Toric IOL Calculation in Eyes With High Posterior Corneal Astigmatism

Accuracy of Toric Intraocular Lens Calculators with Predicted and Measured Posterior Corneal Astigmatism Across Different Types of Astigmatism

INTRODUCTION

This study is a retrospective case series to compare the accuracy of the Barrett toric calculator using predicted posterior corneal astigmatism (PCA) and PCA measurements using swept-source optical coherence tomography (SS-OCT) and a Scheimpflug camera. This evaluation was conducted across different types of anterior and posterior astigmatism.

METHODS

A total of 146 eyes from 146 patients implanted with toric intraocular lenses were included. Mean absolute prediction error, standard deviation of prediction error, and the percentage of eyes with prediction errors within ±0.50 diopters (D) were calculated using vector analysis. Biometric measurements were conducted using the IOLMaster 700 and Pentacam HR. A subgroup analysis was conducted based on the orientation of both anterior and posterior corneal astigmatism.

RESULTS

The Barrett toric calculator with predicted PCA yielded the best results, with 78.1% having a prediction error ≤ 0.50 D, which was a significantly higher percentage than the Barrett formula with the two versions of measured PCA (P < 0.05). In the subgroup with a horizontally steep meridian PCA using the IOLMaster 700, the Barrett formula with predicted PCA yielded the best results, with 78.3% of cases having a prediction error of less than 0.5 D. This percentage was significantly higher than the other two measured PCA subgroups (P < 0.05).

CONCLUSION

The Barrett toric formula with predicted PCA demonstrated a statistically significantly higher proportion of cases with a prediction error ≤ 0.5 D compared to the two measured PCA formulas (from the IOLMaster 700 or Pentacam). This trend persisted even when the posterior corneal astigmatism was horizontally steep.

Accuracy of Toric Intraocular Lens Calculations Using Estimated Versus Measured Posterior Corneal Astigmatism

PURPOSE

To compare the prediction accuracy of toric intraocular lens calculations using estimated vs measured posterior corneal astigmatism (PCA).

DESIGN

Retrospective case series.

METHODS

A total of 110 eyes of 110 patients with uncomplicated toric intraocular lens implantation were included in this study. Predicted postoperative refractive astigmatism was calculated with the Barrett Toric Calculator using the estimated PCA (E-PCA), the measured IOLMaster 700 PCA (I-PCA), and the measured Pentacam PCA (P-PCA). Refractive astigmatism prediction errors (RA-PEs), including their trimmed (tr-) centroid (mean vector), spread (precision), tr-mean absolute RA-PE (accuracy), and percentage within a certain threshold, were determined using vector analysis and compared between groups.

SETTING

University Eye Clinic, Maastricht University Medical Center+, the Netherlands.

RESULTS

The tr-centroid RA-PEs of the E-PCA (0.02 diopter [D] at 82.2°), the I-PCA (0.08 D at 35.5°), and the P-PCA (0.09 D at 69.1°) were significantly different from each other (P < .01), but not significantly different from zero (P = .75, P = .05, and P = .05, respectively). The E-PCA had the best precision (tr-mean 0.40 D), which was not significantly lower than the I-PCA (0.42 D, P = .53) and P-PCA (0.43 D, P = .06). The E-PCA also had the best accuracy (0.40 D), which was not significantly different from the I-PCA (0.42 D, P = .26) and significantly better than the P-PCA (0.44 D, P < .01). The precision and accuracy of the I-PCA did not significantly differ from those of the P-PCA. There were no statistically significant differences in the percentage of eyes within a certain absolute RA-PE threshold.

CONCLUSIONS

The Barrett Toric Calculator using the E-PCA, I-PCA, or P-PCA showed a comparable prediction of postoperative refractive astigmatism in standard clinical practice.

Accuracy of Toric Intraocular Lens Formulas With Measured Posterior Corneal Astigmatism of Different Orientations

PURPOSE

To assess whether the use of measured posterior corneal astigmatism (PCA) values improves the prediction accuracy of toric intraocular lens power formulas, compared to predicted PCA values, when the orientation of the steep axis of PCA is non-vertical.

DESIGN

Retrospective observational cohort study.

