Toric Intraocular Lens Calculation Research Articles

Accuracy of toric intraocular lens power calculation depending on different keratometry values using a novel network based software platform.

To compare different corneal keratometry readings (swept-source-OCT-assisted biometry and Scheimpflug imaging) with a novel software platform for calculation of toric intraocular lenses. Department of Ophthalmology, Ludwig-Maximilians-University, Munich, Germany. Retrospective, non-randomized, clinical trial. Twenty-three eyes undergoing toric intraocular lens implantation were included. Inclusion criteria were preoperative regular corneal astigmatism of at least 1.00 D, no previous refractive surgery, no ocular surface diseases and no maculopathies. Lens exchange was performed with CALLISTO eye (Zeiss). For each patient, the expected postoperative residual refraction was calculated depending on three different corneal parameters of two different devices: standard K-front (K) and total keratometry (TK) obtained by a swept-source-OCT-assisted biometry system (IOL Master 700, Zeiss) as well as total corneal refractive power (TCRP) obtained by a Scheimpflug device (Pentacam AXL, Oculus). Barrett's formula for toric intraocular lenses was used for all calculations within a novel software platform (EQ workplace, Zeiss FORUM®). Results were statistically compared with postoperative refraction calculated according to the Harris dioptric power matrix. The standard K values (mean PE 0.02 D ± 0.45 D) and TK values (mean PE 0.09 D ± 0.43 D) of the IOL Master 700 reached similar results (p = 0.96). 78% of eyes in both K and TK groups achieved SE within ±0.5 D of attempted correction and all eyes (100%) were within ±1.0 D of attempted correction in both groups. By contrast, the prediction error in the IOL calculation using the TCRP of the Scheimpflug device was significantly greater (mean PE -0.56 D ± 0.49 D; p = 0.00 vs. standard K and p = 0.00 vs. TK) with adjusted refractive indices. Thirty-nine and Ninety-one percentage of eyes in the TCRP group achieved SE within ±0.5 D (p = 0.008 K vs. TCRP and p = 0.005 TK vs. TCRP) and ± 1.0 D (p = 0.14 vs. TCRP) of attempted correction, respectively. All three corneal parameters (standard K, TK, TCRP) performed well in calculating toric IOLs. The most accurate refractive outcomes in toric IOL implantation were achieved by IOL calculations based on swept-source-OCT-assisted biometry. The SS-OCT-based K-front and TK values achieve comparable results in the calculation of toric IOLs.

Total keratometry for toric intraocular lens calculation: comparison from two swept-source optical coherence tomography biometers.

To compare the astigmatism prediction accuracy of total keratometry (TK) from the IOLMaster 700 and total corneal power (TCP) from Anterion based on swept-source optical coherence tomography (SS-OCT) technology in toric intraocular lens (toric IOL) calculation. A retrospective observational study. Total corneal astigmatism (TCA) were obtained using IOLMaster 700 and Anterion. Z CALC 2.0 was used to calculate the expected postoperative refractive astigmatism in conjunction with TCA. Prediction errors (PE) in refractive outcomes was analyzed 1 month postoperatively using the vector analysis by the Holladay method, including the mean vector PE magnitude, percentage of cases with vector PE in certain intervals, and the centroid PE. A total of 56 eyes from 56 patients were enrolled in the study with an insertion of an AT TORBI 709 toric IOL. The difference in mean vector PE of postoperative refractive astigmatism between TK and TCP was not statistically significant (0.48D versus 0.46D, P = 0.281). TK and TCP yielded 27.3 and 40.0% of eyes with vector PE ≤ 0.25D, and 58.2 and 63.6% with vector PE ≤ 0.5D (both P > 0.05), respectively. TK and TCP resulted in similar ATR centroid PE of 0.10D@35° ± 0.60D and 0.15D@22° ± 0.57D, respectively, and there were no significant differences between x-PE component and y-PE component. IOLMaster 700 and Anterion provided comparable astigmatic predictability in toric IOL implantation using total keratometry and Z CALC 2.0.

Comparison of toric intraocular lens calculation with the integrated K method and three single biometric devices.

