A New Approach for the Calculation of Total Corneal Astigmatism Considering the Magnitude and Orientation of Posterior Corneal Astigmatism and Thickness

Comparative evaluation of intraoperative aberrometry and Barrett's toric calculator in toric intraocular lens implantation

Purpose

Barrett toric calculator (BTC) is known for its accuracy in toric IOL (tIOL) calculation over standard calculators; however, there is no study in literature to compare it with real-time intraoperative aberrometry (IA). The aim was to compare the accuracy of BTC and IA in predicting refractive outcomes in tIOL implantation.

Methods

This was an institution-based prospective, observational study. Patients undergoing routine phacoemulsification with tIOL implantation were enrolled. Biometry was obtained from Lenstar-LS 900 and IOL power calculated using online BTC; however, IOL was implanted as per IA (Optiwave Refractive Analysis, ORA, Alcon) recommendation. Postoperative refractive astigmatism (RA) and spherical equivalent (SE) were recorded at one month, and respective prediction errors (PEs) were calculated using predicted refractive outcomes for both methods. The primary outcome measure was a comparison between mean PE with IA and BTC, and secondary outcome measures were uncorrected distance visual acuity (UCDVA), postoperative RA, and SE at one month. SPSS Version-21 was used; P < 0.05 considered significant.

Results

Thirty eyes of 29 patients were included. Mean arithmetic and mean absolute PEs for RA were comparable between BTC (-0.70 ± 0.35D; 0.70 ± 0.34D) and IA (0.77 ± 0.32D; 0.80 ± 0.39D) (P = 0.09 and 0.09, respectively). Mean arithmetic PE for residual SE was significantly lower for BTC (-0.14 ± 0.32D) than IA (0.001 ± 0.33D) (-0.14 ± 0.32D; P = 0.002); however, there was no difference between respective mean absolute PEs (0.27 ± 0.21 D; 0.27 ± 0.18; P = 0.80). At one-month, mean UCDVA, RA, and SE were 0.09 ± 0.10D, -0.57 ± 0.26D, and -0.18 ± 0.27D, respectively.

Conclusion

Both IA and BTC give reliable and comparable refractive results for tIOL implantation.

Astigmatism Management with Astigmatism-Correcting Intraocular Lens Using Two Toric Calculators - A Comparative Case Series

Background

To compare refractive outcomes after phacoemulsification and toric IOL implantation using two different toric calculators for initial astigmatism assessment in a real-world setting.

Methods

This was a retrospective, comparative, interventional case series. Patients over 30-year-old who underwent phacoemulsification and toric IOL implantation (AcrySof^® Toric IOL) by the same surgeon between 2017 and 2018 were included. Eyes with irregular astigmatism, previous corneal refractive surgery, intraocular surgery, corneal pathology, macular pathology and pupil abnormalities were excluded. IOL toricity was determined by using a calculator provided by the AcrySof Toric calculator before 2018 and Barrett Toric Calculator after 2018. Patient demographics, corneal topography, vector and preoperative and postoperative refraction were collected and analyzed at three months postoperative.

Results

Thirty-two eyes of 32 patients were included in the final analysis. 0.1D for surgically induced astigmatism was used. Group 1 included 14 eyes assessed with the original (AcrySof) toric IOL calculator, and group 2 included 18 eyes assessed with the Barrett toric IOL calculator. In group 1, postoperative astigmatism less than −1.00D, −0.75 D, and −0.5D was achieved in 88.2%, 76.1% and 53.7% of eyes, respectively, while, in group 2, 89% eyes achieved postoperative residual astigmatism less than 0.5D and all eyes achieved postoperative residual astigmatism less than 0.75D. The proportion of patients with lower postoperative astigmatism was significantly higher in Group 2 (p< 0.05 by chi-square test), a pattern that still held when we divided patients into multiple groups. Vector analysis with the Alpins methods also supported better outcomes in the Barrett group (0.71 D vs 0.35 D).

Conclusion

The Barrett Toric calculator resulted in better results in the prediction of residual astigmatism than original (AcrySof) toric calculators.