METHODS

Four hundred eighteen eyes of 344 patients were included in the study. Prediction errors (PE) for postoperative refractive astigmatism at 4 weeks postoperatively were determined using vector analysis and compared for the following toric intraocular lens power formulas: Barrett Toric with predicted posterior corneal astigmatism (PPCA); Barrett Toric with measured posterior corneal astigmatism (MPCA); EVO Toric PPCA; EVO Toric MPCA; Holladay I with Abulafia-Koch regression. Subgroup analysis compared PEs for eyes with a vertically orientated steep axis of PCA (60-120°) to eyes with a non-vertically orientated steep axis of PCA.

SETTING

Cathedral Eye Clinic, Belfast, United Kingdom and Tan Tock Seng Hospital, Singapore.

RESULTS

Standard keratometry was with-the-rule in 48% of eyes, while the steep PCA axis was vertically orientated in 91% of eyes. For all eyes, EVO-PPCA had a smaller mean absolute error than Barrett-MPCA, Barrett-PPCA, and Abulafia-Koch (P < .01 for all). EVO-PPCA had the highest percentage of eyes within 0.50D of predicted postoperative astigmatism for eyes with vertical PCA (61%), while EVO-MPCA had the highest percentage for eyes with non-vertical PCA (54%). EVO-MPCA had the smallest centroid error for all eyes, and the subgroups (P < .01 for all). Eyes with non-vertical PCA had a lower percentage within 0.50D than eyes with vertical PCA when using PPCA (43% vs 61%, P = .034), but there was no significant difference between these groups when MPCA is used for eyes with non-vertical PCA (54% vs 61%, P = .40).

CONCLUSIONS

When the steep axis of posterior corneal astigmatism is not vertically orientated, the use of measured posterior keratometry values improves prediction accuracy.

Is Astigmatism Correction Necessary for Patients With Cataract Who Have Corneal Astigmatism of Less Than 0.75 D?

PURPOSE

To investigate the proportion of patients with predicted refractive astigmatism (PRA) of 0.75 diopters (D) or greater and associated risk factors among cataract surgery candidates with low corneal astigmatism.

METHODS

A retrospective cross-sectional study was conducted in Zhongshan Ophthalmic Center, Guangzhou, China. Patients with cataract who had preoperative simulated keratometric astigmatism of less than 0.75 D were recruited. The PRA was calculated by Barrett toric calculator using posterior corneal astigmatism (PCA) measured by the IOLMaster 700 (Carl Zeiss Meditec AG) and corneal surgically induced astigmatism (SIA). Two corneal incision locations (temporal [0°/180°], 135° incision) and varying magnitudes (0.10 to 0.60 D) were considered for SIA. Multiple logistic regression analysis was used to explore risk factors associated with PRA of 0.75 D or greater and build predictive model. Sensitivity analysis was performed using PRA threshold of 0.50 D.

RESULTS

A total of 1,750 eyes from 1,750 patients were included (mean age: 60.14 ± 13.24 years, 42.91% male, 1,010 right eyes and 740 left eyes). The 135° incision (odds ratio [OR]: 17.86) and against-the-rule (ATR) astigmatism (OR: 37.55) are the major risk factors for PRA of 0.75 D or greater. Higher simulated keratometric astigmatism (OR: 2.03), larger PCA (OR: 1.64), and surgically induced astigmatism (OR: 1.29) also significantly increased the risk of PRA of 0.75 D or greater. Nomogram model were constructed with an area under curve of 0.90.

CONCLUSIONS

For patients with corneal astigmatism of less than 0.75 D, temporal incision and measured PCA is preferred. Those patients with ATR astigmatism should be considered for astigmatism correction when using a 135° incision. [J Refract Surg. 2023;39(12):850-855.].

Comparison of the Barrett toric calculator using measured and predicted posterior corneal astigmatism and the Kane and Abulafia-Koch calculators

PURPOSE

To compare the accuracy of the Barrett toric calculator with measured and predicted posterior corneal astigmatism (MPCA and PPCA, respectively), the Abulafia-Koch (AK) formula, and the toric Kane formula.

SETTING

Ein-Tal Eye Center, Tel-Aviv, Israel.

DESIGN

Retrospective cohort.

METHODS

Consecutive cases of patients who underwent uneventful cataract extraction surgery with implantation of a toric intraocular lens between March 2015 and July 2019 were retrospectively reviewed. 1 eligible eye from each patient was included. The predicted postoperative refractive astigmatism was calculated using each method and compared with the postoperative refractive astigmatism to give the prediction error.

