Presently, with the development of refractive cataract technology, the requirement for accurate postoperative refraction is increasingly high and surgeons are required to design the best operation plan perioperatively. There are many factors that affect the refractive outcomes of cataract surgery including the influence of small surgical incisions,functional intraocular lens,advanced instruments and the surgery navigation system ,these factors have been gradually solved, but irregular anterior capsular openings also affect the refractive outcomes, especially the size and shape of the capsular bag and the effective intraocular lens position[4,5]. Therefore, we designed a prospective cohort study to investigate the relationship between the morphological parameters of capsulorrhexis and deviation from predicted refraction and the effective position of the intraocular lens.
Two types of intraocular lenses were included in this study. The Tecnis ZCB00 IOL is designed by C-loop haptic and the 509M IOL is designed by plate haptic. The Tecnis IOL material is hydrophobic acrylate, designed by OptiEdge edge. This design reduces the incidence of posterior capsule opacification and improves the stability of the postoperative intraocular lens. The 509M IOL is a single-piece hydrophilic acrylic intraocular lens and is more compatible with human tissue while the plate haptic design makes the intraocular lens more stable and centred. These two types of intraocular lenses represent the two commonly used aspherical monofocal IOLs, which are typical and representative. The morphological features of capsulorrhexis (including the area of capsulorrhexis, horizontal diameter, vertical diameter, circularity, decentration, and package) that were measured at 1 week, 1 month, and 3 months showed that the 509M IOL does not have significant differences over time. However, the area of capsulorrhexis and the horizontal diameter of the Tecnis IOL showed significant differences at 1 week to 1 month and at 1 week to 3 months. These results show that the Tecnis IOL’s capsulorrhexis had the largest area and horizontal diameter at 1 week after the operation, and as time goes by, the area and horizontal diameter gradually decreased up to 1 month and remained stable to 3 months. This indicates that the area and the horizontal diameter gradually stabilize at 1 month after the operation. Further, the circularity showed significant differences at 1month to 3 months postoperatively. These differences, when compared to the 509M IOL, are likely due to the design of the IOL loops. The contractive force around the C-loop haptic IOL is not equivalent on every side of the capsule bag, and the parts of the IOL loops that do not completely and tightly contact the capsule bag can result in poor stability. Therefore, in terms of stability, the C-loop haptic IOL is not as good as the 509M IOL[6]. There is also capsule contraction syndrome at 1 month after surgery that leads to a decrease in the area and horizontal diameter of the capsulorrhexis. As a result, we believe that the stability of the intraocular lens with the plate haptic design is better than that of the C-loop intraocular lens, and they have lower requirements for capsulorrhexis. Meanwhile, some studies show that the material of the optical surface also affects the contraction of the anterior capsule.
The effective position of the intraocular lens can reflect the longitudinal position of the intraocular lens in the eye. It has been shown that changes in anterior chamber depth of approximately 720 μm lead to a 1.00 D refractive deviation[7]. Moving forward to the retina leads to a myopic deviation while moving backward to the retina leads to a hyperopic deviation. Therefore, the ELP is particularly important for cataract surgery, especially for patients with a refractive intraocular len implantation[8,9]
The effective position of the intraocular lens is related to the fibre shrinkage, capsular opacity, and the material of lens[10, 11]. If the opening of the anterior capsular is too small, it can cause contraction of the capsular bag that leads to the displacement of the ELP. Therefore, when the size of the anterior capsular is only wrapped around the edge of the optic surface of the intraocular lens (5.5 mm in diameter), the contraction of the capsular bag can be avoided and the influence on the ELP can be minimized[12].
These results showed that the effective position of the intraocular lens increased gradually at 1 week, 1 month, and 3 months in the 509M IOL group, but there was no significant difference of the ELP in the Tecnis IOL across 1 week, 1 month, and 3 months after the operation. There are reports that this difference is related to the mechanical properties of the IOL[13,14]. Different IOL edges have different effects on the axial motion of the intraocular lens. This finding may be because the 509M IOL is a plate haptic design, and the four points of the intraocular lens all move forward during the contraction of the anterior capsule. This can result in the central axial force of the IOL moving backward, which leads to an increase in the effective position of the intraocular lens. For the C-loop haptic IOL, the small gap between the IOL loops and the optical zone may reduce the influence on the ELP during from the contraction of the anterior capsule.
