Accuracy of 20 Intraocular Lens Power Calculation Formulas in Medium-Long Eyes.

INTRODUCTION: The aim of this work is to compare 20 intraocular lens (IOL) power calculation formulas in medium-long eyes (24.50-25.99 mm) in terms of root mean square absolute error (RMSAE), median absolute error (MedAE), and percentage of eyes with prediction error (PE) within ± 0.50 D. METHODS: The data of patients who underwent uneventful phacoemulsification between January 2017 and September 2023 were reviewed. Pre-surgery IOL power was calculated using Holladay1, SRK/T, Hoffer Q, Holladay 2, and Haigis. Three months after phacoemulsification, refraction was measured. Post-surgery IOL power calculations were performed utilizing the following formulas: Barrett Universal II, Kane, K6, Olsen (OLCR), Olsen (standalone), PEARL-DGS, Ladas Super Formula AI (LSF AI), T2, EVO, VRF, Hoffer QST, Castrop, VRF-G, Karmona, and Naeser 2. RMSAE, MedAE, and percentage of eyes with PE within ± 0.25 D, ± 0.50 D, ± 0.75 D and ± 1.00 were calculated. RESULTS: One hundred twenty-four eyes with axial length ranges between 24.52 and 25.97 mm were studied. The SRK/T formula yielded the lowest RMSAE (0.206) just before Holladay 1 (0.260) and T2 (0.261). In terms of MedAE, the best outcome was obtained by SRK/T (0.12) followed by Barrett Universal II (0.15) and LSF AI (0.15). The highest percentage of eyes with prediction error within ± 0.50 D was achieved by SRK/T, T2, and Holladay 1 (97.58, 93.55, and 93.55%, respectively). CONCLUSIONS: Third-generation formulas (SRK/T, Holladay 1) provided highly accurate outcomes in medium-long eyes and still can be wildly used to calculate IOL power.

Accuracy of the VRF and VRF-G Intraocular Lens Power Calculation Formulas Using Swept-Source Optical Coherence Tomography Biometry.

Purpose: To collate the accuracy of two recently introduced intraocular lens (IOL) formulas (VRF and VRF-G) in cataract patients using a swept-source optical coherence tomography (SS-OCT) biometry (IOL Master 700, Carl Zeiss Meditec AG, Jena, Germany). Patients and Methods: Data records of 295 eyes from 295 patients were included in this scrutiny. The IOLMaster 700 SS-OCT biometer was used for biometric measurements. The VRF and VRF-G formulas were compared with seven 3rd and 4th generation thin and thick-lens formulas: Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, T2, and Barrett Universal II. With optimized lens constants, the mean prediction error (PE) and its standard deviation (SD), the median absolute error (MedAE), the mean absolute error (MAE), and the percentage of eyes with PEs within ±0.25 D, ±0.50 D, ±0.75 D, ±1.00 D, and <±2.00 D were analyzed. Results: Statistically significant differences were found between formulas in the whole group (Friedman test, P = 0.000). The VRF-G and Haigis formulas showed the lowest SD values (0.464 D and 0.466 D respectively). The VRF and Barrett Universal II formulas were less predictable (SD 0.471 D and SD 0.474 D respectively). The biggest proportion of eyes within ±0.50 D was found with VRF-G (76.27%), Haigis (75.59%), VRF (74.92%), and Barrett Universal II (74.92%) formulas. Conclusion: Based on data achieved from the SS-OCT biometry, the VRF-G and Haigis methods were the more precise predictors of postoperative refraction with the biggest proportion of eyes within ±0.50 D.

Accuracy of 24 IOL Power Calculation Methods.

