Cataract is a leading cause of visual disability in the elderly. With the advances in the development of multifocal intraocular lenses (IOLs), the goal of contemporary cataract surgery is shifting toward achieving desirable refractive outcomes and visual quality, rather than simply restoring vision (1, 2). By generating several foci at different distances, multifocal IOLs are designed to reduce the dependence on spectacle after surgery by restoring distance, intermediate, and near vision. The traditional concentric refractive, diffractive, or a combination of refraction and diffraction multifocal IOLs, however, trade off the image quality for spectacle independence. Because the incoming light rays are split to produce 2 or more focal points, patients implanted with those IOLs can experience decreased contrast sensitivity, glare disability, halos, and other optical phenomena (3). Refractive rotationally asymmetrical multifocal IOLs have been introduced to reduce such side effects (4, 5). The design has been shown to improve visual outcomes and provide good patient satisfaction (6–8).

Corneal astigmatism is another refractive error that should be managed to achieve postoperative emmetropia and spectacle-free. We have demonstrated that nearly half of the cataract surgery candidates have corneal astigmatism ≥ 1.00 D, and the magnitude of astigmatism increases with age (9). Meanwhile, 78% of cataract patients over the age of 65 had astigmatism greater than 0.5D (10). According to the EUREQUO database, even for those whose postoperative absolute mean biometry prediction error (spherical equivalent refraction, SEQ) was no more than 0.5 D, 21.2% of them have postoperative cylinder more than 1.0 D (11). Studies of Steven and Shen provided that even low levels of residual astigmatism can degrade visual acuity (12, 13). Therefore, reliable corneal astigmatism control or correction in cataract surgery is critically important for better visual outcomes and patient satisfaction. There are various options for the reduction of corneal astigmatism during cataract surgery, including the position selection of cataract incision, peripheral corneal relaxing incisions, Toric intraocular lens implantation, intrastromal ring implantation and surface ablation (14–16).

Opposite clear corneal incision (OCCI) involves a pair of incisions in the clear cornea that flattens the corneal curvature in that meridian (17). Studies have shown, in terms of reducing postoperative astigmatism, that the procedure is effective and safe in combination with spherical or aspherical monofocal IOL implantation (18–20). However, it was not clear whether OCCI with rotationally asymmetrical multifocal IOL implantation can improve the optical and visual outcomes for cataract patients with astigmatism, thus far achieving the goal of spectacle-free.

In this study, we aim to investigate the efficacy and safety of the technique by comparing the visual and refractive outcomes of a group of cataract patients with or without OCCI during phacoemulsification and rotationally asymmetric multifocal IOL implantation.

In the current study, we found that the opposite clear corneal incision (OCCI) effectively reduces residual astigmatism following multifocal IOL implantation. Patients receiving OCCI exhibited desirable visual acuity outcomes and superior refractive profiles compared to those with conventional incisions.

Modern cataract surgery strives to achieve spectacle-free vision, liberating patients from the constraints of cumbersome eyewear such as thick glasses and bifocals. This ultimately translates into enhanced comfort, convenience, and visual clarity. Correcting presbyopia and astigmatism is crucial for this objective.

The IOLs (Lentis Mplus LS-313 MF15) used in the study feature a rotational asymmetry design with a near add of +1.50 D. The design’s advantage lies in its ability to provide optimal visual outcomes at near to intermediate distances without compromising distance visual acuity, additionally exhibiting a low incidence of photic phenomena (4–8). We found that the patients in both groups had relatively good uncorrected distant, intermediate visual acuity and acceptable near vision (Table 2). This significantly reduces their reliance on spectacles. Throughout the follow-up period, no patients reported glare, halos, dysphotopsia or other postoperative optical symptoms.