To compare astigmatic outcomes using the Integrated K method and anterior surface keratometry from 3 different biometric devices. Lions Eye Institute, Perth, Australia. Retrospective case series. Eyes of patients who underwent uneventful cataract surgery were analyzed. Predicted postoperative astigmatism was calculated for Integrated K method, IOLMaster 700, Lenstar and Pentacam. The mean centroid error in predicted postoperative refractive astigmatism (PE), mean absolute PE and percentage of eyes within 0.5 diopter (D), 0.75 D and 1 D of absolute magnitude of PE were compared. A subset analysis was done where the difference in cylinder magnitude between the 2 methods was more than 0.25 D. Spherical prediction outcomes were also analyzed. 241 eyes of 139 patients were included in the study. The mean centroid PE of Integrated K method (-0.07 @ 69) was significantly different from IOLMaster and Pentacam. The mean absolute PE with Integrated K method (0.33 ± 0.17) was significantly lower than all 3 devices. The percentage of eyes within 0.5 D and 0.75 D of absolute magnitude of PE was 82% and 99% for Integrated K method, 76% and 95% for IOLMaster and Lenstar, and 60% and 86% for Pentacam. In the subset analysis, the improvement in accuracy of the Integrated K method compared with a single device was greater in terms of the percentage of eyes predicted within 0.5 D. The Integrated K method did not impact the spherical prediction outcomes. The integrated K method is more accurate and precise than anterior surface keratometry from a single biometric device.

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

To compare the prediction accuracy of toric intraocular lens calculations using estimated vs measured posterior corneal astigmatism (PCA). Retrospective case series. 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. University Eye Clinic, Maastricht University Medical Center+, the Netherlands. 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. 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.

Refractive outcomes of toric intra-ocular lens implantation in cases of high posterior corneal astigmatism.

To evaluate whether the toric intra-ocular lens (IOL) power calculation based on total corneal astigmatism (TCA) in eyes with high posterior corneal astigmatism (PCA) could result in a systematic over-correction or under-correction after operation. The present study included a mono-centric retrospective study design. The data were collected from 62 consecutive eyes during uncomplicated cataract surgery by a single surgeon with a measured PCA of 0.50 diopters (D) or higher. Toric IOL calculations were made using TCA measurements. The eyes were grouped as either "with-the-rule" (WTR) or "against-the-rule" (ATR) on the basis of the steep anterior corneal meridian. The post-operative refractive astigmatic prediction error was analyzed 1 month post-operatively using the vector analysis by the Alpins method and double-angle plots method. The correction indexes were 1.14 ± 0.29 in the ATR eyes and 1.25 ± 0.18 for the WTR eyes, indicating a tendency toward over-correction. The mean over-correction was 0.22 ± 0.52D in the ATR group and 0.65 ± 0.60D in the WTR group. The magnitude of error (ME) values were significantly different from the ideal value of zero in both groups (ATR: P = 0.03; WTR: P = 0.00). No significant difference in mean absolute error (MAE) in predicted residual astigmatism was found between ATR and WTR groups (0.61 ± 0.42 D versus 0.64 ± 0.39 D; P = 0.54). The ATR group yielded better results, with 48% <0.50D prediction error in the main analysis. The results suggested that in cases of high PCA, the toric IOL calculation, which was performed using TCA, may cause a potential over-correction in the ATR and WTR eyes. For ATR eyes, over-correction led to slight disruption of post-operative visual quality because of the "with-the-rule" residual astigmatism after operation. Therefore, we suggested using TCA for toric IOL calculation in ATR eyes.

Comparison of Astigmatism Prediction Accuracy for Toric Lens Implantation from Two Swept-Source Optical Coherence Tomography Devices.

