Intraocular Lens Power Formulas, Biometry, and Intraoperative Aberrometry: A Review.

The refractive outcome of cataract surgery is influenced by the choice of intraocular lens (IOL) power formula and the accuracy of the various devices used to measure the eye (including intraoperative aberrometry [IA]). This review aimed to cover the breadth of literature over the previous 10 years, focusing on 3 main questions: (1) What IOL power formulas currently are available and which is the most accurate? (2) What biometry devices are available, do the measurements they obtain differ from one another, and will this cause a clinically significant change in IOL power selection? and (3) Does IA improve refractive outcomes? A literature review was performed by searching the PubMed database for articles on each of these topics that identified 1313 articles, of which 166 were included in the review. For IOL power formulas, the Kane formula was the most accurate formula over the entire axial length (AL) spectrum and in both the short eye (AL, ≤22.0 mm) and long eye (AL, ≥26.0 mm) subgroups. Other formulas that performed well in the short-eye subgroup were the Olsen (4-factor), Haigis, and Hill-radial basis function (RBF) 1.0. In the long-eye group, the other formulas that performed well included the Barrett Universal II (BUII), Olsen (4-factor), or Holladay 1 with Wang-Koch adjustment. All biometry devices delivered highly reproducible measurements, and most comparative studies showed little difference in the average measures for all the biometric variables between devices. The differences seen resulted in minimal clinically significant effects on IOL power selection. The main difference found between devices was the ability to measure successfully through dense cataracts, with swept-source OCT-based machines performing better than partial coherence interferometry and optical low-coherence reflectometry devices. Intraoperative aberrometry generally improved outcomes for spherical and toric IOLs in eyes both with and without prior refractive surgery when the BUII and Hill-RBF, Barrett toric calculator, or Barrett True-K formulas were not used. When they were used, IA did not result in better outcomes.

A Comparison of the Accuracy of 6 Modern Toric Intraocular Lens Formulas.

PURPOSE: To compare the accuracy of the Abulafia-Koch, the Barrett, the EVO 2.0, the new Holladay 2 with total surgical-induced astigmatism, the Kane, and the Næser-Savini toric intraocular lens (IOL) power formulas using a large database of toric IOL refractive outcomes. DESIGN: Retrospective consecutive case series. PARTICIPANTS: Eight hundred twenty-three eyes of 823 patients who had a toric IOL inserted during surgery. METHODS: One eligible eye from patients having uncomplicated cataract surgery with insertion of an Alcon SN6AT(2-9) IOL (Alcon Laboratories, Inc, Fort Worth, TX) from 1 surgeon were included in the study. Both preoperative and postoperative biometry were measured using either the IOLMaster 500 or 700 (Carl Zeiss Meditec AG, Jena, Germany). Using vector calculation, the predicted postoperative refractive astigmatism was calculated for each formula. This was compared with the actual postoperative refractive astigmatism to give the prediction error. MAIN OUTCOME MEASURES: Mean absolute prediction error, standard deviation of the prediction error, and percentage of eyes with a prediction error within ±0.50 diopter (D). RESULTS: The Kane formula showed the highest proportion of eyes with a prediction error within ±0.50 D with 65.6%, followed by the Barrett formula (59.9%), Abulafia-Koch formula (59.5%), EVO 2.0 formula (58.9%), Næser-Savini formula (56.7%), and Holladay 2 formula (53.9%). The Kane formula showed a statistically significantly lower mean absolute prediction error (P < 0.001) and a significantly lower variance of the prediction error (P < 0.01) compared with all other formulas. No statistically significant difference existed among the mean absolute prediction errors for the Abulafia-Koch, Barrett, and EVO 2.0 toric formulas. CONCLUSIONS: Use of the Kane toric formula significantly improved the prediction of postoperative astigmatic outcome compared with the other formulas studied.

Accuracy of Intraocular Lens Power Formulas Modified for Patients with Keratoconus.

