### Materials and Methods

### Patients and methods

### Formula constants

### Statistical analysis

*t*-tests were used to establish whether there was a significant systematic bias between the two devices. Bland-Altman plots were used to determine agreement between the two biometers [9]. The Wilcoxon signed-rank test was used to evaluate the differences in MAE, MedAE, and variance by the formulas for the two devices. Statistical significance was defined as a

*p*-value <0.05 (two-tailed).

### Results

*p*= 0.029, paired

*t*-test). The AL-Scan and IOLMaster provided a comparable mean K value of 2.4 mm. The mean difference was 0.11 ± 0.39 diopters (D) (K1) and 0.08 ± 0.39 D (K2), respectively. This value was not statistically significant (

*p*= 0.105 and

*p*= 0.239, paired

*t*-test). The two biometers provided equal ACD measures, with a difference of 0.052 ± 0.20 mm (

*p*= 0.136, paired

*t*-test) (Table 1).

*p*= 0.015, paired

*t*-test) (Table 2).

*p*= 0.032, paired

*t*-test). The ME measurements of CT Asphina 509M-implanted eyes were comparable among the four formulas (Table 4).

*p*= 0.026 and

*p*= 0.044, paired

*t*-test). In CT Asphina 509M-implanted eyes, the two devices showed similar variance in ME calculations by the four formulas; however, the standard deviation for measurements by the four formulas using AL-Scan was greater (

*p*= 0.046, Wilcoxon signed rank test) than that for measurements by the IOLMaster (Table 5). Fig. 1 shows the Bland-Altman plots and 95% limits of agreement between the two devices. Overall, the values of ocular parameters with the two devices showed high agreement and narrow 95% limits of agreement.

### Discussion

*p*= 0.029). In a previous study by Huang et al. [6], patients with severe advanced cataract were excluded based on the Lens Opacities Classification System III [11]. In contrast, we included patients irrespective of cataract grade, excluding only cases of dense posterior capsular opacity resulting in measurement failure with either one of the optical biometers. PCI measures axial eye lengths parallel to the vision axis as the patient fixates on the measurement beam or a coaxial fixation beam [5]. Thus, it is possible that outliers due to fixation problems in eyes with dense cataract led to the significant mean difference in AL between the two devices [12]. Even with correct alignment and accurate fixation, the measurement can be affected by the refractive index of the lens, which also varies with cataract grade. Severe nuclear cataract slightly increases the refractive index [13]. The IOLMaster and AL-Scan use different wavelengths of infrared light (780 and 830 nm, respectively), and longer wavelengths are able to penetrate tissue more deeply. Therefore, in addition to lens opacity, penetration depth can influence the measurement of AL [12,14]. The use of a longer wavelength resulted in a shorter measured optical distance [15]. Drexler et al. [5] demonstrated that AL measurement precision using PCI did not correlate with AL, but with cataract grade.

*p*= 0.015). Steep keratometric values can contribute to lower IOL power with the AL-Scan (mean average of K, 43.98 in IOLMaster vs. 44.41 in AL-Scan). In addition, the IOL power to achieve emmetropia is determined by the AL, K value, types of formulas that applied. Each formula estimates the effective lens position (ELP) in its own way. The SRK/T and Hoffer Q are two-variable formulas that rely on AL and central corneal power to predict the ELP. In the SRK/T formula, ACD is calculated using the Fedorov corneal height equation. On the other hand, the Hoffer Q formula applies a self-developed tangent curve to obtain the ACD. Additionally, the Haigis formula considers AL, K value, and also ACD when predicting ELP. The Holladay2 formula uses a white-to-white diameter in addition to the AL, K value, and ACD. As such, discrepancies in IOL power can be caused by the method used to predict ACD. Additionally, discrepancy in the IOL power calculations can be due to systematic errors in biometry, surgical technique, and the formulas [16]. The individual errors that arise between these multiple factors can cause a significant difference in power calculations for the CT Asphina 509M IOL, using the Hoffer Q formula.

*p*= 0.032). This difference could be caused by steep keratometric values (mean average of K, 43.98 in the IOLMaster vs. 44.41 in the AL-Scan). Considering that the SRK/T and Hoffer Q formulas are two-variable formulas, they appeared to be more affected by changes in keratometric values than the Haigis and Holladay2 formulas.