RESULTS

80 eyes of 80 patients were included in this study. The mean centroid and the mean and median absolute prediction errors using Kane (0.25 diopters [D] ± 0.54 @ 6 degrees, 0.50 D ± 0.31 and 0.45 D, respectively) were significantly different compared with MPCA (0.12 D ± 0.52 @ 16 degrees, P < .001, .44 D ± 0.28 and 0.36 D, P = .027, respectively), PPCA (0.09 D ± 0.49 @ 12 degrees, P < .001, .41 D ± 0.27 and 0.35 D, P < .001, respectively), and AK (0.11 D ± 0.49 @ 11 degrees, P < .001, .42 D ± 0.27 and 0.35 D, P = .004, respectively). No significant differences were found between the calculators in the predictability rates within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D.

CONCLUSIONS

The measured posterior corneal curvature in the Barrett calculator yielded comparable outcomes to its prediction by the Barrett and AK formulas. The Kane calculator showed a slight against-the-rule prediction error compared with the other methods, resulting in a small higher median absolute error with marginal clinical importance.

Comparison of accuracy of a toric calculator with predicted vs measured posterior corneal astigmatism

PURPOSE

To compare the accuracy of postoperative residual astigmatism prediction using the Barrett toric calculator with predicted vs measured posterior corneal astigmatism (PCA).

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.

DESIGN

Retrospective case series.

METHODS

We included 602 eyes with monofocal nontoric intraocular lens implantation. Biometry and PCA were obtained from the IOLMaster 700. Anticipated postoperative refractive astigmatism was calculated with the Barrett toric calculator for predicted and measured PCA, and the astigmatism prediction errors (PEs) for each were calculated using vector analysis. The vector PE magnitudes and percentage of eyes within certain amounts of vector PEs were compared between 2 methods.

RESULTS

Compared with the Barrett toric calculator with predicted PCA, the Barrett toric calculator with measured PCA produced significantly smaller mean vector PE (0.54 diopter [D] vs 0.57 D) and higher percentage of eyes with vector PE of ≤0.5 D (57.6% [347/602] vs 52.5% [316/602]) (both P < .05). In eyes with predicted residual astigmatism of ≥0.5 D, the Barrett toric calculator with measured PCA again yielded a significantly higher percentage of eyes with vector PE of ≤0.5 D (51.2% [226/441] vs 44.7% [197/441], P < .05).

CONCLUSIONS

Accuracy of residual astigmatism prediction is improved using the Barrett toric calculator with measured PCA rather than predicted PCA.

Astigmatism Profile in a Large Series of Brazilian Patients

PURPOSE

To assess anterior, posterior, and total corneal astigmatism in a large sample of Brazilian patients.

METHODS

In this retrospective cross-sectional study, all patients whose corneas were imaged with the Galilei G6 (Ziemer Ophthalmology) between January 2017 and February 2019 at HOPE Eye Hospital, in Recife, Brazil, were eligible to participate. Anterior, posterior, and total corneal astigmatism values were collected and analyzed.

RESULTS

The study included 3,253 eyes of 1,919 patients. The mean magnitude of the anterior, posterior, and total corneal astigmatism was 1.50 ± 1.11, 0.34 ± 0.15, and 1.29 ± 0.98 diopters (D), respectively. Corneal astigmatism was greater than 0.50 D in the anterior cornea of 86.3% of eyes (2,807 eyes) and in the posterior cornea of 13.2% of eyes (429 eyes). Vertical alignment of the steepest corneal meridian was observed in the anterior cornea of 74.5% of eyes (2,423 eyes) and in the posterior cornea of 93.1% of eyes (3,029 eyes). The correlation between the astigmatism magnitude of the anterior and posterior cornea was strong when the steep anterior meridian was aligned vertically (r = 0.720; P < .001), and absent when it was aligned horizontally (r = 0.102; P = .036).

CONCLUSIONS

Corneal astigmatism values in the Brazilian population were similar to those found in other ethnicities, suggesting that toric calculators, nomograms, coefficients of adjustment, and formulas that were developed based on astigmatism values of other populations may be used in Brazilian patients with comparable accuracy. [J Refract Surg. 2023;39(1):56-60.].

Intraocular lens constant optimization in toric intraocular lens calculation using keratometry and total corneal power

PURPOSE

To evaluate intraocular lens (IOL) constant optimization in toric IOL calculation with keratometry (K) and total corneal refractive power (TCRP).