PURPOSE: To assess the accuracy of intraocular lens (IOL) power formulas modified specifically for patients with keratoconus (Holladay 2 with keratoconus adjustment and Kane keratoconus formula) compared with normal IOL power formulas (Barrett Universal 2, Haigis, Hoffer Q, Holladay 1, Holladay 2, Kane, and SRK/T). DESIGN: Retrospective consecutive case series. PARTICIPANTS: A total of 147 eyes of 147 patients with keratoconus. METHODS: Data from patients with keratoconus who had preoperative IOLMaster biometry were included. A single eye per qualifying patient was randomly selected. The predicted refraction was calculated for each of the formulas and compared with the actual refractive outcome to give the prediction error. Subgroup analysis based on the steepest corneal power measured by biometry (stage 1: ≤48 diopters [D], stage 2: >48 D and ≤53 D, and stage 3: >53 D) was performed. MAIN OUTCOME MEASURE: Prediction error. RESULTS: On the basis of the mean absolute prediction error (MAE), the formulas were ranked as follows: Kane keratoconus formula (0.81 D), SRK/T (1.00 D), Barrett Universal 2 (1.03 D), unmodified Kane (1.05 D), Holladay 1 (1.18 D), unmodified Holladay 2 (1.19 D), Haigis (1.22 D), Hoffer Q (1.30 D), and Holladay 2 with keratoconus adjustment (1.32 D). The Kane keratoconus formula had a statistically significant lower MAE compared with all formulas (P < 0.01). In stage 3 keratoconus, all nonmodified formulas had a hyperopic mean prediction error ranging from 1.72 to 3.02 D. CONCLUSIONS: The Kane keratoconus formula was the most accurate formula in this series. The SRK/T was the most accurate of the traditional IOL formulas. All normal IOL formulas resulted in hyperopic refractive outcomes that worsened as the corneal power increased. Suggestions for target refractive aims in each stage of keratoconus are given.

Analysis of Posterior Corneal Surgically Induced Astigmatism Following Cataract Surgery With a 1.8-mm Temporal Clear Corneal Incision.

PURPOSE: To determine posterior corneal surgically induced astigmatism (SIA) when using a temporal clear corneal incision and the IOLMaster 700 (Carl Zeiss Meditec AG) for biometric measurements and to determine whether posterior corneal SIA can be predicted from preoperative data. METHODS: A total of 258 consecutive eyes of 258 patients underwent cataract surgery with a 1.8-mm temporal clear corneal incision. Biometry measurements were taken preoperatively and 6 weeks postoperatively using the IOLMaster 700. Using vector analysis, the SIA of the posterior cornea was calculated. RESULTS: The centroid of posterior corneal SIA was 0.01 diopters (D) @159 ± 0.14 D. The mean posterior corneal SIA was 0.12 D ± 0.07 D. Posterior corneal SIA magnitude was 0.25 D or less in 95% of patients. There was no correlation found between posterior corneal SIA magnitude and any preoperative measurement. CONCLUSIONS: The authors suggest not adjusting for posterior corneal SIA if using a small caliber, temporal incision. It was not possible to predict posterior corneal SIA from preoperative biometric measurements. [J Refract Surg. 2023;39(6):381-386.].

Identification and characterization of Huntington related pathology: an in vivo DKI imaging study.

An important focus of Huntington Disease (HD) research is the identification of symptom-independent biomarkers of HD neuropathology. There is an urgent need for reproducible, sensitive and specific outcome measures, which can be used to track disease onset as well as progression. Neuroimaging studies, in particular diffusion-based MRI methods, are powerful probes for characterizing the effects of disease and aging on tissue microstructure. We report novel diffusional kurtosis imaging (DKI) findings in aged transgenic HD rats. We demonstrate altered diffusion metrics in the (pre)frontal cerebral cortex, external capsule and striatum. Presence of increased diffusion complexity and restriction in the striatum is confirmed by an increased fiber dispersion in this region. Immunostaining of the same specimens reveals decreased number of microglia in the (pre)frontal cortex, and increased numbers of oligodendrocytes in the striatum. We conclude that DKI allows sensitive and specific characterization of altered tissue integrity in this HD rat model, indicating a promising potential for diagnostic imaging of gray and white matter pathology.