PURPOSE: To scrutinize the accuracy of 24 intraocular lens (IOL) power calculation formulas in unoperated eyes. METHODS: In a series of consecutive patients undergoing phacoemulsification and implantation of the Tecnis 1 ZCB00 IOL (Johnson & Johnson Vision), the following formulas were evaluated: Barrett Universal II, Castrop, EVO 2.0, Haigis, Hoffer Q, Hoffer QST, Holladay 1, Holladay 2, Holladay 2 (AL Adjusted), K6 (Cooke), Kane, Karmona, LSF AI, Naeser 2, OKULIX, Olsen (OLCR), Olsen (standalone), Panacea, PEARL-DGS, RBF 3.0, SRK/T, T2, VRF, and VRF-G. The IOLMaster 700 (Carl Zeiss Meditec AG) was used for biometric measurements. With optimized lens constants, the mean prediction error (PE) and its standard deviation (SD), the median absolute error (MedAE), the mean absolute error (MAE), and the percentage of eyes with prediction erros within ±0.25, ±0.50, ±0.75, ±1.00, and ±2.00 D were analyzed. RESULTS: Three hundred eyes of 300 patients were enrolled. The heteroscedastic method revealed statistically significant differences (P < .05) among formulas. Newly developed methods such as the VRF-G (standard deviation [SD] ±0.387 D), Kane (SD ±0.395 D), Hoffer QST (SD ±0.404 D), and Barrett Universal II (SD ±0.405) were more accurate than older formulas (P < .05). These formulas also yielded the highest percentage of eyes with a PE within ±0.50 D (84.33%, 82.33%, 83.33%, and 81.33%, respectively). CONCLUSIONS: Newer formulas (Barrett Universal II, Hoffer QST, K6, Kane, Karmona, RBF 3.0, PEARL-DGS, and VRF-G) were the most accurate predictors of postoperative refractions. [J Refract Surg. 2023;39(4):249-256.].

Comparison of the prediction accuracy of 13 formulas in long eyes.

PURPOSE: To investigate the accuracy of modern intraocular lens (IOL) power calculation formulas in eyes with axial length (AL) ≥ 26.00 mm. METHODS: A total of 193 eyes with one type of lens were analysed. An IOL Master 700 (Carl Zeiss Meditec, Jena, Germany) was used for optical biometry. Thirteen formulas and their modifications were evaluated: Barrett Universal II, Haigis, Hoffer QST, Holladay 1 MWK, Holladay 1 NLR, Holladay 2 NLR, Kane, Naeser 2, SRK/T, SRK/T MWK, T2, VRF and VRF-G. The User Group for Laser Interference Biometry lens constants were used for IOL power calculation. The mean prediction error (PE) and its standard deviation (SD), the median absolute error (MedAE), the mean absolute error (MAE) and the percentage of eyes with PEs within ± 0.25 D, ± 0.50 D and < ± 1.00 D were calculated. RESULTS: The modern formulas (Barrett Universal II, Hoffer QST, Kane, Naeser 2 and VRF-G) produced the smallest MedAE among all methods (0.30 D, 0.30 D, 0.30 D, 0.29 D and 0.28 D, respectively). The percentage of eyes with a PE within ± 0.50 D ranged from 67.48% to 74.85% for SRK/T and Hoffer QST, Naeser 2 and VRF-G, respectively. CONCLUSIONS: Dunn's post hoc test of the absolute errors revealed statistically significant differences (P < 0.05) between some of the newer formulas (Naeser 2 and VRF-G) and the remaining ones. From a clinical perspective the Hoffer QST, Naeser 2 and VRF-G formulas were more accurate predictors of postoperative refraction with the largest proportion of eyes within ± 0.50 D.

Comparison of the Barrett Universal II, Kane and VRF-G formulas with existing intraocular lens calculation formulas in eyes with short axial lengths.

BACKGROUND: To compare the accuracy of recently developed modern intraocular lens (IOL) power formulas (Barrett Universal II, Kane and VRF-G) with existing IOL power formulas in eyes with an axial length (AL) ≤ 22 mm. METHODS: This analysis comprised 172 eyes of 172 patients operated on by one surgeon (LT) with one IQ SN60WF (Alcon Labs, Fort Worth, TX, USA) hydrophobic lens. Ten IOL formulas were evaluated: Barrett Universal II (BUII), Haigis, Hoffer Q, Holladay 1, Holladay 2, Kane, SRK/T, T2, VRF and VRF-G. The median absolute error (MedAE), mean absolute error (MAE), standard deviation (SD) and all descriptive statistics were evaluated. Percentages of eyes with a prediction error within ±0.25 D, ±0.50 D, ±0.75 D and ±1.00 D were calculated using standard optimised constants for the entire range of axial lengths. RESULTS: The VRF-G, Haigis and Kane produced the smallest MedAE among all formulas (0.242 D, 0.247 D and 0.263 D, respectively) and had the highest percentage of eyes with a PE within ±0.50 D (75.67%, 73.84% and 75.16%, respectively). The Barrett was less accurate (0.298 D and 68.02%, respectively). Statistically significant differences were found predominantly between the VRF-G (P < 0.05), Kane (P < 0.05) and Haigis (P < 0.05) and all other formulas. The percentage of eyes with a PE within ±0.50 D ranged from 66.28% to 75.67%. CONCLUSIONS: In eyes with AL ≤ 22.0 mm, the VRF-G, Haigis and Kane were the most accurate predictors of postoperative refraction, and the Barrett formula was less predictable.

