Comparison of efficacy between coaxial microincision and standard-incision phacoemulsification in patients with age-related cataracts: a meta-analysis

Age-related cataracts are a common condition and one of the most important causes of blindness. With the population increasing at a rate of more than 10 million people per year and as life expectancy continues to rise, 0.4 to 1.2 million new cataract patients are expected every year in China, and the number of cataract-related blindness cases is expected to increase to 5.0625 million in 2020 [1]. Due to improvements in medical technology and surgical instruments, phacoemulsification has now become a mainstream treatment for cataracts. Cataract surgery has gradually evolved from blindness prevention surgery to refractive surgery, with the aim of not only restoring vision but also improving visual quality and quality of life. The choice of surgical incision plays a crucial role in the efficacy of surgery, as the incision damages the surrounding tissues and affects the surgical approach. The size of microincisional phacoemulsification surgery (MICS) incisions ranges from 1.8 mm to 2.2 mm, whereas standard-incision phacoemulsification surgery (SICS) incisions range from 2.8 mm to 3.2 mm [2]. As the field of cataract surgery has trended towards minimally invasive approaches in recent years, some scholars now hold the view that smaller incisions contribute to less surgically induced astigmatism (SIA) [3‐5] and hasten healing of the incision, thus leading to faster post-surgical recovery [6‐8]. However, smaller incisions require high technical proficiency on the part of the surgeon, as well as sophisticated surgical instruments. Smaller incisions increase the difficulty of surgery and influence the outcomes, as they limit the range of movement of the surgical instruments. Research results on the comparative efficacy of MICS and SICS in patients with age-related cataracts are inconsistent [9‐11]; while some scholars suggest that MICS can effectively reduce SIA in both the short term and the long term compared with SICS [11], other studies indicate no significant difference between MICS and SICS with regard to long-term SIA [9]. Which has more advantages? MICS or SICS? Therefore, in this study, we used meta-analysis methods to examine the advantages and disadvantages by comparing the efficacy of MICS and SICS.

Due to the rapid development of phacoemulsification and the trend towards minimally invasive surgery, incision size has begun to play a critical role in cataract surgery. Smaller incisions heal more rapidly and result in improved stability and impermeability of the anterior chamber, as well as less SIA and faster recovery of visual quality [6, 17, 19, 20]. However, research findings regarding the difference between MICS and SICS for the treatment of age-related cataracts are inconsistent. Some scholars suggest that MICS effectively reduces the AVE [9], ECC Loss % [10], corneal oedema [10] and SIA in both the short term and the long term compared to SICS [11]. However, some studies show no significant difference between MICS and SICS in the AVE [11], ECC Loss % [11], corneal oedema [11] and SIA in the long term [9]. These inconsistent conclusions create confusion for readers and clinicians. A previous study by Shentu and colleagues compared MICS with SICS, but it only evaluated outcomes up to 60 days after surgery. Comparisons of postoperative SIA only included short-term outcomes. Thus, a need remains for studies comparing long-term postoperative outcomes of MICS and SICS. Furthermore, difficulties in conducting clinical RCTs and limitations in sample size exacerbate differences among studies due to random error. To provide credible and conclusive evidence to readers, this study used meta-analysis methods, which can overcome the limitations of traditional clinical RCTs. A total of 11 studies were included in this meta-analysis. The current study is representative, as it involves studies conducted in several regions, and outcomes of SIA, EPT, AVE, CCT, ECC, ECC Loss %, intraoperative complications, and postoperative complications were selected to evaluate the effects of surgery. All selected outcomes are objective, and the risk of bias was low for all outcomes.

The results of this meta-analysis showed no statistically significant difference between MICS and SICS with regard to EPT, indicating that the duration of surgery does not differ between MICS and SICS. However, the AVE was significantly different between MICS and SICS. The surgical instruments used in MICS are more delicate, leading to lower AVE than in SICS.

The size and placement of the incision affect corneal curvature and SIA [21], which is the key factor that influences postoperative visual acuity [9]. Hayashi’s study showed that decreasing the size of the incision by 0.5 mm leads to a 0.25 D decrease in SIA [22]. The results of our study show a significant difference in SIA at 1, 7, 30, and 90 days postoperatively, indicating that MICS causes less SIA than SICS in both the short term and the long term. We therefore conclude that smaller incisions decrease SIA, which is consistent with the results of Kahraman and other authors [3‐5]. What’s more, it is an important evidence that MICS has more superiority at a low SIA and better visual quality than SICS.