A multicenter study of the distribution pattern of posterior corneal astigmatism in Chinese myopic patients having corneal refractive surgery

Including posterior corneal astigmatism (PCA) into consideration may increase the accuracy of astigmatism correction after corneal refractive surgery. In the present study we aim to investigate the distribution pattern of PCA in a large number of myopic patients from multiple ophthalmic centers. There were 7829 eyes retrospectively included in the study. Pentacam data of the eyes were retrieved from the machine and only results with image quality labelled with ‘OK’ were included. Distribution of PCA was slightly positively skewed (Skewness = 0.419, Kurtosis = 0.435, KS P < 0.0001). Mean PCA was 0.34 ± 0.14 D (range: 0.00 D-0.99 D). PCA was ≥ 0.25 D in 74.91% of the eyes and was ≥ 0.50 D in 11.61% of the eyes. In 97.55% of the eyes the steep meridian of PCA was vertical (SMV). PCA magnitude was significantly higher in eyes with SMV PCA (P < 0.0001) or high manifest astigmatism (MA, P < 0.0001). There was a significant correlation between anterior corneal astigmatism (ACA) magnitude and PCA magnitude in all of the eyes (r = 0.704, P < 0.0001). There was also a trend of decreasing frequency and magnitude of SMV PCA with aging (both P < 0.0001). In conclusion, PCA is present in myopic patients having corneal refractive surgery and PCA magnitude is increased with higher MA or ACA. Consideration of the impact of PCA on laser astigmatism correction may be necessary.

García Á, Piñero DP. Comparison of Standard and Total Keratometry Astigmatism Measured with three Different Technologies

Purpose:

To compare the keratometric and total corneal astigmatism measures provided by three different technologies as well as to assess the level of interchangeability among them.

Methods:

A Prospective, comparative study enrolling 94 eyes from 53 patients (age, 29-77 years) was carried out. All participants were patients with the diagnosis of cataract or patients with a transparent crystalline lens but seeking surgical presbyopia correction. A complete eye examination was performed in all eyes, including corneal analysis with three different devices: IOL-Master 700 (Carl Zeiss Meditec), Cassini (i-Optics), and Pentacam (Oculus Optikgeräte GmbH). Interchangeability of standard and total keratometric readings (equivalent keratometric readings for Pentacam) and astigmatism measures with these three systems were evaluated with the Bland-Altman analysis.

Results:

Significantly higher standard and total keratometric readings were obtained with the IOL-Master compared to the other two systems (p<0.001). Likewise, a significantly higher magnitude of standard and total keratometric astigmatism was obtained with the Cassini system (p<0.001). Ranges of the agreement for corneal power measurements between devices varied from 0.58 D to 1.53 D, whereas they ranged from 0.46 D to 1.37 D for standard and total astigmatism measurements.

Conclusion:

Corneal power and astigmatism measures obtained with IOL-Master 700, Cassini, and Pentacam systems cannot be used interchangeably. The impact of these differences on the refractive predictability achieved with different types of intraocular lenses (IOL) should be evaluated in the future in order to define which is the best corneal evaluation approach for optimizing the IOL power calculations.

Accuracy of corneal astigmatism correction with two Barrett Toric calculation methods

AIM

To compare the prediction error between Barrett Toric calculator and the new online AcrySof Toric calculator which incorporated Barrett astigmatism algorithm in Chinese cataract eyes with normal axial length and anterior chamber depth (ACD).

METHODS

Prospective case-control study. All the cases had axial length (21-26 mm) with ACD no less than 2.4 mm. Keratometric values were measured by LenSTAR 900. The Barrett Toric calculator was used in group 1. In group 2, SRK-T formula was used to determine the spherical power of the Toric lens, and subsequent calculation of the cylinder type was performed using the new online Alcon Toric calculator. At 1 and 3mo after surgery, a comprehensive subjective optometry was performed. The predicted residual astigmatism calculated by the two calculators was compared with that obtained by postoperative refraction, and the difference was defined as the astigmatism correction error [error of refractive astigmatism (ERA)]. The error magnitude (EM) refers to the algebraic deviation of ERA, and the error vector (EV) indicates the vector deviation of ERA. The influence of the two calculation methods on the correction accuracy of toric IOL was quantitatively analyzed.