To compare the astigmatism prediction accuracy for toric intraocular lens (IOL) implantation between two swept-source optical coherence tomography (SS-OCT) devices: Argos (Movu, a Santec Company) and the IOLMaster 700 (Carl Zeiss Meditec). This was a retrospective chart review of 59 eyes (44 patients) with corneal astigmatism and cataract that underwent cataract surgery or refractive lens exchange surgery with a toric IOL. Biometry was performed on all patients prior to cataract surgery and the Barrett toric IOL calculator was used. Visual acuity was measured postoperatively. Manifest refraction was measured at 1 month and compared to the predicted postoperative residual refraction. Preoperative K measurements between devices were also compared. Mean cylinder prediction error was -0.17 ± 0.43 for Argos and 0.12 ± 0.56 for IOLMaster 700. The cylinder prediction error 0.5 D or less was not significantly different between the devices, with 83.1% (49 eyes) for Argos and 76.3% (45 eyes) for IOLMaster 700 (p = 0.206). Spherical equivalent prediction error was 0.13 ± 0.39 for Argos and 0.25 ± 0.50 for IOLMaster 700. The mean spherical equivalent prediction error 0.5 D or less was significantly different between the devices, with 79.7% (47 eyes) for Argos and 61.0% (36 eyes) for IOLMaster 700 (p = 0.016). The prediction accuracies were similar between the devices, except for spherical equivalent, where a higher percentage of eyes were 0.5 D or less of the prediction with the Argos compared to the IOLMaster.

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

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

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

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

Saving of Time Using a Software-Based versus a Manual Workflow for Toric Intraocular Lens Calculation and Implantation.

Background: To determine whether there is a significant saving of time when using a digital cataract workflow for digital data transfer compared to a manual approach of biometry assessment, data export, intraocular lens calculation, and surgery time. Methods: In total, 48 eyes of 24 patients were divided into two groups: 24 eyes were evaluated using a manual approach, whereas another 24 eyes underwent a full digital lens surgery workflow. The primary variables for comparison between both groups were the overall time as well as several time steps starting at optical biometry acquisition until the end of the surgical lens implantation. Other outcomes, such as toric intraocular lens misalignment, reduction of cylinder, surgically induced astigmatism, prediction error, and distance visual acuity were measured. Results: Overall, the total diagnostic and surgical time was reduced from 1364.1 ± 202.6 s in the manual group to 1125.8 ± 183.2 s in the digital group (p < 0.001). The complete time of surgery declined from 756.5 ± 82.3 s to 667.3 ± 56.3 (p < 0.0005). Compared to the manual approach of biometric data export and intraocular lens calculation (76.7 ± 12.3 s) as well as the manual export of the reference image to a portable external storage device (26.8 ± 5.5 s), a highly significant saving of time was achieved (p < 0.0001). Conclusions: Using a software-based digital approach to toric intraocular lens implantation is convenient, more efficient, and thus more economical than a manual workflow in surgery practice.

A Review of Smartphone Apps Used for Toric Intraocular Lens Calculation and Alignment.

Smartphone apps are becoming increasingly popular in ophthalmology, one specific area of their application being toric intraocular lens (IOL) surgery for astigmatism correction. Our objective was to identify, review and objectively score smartphone apps applicable to toric IOL calculation and/or axis alignment. This review was divided into three phases. A review was conducted on four major app databases (phase I): National Health Service (NHS) Apps Library, Google Play Store, Apple App Store and Amazon Appstore. A systematic literature review (phase II) was conducted to identify studies for included apps in phase I of our study. Keywords used in both searches included: “toric lens”, “toric IOL”, “refraction”, “astigmatism”, “ophthalmology”, “eye calculator”, “ophthalmology calculator” and “refractive calculator”. Included apps were objectively scored (phase III) by three independent reviewers using the mobile app rating scale (MARS), a validated tool that ranks the quality of mobile health apps using a calculated mean app quality (MAQ) score. Phase I of our study screened 2428 smartphone apps, of which six apps for toric IOL calculation and four apps for axis marking were eligible and were selected for quantitative analysis. Phase II of our study screened 477 studies from PubMed, Medline and Google Scholar. Three studies validating two apps (toriCAM, iToric Patwardhan) in a clinical setting as adjunct tools for preoperative axis marking were identified. Phase III ranked Toric Calculator for iPhone (Apple iOS, MAQ 4.13; average MAQ 3.34 ± 0.54) as the highest-scoring toric IOL calculator, and iToric Patwardhan (Android OS, MAQ 4.13; average MAQ 3.41 ± 0.44) was the highest-scoring axis marker in our study. Our review identified and objectively scored ten smartphone apps available for toric IOL surgery adjuncts. Toric Calculator for iPhone and iToric Patwardhan were the highest-scoring toric IOL calculator and axis marker, respectively. Current literature, though limited, suggests that axis marking smartphone apps can achieve similar levels of misalignment reduction when compared to digital systems.

