CTR is widely used in clinical treatment of cataracts complicated with lens dislocation. CTR can effectively balance the tension of zonular fibers, uniformly distribute the tension of the capsular bag, maintain the shape of the capsular bag, reduce loss of the vitreous body, and increase attachment between posterior capsule and IOL surface. These effects of CTR increase IOL stability after cataract extraction involving IOL implantation and reduce the occurrence of posterior capsule opacification and IOL dislocation [7, 22–34]. Whether and how CTR implantation can also benefit patients with weakened zonular fibers but no lens dislocation is unclear. The present randomized controlled trial suggests that CTR in such patients can reduce the incidence of capsular shrinkage, maintain capsular bag stability, make IOL inclination more manageable and stable, as well as increase the rate of complete attachment between the posterior capsule of the lens and posterior surface of the IOL.
Vanags et al [27] demonstrated that CTR implantation during cataract surgery with lens dislocation can lead to better capsular shape, IOL position and lower risk of capsular shrinkage at 1 week to 2 years after surgery than without CTR implantation. Studies in patients [ 37, 38] and animals [39] showed similar results even in cases without weak zonules. However, there are other studies showing no improvement in the incidence of IOL dislocation by CTR implantation at 3 months after cataract surgery [29, 30]. In the current study, CTR implantation showed the ability to prevent capsular shrinkage starting from 1 week postoperatively in patients with high myopia. At 3 months after surgery, this effect was even more significant, suggesting that CTR is effective in delaying shrinkage and maintaining capsular bag stability in the longer term, especially in patients with severe myopia.
In contrast to these results in patients with myopia, our analysis of patients with PPV showed no clear beneficial effects of CTR, especially on the anterior capsulorhexis shrinkage, likely due to the adverse effects of silicone oil or gas bubbles injected after vitrectomy. Thus, the benefits of CTR implantation may not compensate the adverse effects of silicone oil or gas bubbles, which reduce elasticity and alter capsule structure as well as its response to capsulorhexis.
Capsular contraction syndrome is a more serious complication following capsular shrinkage [27, 28], which is usually accompanied by posterior capsule opacification and even causes IOL dislocation. Timely intervention is needed in order to prevent further visual impairment. Incidence of significant capsular contraction syndrome was lower in among our CTR patients (4.55%, 1 case in PPV subgroup, 0 in myopia subgroup) than among control patients (15.00%, 0 in PPV subgroup, 3 cases in myopia subgroup) at 3 months after surgery, which made it mandatory for these patients to have Nd:YAG treatment. This finding suggests that CTR implantation can reduce the incidence of, but not completely eliminate, capsular shrinkage and contraction, especially in patients with severe myopia [39].
We also found that the rate of complete attachment between the posterior capsule of the lens and posterior surface of the IOL was higher in the CTR group than the control group after only 1 week and even higher after 3 months. This may be because the CTR can mechanically compress the capsular bag closer to the IOL surface [26, 34, 40, 41]. However, this effect of CTR was not obvious in patients with strong myopia, perhaps because such eyes are axially longer, and the capsular bag is larger. We speculate that the CTR used in this study, with a diameter of 11 mm, may not be large enough to completely open the capsular bag in patients with strong myopia.
Previous animal and human studies demonstrated that IOL eccentricity and inclination were small and remained stable within 2 years after CTR implantation in cataract surgery [37, 39]. We found that the vertical inclination angle gradually decreased in CTR patients but increased in control patients. Horizontal IOL inclination remained stable within 3 months after surgery in CTR and control patients. These results support the idea that IOL inclination after CTR implantation is manageable and stable [22, 42].
Whether CTR implantation during cataract surgery changes postoperative refractive prediction error is unclear. A retrospective study on CTR implantation in 25 patients with abnormal zonules found that the position of the posterior chamber IOL exceeded the predicted value by + 0.5 to + 2.0 D [31]. A randomized controlled trial in 52 cataract patients without other complications showed hyperopia drift after CTR implantation [29]. Those authors recommended reducing preoperative refractive predictions by 0.5 D. The present study suggests, in contrast, that preoperative refractive predictions should not be adjusted for patients undergoing CTR implantation: we did not observe substantial differences in the values for CTR and control patients, consistent with other studies [33, 43–45]. It is noteworthy that both UDVA and BCDVA were better in CTR patients than in controls.
There are a few noteworthy limitations in this study. First, CTR with 11 mm diameter was used in all patients. Individualized optimization of CTR diameter is more desirable especially in case of high myopia and may benefit cataract patients more. Second, the IOL profile of some patients was not fully visible in anterior segment optical coherence tomography because of limited pupil dilation. Only IOL tilt was measured in our study, making IOL inclination angle measurements less conclusive. Third, patients were followed up for only 3 months, based on studies suggesting that many beneficial and adverse effects of CTR implantation occur within that time. Fourth, we did not collect complete data on the area of anterior continuous curvilinear capsulorhexis at 1 day after surgery, which prevented us from studying early changes in anterior continuous curvilinear capsulorhexis, such as within 1 week.
Despite these limitations, our study provides evidence that the benefits of CTR implantation outweigh its disadvantages in cataract patients with mild abnormal zonules such as those with high myopia or previous PPV.