Several traditional and surgical clinical therapies are implemented for correction of corneal astigmatism. Many kinds of IOLs are available which are designed with multiple characteristics for the improvement of the clinical outcomes including visual acuity, correction of astigmatism, and rotational stability. Toric IOLs are increasingly used to correct corneal astigmatism at the time of cataract surgery and have greatly improved post-operative visual performance. In addition to the implantation of toric IOLs, transparent corneal incision release is more commonly used. However, due to the requirements for the position of the surgical incision, the limitation of the astigmatism correction, and the poor predictability of the postoperative effect , surgeons prefer to choose a method that can treat corneal astigmatism while performing routine cataract surgery procedures. With growing interests in reducing undesirable residual astigmatism, a well-designed toric IOLs greatly improves the postoperative visual quality and surgical satisfaction of patients , and are considered as the best way for the treatment of cataract with corneal astigmatism.
Accurate preoperative biometry is the basis of the calculation of toric IOL cylinder power and targeted axial position. The measurements for axial lengths are limited, but there are many methods available for the measurement of corneal curvature. Kim  et al. have found that there was no statistical difference in the corneal curvature measured by the keratometer, IOL master and Pentacam corneal topography, and there was no statistical difference in the calculated IOL cylinder power and the targeted axial position by the toric IOL calculation formula. Therefore, in this study we used the currently recognized gold standard - IOL master to measure the corneal curvature.
Anterior corneal astigmatism (ACA) shows great variability among people compared to the posterior corneal astigmatism (PCA) which tend to be more unique with sight differences. 85.0% ~ 96.1% of PCA in the population is -0.01D ~ -1.10D astigmatism against the rule, with the mean value of about − 0.3D . PCA is of great significance in the calculation of toric IOL degree. If PCA is ignored, when ACA is with the rule, the whole corneal astigmatism will be over-estimated to 0.22D on an average, while ACA is against the rule, the whole corneal astigmatism will be underestimated to 0.22D on average . If PCA is larger, the effect on whole corneal astigmatism will be greater. The two toric IOL online calculators used in this study only input the ACA value, without considering the actual PCA value. As feasible in most cases, the PCA was − 0.5D astigmatism against the rule by default, but when the PCA is special (the value is too large or too small, or the direction is astigmatism with the rule), the calculation error will be larger. Therefore, in addition to judging the regularity of corneal astigmatism, we also directly measured PCA by Pentacam corneal topography. If PCA is special, we need to be more careful in the calculation of toric IOL cylinder power and the toric IOL cylinder power needs to be increased or decreased according to the vector analysis results.
The postoperative UCDVA is the most direct and important index used to evaluate the success of cataract surgery, and in our study the postoperative UCDVA in Rayner group was 0.17 ± 0.20. The postoperative residual astigmatism is the objective index indicated to evaluate the astigmatism correction effect of toric IOL and the average residual astigmatism in Rayner group was (0.69 ± 0.40) D. Through the literature reviews, a four-year clinical study from the Pasteur medical center showed  that the postoperative UCDVA after the implantation of Rayner toric IOL in 84 cases was 0.3, and the residual astigmatism was 0.8D, which was consistent with results of this study.
The rotational degree of IOL reflects the stability of toric IOL in the capsule. In order to achieve a good postoperative effect, the axial rotation of toric IOL should be controlled within 5° . In this study, 80% of patients in the Rayner group rotated below 5° and 20% of patients (5 eyes) rotated between 5° and 10°, with an average rotational degree of (3.5 ± 1.6)°. 76% of patients in the Alcon group rotated below 5° and 24% of patients (6 eyes) rotated between 5° and 10°, with an average rotational degree of (4.0 ± 2.1)°. By reviewing the literature, a study by Molham et al. showed  that the average postoperative rotational degree of Rayner 623T was 3.44°, and the range of rotational degree was 0 ~ 12°. In another study, Mendicute et al. found that Alcon Acrysof Toric had better rotational stability, and the rotational degree was all below 12° , which was consistent with results of this study. Both brands of toric IOLs adopted a one-piece design to increase the rotational stability of IOL. Correspondingly, the three-piece toric IOL has poor rotational stability, with about 41% of the postoperative rotational degree greater than 10° , and therefore not recommended to use and gradually withdrawn from the market. In addition to the one-piece design, the excellent rotational stability of Rayner 623T is due to its unique anti-vaulting haptic (AVH) loop design. The total length of IOL is 12.5 mm and when the diameter of the capsule is ≥ 12.5 mm, the loop is fully extended. When the diameter of the capsule shrinks to 10.5 mm after surgery, the outer loop begins to resist the pressure generated by the capsule contraction. As the diameter of the capsule reaches 10 mm, the outer loop begins to contact with the inner loop, generating an additional progressive support force, and when the diameter of the capsule reaches 9.5 mm, the outer loop is in full contact with the inner loop, and the contact between the top of the loop and the optical part produces a strong supporting force to resist the impact of the capsule contraction on IOL.
The National Eye Institute 25-Item Visual Function Questionnaire (NEI VFQ-25) can quickly and accurately determine the quality of life related to visual function of patients through more than 20 questions, and thus is widely used in clinical and scientific research of ophthalmology. The scores of Rayner group and Alcon group were both higher and showed no statistical difference, reflecting the good postoperative visual related quality of life in the two groups. In addition, there was no statistically significant difference in contrast sensitivity or objective visual quality at each spatial frequency between the two groups 3 months post-surgery (P > 0.05). We have seen that both toric IOLs are equally beneficial and precise to correct residual astigmatism after cataract surgery, and was have ascertained with good rotational stability, postoperative visual function, and high visual quality of life for patients. As far as we know, this is the first time NEI VFQ-25, contrast sensitivity and objective visual quality have been simultaneously introduced into studies to investigate the clinical effect of toric IOL, providing more dimensional evidence to support the evaluation of postoperative visual quality and quality of life of patients.
There are still some shortcomings in this study: ① All patients have underwent a detailed and necessary preoperative ophthalmic examination as possible, but due to the limited availability of examination equipment, it was not possible to measure and compare the size of lens capsule in the two groups before the surgery. Since the size of the capsule can affect the rotational stability of toric IOL, in the future studies, the measurements of capsule size can be carried out to improve the preoperative measurements; ② In the measurement of rotational degree of IOL, it is always ideal to compare the IOL axial position immediately after surgery and 3 months post-surgery, but the IOL cannot be placed on the targeted axial position calculated before surgery due to a variety of subjective and objective reasons. Because we used the intraoperative navigation system, the intraoperative axial position anchoring was very accurate, and at the end of the surgery, the operator repeatedly confirmed that the IOL marker line has been placed in the targeted axial position. Therefore, from the perspective of patients maximum benefit, photographs of anterior segment under slit lamp at sitting position at the end of the surgery were not taken, as we were worried that above operations may cause discomfort, and even increase the risk of postoperative infection in patients. Under conditions of good sterility and patient’s cooperation, photographs of anterior segment under slit lamp at sitting position at the end of the surgery can be taken to calculate the rotation axis of the IOL more accurately and scientifically.