METHODS

Predicted spherical equivalent (SE) and residual astigmatism (RA) with K and TCRP were retrospectively calculated using the Haigis, Holladay 1, and SRK/T formulae and optimized IOL constants. The results of the Barrett calculator and the Abulafia-Koch formula with K were also calculated. The median absolute error in SE (MedAE-SE), mean absolute error in RA (MAE-RA), and centroid error (CE) were analyzed.

RESULTS

Seventy-nine eyes of 71 patients implanted with toric IOLs were included. With K, there were no significant differences between the results before and after constant optimization using all the formulae. With TCRP, constant optimization significantly reduced MedAE-SE; however, significantly increased MAE-RA and CE using the Holladay 1 and SRK/T formulae. MedAE-SE, MAE-RA, and CE using the Haigis formula did not show significant differences. The difference in the predicted RA before and after constant optimization increased with IOL toricity. The MedAE-SE predicted by TCRP was significantly higher than that predicted by K despite constant optimization. The MAE-RA and CE predicted by TCRP were significantly lower than those predicted by K without posterior corneal astigmatism optimization; however, were not significantly different from those predicted by the Barrett and Abulafia-Koch formulae.

CONCLUSIONS

Constant optimization is recommended when using the TCRP in toric IOL calculations, particularly for patients with large astigmatism. However, TCRP did not yield more accurate results than optimized K in toric IOL calculations despite constant optimization.

Evaluation of Ocular Residual Astigmatism in Eyes with Myopia and Myopic Astigmatism and Its Interaction with Other Forms of Astigmatism

Purpose

To evaluate the prevalence, magnitude, and direction of ocular residual astigmatism (ORA) in eyes with myopia and myopic astigmatism, and its interaction with refractive, anterior corneal, posterior corneal, and true net power astigmatism.

Patients and Methods

Refractive surgery candidates with myopia and myopic astigmatism were studied. Refractive astigmatism (RA) was measured using the Nidek^® AR-310A autorefractometer. Anterior corneal astigmatism (ACA), posterior corneal astigmatism (PCA), and true net power astigmatism (TNP) were measured using the Wavelight^® Oculyzer II. Astigmatism was converted from polar to vector notation. ORA was calculated by vector subtraction of ACA from RA vertexed to corneal plane. Compensation factor (CF) was calculated as the ratio of ORA that compensates ACA for both J₀ and J₄₅.

Results

154 eyes of 88 patients (mean age 31.7±7.1 years) were included. With-the-rule (WTR) astigmatism was the most common for both RA (55.6%) and ACA (74%), while against-the-rule (ATR) was the most common for PCA (87.7%) and ORA (74.0%). The axes of RA and ACA were within 10° of each other in 46.8% of the eyes, and within 30° of each other in 76.0%. The mean difference in value between the axis of RA and ACA was 25.6°. 71.4% of eyes in the study had an ORA ≥ 0.5D, 44.1% had ORA ≥ 0.75D and 26% had ORA ≥ 1D. There was a statistically significant difference between ACA and each of RA and TNP. Using TNP to calculate ORA instead of ACA reduced its magnitude. RA is positively correlated to ACA and more strongly to TNP. The most common pattern of compensation between ORA and ACA was under-compensation for J₀ (49%) and same-axis-augmentation for J45 (35%).

Conclusion

ORA, PCA, and the interaction between ORA and ACA can affect results during refractive planning.

Incidence and Risk Factors of Repositioning Surgery to Correct Misalignment of Toric Intraocular Lenses after Cataract Surgery: A Single-Center Retrospective Observational Study

PURPOSE

The aim of this study was to analyze the incidence and outcomes of repositioning surgery to correct misalignment of several toric intraocular lenses (IOLs) after cataract surgery.

METHODS

In this retrospective study, patients who underwent repositioning surgery to correct misalignment of toric IOLs following cataract surgery between January 2019 and December 2021 were enrolled. The medical data on patients' age, gender, preoperative axial length, corneal astigmatism, the axis of astigmatism, IOL models, IOL axis, uncorrected distance visual acuity, residual refraction, and postoperative outcomes were analyzed.