A Critical Assessment of Friedenwald's Technique for Estimating the Coefficient of Rigidity of the Cornea.

Purpose: To determine if Friedenwald's technique for estimating the coefficient of corneal rigidity (Ko, units mmHg/µL), could differentiate between the cornea in keratoconus, normal eyes, and after crosslinking (CXL). Methods: Two operators (1 and 2) independently measured Ko in three groups (keratoconus, normal, and post-CXL corneas), and repeated the procedure in some where their care remained unchanged and others after routine CXL (>28 days postop, epi-off treatment, 3.0 mW/cm2, 30 min). The data were subsequently used to quantify interoperator error, test-retest/intersessional reliability for estimation of Ko, the significance of intergroup differences, and the effect of CXL on Ko. Results: The major findings were: (i) Ko values were not normally distributed; (ii) mean (±sd, 95% CI) interoperator error was -0.002 (±0.019, -0.006 to 0.003, n = 95) and the limit of agreement between the operators was ±0.039; (iii) RMS differences in the intersessional estimation of Ko values were 0.011 (operator 1) and 0.012 (operator 2); (iv) intergroup differences in Ko were not significant (p > 0.05); (v) intersessional change in Ko (y) was linearly related to Ko estimated (x) at 1st session (for operator 2 y = 1.187x-0.021, r = 0.755, n = 16, p < 0.01); and (vi) change in Ko (y 1) after CXL was linearly related to Ko (x 1) at preop (for operator 2 y 1 = 0.880x 1-0.016, r = 0.935, n = 20, p < 0.01). Conclusion: Friedenwald's technique for estimating the Ko is prone to substantial interoperator error and intersessional differences. According to the technique, the change in Ko following CXL is on par with the expected intersessional change observed in controls.

Intraocular lens power calculation in patients with irregular astigmatism.

PURPOSE: Accurate intraocular lens (IOL) calculation in subjects with irregular astigmatism is challenging. This study evaluated the accuracy of using Scheimpflug-derived central 2-mm equivalent keratometry reading (EKR) values for IOL calculation in irregular astigmatism. METHODS: This retrospective study included subjects (31 eyes of 30 patients) who underwent cataract surgery and IOL calculation using the 2-mm central EKR methods. We compared prediction error (PE) and absolute PE (APE) outcomes using SRK/T and Barrett Universal II formulas for keratometry data obtained from the IOLMaster 500 and Pentacam (anterior corneal sim k) devices. RESULTS: Cataract surgery and IOL calculation using the 2-mm central EKR methods resulted in improved visual acuity (uncorrected: from 1.13 ± 0.38 to 0.65 ± 0.46 logMar, p < 0.01; best-corrected: from 0.45 ± 0.24 to 0.26 ± 0.20 logMar, p < 0.01) after surgery. The percentage of subjects with best-corrected visual acuity of 6/6 was 22%, < 6/9 was 58%, and < 6/12 was 71%. For both the SRK/T and the Barrett formulas, the PE was similar to those obtained by IOLMaster (> 0.14) but lower than those obtained by the anterior corneal sim k (p < 0.02). IOLMaster provided keratometry reading in only 23/31 (74.1%) of cases. CONCLUSIONS: The use of Scheimpflug central 2-mm EKR for IOL calculation in irregular astigmatism was beneficial in terms of visual acuity improvement. It had comparable refractive prediction performance to the IOLMaster 500 and better than the anterior corneal sim K. The 2-mm EKR method can be used when IOLMaster cannot provide a reliable reading in abnormal corneas.

The relationship between angle kappa and astigmatism after phacoemulsification with implanting of spherical and aspheric intraocular lens.