Comparative assessment of the accuracy of toric intraocular lens calculations

To compare the accuracy of toric intraocular lens (IOL) calculations on three modern toric calculators. The study comprised 35 eyes of 35 patients who underwent phacoemulsification with toric IOL implantation (EnVista Toric). Residual postoperative refractive astigmatism was calculated on three calculators: EnVista Toric Calculator, ASSORT Toric IOL Calculator and the Kane formula. Prediction error for each calculator was determined using vector analysis. The mean absolute deviation of predicted postoperative refractive astigmatism over actual astigmatism in diopters was distributed in the following way: 0.82±0.58, 0.70±0.67 and 0.72±0.76 using EnVista Toric Calculator, ASSORT Toric IOL Calculator and the Kane formula, respectively. Centroid prediction error was 0.08 (EnVista Toric Calculator), 0.06 (ASSORT) and 0.10 (Kane formula). There was a significantly smaller deviation using ASSORT and the Kane formula compared to the online calculator (p<0.05). Toric calculators ASSORT Toric IOL Calculator and the Kane formula showed higher accuracy of toric IOL calculation than EnVista Toric Calculator.

Ten commandments for biometry in tricky situations.

Recently, the number of litigations on cataract surgeons has increased. Because of the increasing ambitions of surgeons and demands for a spectacle-free life, the incidence of unhappy patients is at an all-time high. To an ophthalmologist, the fruits of a good surgery are dependent largely on their skills. However, more importantly, the roots of good results of a surgery are laid by a perfect IOL (intraocular lens) power calculation. Inaccurate biometry is one of the major reasons for unhappy patients, especially in some challenging scenarios. To hit the bull's eye, as far as target refraction is concerned, it is necessary to understand the benefits and limitations of currently available cutting-edge technology and formulae and apply them to the cataract surgery practice. The aim of the video is to familiarize modern-day ophthalmologists to these situations to achieve a perfect IOL power calculation. Using a step-by-step approach, we decoded biometry in special scenarios like poor cornea, ocular surface disorders, dry eyes, toric IOL calculation, cases with posterior corneal astigmatism, irregular corneas like keratoconus, pellucid marginal degeneration, post Lasik ectasia and penetrating keratoplasty. In this video we tried to address the solution to these special conditions and how to attain target refraction in such cases. A few more issues are addressed like biometry post retina surgery, very dense cataract where it is difficult to obtain axial length, and cases with extreme axial lengths. In this case-based approach, with relevant example, we tried to provide solutions for biometry in tricky scenarios like poor cornea, biometry post refractive surgery, dense cataracts, and cataract post retinal surgery. On following these commandments, not only will the litigations stop but our patients will be happier as well. https://youtu.be/dNXP2nDYUZo.

Should Artificial Tears Be Used During the Preoperative Assessment of Toric IOLs Before Age-Related Cataract Surgery? The TORIDE Study.

