Posterior capsule opacification (PCO) is one of the major postoperative complications of cataract surgery and is the main cause of long-term vision loss after surgery. Its incidence varies depending on the patient’s age, surgical approach, whether other eye diseases are present, IOL material, type, follow-up time and diagnostic criteria for posterior capsule clouding. However, it is generally accepted that the incidence is high within 5 years after surgery, is age-related, and is most common in children and progresses rapidly. The factors affecting its development are numerous and complex. Among them, the different treatment of the capsule membrane during surgery also has a greater impact on posterior capsule clouding. Scholars at home and abroad have done a lot of research work in this area, which provides important guidance for clinical prevention of posterior capsular turbidity. (1) The effect of capsule truncation on posterior capsule clouding: Posterior cataract is mainly caused by the migration, proliferation and differentiation of postoperative residual crystalline epithelial cells to the posterior capsule, and in the past, some scholars proposed to make large anterior capsule truncation as much as possible in an attempt to reduce the occurrence of PCO. However, recent studies have shown that after large capsular amputation, especially the open-can type with untidy edges, more crystal epithelial cells are released from contact inhibition, which, together with the proliferation of crystal epithelial cells migrating from the equatorial region, actually increases the occurrence of PCO. The current intracapsular IOL implantation requires a small anterior capsular amputation to provide a complete and stable capsular bag for IOL’s to maintain orthotropic position for long term fixation, and also allows the IOL optical surface to be tightly fitted to the posterior capsule and the loop to form a mechanical barrier in the vault of the capsular bag to reduce the occurrence of PCO [1]. The envelope capsulotomy is popular with many surgeons because it has a large, visible anterior capsule margin that provides adequate support for the loop after IOL insertion and keeps the IOL in the capsular bag, leaving an adequate anterior capsule to protect the corneal endothelium when removing the cortex [2]. Clinical data confirm that envelope type capsulotomy is a practical and effective method in reducing the incidence of PCO, although it is worse than continuous circumferential tearing of the capsule, but superior to open canister type capsulotomy. Yao Shuling and Chen Daben [3] found that: modified envelope capsulotomy has a high rate of intraoperative capsular bag integrity. The damage to the ocular tissue was small, and the incidence of postoperative capsular clouding was significantly lower. It was concluded that modified envelope capsulotomy with adequate hydrodynamic separation of the cortex, delivery of the nucleus and cortical irrigation in the capsular bag, and circumferential tearing of the capsule after IOL implantation in the capsular bag. These measures reduced the disruption of the blood-atrial water barrier and the damage to the corneal endothelium. Also, the reduction of residual cortical and epithelial cells also deprives the small amount of residual epithelial cells of a proliferative environment, thus reducing the occurrence of PCO. Others [4] have suggested that there is no difference in the incidence of posterior capsular clouding between the two. However, although they are also called “envelope capsulotomy” and “modified envelope capsulotomy”, respectively, there are major differences between the two authors’ surgical approaches. Aminollah Nikeghbali’s study [2] found a highly significant difference in the incidence of PCO in anterior capsular CCC compared to envelope capsulotomy, although this technique is practical and effective, it does not provide a completely smooth margin like continuous circumferential capsulotomy (CCC). The reasons for analyzing the CCC technique as the best anterior capsulotomy modality to reduce the incidence of PCO are: the long-term stable fixation and centering of the IOL in the capsular bag; increased cortical clearance when combined with hydrodynamic separation; and adhesions between the free edge of the anterior capsule and the posterior capsule that may prevent residual epithelial cells from entering the optic axis.Hakkl Birincit et al [5] also found a lower incidence of PCO with anterior capsulotomy than envelope capsulotomy, with significant difference. It is now believed that continuous circumferential capsulotomy is the best procedure to reduce PCO. (2) Influence of the size of the torn capsule and the position between the free edge and the IOL optic part on PCO: With the common application of cataract ultrasound emulsification technology, anterior capsule CCC has become the conventional torn capsule method, and a study by Yizhi Liu et al. showed that eyes with the edge of the torn capsule enclosure completely or partially attached to the IOL optic surface could maintain a high percentage of central transparency of the posterior capsule membrane [6], while the optical part of the IOL The latest design of the right-angle edge of the IOL produces a sharp capsular ridge in the posterior capsule also presupposes that the central CCC and the edge of the optical portion are located within the capsular bag. Zhang Zhenping et al [7] observed that no PCO occurred in the IOL right-angle rim group when the size of the annular tear capsule opening was moderate; when the annular tear capsule opening was too large or deviated, PCO occurred in 57.1% of cases, and there was a significant difference between the two. Wang Hong et al [8] conducted