Corneal oedema is common after cataract surgery, and it can affect postoperative visual acuity and quality [11] by reducing the transparency of the cornea. The CCT reflects the degree of postoperative corneal oedema. The results of this study show no statistically significant difference in CCT at 1 7, 30, or 90 days postoperatively, indicating that MICS is similar to SICS in its effects on postoperative corneal oedema. Corneal endothelial cells play an important role in normal physiological function, and they are crucial for maintaining the transparency of the cornea [11]. The duration and energy level of ultrasound exposure, as well as the infusion of viscoelastic agents into the anterior chamber during surgery, can damage endothelial cells [15, 23]. This meta-analysis shows no significant difference in the ECC at 7 and 30 days, nor any difference in ECC Loss % at 7, 30, and 90 days postoperatively. Theoretically, MICS could hasten the closure of the anterior chamber [18] and decrease endothelial cell damage and loss [7]. However, the results of this study show no significant difference between MICS and SICS. Thermal damage associated with surgical instruments and larger energy consumption may contribute to ECC Loss %; the specific mechanisms involved require further research. CCT, ECC, and ECC Loss % are associated with corneal oedema and corneal function, which affect visual recovery and surgery safety. Thereby, the results provide evidence that MICS and SICS is similar in surgery safety.

The intraoperative and postoperative complications play important roles in evaluating the safety of cataract surgery. The commonly reported complications were corneal wrinkle, anterior chamber collapse, posterior capsule rupture, iris prolapsed through the incision, and corneal edema. As reported in the included studies, the corneal edema could be resolved by treatment. No s statistically significant differences between MICS and SICS on complications indicates that MICS is similar to SICS on surgery safety.

Endophthalmitis [24] and macular thickness [25] outcomes are also related to incision size. However, we did not analyse these outcomes because the number of relevant RCT reports is limited. The detailed mechanisms underlying the differences in MICS and SICS deserve further research; health economics evaluations of these treatments are also needed.

There were some limitations in this meta-analysis. First, some of the included studies provided no details on the method of randomization, allocation of concealment, or the intention-to-treat (ITT) analysis of patients who were lost to follow-up. The unclear risk of bias in these studies may affect the credibility of the results. Second, the presence of significant heterogeneity between included studies influences the credibility of the results. A sensitivity analysis was used to assess the robustness of the meta-analysis results and to analyze the source of heterogeneity by sequentially omitting individual studies. However, the sensitivity analysis is not suitable for SIA at 90 days postoperatively and CCT at 90 days postoperatively. The heterogeneity is obvious among studies included in analysing SIA at 90 days postoperatively (I² = 83%, P = 0.003). The sensitivity analysis could not ascertain the source of heterogeneity, and the meta-regression analysis could not be used because the number of included studies is too few. Thus, a random-effects model was used to analyze SIA at 90 days postoperatively. Regarding CCT at 90 days postoperatively, the heterogeneity was encountered (I2 = 53%, P = 0.15). A fixed-effects model was selected for the heterogeneity show no statistical differences (P = 0.15) and the number of included studies limits further analysis. Additionally, the statistical results of the fixed-effects model are consistent with that of the random-effects model on SIA at 90 days postoperatively and on CCT at 90 days postoperatively. The detection of heterogeneity is related to the diversity of clinical characteristics which affect the uniformity of the involved studies. For example, the patients maybe have different ages or come from different regions and races. Plus, the surgeries maybe were conducted by different doctors using different equipments in each included study. Third, as we could not gain access to unpublished results, publication bias cannot be fully excluded.

The results of this meta-analyses show that MICS has more superiorities than SICS and that the switching from SICS to MICS is reasonable. Compared to SICS, MICS can reduce short-term and long-term SIA but produces no difference in corneal oedema, endothelial cell loss, operation time, intraoperative complications, or postoperative complications. The surgery safety of MICS is similar to that of SICS. Therefore, MICS has more advantages than SICS in reducing SIA. We would like to recommend the clinicians to promote MICS. Higher-quality randomized controlled studies are needed to validate these findings.