Functions of the capsular tension ring

I would like to make 2 comments about the recent capsular tension ring (CTR) article by Boomer and Jackson.1 1. Can implanting a CTR affect the intraocular (IOL) power formula? In the article, Boomer and Jackson state that the “CTR sat between the IOL haptics and ciliary body, which raised the question of whether a CTR modifies the effective lens position (ELP) and, ultimately, the accuracy of IOL calculations and refractive outcome.” To investigate this issue, Boomer and Jackson conducted the study. A previous study using the Miyake technique2 showed a CTR sitting in the capsular bag after cataract removal. The CTR did not strengthen the capsular bag or alter its anatomical position. When an IOL was placed in the bag, the CTR did not change the IOL's position. However, if the CTR was larger than the capsular bag, the 2 ends of the CTR overlapped in the bag. If the CTR was smaller than the capsular bag, the CTR did not provide enough tension around the equator of the capsular bag and left a large opening between the 2 ends of the CTR, providing a potential opportunity for lens epithelial cells to migrate to the posterior capsule and eventually contribute to PCO. Based on these findings, a CTR is unlikely to affect the IOL power formula because the position of the IOL in the capsular bag is not affected by a CTR. The study by Boomer and Jackson provides scientific and clinical data to support the earlier study. 2. How does a CTR improve refractive outcome? In the article, Boomer and Jackson state “[t]he CTR subset analysis demonstrated a trend toward more accurate outcomes when using Holladay 2 formula but not SRK/T when compared with contralateral eyes without a CTR. Both formulas showed lower variances in the CTR eyes.” Therefore, the authors conclude the CTR not only assisted surgeons in surgery but also improved refractive outcomes and patient satisfaction. Previous studies2–5 suggest the CTR has 2 basic functions: facilitating phacoemulsification during surgery and maintaining IOL centration after surgery in eyes with zonular dehiscence. An in vitro study2 demonstrates that IOL decentration can be avoided when a CTR in implanted in a capsular bag with broken zonules. This finding is supported by clinical studies.3–5 If visual and refractive outcomes are better in eyes with a CTR than in those without a CTR, the CTR should be credited because it prevented IOL tilt and decentration in the eyes with zonular dehiscence after cataract surgery. The CTR is not a refractive device, but implanting a CTR may achieve good visual and refractive outcomes after cataract surgery in eyes with zonular dehiscence. In Boomer and Jackson's article, the refractive prediction error was used to compare refractive outcomes between eyes with a CTR and those without a CTR. Several factors such as IOL decentration, the time of the postoperative refraction, and the astigmatism-reduction procedure during cataract surgery may have affected the measurement. These factors are critical and must be controlled to achieve accurate measurements. In summary, a CTR can facilitate phacoemulsification during surgery and maintain IOL centration after surgery in eyes with zonular dehiscence. Good visual and refractive outcomes following CTR implantation in these eyes are likely due to IOL centration.