RESULTS

Among the 1,135 eyes implanted with toric IOLs at Qingdao Eye Hospital, 23 (2.026%, 23/1,135) underwent repositioning surgery. Univariate analysis revealed that the incidence of repositioning surgery was significantly lower with AcrySof (0.636%, 5/786) than with ZEISS (2.959%, 5/169) and TECNIS (7.222%, 13/180) IOL platforms; the incidence of repositioning surgery with monofocal toric IOLs (1.169%, 11/941) was significantly lower than multifocal toric IOLs (6.186%, 12/194) (p < 0.001); additionally, a significant difference in age was also observed (p = 0.002). Multivariate logistic regression analysis showed that the IOL platform (p = 0.004) and younger age (p = 0.006) were independent risk factors for repositioning surgery.

CONCLUSION

The incidence of repositioning surgery of toric IOLs after cataract surgery was 2.026%. It was linked to the IOL platform, multifocal toric IOLs, and younger age.

Toric Intraocular Lens Calculations With the Barrett Calculator: A Comparison of the Calculator With and Without the Integrated K Method

PURPOSE

To compare the accuracy of the Barrett Integrated K (IK) toric calculator with the standard Barrett toric calculator.

METHODS

Consecutive patients who underwent cataract extraction with implantation of a toric intraocular lens at the Rabin Medical Center, Israel, were reviewed. Errors in predicted postoperative refractive astigmatism were calculated for the Barrett toric calculator using biometry measurements only and with the IK tool using biometry and tomography. Both methods were assessed with predicted and measured posterior corneal astigmatism (PPCA and MPCA, respectively).

RESULTS

The study included 73 eyes of 59 patients. The mean centroid prediction error using PPCA (0.08 ± 0.80 D @ 78°) was significantly different compared with MPCA (0.07 ± 0.80 D @ 48°, P = .016). In addition, a significant difference between IK-PPCA (0.06 ± 0.80 D @ 80°) and IK-MPCA (0.05 ± 0.80 D @ 38°) was found (P = .023). The median absolute prediction error ranged from 0.55 D using IK-PPCA to 0.60 D using PPCA, with no significant differences between the four calculation versions. No significant differences were found between the calculators in the predictability rates within ±0.50, ±0.75, and ±1.00 D. Analysis of one eye of each patient showed similar results.

CONCLUSIONS

The IK calculator yielded comparable outcomes to the standard Barrett calculator. Although differences in the mean centroid errors were found, they were clinically insignificant and predominantly seen in the axis of the predicted astigmatism error. These minor differences were mainly attributed to the incorporation of the MPCA in the calculation. [J Refract Surg. 2022;38(9):565-571.].

Measured Corneal Astigmatism Versus Pseudophakic Predicted Refractive Astigmatism in Cataract Surgery Candidates

PURPOSE

To compare standard and total corneal astigmatism measurements to the predicted pseudophakic (nontoric) refractive astigmatism in candidates for cataract surgery.

DESIGN

A retrospective, cross-sectional study.

METHODS

A single-center analysis of consecutive eyes measured with a swept-source optical coherence tomography biometer at a large tertiary medical center between February 2018 and June 2020. Corneal astigmatism was calculated based on standard keratometry astigmatism (KA), total corneal astigmatism (TCA), and predicted refractive astigmatism (PRA) for a monofocal nontoric intraocular lens (IOL) implantation calculated by the Barrett toric calculator using the predicted posterior corneal astigmatism (PRA_{(Predicted-PCA)}) and the measured posterior corneal astigmatism (PRA_{(Measured-PCA)}) options. Separate analyses were performed for each eye.

SETTING

Ophthalmology Department, Shaare Zedek Medical Center, Jerusalem, Israel.

RESULTS

In total, 8152 eyes of 5320 patients (4221 right eyes [OD] and 3931 left eyes [OS], mean age 70.6±12.2 years, 54.2% females) were included in the study. The mean vector values (centroid) for KA, TCA, PRA_{(Predicted-PCA)}, and PRA_{(Measured-PCA)} were 0.07 diopters [D] at 19.5°, 0.27 D at 7.5°, 0.44 D at 2.9°, and 0.43 D at 179.3°, respectively (P < .01), for OD and 0.02 D at 150.3°, 0.23 D at 169.7°, 0.40 D at 179.4°, and 0.42 D at 169.5°, respectively (P < .01), for OS. More than 73% of eyes had a PRA >0.5 D.

CONCLUSIONS

Standard and total corneal astigmatism measurements differ significantly from the PRA by the Barrett toric calculator. The PRA, rather than the KA or TCA, should be used as the reference guide for astigmatism correction with toric IOL implantation.