PURPOSE: To determine the significance of any association between either change in angle kappa (Κ°) or the rectilinear displacement (L, mm) of the first Purkinje image relative to the pupil center and unexpected changes in astigmatism after phacoemulsification. METHODS: Orbscan II (Bausch and Lomb) measurements were taken at 1, 2, and 3 months after unremarkable phacoemulsification in patients implanted with spherical (group 1, SA60AT, Alcon) or aspheric (group 2, SN60WF, Alcon) nontoric IOLs. The outputs were used to calculate L. Astigmatism, measured by autorefractometry and subjective refraction, was subjected to vector analysis (polar and cartesian formats) to determine the actual change induced over the periods 1-2 and 2-3 months postop. RESULTS: Chief findings were that the mean (n, ±SD, 95%CI) values for L over each period were as follows: Group 1, 0.407 (38, ±0.340, 0.299-0.521), 0.315 (23, ±0.184, 0.335-0.485); Group 2, 0.442 (45, ±0.423, 0.308-0.577), 0.372 (26, ±0.244, 0.335-0.485). Differences between groups were not significant. There was a significant linear relationship between (A) the change in Κ (ΔΚ = value at 1 month-value at 2 months) and Κ at 1 month (x), where ΔΚ =0.668-3.794X (r = 0.812, n = 38, P = <0.001) in group 1 and ΔΚ = 0.263x -1.462 (r = 0.494, n = 45, P = 0.002) in group 2, (B) L and the J45 vector describing the actual change in astigmatism between 1 and 2 months in group 2, where J45 (by autorefractometry) =0.287L-0.160 (r = 0.487, n = 38, P = 0.001) and J45 (by subjective refraction) =0.281L-0.102 (r = 0.490, n = 38, P = 0.002), and (C) J45 and ΔΚ between 2 and 3 months in group 2, where J45 (by subjective refraction) =0.086ΔΚ-0.063 (r = 0.378, n = 26, P = 0.020). CONCLUSION: Changes in the location of the first Purkinje image relative to the pupil center after phacoemulsification contributes to changes in refractive astigmatism. However, the relationship between the induced change in astigmatism resulting from a change in L is not straightforward.

The effect of corneal crosslinking on the rigidity of the cornea estimated using a modified algorithm for the Schiøtz tonometer.

Purpose: The aim of this study was to test a method for estimating corneal rigidity before and after cross-linking (CXL) using a Schiøtz tonometer. Methods: The study was performed in the Kyiv City Clinical Ophthalmological Hospital "Eye Microsurgical Center", Ukraine. This was a prospective, consecutive, randomized, masked, case-by-case, clinical study. Corneal rigidity, indicated by the gradient (G) between lg applied weight and corresponding lg scale reading during Schiøtz tonometry, were obtained by increasing (A-mode) then reducing (D-mode) weights by two operators [A] in keratoconus, post-CXL and control subjects for estimation of (i) interoperator and (ii) intersessional errors, (iii) intergroup differences; [B] before and after CXL. Central corneal thickness CCT was measured by scanning slit pachymetry. ANOVA, t tests, linear regression were the statistical tools used. Results: Average interoperator difference (ΔG) was -0.120 (SD = ±0.294, 95%CI = -0.175 to -0.066). A significant correlation between ΔG and the mean of each pair of G values was found (r = -0.196, n = 112, P = 0.038). Intersessional differences in mean G values were insignificant (P > 0.05). There was a significant correlation between G at first session (X1) and difference between sessions (ΔG) [Operator 1, ΔG = 0.598x1-0.461, r = 0.601, n = 27, P = 0.009]. Significant intergroup differences in G were found (Operator 1, one-way ANOVA, F = 4.489, P = 0.014). The difference (Δ) between the pre-(X2) and post-CXL treatment G values was significantly associated with the pre-CXL treatment value (Operator 1, Δ = 1.970x2-1.622, r = 0.642, n = 18, P = <.001). G values were correlated with CCT in keratoconus and post-CXL. Conclusion: Corneal rigidity (G) estimated using the Schiøtz tonometer can be useful for detecting changes after CXL. However, G values are linked to CCT, can vary from time-to-time and the procedure is operator dependent.

Clinical Accuracy of 18 IOL Power Formulas in 241 Short Eyes.

