This single-center, multi-surgeon, prospective, clinical trial was conducted at the Medical University of Vienna. A total of 130 eyes of 82 patients were included in the study. Surgeries were conducted between June 2022 and March 2023. All surgeries were performed by five highly experienced cataract surgeons (D.S., C.L., R.M., C.A-F., M.S.). All study procedures adhered to the Tenets of the Declaration of Helsinki. The study was approved by the local ethics committee (EK 1978/2018) and registered at a public clinical trial registry (NCT03803852) prior to the beginning of the study. All patients provided written informed consent prior to study inclusion.

Inclusion criteria were total corneal astigmatism of 1.00 D or more measured by anterior-segment optical coherence tomography (AS-OCT) in combination with a Placido disc (MS-39, CSO, Firenze, Italy), uni- or bilateral age-related cataract, age from 45 to 95 years, need for a spherical IOL between 6.00 and 30.00 D and a preoperative pupil width of at least 5.5 mm.

Exclusion criteria were previous ocular surgeries or ocular trauma, blind fellow eye, history of uveitis, expected zonular weakness, proliferative diabetic retinopathy, uncontrolled glaucoma, pregnancy, corneal abnormalities such as corneal scars and other uncontrolled ocular or systemic diseases. Patients with pseudoexfoliation syndrome or diffuse zonular weakness at the time of surgery without the need for a CTR were not excluded. Primary outcome measures were absolute postoperative TIOL rotation from EOS to 4–6 months and the refractive outcome for each patient.

One to two weeks prior to surgery, preoperative diagnostics were performed. Preoperative examinations included visual acuity by an autorefractor keratometer Nidek ARK-1 (Nidek Co Ltd, Tokyo, Japan), biometry using an IOL Master 700 (Carl Zeiss Meditec AG, Jena, Germany), AS-OCT combined with Placido tomography MS-39 (CSO, Firenze, Italy), AS-OCT Casia 2 (Tomey Corporation, Nagoya, Japan) under miotic and mydriatic pupil conditions, standard macular OCT measurements with a high-definition optical coherence tomography (HD-OCT) Cirrus 6000 (Carl Zeiss Meditec, Jena, Germany) and a standard slit-lamp examination. Aqueous depth, lens thickness and lens equatorial diameter were obtained with the AS-OCT under mydriatic conditions. Axial length (AXL) and anterior chamber depth were obtained with the IOL Master 700.

The spherical equivalent (SE) of the TIOL was determined using an IOL Master 700 print using a “Mean Formula” between Barrett TK Universal II (total keratometry) and the Haigis (with TK values) formulae. Due to the novelty of the TIOL, no optimized A-constants were available at the time of study inclusion and therefore a mean of these two institutional used formulae was used.

The magnitude of the cylinder for the TIOL was calculated in the Alcon online toric calculator (Holladay formula) using the refractive analysis values of the MS-39 AS-OCT (K-Index 1.3375) within the 4.5 mm optical zone (total keratometry including the backside of the cornea). The surgically induced astigmatism (SIA) was set to zero. The TIOL was implanted to the steep axis (Ks) of the MS-39 AS-OCT refractive analysis measurement.

The Clareon TIOL has an overall diameter of 13.0 mm and an optic diameter of 6.0 mm with no haptic angulation. It features the identical design, meaning the same mechanical and optical attributes, as its predecessor lens, the well-established AcrySof IQ TIOL. The AcrySof TIOL is also popular for its bioadhesive material, providing good rotational stability in different studies [12]. The new IOL contains hydroxyethyl methacrylate instead of phenylethyl methacrylate aimed to eliminate glistenings and surface light scattering [13]. The Clareon TIOL is available from 6.00 to 30.00 D in SE and from 1.00 to 6.00 D (T2 = 1.00 D, T3 = 1.50 D, T4 = 2.25 D, T5 = 3.00 D, T6 = 3.75 D, T7 = 4.50 D, T8 = 5.25 D, T9 = 6.00 D) corrective cylindric power at the IOL plane. The IOL has a negative spherical aberration of 0.2 µm.

All surgeries were performed using a Lumera 700 (Carl Zeiss Meditec AG, Jena, Germany) surgical microscope. Prior to the surgery, the scleral reference picture of each patient from the IOL Master 700 was imported to the Callisto System. Two safety marks on the limbus were done at the planned steep axis using a surgical pen after synchronizing the reference picture with the actual picture of the surgical microscope. A temporal posterolimbal corneal incision of 2.2 to 2.4 mm was performed in all cases. According to the surgeon’s preference, one to two side ports approximately 45° apart from the posterolimbal corneal incision were created. After an approximately 5.0 to 5.5 mm capsulorhexis, nucleus removal, coaxial irrigation and aspiration of the remaining cortex were performed. For implantation of the TIOL, strictly cohesive ophthalmic viscoelastic device (OVD) only was used (Provisc, Alcon, Fort Worth, TX). After rotating the IOL to the planned axis, thoroughly the OVD was removed with special attention to the retrolental space and capsular bag fornix. After stromal hydration of the wounds, intracameral antibiotic was injected (Cefuroxime 1 mg/0.1mL). Again, the TIOL axis was checked and verified with the Callisto marking system and the axis markings on the limbus.

To eliminate measurement errors, a video clip was recorded immediately after wound closure at the EOS. This clip compared the actual axis of the IOL to scleral landmarks, using a method previously described by our study group [14]. In short, a surgical swab was used to move the conjunctiva to distinguish between movable conjunctival and non-movable scleral and episcleral landmarks. These landmarks were used to compare the actual IOL axis at the EOS to the IOL axis at follow-up visits at 1 h, 1 week, 1 month and 4–6 months.

At every follow-up visit, a retroillumination picture using a high-definition digital camera DCS720x (Kodak, Rochester, New York, USA) was performed. These pictures were imported into the semi-automated evaluation software Rotix [14]. Two lines were drawn to determine the IOL axis, one between two non-movable vessels serving as the reference axis and a second one between the axis markings of the IOL. The Rotix software then automatically calculates the axis difference between follow-up visits. At the 6 months follow-up visit, subjective refraction and vision testing were performed using a Snellen chart at 6 m distance applying the cross-cylinder method. To determine the SIA, a total keratometry (TK), using the postoperative cataract module of the AS-OCT, was performed at 6 months.

According to current ISO and American National Institute Standards (ANSI), at least 100 IOLs should be evaluated to assess the rotational stability of a TIOL. From earlier studies, we know that between 20% and 25% of patients were either lost to follow-up or not evaluable for the primary outcome due to non-visibility of landmarks at the sclera at the EOS or at follow-ups. Therefore, a sample size of 130 eyes was calculated.

Explorative data analysis was performed for rotational stability measurements at all time points. Rotational stability data is presented as mean ± standard deviation and as median [range] in absolute values. Preoperative corneal astigmatism, postoperative refractive astigmatism, and SIA are presented in double-angle plots recently developed by Abulafia et al. [15]. As a secondary objective correlation between AXL, lens thickness and lens equatorial diameter were computed using Spearman’s rho. The binominal test was used to calculate the difference in the direction of rotation between EOS and 6 months. P values less than 0.05 were considered statistically significant throughout, and no multiplicity correction was applied.