a three-year postoperative follow-up of the posterior capsule of the crystal in patients with consecutive annular tear capsules >5.5 mm and <5.5 mm in diameter. A significantly higher chance of developing PCO was found for >5.5 mm than for the other group of patients with <5.5 mm. It was also concluded that the ideal tear capsule size should be such that the edge of the truncated capsule crosses the edge of the optic portion of the IOL by 0.5 mm. The study of Zhu Gang [9] suggested that there was no significant difference in postoperative PCO between the CCC diameter <5.0mm group and the group with diameter between 5.0mm-6.0mm; while there was a significant difference between the CCC diameter >6.0mm group and the first two groups, and the smaller the CCC diameter the more obvious the degree of clouding of the anterior crystal capsule and the contraction of the CCC capsule opening, and the larger the area of clouding, so for some postoperative need to examine the periphery in detail The torn capsule area should not be too small for those who need to examine the peripheral fundus in detail after surgery. The tearing capsule area is too large, especially when the tearing capsule diameter is >7.0 mm, it will destroy part of the lens suspensory ligament, and the balance between the centripetal force of capsule contraction and centrifugal force is out of balance, especially making the capsule relax at the damaged lens suspensory ligament and producing posterior lens capsule folds [9]. A study by Huiying Wang et al [10] demonstrated that the incidence of PCO was higher in asymmetric CCC than in symmetric CCC, while the incidence of PCO was significantly higher in symmetric continuous circumferential torn capsules >5.5 mm in diameter than in those ≤5.5 mm in diameter. Their [9] [10] analysis suggests that the mechanism may be that after implantation of the IOL in the capsular bag, when the free edge of the capsule mouth is fully attached to the optic portion of the IOL, the bag can remain airtight, and the “memory” of the IOL loop in the bag causes the angle of the bag to extend posteriorly, while the front of the IOL in contact with the capsule mouth forms The contraction of the fibrous ring at the front of the IOL in contact with the opening of the capsule creates a centripetal tension within the capsule, allowing the IOL to fit tightly with the posterior capsule of the lens, thus forming a closed space and preventing the migration and proliferation of epithelial cells to the central area of the posterior capsule. At the same time, the anterior capsule membrane applies uniform pressure to the IOL posteriorly so that the posterior capsule remains flat. On the contrary, when the free edge of the capsulorhexis is not fully or partially attached to the optic portion of the IOL, the capsular bag cannot form a confined space and the lens epithelial cells as well as some inflammatory cells can easily enter the bag under the action of growth factors, thus, the incidence of PCO is greatly increased [10]. Therefore, the ideal CCC should be 5.0-6.0 mm in diameter of the tearing capsule size, with the capsule opening squarely rounded, centered, and symmetrical, and the size should be such that the edge of the anterior capsule membrane crosses the edge of the optic portion of the IOL by 0.5 mm as appropriate. (iii) The effect of posterior capsule membrane treatment on posterior capsule clouding: complete removal of cortex and posterior capsule polishing can reduce the residual crystal material in the posterior capsule, which is meaningful to reduce the incidence of PCO, but since no surgical procedure can guarantee complete removal of crystal epithelial cells, and posterior capsule membrane tearing makes the crystal epithelial cells unable to migrate in the area, thus can reduce the incidence of PCO. Therefore, some scholars believe that it is advisable to perform posterior capsule continuous circumferential capsular tear (PCCC) at the same time [11]. Tu YF [12] and Maidan et al [13] confirmed that one-stage posterior capsule continuous circumferential tearing is a feasible method to prevent postoperative PCO. Yu Zhengxing et al [14] concluded that posterior capsulotomy with an electric capsulotomy needle is easy to operate and can ensure circumferential posterior capsulotomy, and no special complications were observed, so it is a good method for posterior capsulotomy. However, Dong said that although there is no crystalline epithelial cell migration area after PCCC, the intact vitreous anterior membrane can still be used as a scaffold by crystalline epithelial cells to proliferate and migrate, and their study found that ultrasound emulsification combined with PCCC and anterior vitrectomy can effectively prevent the occurrence of clouding in the central visual area after cataract surgery [11]. However, with the loss of vitreous, the incidence of complications such as retinal detachment and macular edema would increase, so Hu Taofang et al [15] completed PCCC without anterior vitrectomy and only tore the anterior vitreous membrane, which also destroyed its integrity, and their intraoperative vitreous detachment rarely occurred and did not produce posterior obscuration after surgery, with more satisfactory clinical results. However, these surgical methods may produce some complications due to breaking the integrity of the vitreous, and their long-term results are to be further observed. Wang et al [16] randomly divided 59 patients with 65-eye pediatric cataract IOL implantation into two groups. Group A underwent one-stage continuous posterior annular capsule tearing combined with postoperative subconjunctival injection of 5-fluorouracil. Group B underwent one-stage continuous posterior