To assess the impact of the use of artificial tears during the preoperative work-up performed before age-related cataract surgery, when a toric intraocular lens (IOL) was indicated. This was a monocentric prospective study assessing 73 eyes of 51 patients, included consecutively after a preoperative work-up performed without artificial tears (no artificial tears group), when a toric IOL was indicated. Each included patient underwent a second series of examinations: biometry using the IOLMaster 700 (Carl Zeiss Meditec AG) and topography using the OPD-Scan II (Nidek), 1 minute after artificial tears instillation (artificial tears group; hyaluronate de sodium 0.15%, threalose 3% [Théalose; Théa]). Changes in anterior corneal astigmatism and subsequent changes in toric IOL calculation were analyzed. The error in predicted residual astigmatism was calculated. Anterior corneal astigmatism and total corneal astigmatism measured with the IOLMaster 700 were significantly modified when artificial tears were instilled before the examinations (1.51 ± 0.57 diopters [D], range: 0.75 to -3.55 vs 1.42 ± 0.63 D, range: 0.42 to 3.35 D; P = .043 and 1.59 ± 0.54 D, range: 0.87 to 3.48 vs 1.51 ± 0.59 D, range: 0.56 to 3.27 D, P = .038, respectively). This modification led to a change in IOL cylinder calculation in 43.8% of cases and to a change in implantation axis greater than 10° in 17.7% of cases. These changes were significantly greater in patients with a breakup time (BUT) less than 5 seconds (57.5% and 27.8%, with P = .009 and .029, respectively). In the subgroup of patients with a BUT of less than 5 seconds, the mean absolute error in predicted astigmatism was significantly lower after artificial tears instillation (0.48 ± 0.50 D, range: 0.00 to 2.79 vs 0.37 ± 0.25 D, range: 0.00 to 1.10 D, P = .048). Dry eye significantly impacted toric IOL calculations and should be taken into account during the preoperative assessments. Using artificial tears reduced the number of refractive errors. [J Refract Surg. 2021;37(11):759-766.].

Predicted vs measured posterior corneal astigmatism for toric intraocular lens calculations.

To evaluate the astigmatic correction obtained with a toric intraocular lens using the keratometric readings (Ks) from a swept-source optical coherence tomography (SS-OCT) biometer and the Barrett toric formula with its predicted posterior corneal astigmatism (PCA) value and to compare the results with those expected by using the OCT Ks and a measured PCA from a scheimpflug topographer and by using the SimKs and the measured PCA from the Scheimpflug topographer. Private practice, Lynwood, California. Retrospective observational study. All measurements were performed by the SS-OCT biometer and the Scheimpflug topographer and using the Barrett toric formula. We evaluated 122 eyes of 122 patients. The mean absolute errors in predicted residual astigmatism for the entire series were 0.41 ± 0.19 diopters (D) (0.00 to 0.85 D) using the OCT Ks and predicted PCA, 0.45 ± 0.25 D (0.00 to 1.01 D) using the OCT Ks and measured PCA, and 0.49 ± 0.25 D (0.00 to 1.30 D) using the SimKs and measured PCA. The statistically significant differences between the errors had a P value of .062 for the entire series (n = 122), .26 for the subgroup with against-the-rule astigmatism (n = 68), .47 for the subgroup with oblique astigmatism (n = 11), and .05 for the subgroup with with-the-rule astigmatism (n = 43). The percentage of eyes within ±0.50 D were 74% (n = 90), 71% (n = 87) and 64% (n = 78) (P = .13) and within ±0.75 D were 99% (n = 121), 95% (n = 116) and 84% (n = 102) (P < .001), respectively. The Barrett toric formula and its predicted PCA performed better with the OCT K readings than with the topographer SimKs and a measured PCA.

The Castrop formula for calculation of toric intraocular lenses

PurposeTo explain the concept behind the Castrop toric lens (tIOL) power calculation formula and demonstrate its application in clinical examples.MethodsThe Castrop vergence formula is based on a pseudophakic model eye with four refractive surfaces and three formula constants. All four surfaces (spectacle correction, corneal front and back surface, and toric lens implant) are expressed as spherocylindrical vergences. With tomographic data for the corneal front and back surface, these data are considered to define the thick lens model for the cornea exactly. With front surface data only, the back surface is defined from the front surface and a fixed ratio of radii and corneal thickness as preset. Spectacle correction can be predicted with an inverse calculation.ResultsThree clinical examples are presented to show the applicability of this calculation concept. In the 1st example, we derived the tIOL power for a spherocylindrical target refraction and corneal tomography data of corneal front and back surface. In the 2nd example, we calculated the tIOL power with keratometric data from corneal front surface measurements, and considered a surgically induced astigmatism and a correction for the corneal back surface astigmatism. In the 3rd example, we predicted the spherocylindrical power of spectacle refraction after implantation of any toric lens with an inverse calculation.ConclusionsThe Castrop formula for toric lenses is a generalization of the Castrop formula based on spherocylindrical vergences. The application in clinical studies is needed to prove the potential of this new concept.