In the OCCI group, placing incisions at the steep keratometry meridian significantly reduced the residual astigmatism compared to the SCCI group. Two-thirds of the eyes in the SCCI group had postoperative astigmatism exceeding 0.5 D, with one-third exceeding 1.0 D. Conversely, three-fourths of OCCI eyes had postoperative astigmatism below 0.5 D, with none exceeding 1.0 D (Figure 4). Vector analysis further support OCCI’s efficacy. Both difference vector (DV) and index of success (IoS) were statistically significantly smaller in the OCCI group, and the polar plots showed a more centralized distributions of astigmatic indices. These findings align with studies using similar incision techniques for monofocal IOLs (22–24), confirming the efficacy of corneal curvature optimized incision planning with multifocal IOLs. Combined with the astigmatism analysis, OCCI emerges as a readily available and cost-effective alternative to expensive toric multifocal IOLs for mild to moderate astigmatism correction.

Intriguingly, the improved astigmatism correction observed with the OCCI did not translate directly into a difference in uncorrected visual acuity (UCVA) across distance, intermediate and near distances between the two groups (Table 2). This discrepancy between astigmatic and visual outcomes can be attributed to several factors.

First, while the difference in residual astigmatism between the two groups was statistically significant, it was relatively small (only around 0.5 D). Moreover, approximately 40% of the eyes in both groups exhibited with-the-rule (WTR) astigmatism postoperatively. It has been reported that cylindrical correction offers limited visual acuity improvement for WTR astigmatism when the magnitude of astigmatism is lower than −0.75 D (25). The combination of the relatively small astigmatic reduction and the mixed effects of astigmatic orientation may partly explain the comparable visual outcomes.

Second, patients with multifocal IOLs demonstrate some tolerance for residual astigmatism (12). And it is particularly true for low levels of astigmatism. Hayashi observed that when astigmatism was less than 1.0 D, eyes implanted with a multifocal IOLs performed better in terms of the visual acuity at both distance and near (26). Additionally, studies have suggested that a lower IOL addition shows better astigmatic defocus tolerability (27, 28). The optical design of IOLs may also influence astigmatic tolerance. McNeely reported high tolerance for residual astigmatism with the Mplus LS-312 MF30, which shares the rotationally asymmetric multifocal design as the MF15 IOL used in the current study, albeit with a higher IOL addition (29).

Third, the current study only measured visual acuity as visual outcomes, which may not fully capture the impact of astigmatism on other aspects of visual performance, such as contrast sensitivity, functional vision, and patient satisfaction (12, 26, 29). Other factors can also affect visual acuity after multifocal IOL implantation, including high order aberrations (30). This may further explain why a significant difference was observed in astigmatism correction but not in visual acuity. Further studies examining these parameters are warranted to fully evaluate the relationship between residual astigmatism and overall visual wellbeing in patients with multifocal IOLs.

The limitations of this study should also be mentioned here. Firstly, due to the retrospective non-randomized design, although the baseline characteristics were balanced between the two groups, potential confounders cannot be fully controlled for. Secondly, only anterior corneal curvature was assessed in the study. The posterior curvature is also an important component of corneal refraction. However, the keratometric astigmatism was consistent with the manifest refractive measurements, both prior to and following surgery. Thirdly, as mentioned earlier, only the visual acuity and refractive outcomes were measured and analyzed in the present study, in addition to the relatively shorter follow-up, further studies should be conducted to include other visual-related measurements, such as contrast sensitivity, wavefront parameters, and patient satisfaction or scales of vision-related quality of life.

In conclusion, the current study confirms that incisions placing at steep K meridian can safely reduce residual astigmatism after cataract surgery. Corneal curvature optimized incision planning, specifically opposite clear corneal incision, combined with rotationally asymmetric multifocal intraocular lens implantation provides optimal visual and refractive outcomes.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Review Board of Zhongshan Hospital (Xiamen), Fudan University. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

XQ: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. PY: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – review & editing. XW: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Supervision, Writing – review & editing. YW: Formal analysis, Funding acquisition, Project administration, Resources, Validation, Visualization, Writing – review & editing. YH: Conceptualization, Data curation, Investigation, Methodology, Software, Supervision, Writing – review & editing. ZC: Conceptualization, Data curation, Investigation, Methodology, Software, Supervision, Writing – review & editing. YY: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.