Accuracy of Formulas for Intraocular Lens Power Calculation After Myopic Refractive Surgery.

PURPOSE: To assess the accuracy of the following intraocular lens (IOL) power formulas: Barrett True-K No History (BTKNH), Emmetropia Verifying Optical 2.0 Post Myopic LASIK/PRK (EVO 2.0), Haigis-L, American Society of Cataract and Refractive Surgery (ASCRS) average, and Shammas, designed for patients who have undergone previous myopic refractive surgery, independent of preexisting clinical history and corneal tomographic measurements. METHODS: Data from 302 eyes of 302 patients who previously underwent myopic refractive surgery and had cataract surgery done by a single surgeon with only one IOL type inserted were included. The predicted refraction was calculated for each of the formulas and compared with the actual refractive outcome to give the prediction error. Subgroup analysis based on the axial length and mean keratometry was performed. RESULTS: On the basis of mean absolute prediction error (MAE), the formulas were ranked as follows: Haigis-L (0.61 diopters [D]), ASCRS average (0.63 D), BTKNH (0.67 D), EVO 2.0 (0.68 D), and Shammas (0.69 D). The Haigis-L had a statistically significant lower MAE compared with all formulas (P < .05) except the ASCRS average. Hyperopic mean prediction errors were seen in all formulas for axial lengths of greater than 30 mm or mean keratometry values of 35.00 diopters or less. CONCLUSIONS: The Haigis-L and the ASCRS average formulas provided the most accurate results in the overall population evaluated in this study. Moreover, according to data observed, it is important to be careful handling very long eyes and very flat corneas because hyperopic refractions could be more common. [J Refract Surg. 2022;38(7):443-449.].

A Comparison of Refractive Accuracy Between Conventional and Femtosecond Laser Cataract Surgery Techniques Using Modern IOL Formulas.

PURPOSE: To compare the refractive outcome prediction accuracy between conventional (CCS) and femtosecond laser assisted (FLACS) cataract surgery techniques using optimized lens constants for modern intraocular lens (IOL) formulas. PATIENTS AND METHODS: Our retrospective, comparative, interventional case series, compared data from 196 eyes undergoing CCS and 456 eyes undergoing FLACS with Acrysof IOL (Alcon laboratories, Inc) implantation. After optimizing IOL constants, the predicted refractive outcome was calculated for all formulas for each case. This was compared to the actual refractive outcome to provide the prediction error. The performance of CCS and FLACS was compared by the absolute prediction error and percentage of eyes within 0.25D, 0.5D and 1.0D of anticipated refractive outcome. RESULTS: There was no statistically significant difference in median absolute error between the CCS and LACS groups for the Kane (0.256, 0.236; p=0.389), SRK T (0.298, 0.302, p=0.910), Holladay (0.312, 0.275; p=0.090), Hoffer Q (0.314, 0.289; p=0.330), Haigis (0.309, 0.258; p=0.177), Barrett Universal 2(0.250, 0.250; p=0.866), Holladay 2 (0.250, 0.258; p=0.860) and Olsen (0.260, 0.255; p=0.570) formulas. Similarly, there was no consistent difference between the two techniques for percentage of patients within 0.25, 0.50 and 1.0D of predicted refractive outcome for each formula. CONCLUSION: There was no difference in refractive outcome prediction accuracy between the CCS and FLACS techniques.

Accuracy of Artificial Intelligence Formulas and Axial Length Adjustments for Highly Myopic Eyes.