Toric Intraocular Lens Calculation Considering Anterior Surgically Induced Astigmatism and Posterior Corneal Astigmatism

ABSTRACT Purpose To evaluate the prediction error (PE) after applying the Abulafia–Koch formula in an online calculator with and without consideration of anterior corneal surgically induced astigmatism (SIACornea). Methods SIACornea models were calculated with a historical database of 204 right eyes (REs) from a single surgeon, either for manual (2.2 mm) or femtosecond (2.5 mm) temporal clear corneal incisions. PE was assessed in 58 REs operated by the same surgeon with a monofocal toric IOL and calculated, considering the PCA estimation in an online calculator with the combination of each one of the following SIACornea calculation approaches: (A) considering only significant centroids after stratification, (B) all centroids after stratification and (C) a single centroid without stratification. Results The consideration of all centroids resulted in an underestimation of SIACornea in cases of preoperative against-the-rule astigmatism (ATR-A) and an overestimation in with-the-rule astigmatism (WTR-A). After stratification, SIACornea was only significant in preoperative ATR and oblique astigmatism cases for femtosecond incisions. PE considering PCA only was 0.03@160º. The combination with SIACornea resulted in a WTR-A surprise in preoperative ATR-A and WTR-A, however only being significant for preoperative ATR-A in calculation approaches B (0.29@84º) and C (0.21@80º). SIACornea addition to PCA estimation only reduced the centroid for oblique preoperative astigmatism. Conclusions Surgeons should consider the calculation of the SIACornea after stratification by astigmatism type when using the same incision location (i.e. temporal). However, SIACornea derived from the anterior corneal surface should not be combined with PCA estimation for IOL power calculations.

Toric IOL Calculation in Eyes With High Posterior Corneal Astigmatism.

To evaluate different calculation approaches for toric intraocular lens (IOL) calculation in cases with high posterior corneal astigmatism (PCA). Consecutive patients who underwent cataract extraction with implantation of toric IOLs by a single surgeon were reviewed. Eyes with measured PCA of 0.80 diopters (D) or greater were included. Errors in the predicted postoperative refractive astigmatism were calculated for the Abulafia-Koch formula, vector summation of anterior keratometry with posterior tomography, and the Barrett toric calculator using predicted and measured PCA. One hundred seventy-three consecutive cases of toric IOL implantation were reviewed. Seventeen eyes (10%) had PCA of 0.80 D or greater and were investigated. The mean absolute error was the lowest with Barrett's measured PCA (0.55 ± 0.38) followed by Barrett's predicted PCA mean absolute error (0.65 ± 0.31), vector summation (0.69 ± 0.33), and the Abulafia-Koch formula (0.80 ± 0.36). The rate of eyes with prediction errors within 0.25 D or less was the highest for Barrett's measured PCA (29.4%) followed by Barrett's predicted PCA (5.9%) and no eyes for the Abulafia-Koch formula and vector summation. The mean centroid prediction errors were lowest for Barrett's measured PCA and Barrett's predicted PCA (0.14 ± 0.66 @70, 0.14 ± 0.73 @179, respectively), followed by vector summation (0.35 ± 0.70 @5), and the Abulafia-Koch formula (0.39 ± 0.80 @179). The results suggest that in cases of high PCA, the Barrett toric calculator using direct measurements of PCA may have a potential advantage over predicted PCA in toric IOL calculations and vector summation of the anterior and posterior corneal astigmatism. [J Refract Surg. 2020;36(12):820-825.].

Refractive outcome of toric intraocular lens calculation in cases of oblique anterior corneal astigmatism.

