Commentary on: IOL dynamics after capsular tension ring implantation

Capsular tension rings (CTRs) have conventionally been used in cases of zonular weakness and subluxation to provide uniform equatorial tension and stretch the posterior capsule (PC) to stabilize the capsular bag.[1] The uniform capsular stretch induced by these rings has also been postulated to prevent anterior capsular phimosis, as well as prevent lens decentration and tilt.[1] The role of CTR in preventing posterior capsular opacification (PCO) is less well-established. A meta-analysis demonstrated the potential benefit of CTR to prevent PCO and decrease Nd:YAG rates.[2] The proposed hypothesis for the prevention of PCO is the mechanical prevention of the posterior migration of lens epithelial cells by the ring. Complete apposition of the posterior capsule to the posterior surface of the IOL optic is increasingly being recognized as a significant factor in preventing the development of PCO.[3,4] Modifications of IOL materials have been suggested to improve PC-optic adhesion and thereby minimize the rates of laser capsulotomies.[4] In this study, the authors have evaluated the role of implanting a CTR to promote PC-optic apposition and thereby prevent lens decentration and tilt and minimize the incidence of PCO.[5] They observed a significant decrease in the distance between the PC and posterior surface of IOL after implantation of the CTR, and the decrease was most marked in the cases implanted with size 13 CTR. However, they did not document intraoperative complete PC-optic apposition in any case, and there was no postoperative data to conclusively establish the benefit of CTR in promoting complete PC-optic apposition and preventing PCO. A recent study by Kaur et al.[4] evaluated the relation between initial posterior capsular morphology and long-term PC-optic apposition. They observed that initial smooth PC morphology correlated with a higher incidence of complete PC-optic apposition at two years. They also conclusively demonstrated the association between complete PC-optic apposition and decreased incidence of PCO and laser capsulotomy rate. CTR stretches the PC, reducing the undulations and folds and making it smooth. This, combined with the equatorial stretch, may facilitate PC-optic apposition in the postoperative period. The authors selected the CTR size based on their own nomogram, which employs the horizontal white-to-white (WTW) diameter rather than the conventional axial length.[5] A CTR of size 13 was used by the authors if the WTW was greater than 12 mm. They used three different CTR sizes in their study population and observed the greatest decrease in PC-optic distance with the largest CTR (size 13). This is to be expected as a wider circumference of the ring will cause more equatorial stretch and capsular tension. However, a greater reduction in PC-optic distance cannot be the only basis for the selection of CTR size. The authors further recommend a size 13 CTR in cases with WTW <12 mm as well; however, they themselves have not evaluated the outcomes or any other complications that may arise from putting a larger sized CTR in smaller eyes. Safety as well as efficacy of any new nomogram must be established before recommending its use. The authors also propose that implanting a CTR may prevent long-term IOL decentration, rotation, and tilt. The effective lens position may be more predictable with a CTR in situ, leading to enhanced accuracy of the postoperative refractive outcomes, especially in cases with premium IOLs. The role of CTR in preventing IOL decentration and tilt in eyes with normal axial length remains controversial. A randomized controlled trial (RCT) did not observe any significant influence of CTR implantation on the postoperative axial IOL position and effective lens position.[6] Contrary to expectations, another RCT observed an increased decentration and tilt attributed to CTR implantation in cases with plate-haptic IOLs.[7] A recent study by Lin et al.[8] observed no impact of CTR on C-loop IOL decentration and tilt in eyes with axial length less than 30 mm. Of note, they observed a significant decrease in IOL decentration and tilt, increased position stability, and improved visual quality in eyes with axial length of 30 mm or longer, thereby suggesting a role of CTR in high myopic eyes implanted with C-loop IOLs.[8] To conclude, CTRs have conventionally been used for the stabilization of the capsular bag; however, they may have a role in promoting long-term IOL stability and prevention of PCO. The authors have conclusively demonstrated a significant decrease in the space between the PC and IOL optic after implantation of a CTR. However, it is as yet unclear whether the implantation of a CTR hastens the complete apposition of PC to the IOL. The current evidence does not support the use of CTR in eyes with normal axial length to decrease IOL decentration and tilt. In addition, the size of CTR that provides maximal advantage without causing any adverse effect needs to be determined. A long-term prospective RCT is required to demonstrate a definite long-term benefit of CTR implantation in terms of complete PC-optic apposition as well as prevention of PCO.