =  − 0.82, 95% CI = [− 1.09, − 0.55], P = 0.73, I2 = 0%; Fig. 10F), which proved that the astigmatism in Yamane technique was smaller than that in the suture group.

Meta-analysis on the best corrected visual acuity of subgroup techniques. A Comparison of Gabor technique and suture SF-IOL with the best corrected visual acuity. B Comparison of Yamane technique and suture SF-IOL with the best corrected visual acuity

Meta-analysis on the absolute postoperative spherical equivalent and the postoperative astigmatism of subgroup techniques. A Comparison of Gabor technique and suture SF-IOL with the absolute postoperative spherical equivalent. B Comparison of Gabor technique and suture SF-IOL with the absolute postoperative spherical equivalent after exclude research. C Comparison of Yamane technique and suture SF-IOL with the absolute postoperative spherical equivalent. D Comparison of Yamane technique and suture SF-IOL with the absolute postoperative spherical equivalent after exclude research. E Comparison of Gabor technique and suture SF-IOL with the postoperative astigmatism. F Comparison of Yamane technique and suture SF-IOL with the postoperative astigmatism

To sum up, according to the analysis of the research results, the postoperative IOL-related astigmatism and absolute postoperative spherical equivalent of sutureless SF-IOL were lower than that of suture SF-IOL, indicating that the degree of refractive error after sutureless SF-IOL was lower. Meanwhile, the operation time of sutureless SF-IOL was shorter than that of suture SF-IOL. The subgroup analysis showed that the absolute postoperative spherical equivalent and astigmatism values in Yamane technique were lower than those in suture SF-IOL, with statistical value. This finding also proved that Yamane’s technique is superior to Gabor’s technique. Therefore, through the above analysis and summary, we believe that, compared with suture SF-IOL, Sutureless SF-IOL has the advantages of shorter operation time, stable postoperative refractive state and the incidence of postoperative complications. Yamane technique is superior to suture SF-IOL and Gabor’s technique in subgroup analysis.

In 1997, Italian scholars Ricardo Maggi and Carlo Maggi [24] put forward the concept of sutureless SF-IOL for the first time in view of the possible postoperative complications caused by suture. They chose an intraocular lens with three long 8.5 mm rings (made of polytetrafluoroethylene), which were fixed to the sclera through a special needle at 2:00, 6:00, and 10:00. This surgical method uses conjunctiva and sclera to cover the intraocular lens loop to avoid exposure to the outside of the eye, thus reducing the incidence of intraocular infection after operation. In addition, when using this method, if intraocular lens displacement or deviation occurs during operation, it could be corrected by adjusting the length of the ring. This method provides a new fixation method and fixed site for suture-free scleral interlamellar intraocular lens implantation. German scholar Gabor proposed seamless intraocular lens implantation in the ciliary sulcus in 2007 [25]. This method uses a standard three-piece foldable intraocular lens. The scleral tunnel is made by a common No. 24 cannula needle at the distance from the limbal of 1.5–2.0 mm, and then the IOL loop is brought into the scleral tunnel by tweezers, and the IOL loop is buried in the sclera. This method is the first time that the concept of “sutureless and glueless” has been applied to the clinic. During the follow-up period, no serious complications were noted, and in the later follow-up, 96.8% of the 63 patients had stable IOL. The work of Gabor provides a practical basis for the follow-up research, but the operation of the intraocular lens loop into the scleral tunnel is more difficult and takes a long time because of the equipment. In 2008, Agarwal [26] proposed to make a scleral flap to fix the IOL loop, which makes it more convenient to fix the IOL loop. Compared with the method proposed by Gabor, Agarwal expands the operating space by changing the shape of the sclera incision to make the IOL loop easier to draw out from the eye. However, excessive sclerotomy may cause postoperative scleral thinning and softening, resulting in other serious complications, and the technique closes the scleral flap with fibrin glue, which may lead to postoperative prion-associated infection [12]. In 2014, Yamane of Yokohama City University in Japan introduced a new technique at the annual meeting of ophthalmology in the United States [27]. This technique uses two No. 27 needles to perform scleral lamellar anatomy. It combines the advantages of Gabor and Akira’s methods, not only reducing the size of scleral incision and the probability of incision leakage and low intraocular pressure but also simplifying the operation procedure and shortening the operation time. Although some defects, such as difficulty in intraoperative operation and unstable intraocular lens fixation after operation [28], could still be noted, this method has been popularized after the report. In view of the poor stability of postoperative IOL, Yamane [29] proposed to use two No. 30 cannula needles to make a scleral tunnel and increase the fixation of IOL by cauterizing the end of IOL loop. The scleral damage of the 30 G needle used in this operation is less than that of the Nos. 25 and 27 G needle, and the smaller the diameter of the cannula needle is, the higher the stability of the scleral tunnel. No cases of dislocation were identified during the follow-up period in this study. So far, sutureless SF-IOL has been rapidly promoted.

At present, sutureless SF-IOL has become the mainstream surgical scheme for the clinical treatment of aphakic eyes, because it does not require suture, adhesion, scleral cauterization, and other operations. As a result, the tissue injury is greatly reduced, the incidence of postoperative complications is reduced, and the postoperative recovery time is shortened [14]. According to the comparative analysis of the present study, this method has the advantages of shorter operation time, more stable refractive state, and lower incidence of complications than suture SF-IOL.

The topic of comparing various secondary IOL techniques is a difficult and controversial issue, as well-designed comparative studies are rare and challenging to conduct due to the variations in each technique and the learning curve for each operator. The postoperative outcomes especially the operation time and visual acuity may be greatly influenced by the experience of the surgeon. Meanwhile, the reason of aphakia may influence the postoperative outcomes. Surgically, traumatically or congenitally induced aphakia may be accompanied with glaucoma, macular oedema and other ocular dysplasia. However, we believe that by comparing one surgical method with other surgical methods to find out the shortcomings of this surgical method and constantly adjust it is a feasible way to improve the quality of medical care. Besides, the main limitation of this study is the retrospective nature of most studies. The location of the IOL is determined by the surgeon’s preference and the patient’s eye history, leading to differences in baseline characteristics, which may affect the results between groups. Standardization among studies is also lacking, resulting in inconsistencies in clinical indications, surgical techniques, surgeon experience, reported results and limited duration in several studies. Meanwhile, duration of follow up is very important. The visual acuity, refractive errors, inclination of intraocular lens, and the postoperative complications may change with time. Thus, the quality of the evidence of the results differs, and it may lead to inconsistencies and statistical heterogeneity. In addition, the sample size of the study is small, which leads to the low statistical ability of some analyses. Due to the limited number of studies, this paper could not fully compare the differences among Yamane, Gabor, and Agarwal’s techniques.