RESULTS

The |EM| obtained at 1mo after surgery were 0.21±0.12 D, 0.22±0.18 D in group 1 and group 2 respectively, and correspondingly turned to be 0.19±0.13 D, 0.20±0.19 D at 3mo after surgery, with no statistical difference (P=0.633, P=0.877). The vector analysis showed that |EV| values in two groups at 1mo after surgery were 0.29±0.14@105 (D@angle) and 0.35±0.20@113 (D@angle), respectively, whereas |EV| values 3mo after surgery were 0.27±0.16@86 (D@angle) and 0.32±0.23@102 (D@angle), respectively. The differences between the groups were not statistically significant (P=0.119, P=0.261).

CONCLUSION

The clinical effect of Barrett Toric calculator has a much more accurate tendency than that of new online AcrySof Toric calculator, but is not evident in cases with normal axial length and normal anterior posterior ratio.

Microincision cataract surgery with implantation of a bitoric intraocular lens using an enhanced program for intraocular lens power calculation

PURPOSE

To evaluate the potential benefit of a new version of an online toric intraocular lens calculator in eyes implanted with a bitoric intraocular lens.

PATIENTS AND METHODS

Retrospective observational comparative study in patients that underwent cataract surgery with implantation of the bitoric intraocular lens AT TORBI 709M (Carl Zeiss Meditec AG, Jena, Germany). Visual and refractive outcomes were evaluated at 1 month after surgery. The selection of the toric intraocular lens power was performed with the software Z CALC 2.0 (Carl Zeiss Meditec AG). The absolute refractive prediction errors for the spherical equivalent and cylinder were calculated and compared with the values that would have been obtained using version 1.5 of the same software.

RESULTS

A total of 393 eyes of 276 patients were evaluated. Mean postoperative sphere and cylinder were +0.03 ± 0.54 and -0.19 ± 0.30 D, respectively. A total of 95.67%, 98.22%, and 95.17% of eyes had a postoperative sphere, cylinder, and spherical equivalent within ±1.00 D, respectively. Mean absolute refractive prediction error for spherical equivalent was 0.34 ± 0.27 D with the two versions of the Z CALC software. In contrast, a significantly higher absolute refractive prediction error value for the cylinder was found with Z CALC 1.5 compared to version 2.0 (0.35 ± 0.32 vs 0.28 ± 0.30 D, p < 0.001). The absolute refractive prediction error for cylinder was ⩽0.25 D in 62.3% and 47.5% when using the versions 2.0 and 1.5, respectively.

CONCLUSION

The use of an optimized software for toric intraocular lens power calculation, considering the contribution of posterior corneal astigmatism, improved the astigmatic outcome with a bitoric intraocular lens.

Validation of corneal topographic and aberrometric measurements obtained by color light-emitting diode reflection topography in healthy eyes

PURPOSE

To evaluate the intrasession repeatability of anterior corneal topographic and aberrometric measurements provided by a color-LED topographer as well as their interchangeability with those provided by a Scheimpflug-based system in healthy eyes.

METHODS

Thirty-five healthy eyes of 35 patients (age, 16-66 years) were enrolled. A complete eye examination was performed in all cases including a complete corneal analysis with the Scheimpflug-based system Pentacam (Oculus Optikgeräte) (one measurement) and the Cassini system (i-Optics) (three consecutive measurements). Intrasession repeatability of the Cassini measurements was assessed with the within-subject standard deviation (S_w) and the intraclass correlation coefficient (ICC). The Bland-Altman analysis was used to evaluate the agreement between both devices.

RESULTS

Mean S_w for keratometric readings was 0.02 mm (ICC ≥ 0.992), ranging between 0.16 and 0.05 D (ICC 0.930-0.978) for anterior and total astigmatic measurements. Mean S_w for asphericity and corneal diameter were 0.06 (ICC 0.926) and 0.03 mm (IC 0.997), respectively. Aberrometric parameters showed ICCs ≥ 0.816, except for Z₄² (ICC 0.741) and Z₄⁴ (ICC 0.544). When comparing devices, statistically significant differences were found for most of topographic and aberrometric data (p ≤ 0.044). Likewise, ranges of agreement between devices were clinically relevant (keratometry > 0.06 mm; total astigmatic components > 0.69 D; asphericity 0.35; second-, third-, and fourth-order Zernike terms, more than 0.20, 0.13, and 0.01 μm, respectively).

CONCLUSIONS

Consistent anterior corneal topographic, total corneal astigmatic, and aberrometric measurements are obtained with color-LED topography in healthy eyes, which are not interchangeable with those provided by the Scheimpflug-based topography.