To establish whether toric intraocular lens (IOL) calculation on the basis of anterior corneal measurements alone, in corneas with oblique anterior astigmatism, will result in a systematic overcorrection or undercorrection of postoperative refractive astigmatism, and to establish whether adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism is needed in such eyes. The Queen Elizabeth Hospital, Department of Ophthalmology, Adelaide, South Australia. Retrospective case series. Data were collected from consecutive eyes with oblique anterior corneal astigmatism undergoing cataract surgery or refractive lens exchange. Toric IOL calculations were made using unadjusted anterior corneal astigmatism measurements and an astigmatically neutral technique. By comparison of targeted vs achieved astigmatic correction using vector analysis, the astigmatic power prediction error and angle of error were derived. In 50 eyes, the mean postoperatively measured refractive astigmatism was 0.42 diopters (D) (SD 0.33 D), the mean targeted refractive astigmatism was 0.15 (SD 0.18), and the vector-derived mean absolute prediction error was 0.23 D (SD 0.21). All 50 eyes (100%) fell at or within ±1.00 D of the target and 45 eyes (90%) at or within ±0.50 D. The geometric mean astigmatism correction index was 0.98, and the mean absolute angle of error was 8.63 degrees (SD 8.55). There is no systematic error attributable to posterior corneal astigmatism in toric IOL calculation and no need for adjustment of anteriorly measured corneal keratometric values for toric IOL calculation in eyes with oblique anterior corneal astigmatism. To do so may introduce an error in astigmatic outcome.

Clinical Outcomes of Toric Intraocular Lenses: Differences in Expected Outcomes When Using a Calculator That Considers Effective Lens Position and the Posterior Cornea vs One That Does Not.

PurposeTo compare toric intraocular lens (IOL) outcome accuracy after using an online toric calculator that accounted for posterior corneal astigmatism versus a traditional calculator that only accounted for anterior corneal astigmatism.Patients and MethodsThis was a single-arm, non-masked, non-randomized prospective study in a single private practice in Norfolk, Virginia, USA, evaluating clinical outcomes of toric IOL implantation based on a calculator that considered posterior corneal astigmatism (PCA) and effective lens position (ELP). Of interest was the distribution of the residual refraction (sphere and cylinder) at 40–70 days postoperative. Residual refractive cylinder (RRC) was compared to the back-calculated theoretical results using a legacy calculator that did not consider PCA. Distance visual acuity (best-corrected and uncorrected) and the manifest refraction were also measured, along with preoperative and postoperative keratometry.ResultsForty-six eyes of 34 subjects were available for analysis. All eyes had a spherical equivalent refraction within 0.5D of intended. Uncorrected visual acuity was 20/25 or better in 86% of eyes targeted for emmetropia. Residual cylinder was 0.50D or less in 96% of eyes, with a maximum of 0.75D measured. The difference between residual cylinder and the expected cylinder from calculations was significantly lower for the calculator that included consideration of PCA and ELP relative to the one that did not.ConclusionUse of a toric IOL calculator that includes consideration of posterior corneal astigmatism is recommended to optimize clinical outcomes.

A Direct Method for Determining Toricity Ratios of Toric Intraocular Lens Calculators

This study develops a method to determine toricity ratios used by arbitrary toric intraocular lens calculators. Access to this information allows for the improvement of refractive results. We derive the Sayegh-Gabra formula, which uses input and output parameters in a toric calculator to extract toricity ratios that are typically not disclosed. We illustrate the method on a number of commercial calculators. For each calculator, high, average, and low axial length values are crossed with high, average, and low mean corneal power values to generate a 3 × 3 matrix. A toricity ratio is generated for each axial length and mean corneal power pair. We thus identify several toric lens manufacturers’ calculators that use a constant toricity ratio, often 1.46. Some others use a variable ratio centered at 1.46, but varying as axial length and mean K increases over a range of values corresponding to physiological myopia and hyperopia. There is an emerging trend away from constant toricity ratios. Using our methodology, it is possible to extract the toricity ratio used by specific calculators/manufacturers, distinguish those using constant versus variable toricity ratios, and use this information to improve surgical outcomes by refining current and future toric intraocular lens calculators.