PURPOSE: To compare the accuracy of artificial intelligence formulas (Kane formula and Radial Basis Function [RBF] 2.0) and other formulas, including the original and modified Wang-Koch (MWK) adjustment formulas for Holladay 1 (H1-MWK) and SRK/T (SRK/T-WK and SRK/T-MWK), the Barrett Universal II (BUII), the emmetropia-verifying optical (EVO), and the Haigis equation in highly myopic eyes. DESIGN: Retrospective consecutive case-series study. METHODS: A total of 370 eyes with an axial length (AL) ≥26.0 mm of 370 patients were enrolled, and subgroup analyses was performed based on ALs. The median absolute error (MedAE), the percentages of eyes with hyperopic outcome and within ±0.25 diopters (D), ±0.50 D, and ±1.00 D of prediction error were determined. RESULTS: Overall, the Kane equation had the lowest MedAE (0.26 D), followed by H1-WK (0.27 D) and H1-MWK (0.28 D). There were no significant differences in MedAE among the Kane equation, the RBF 2.0, the BUII, the H1-MWK, and the H1-WK, whereas the Kane equation had a significantly lower MedAE than EVO (P < .001), SRK/T-MWK (P = .001), SRK/T-WK (P = .006), and Haigis (P < .001). In extremely myopic eyes with an AL ≥30.0 mm (n = 115), the Kane equation had a significantly lower MedAE than the RBF 2.0 (P = .001), the EVO (P = .019), the BUII (P = .013), and the Haigis method (P = .005), whereas no significant differences were found among the Kane, H1-MWK, and H1-WK equations. CONCLUSIONS: The Kane equation was comparable to RBF 2.0, BUII, H1-MWK, and H1-WK in highly myopic eyes and was better than RBF 2.0 and BUII in extremely myopic eyes. The Kane, H1-MWK, and H1-WK methods were equally accurate in eyes with high to extreme myopia.

Intraocular lens formula comparison in axial hyperopia with a high-power intraocular lens of 30 or more diopters.

PURPOSE: To compare the accuracy of intraocular lens (IOL) power calculation formula predictions (Barrett Universal II, Emmetropia Verifying Optical [EVO] 2.0, Haigis, Hill-RBF 2.0, Holladay 1, Holladay 2, Hoffer Q, Kane, Olsen, and SRK/T) when using the Alcon SA60AT IOL of 30 or greater diopter (D) power. SETTING: Kaiser Permanente, California, USA. DESIGN: Multicenter retrospective consecutive case series. METHODS: Data from patients having uneventful cataract surgery with insertion of a ≥30 D SA60AT IOL and preoperative LENSTAR 900 biometry were included. A single eye per qualifying patient was randomly selected for inclusion in the analysis. Lens constants were optimized using a large dataset of the same IOL model including the full range of axial lengths. The optimized lens constants were then used to calculate the predicted refraction for each formula, which was compared with the actual refractive outcome to give the prediction errors. RESULTS: Included in the study were 182 eyes of 182 patients. From highest to lowest, the percentage of eyes with a prediction error within ±0.50 D was the Kane (58.8%), EVO 2.0 (57.7%), Haigis (55.5%), Holladay 2 (54.9%), Olsen (53.3%), Holladay 1 (50.5%), Hill-RBF 2.0 (43.9%), SRK/T (42.9%), Barrett Universal II (36.8%), and Hoffer Q (35.7%) formulas. The Kane formula had a statistically significant lower mean absolute prediction error compared with all formulas (P < .05) except the EVO 2.0 formula. CONCLUSIONS: The Kane formula had the lowest prediction error of the formulas studied, which was statistically significant compared with all formulas except the EVO 2.0 formula.

Refractive Predictability Using the IOLMaster 700 and Artificial Intelligence-Based IOL Power Formulas Compared to Standard Formulas.