There were significant differences in the ELP in two groups at 1 week, 1 month, and 3 months (P < 0. 01), and the ELP value of the Tecnis IOL group was higher than that of the 509M IOL group (P < 0. 01). These results indicate that the ELP is larger in the C-loop haptic IOL. Presently, the formulas for the intraocular lens (Haigis, Holladay 2, Olsen, and Barrett Universal II) all include the ELP in their calculations. We should fully consider the ELP of different IOLs when calculating the IOL degree to improve the accuracy of degree predictions following an operation.
A precisely positioned, predictably sized CCC not only is an important guarantee for the surgeon to complete the operation safely but also ensures a lasting curative effect for the patient after surgery. In this study, the effects of the capsulorrhexis morphological features on the deviation from predicted refraction and ELP were observed by using the relevant parameters of area, horizontal diameter, vertical diameter, circularity, decentration, and package. We found that there was a positive correlation between the area of capsulorrhexis and the deviation from predicted refraction at 1 month and 3 months in Tecnis IOL group, as well as horizontal diameter at 1 month and vertical diameter at 3 months. For every 1 mm2 increase in size, the deviation from predicted refraction will increase by 0.0152 D. For every 1 mm increase in horizontal diameter, the deviation from predicted refraction will increase by 0.07 D. In addition, for every 1 mm increase in vertical diameter, the deviation from predicted refraction will increase by 0.05 D. For the 509M IOL, there were no significant correlations between the morphological parameters and the deviation from predicted refraction except for the package of the capsule bag (P < 0.05). This single-piece hydrophilic acrylic intraocular lens has good flexibility and the loop can adapt to different sizes of the capsule bag due to the unique design of the bending loops so that asymmetric contraction force in different directions can be balanced and maintain stability after IOL implantation. Yu Fang et al. [15] compared the stability of a single-piece and a three-piece aspheric intraocular lens from the same company and found that the stability of a single-piece IOL is better than that of a three-piece IOL.
Simultaneously, in the correlation analysis between the capsulorrhexis morphological features and the ELP, it was found that the area, horizontal diameter, and vertical diameter of the capsulorrhexis were correlated with the ELP in the Tecnis IOL group, while the package was correlated with ELP in both groups. Studies have shown that in all capsulorrhexis parameters, the package affects the horizontal and vertical shift of the intraocular lens. Improvements to the package of capsulorrhexis leads to a smaller shift of the intraocular lens, a more stable IOL position, a central positon and a smaller refractive deviation after operation[16]. Dick et al. proposed that the centre of the capsulorrhexis should be located on the optic axis, that the capsulorrhexis should be perfectly round and that the best diameter is 5.25 mm, which could be the most effective way to prevent the aberration, coma, and ametropia caused by the contraction of the capsular bag, the posterior cataract, and the tilt of the intraocular lens[17]. Kim et al.[18]proposed that the posterior continuous circular capsulorrhexis has a more-stable refractive outcome and prevents the effect of posterior capsular opacity on the stability of the IOL. In recent years, the emergence of electronic capsulorrhexis and femtosecond-assisted capsulorrhexis has enabled the capsulorrhexis to develop in a more precise direction. It was found that the excellent rate of the conventional artificial capsulorrhexis group was only 20% ,the failure rate was 60% ,while the excellent rate of the electronic capsulorrhexis group was 100%, and the difference between the two groups was statistically significant[19]
Overall, our study found that the 509M IOL with a plate design IOL has better refractive stability than the Tecnis IOL with C-loop haptic, and the four-point force is symmetrical, which is effective at reducing and offsetting each other. The buffering capacity prevents it from being affected by external forces, and reduces the tilt and decentration of the IOL. The deviation from predicted refraction of the IOL designed by C-loop haptic is positively correlated with the area of the capsulorrhexis, the horizontal diameter and vertical diameter, and the morphological parameters of the different types of IOL that also affect the changes in the ELP.
In the future, we will increase the sample size, increase the different types of intraocular lenses, and extend the follow-up time to supplement and improve these data and provide a reference and clinical basis for the size and shape of the capsulorrhexis for different intraocular lenses.
The success of CCC in cataract surgery affects the refractive shift and the effective position of the intraocular lens. With improvements in surgical techniques and the application of femtosecond, cataract surgery has become more accurate. Only the full mastery of CCC can minimize the postoperative refractive shift and the ELP, which will enable the patient to achieve satisfactory visual effects after surgery.