capsular tearing alone. At 3-year postoperative follow-up, there was a significant difference between the two groups. Suggestion: One-stage continuous circumferential posterior capsulotomy combined with subconjunctival injection of 5-fluorouracil without anterior vitrectomy was also effective in preventing the occurrence of PCO after cataract IOL implantation in children. (iv) Effect of intra-capsular IOL implantation on PCO: Tang Yurong [17] conducted a 6 months to 3 years follow-up after extra-capsular cataract extraction in 234 eyes and extra-capsular cataract extraction combined with intra-capsular IOL implantation in 109 eyes, and the results showed that PCO occurred in 38% of eyes without IOL implantation and in 17% of eyes with IOL implantation, with significant differences. Hakkl Birinci [5] also concluded that PCO occurred more frequently after ECCE without IOL implantation, suggesting that at least some components of the optical portion of the IOL prevented cell migration. A study by Zhiwei Wen [18] found a significantly lower incidence of PCO in the capsular bag implanted IOL than in the ciliary sulcus implanted group, with a significant difference. He analyzed that the reason for this is that the implantation of a one-piece biconvex IOL in the capsular bag creates a symmetrical extension in the capsular bag, which strains the posterior capsule and increases the contact between the optical surface of the IOL and the posterior capsule, creating a mechanical “barrier” between the optical surface of the IOL and the posterior capsule. Moreover, IOL fixation in the capsule avoids irritation of the uvea and helps to reduce the disruption of the blood-atrial water barrier and inflammatory response. At present, there is no controversy that IOL should be implanted after cataract extraction. (v) Effect of capsular bag tension ring on the incidence of PCO: The capsular bag tension ring not only provides a complete equatorial round corridor of the capsular bag for most posterior chamber type IOLs, but also effectively maintains the integrity of the lens capsular bag, protects the opening of the continuous annular tear capsule and the normal shape of the IOL, inhibits the contraction of the capsular bag, prevents the eccentricity of the IOL due to the pulling of the continuous annular tear capsule, and can mechanically It also prevents the lens epithelial cells, degenerated fibroblasts and collagen fibers from invading into the posterior capsule, which prevents deformation and clouding of the posterior capsule. Animal tests and clinical application studies have demonstrated the effectiveness of capsular bag tension rings.Okihiro Nishi, et al [19] studied 60 patients with senile cataracts and designed an open PMMA material capsular bag bending ring with flat sides and a rectangular ring cross-section of 0.7 mm in length and 0.2 mm in width to sharpen the bending of the capsule at the equator. This ring was implanted into the operative eye with a hydrogel IOL, and the contralateral eye was used as a control with an IOL implanted but without the capsular bag ring. Postoperative examination. The results were a significant reduction in anterior capsule clouding and wrinkling in the eye with the ring and a significant reduction in the mean PCO incidence compared to the eye without the ring. For those treated with YAG laser 3 years after surgery, there was a significant difference between eyes with the ring compared to eyes without the ring. This ring is useful for patients who will undergo vitreoretinal surgery and laser photocoagulation, as well as for pediatric cataract cases that have a higher risk of PCO complications and require ND-YAG laser posterior capsulotomy. Their analysis concluded that the sharp edge of the capsular bag ring increased the curvature of the capsular membrane, prompting tight contact, inhibiting the migration of crystalline epithelial cells (LECs) and promoting contact inhibition of epithelial cell migration, and that LECs stopped proliferating when they reached the wall of the right-angled basal cushion because of contact inhibition, while the cells readily climbed on the capsular membrane of the U-shaped basal cushion. They also found that PCO could not be completely prevented by the ring even though it was not obvious in the eyes with the ring. Therefore, the role of the capsular bag ring in preventing PCO is limited. In conclusion, there are many factors affecting the occurrence of posterior capsular opacification, and the capsular membrane factor is only one of many factors. Although the surgical operation and capsulotomy method have been improved and developed to be more mature, and play an important role in preventing posterior capsular clouding, the incidence of posterior capsular clouding cannot be reduced to a satisfactory level, and some methods such as PCCC combined with anterior vitreous osteotomy are effective in preventing PCO, but there is a risk of long-term complications and high technical requirements. Most of the non-surgical methods of prevention and treatment are only in vitro trials have achieved some results, and there is still a distance to clinical use, there is no ideal as a clinical routine use of PCO prevention methods, for the obvious impact on vision PCO or YAG laser and surgical incision of the posterior capsule method is the most effective, but these two methods have destroyed the posterior capsule, can bring some common or different complications, such as : elevated intraocular pressure, corneal thermal damage, reduced endothelial cell count, iritis, and damage to the optical portion of the IOL [20]. The exploration of non-surgical methods of prevention and treatment will become a future direction and research hotspot.