PURPOSE: To investigate the accuracy of intraocular lens (IOL) power calculation formulas using swept-source optical coherence tomography (SS-OCT). METHODS: Eyes with biometry measurement by IOLMaster 700 (Carl Zeiss Meditec AG), uncomplicated phacoemulsification, and IOL implantation were enrolled in this retrospective study. Newly released artificial intelligence-based formulas including Hill-Radial Basis Function (RBF) 2.0, Kane, and PEARL-DGS were compared with Gaussian optics-based standard formulas. The refraction predicted by each formula was compared with the actual refractive outcome in spherical equivalent. RESULTS: A total of 410 eyes of 410 patients were included in this study. Using optimized constants for SS-OCT biometry led to a significant decrease in median absolute error (MedAE) for Barrett, Haigis, and Hoffer Q formulas compared with using User Group for Laser Interference Biometry constants (P < .05). Overall, Olsen (0.283 diopters [D]) and Kane (0.286 D) formulas had significantly lower MedAEs than RBF 2.0 (0.314 D), Haigis (0.322 D), SRK/T (0.371 D), Holladay 1 (0.376 D), and Hoffer Q (0.379 D) formulas under constant optimization (P < .05). The first four formulas with the lowest standard deviations of prediction error were Kane (0.451 D), Olsen (0.456 D), EVO 2.0 (0.460 D), and Barrett (0.470 D). Olsen (47.1%), Barrett (45.9%), Kane (45.4%), and EVO 2.0 (45.1%) formulas had greater proportions of eyes within ±0.25 D of the predicted refraction than Hoffer Q (35.9%), SRK/T (35.9%), and Holladay 1 (33.4%) formulas (P < .05). CONCLUSIONS: Constant optimization for SS-OCT biometry further improves the performance of formulas. The most accurate prediction of postoperative refraction can be achieved with Barrett, EVO 2.0, Kane, and Olsen formulas. [J Refract Surg. 2020;36(7):466-472.].

Assessment of the accuracy of new and updated intraocular lens power calculation formulas in 10 930 eyes from the UK National Health Service.

PURPOSE: To compare the accuracy of new/updated methods of intraocular lens (IOL) power calculation (Kane, Hill-RBF 2.0, and Holladay 2 with new axial length adjustment) with that of established methods (Barrett Universal II, Olsen, Haigis, Holladay 1, Hoffer Q, and SRK/T). SETTING: Bristol Eye Hospital, University Hospitals Bristol National Health Service, Foundation Trust, Bristol, UK. DESIGN: Retrospective consecutive case series. METHODS: Data from patients having uneventful cataract surgery with the insertion of 1 of 4 IOL types were included. Optimized IOL constants were used to calculate the predicted refraction of each formula for each patient. This was compared with the actual refractive outcome to give the prediction error. A subgroup analysis occurred based on the axial length and IOL type. RESULTS: The study included 10 930 eyes of 10 930 patients with the Kane formula having the lowest mean absolute prediction error (MAE), which was statistically significant (P < .001 in all cases) followed by the Hill 2.0, Olsen, Holladay 2, Barrett Universal 2, Holladay 1, SRK/T, Haigis, and Hoffer Q formula. The percentage of eyes predicted within ±0.5 D was Kane, 72%; Hill 2.0, 71.2%; Olsen, 70.6%; Holladay 2, 71%; Barrett 2, 70.7%; SRK/T, 69.1%; Haigis, 69%; and Hoffer Q, 68.1%. The Kane formula had the lowest MAE for short, medium, and long axial length subgroups and for each IOL type assessed. The updated versions of the Holladay 2 and Hill 2.0 formulas have resulted in improved accuracy. CONCLUSIONS: Overall and in each axial length subgroup, the Kane formula was more accurate than the other formulas.

Comparison of the Kane formula with existing formulas for intraocular lens power selection.