PURPOSE: To analyze the accuracy of 18 intraocular lens (IOL) power calculation formulas in eyes with axial length (AL) ≤ 22 mm. METHODS: We analyzed 241 eyes of 241 patients. Eighteen formulas were evaluated: Barrett Universal II (BUII), EVO 2.0, Haigis, Hoffer Q, Holladay 1 and 2, Cooke K6, Kane, LadasSuperFormula AI, Naeser 2, Olsen, Panacea, Pearl-DGS, RBF 2.0, SRK/T, T2, VRF and VRF-G. Optical biometry was performed with an IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany). With lens constants optimized for the whole range of AL, the mean prediction error (PE) and its standard deviation (SD), the median absolute error (MedAE), the mean absolute error (MAE) and the percentage of eyes with PEs within ±0.25 D, ±0.50 D and <±1.00 D were calculated. RESULTS: Post-hoc analysis of the absolute PE revealed statistically significant differences (P < .05) between some of the newer formulas (K6, Kane, Naeser 2, Olsen and VRF-G), which obtained the lowest MedAE (respectively, 0.308, 0.300, 0.277, 0.310 and 0.276 D) and the remaining ones. These formulas yielded also the highest percentage of eyes with a PE within ±0.50 D (70.54%, 72.20%, 71.37%, 70.95% and 73.03%, respectively), whereas Panacea and SRK/T yielded the lowest percentage (62.24%), with a stastically significant difference (P < .05) with respect to most formulas. CONCLUSION: In eyes with AL ≤22.0 mm, new formulas (K6, Kane, Naeser 2, Olsen and VRF-G) offer the most accurate predictions of postoperative refraction.

The influence of routine uncomplicated phacoemulsification on the orthogonality of the cornea.

Purpose: The aim of this study was to determine the effect of routine uncomplicated phacoemulsification on the orthogonal distribution of mass within the central optical zone of the cornea. Methods: Astigmatism at both corneal surfaces was evaluated using Orbscan II (Bausch &and Lomb) before and up to 3 months after routine phacoemulsification (one eye/patient). The data were subjected to vector analysis to estimate the pre-and postoperative total astigmatism of the cornea (TCA). Results: Reporting the chief findings in minus cylinder (diopters, DC) over the central 3 mm (A) and 5 mm (B) optical zones. Mean TCA powers (±sd) at pre- and 3-months postop were A) -4.45DC (±2.00) and -5.69DC (±2.69), B) -2.91DC (±2.22) and -2.71DC (±1.60). Change in mean power was significant over 3 mm (P < 0.01, n = 49) but not over 5 mm. Inter-zonal differences were significant (P < 0.01). There was a significant linear relationship between the change in TCA power (y = preoperative-postoperative) and TCA at preoperative stage (x) where, A) y = 0.45x + 3.12 (r = 0.336, n = 49, P = 0.018), B) y = x + 2.65 (r = 0.753, n = 49, P = <0.01). Over the central 3 mm zone only, change (preoperative-postoperative) in axis (°) of TCA (y1) was significantly associated with TCA axis at preoperative stage (x1) where y1 = 1.391x1-0.008x12-0.701 (r = 0.635, n = 49, P < 0.01). Conclusion: Changes in TCA power and axis at 3 months postop, determined using Orbscan II, are indicative of orthogonal alterations in the distribution of corneal tissue. Over the central 3 mm zone, the association between y1 and x1 shows that a change in TCA axis is more profound when preoperative axis is near 90° i.e., against-the-rule.

VRF-G, a New Intraocular Lens Power Calculation Formula: A 13-Formulas Comparison Study.

PURPOSE: To compare the accuracy of a newly developed intraocular lens (IOL) power formula (VRF-G) with twelve existing formulas (Barret Universal II, EVO 2.0, Haigis, Hill-RBF 2.0, Hoffer Q, Holladay 1, Kane, Næeser 2, PEARL-DGS, SRK/T, T2 and VRF). METHODS: Retrospective case series including 828 patients having uncomplicated cataract surgery with the implantation of a single IOL model (SN60WF). Using optimised constants, refraction prediction error of each formula was calculated for each eye. Subgroup analysis was performed based on the axial length (short ≤22.0mm; medium >22.0mm to <26.0mm; long ≥26.0mm). Main outcomes included mean prediction error (ME) mean (MAE) and median absolute error (MedAE), in diopters (D), and the percentage of eyes within ±0.25D, ±0.50D, ±0.75D and ±1.00D. RESULTS: Formulas absolute errors were statistically different among them (p<0.001), with Kane having the lowest MAE of all formulas, followed by EVO 2.0 and VRF-G, which had the lowest MedAE. The Kane formula had the highest percentage of eyes within ±0.25D (47.0%) and ±1.00D (97.7%) and the VRF-G formula had the highest percentage of eyes within ±0.50D (79.5%). For all AL subgroups, Kane, EVO 2.0 and VRF-G formulas had the most accurate performances (lowest MAE). CONCLUSION: New generation formulas may help us in achieving better refractive results, lowering the variance in accuracy in extreme eyes - Kane, EVO 2.0 and VRF-G formulas are promising candidates to fulfil that goal.

The Impact of Changes in Corneal Back Surface Astigmatism on the Residual Astigmatic Refractive Error following Routine Uncomplicated Phacoemulsification.

PURPOSE: To determine the significance of any association between intersessional changes in ocular residual astigmatism (RA) and astigmatism at corneal front (FSA) and back (BSA) surfaces following uneventful routine phacoemulsification. METHODS: Astigmatism was evaluated by autorefractometry and subjective refraction and at both the corneal surfaces with Orbscan II™ (Bausch & Lomb) over central 3 mm and 5 mm optical zones at 1, 2, and 3 months after routine phacoemulsification in 103 patients implanted with monofocal nontoric intraocular lenses (IOLs, one eye/patient). Data were subjected to vector analysis to determine the actual change (Δ) in astigmatism (power and axis) for the refractive and Orbscan II findings. RESULTS: The number of cases that attended where ΔRA was ≥0.50 DC between 1 and 2 months was 52 by autorefractometry and 36 by subjective refraction and between 2 and 3 months was 24 by autorefractometry and 19 by subjective refraction. Vector analysis revealed significant correlations between ΔFSA and ΔRA for data obtained by autorefractometry but not by subjective refraction. At all times, ΔBSA was greater than ΔFSA (p < 0.01). Key findings for ΔBSA values over the central 3 mm zone were between (A) the sine of the axis of ΔRA (y) and sine of the axis of ΔBSA (x) for the data obtained by autorefractometry (between 1 and 2 months, y = 0.749 - 0.303x, r = 0.299, n = 52, p=0.031) and subjective refraction (between 2 and 3 months, y = 0.6614 - 0.4755x, r = 0.474, n = 19, p=0.040) and (B) ΔRA (y) and ΔBSA (x) powers between 2 and 3 months postoperatively for the data obtained by autorefractometry (ΔRA = 0.118 ΔBSA + 0.681 r = 0.467, n = 24, p=0.021) and subjective refraction (ΔRA = 0.072 ΔBSA + 0.545 r = 0.510, n = 19, p=0.026). CONCLUSION: Changes in the ocular residual refractive astigmatic error after implanting a monofocal nontoric IOL are associated with changes in astigmatism at the back surface of the cornea within the central optical zone.

Development and Clinical Accuracy of a New Intraocular Lens Power Formula (VRF) Compared to Other Formulas.

PURPOSE: To develop and compare the accuracy and reproducibility of the VRF intraocular lens (IOL) power calculation formula with well-known methods. DESIGN: Development and validation study. METHODS: This analysis comprised 823 eyes of 823 patients at Kiev Clinical Ophthalmology Hospital Eye Microsurgery Center, Kiev, Ukraine, operated on by 1 surgeon with 3 different types of hydrophobic lenses: IQ SN60WF (494 eyes) and ReSTOR SN6AD1 (169 eyes) (Alcon Labs, Fort Worth, Texas, USA) and AMO Tecnis MF ZMB00 (160 eyes) (J&J Vision, Santa Ana, California, USA). The full data set was divided into 2 subsets, the first to develop the new formula and the second to evaluate their performance with other most commonly used modern methods of IOL power calculation (Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2). The VRF algorithm is empirical; it uses 4 predictors for estimation of postoperative lens position, including axial length, corneal power (K), preoperative anterior chamber depth (corneal epithelium to lens), and horizontal corneal diameter. The results are also stratified into groups of short (≤22 mm), medium (>22 to <24.5 mm), medium-long (≥24.5 to <26 mm), and long (≥26 mm) axial length. RESULTS: The mean error, median absolute error, and mean absolute error were evaluated for all 7 methods with 1 IOL type. The VRF formula had the lowest median (0.305 diopter [D]) absolute error over the entire axial length range, and was comparable with the formulas for T2 (0.321 D) and Holladay 1 (0.326 D). CONCLUSION: The new formula was comparable with well-known methods and was better over the entire axial length range.