OBJECTIVE: To compare the accuracy of a new intraocular lens (IOL) power formula (Kane formula) with existing formulas using IOLMaster, predominantly model 3, biometry (measures variables axial length, keratometry and anterior chamber depth) and optimised lens constants. To compare the accuracy of three new or updated IOL power formulas (Kane, Hill-RBF V.2.0 and Holladay 2 with new axial length adjustment) compared with existing formulas (Olsen, Barrett Universal 2, Haigis, Holladay 1, Hoffer Q, SRK/T). METHODS AND ANALYSIS: A single surgeon retrospective case review was performed from patients having uneventful cataract surgery with Acrysof IQ SN60WF IOL implantation over 11 years in a Melbourne private practice. Using optimised lens constants, the predicted refractive outcome for each formula was calculated for each patient. This was compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length as follows: short (≤22.0 mm), medium (>22.0 to <26.0 mm) and long (≥26.0 mm). RESULTS: The study included 846 patients. Over the entire axial length range, the Kane formula had the lowest mean absolute prediction error (p<0.001, all formulas). The mean postoperative difference from intended outcome for the Kane formula was -0.14+0.27×1 (95% LCL -1.52+0.93×43; 95% UCL +0.54+1.03×149). The formula demonstrated the lowest absolute error in the medium axial length range (p<0.001). In the short and long axial length groups, no formula demonstrated a significantly lower absolute mean prediction error. CONCLUSION: Using three variables (AL, K, ACD), the Kane formula was a more accurate predictor of actual postoperative refraction than the other formulae under investigation. There were not enough eyes of short or long axial length to adequately power statistical comparisons within axial length subgroups.

Accuracy of 3 new methods for intraocular lens power selection.

PURPOSE: To evaluate the accuracy of 3 new methods for intraocular lens (IOL) power selection (Hill-Radial Basis Function [Hill-RBF] method, FullMonte method, and the Ladas Super Formula) compared with that of the Holladay 1 and Barrett Universal II formulas. SETTING: Ophthalmology Department, Alfred Hospital, Melbourne, Australia. DESIGN: Retrospective case series. METHODS: Patients who had uneventful cataract surgery with insertion of the Acrysof IQ SN60WF IOL over 5 years were included in the study. Data obtained from the electronic medical record and the IOLMaster device were entered into the respective calculators using self-designed computer programs. Using optimized lens constants, the predicted refractive outcome using each of the 5 methods/formulas was calculated and compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length as follows: short (≤22.0 mm), medium (>22.0 to <24.5 mm), medium-long (≥24.5 to <26.0 mm), and long (≥26.0 mm). RESULTS: The study comprised 3122 eyes of 3122 patients. A statistically significant difference in the mean absolute prediction error (MAE) between the 5 methods for IOL power calculation was found (P < .001), with the Barrett Universal II formula being the most accurate. The Ladas Super Formula had the third lowest MAE, the Hill-RBF the fourth lowest MAE, and the FullMonte the highest MAE of the 5 methods assessed. CONCLUSION: New methods for predicting the postoperative refraction failed to yield more accurate results than current formulas.

Intraocular lens power formula accuracy: Comparison of 7 formulas.

PURPOSE: To assess the accuracy of 7 intraocular lens (IOL) power formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2) using IOLMaster biometry and optimized lens constants. SETTING: Public hospital ophthalmology department. DESIGN: Retrospective case series. METHODS: Data from patients having uneventful cataract surgery with Acrysof IQ SN60WF IOL implantation over 5 years were obtained from the biometry and patient charts. Optimized lens constants were calculated for each formula and used to determine the predicted refractive outcome for each patient. This was compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length (AL) as follows: short (≤22.0 mm), medium (>22.0 to <24.5 mm), medium long (≥24.5 to <26.0 mm), and long (≥26.0 mm). RESULTS: The study included 3241 patients. The Barrett Universal II formula had the lowest mean absolute prediction error over the entire AL range (P < .001, all formulas) as well as in the medium (P < .001, all formulas), medium-long (P < .001, except Holladay 1 and T2), and long AL (P < .001, except T2) subgroups. No statistically significant difference was seen between formulas in the short AL subgroup. Overall, the Barrett Universal II formula resulted in the highest percentage of eyes with prediction errors between ±0.25 diopter D, ±0.50 D, and ±1.00 D. CONCLUSION: In eyes with an AL longer than 22.0 mm, the Barrett Universal II formula was a more accurate predictor of actual postoperative refraction than the other formulas. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.