Leaving trusted paths: Estimating corneal keratometric index in cataract surgery eyes with zero-power implants.

PURPOSE: This study aimed to estimate the corneal keratometric index in the eyes of cataract surgery patients who received zero-power intraocular lenses (IOLs). METHODOLOGY: This retrospective study analyzed postoperative equivalent spherical refraction and axial length, mean anterior curvature radius and aqueous humor refractive index to calculate the theoretical corneal keratometric index value (nk). Data was collected from 2 centers located in France and Germany. RESULTS: Thirty-six eyes were analyzed. The results revealed a mean corneal keratometric index of 1.329 ± 0.005 for traditional axial length (AL) and 1.331 ± 0.005 for Cooke modified axial length (CMAL). Results ranged from minimum values of 1.318/1.320 to maximum values of 1.340/1.340. CONCLUSION: The corneal keratometric index is a crucial parameter for ophthalmic procedures and calculations, particularly for IOL power calculation. Notably, the estimated corneal keratometric index value of 1.329/1.331 in this study is lower than the commonly used 1.3375 index. These findings align with recent research demonstrating that the theoretical corneal keratometric index should be approximately 1.329 using traditional AL and 1.331 using CMAL, based on the ratio between the mean anterior and posterior corneal curvature radii (1.22).

Refractive errors occurring with tilt of intraocular lenses.

A thin lens technique was developed to determine how the effective powers of toric monofocal intraocular lenses (IOLs) are influenced by tilt and the refractive errors associated with the tilt. A series of steps determined the effective power of the cornea at the IOL, the IOL power, the effective power of the tilted IOL, the correction required at the front of the eye and the power of an IOL that would compensate for the tilt. The correction was determined by starting at the ideal reduced image vergence at the IOL, backwards raytracing to obtain a reduced image vergence at the cornea, and subtracting the cornea power from this reduced image vergence. Examples are presented for different situations where the IOL is either tilted about the vertical or an oblique axis. Raytracing with a thick lens verified the accuracy of the technique.

Change in refractive errors with changes in IOL parameters.

This study considered two questions associated with intraocular lens (IOL) power and refraction: (1) Given a refraction with a particular IOL in the eye, what will be the refraction for the IOL or another IOL if located differently with regard to tilt or anterior-posterior position? (2) For a target refraction, what is the power of another IOL if located differently with regard to tilt or position? A thin lens technique was developed to address these questions. For the first question, light was traced through the initial correcting spectacle lens to the cornea, refracted at the cornea, transferred to the position of the initial IOL, refracted at this IOL, transferred to the position of a new IOL (which may be the same IOL but with a different position and/or tilt), refracted backwards through the new IOL, transferred to the cornea and refracted out of the eye to give a new correcting spectacle lens power. For the second question, light was traced through the initial correcting spectacle lens to the cornea, refracted at the cornea, transferred to the position of the initial IOL, refracted at the initial IOL and transferred to the position of a new IOL. Light was also traced through the second correcting spectacle lens, refracted at the cornea and transferred to the position of the second IOL. The difference between the reduced image vergence for the first raytrace and the reduced object vergence for the second raytrace gave the effective power of the second IOL, and from this, the power of the second IOL was determined. Examples are presented for different situations, including a case report.

Four-flanged polypropylene optic piercing technique for scleral fixation of multifocal intraocular lens.

BACKGROUND: To evaluate the feasibility of creating flanges using an optic piercing technique with a 6 - 0 polypropylene monofilament for scleral fixation of dislocated one-piece diffractive multifocal intraocular lenses (IOLs). STUDY DESIGN: Experimental study and case series. SUBJECTS: Optical bench test and eyes with IOL dislocation. METHODS: Two separate 6 - 0 polypropylenes were penetrated twice at the opposite peripheral optic of the TECNIS Synergy IOL (Johnson & Johnson Vision). The root mean square of the modulation transfer function (MTFRMS), at between + 1.00 and - 4.00 D of defocus, was measured in the TECNIS Synergy IOL both with and without optic piercing in the optical bench study. This case series included three eyes from two patients who underwent scleral-fixation of multifocal IOLs using the four-flanged polypropylene optic piercing technique. The postoperative corrected distance visual acuity (CDVA) at 4 m, the uncorrected near visual acuity (UNVA) at 40 cm, and IOL centration were evaluated. RESULTS: The optical bench test showed no differences in MTFRMS values measured in the TECNIS Synergy IOL, either with or without optic piercing at all defocuses. In all three case series, the postoperative CDVA at 4 m was 20/20 and UNVA at 40 cm was J1. Postoperative anterior segment photographs showed good centration of IOLs in all cases. CONCLUSION: The four-flanged polypropylene optic piercing technique for multifocal IOL scleral fixation can provide excellent clinical outcomes and IOL stability after surgery without diminishing the performance of the multifocal IOLs.

Update on Biometry and Lens Calculation - A Review of the Basic Principles and New Developments. / Update Biometrie und Linsenberechnung ­ ein Review zu Grundlagen und neuen Entwicklungen.

These days, accurate calculation of artificial lenses is an important aspect of patient management. In addition to the classic theoretical optical formulae there are a number of new approaches, most of which are available as online calculators. This review aims to explain the background of artificial lens calculation and provide an update on study results based on the latest calculation approaches. Today, optical biometry provides the computational basis for theoretical optical formulae, ray tracing, and also empirical approaches using artificial intelligence. Manufacturer information on IOL design and IOL power recorded as part of quality control could improve calculations, especially for higher IOL powers. With modern measurement data, there is further potential for improvement in the determination of the axial length to the retinal pigment epithelium and by adopting a sum-of-segment approach. With the available data, the cornea can be assumed to be a thick lens. The Kane formula, the EVO 2.0 formula, the Castrop formula, the PEARL-DGS, formula and the OKULIX calculation software provide consistently good results for artificial lens calculations. Excellent refractive results can be achieved using these tools, with approximately 80% having an absolute prediction error within 0.50 dpt, at least in highly selected study populations. The Barrett Universal II formula also produces excellent results in the normal and long axial length range. For eyes with short axial lengths, the use of Barrett Universal II should be reconsidered; in this case, one of the methods mentioned above is preferable. Second Eye Refinement can also be considered in this patient population, in conjunction with established classic third generation formulae.

Biometry and Intraocular Lens Power Calculation in Eyes with Prior Laser Vision Correction (LVC) - A Review.

BACKGROUND: An intraocular lens (IOL) calculation in eyes that have undergone laser vision correction (LVC) poses a significant clinical issue in regards to both patient expectation and accuracy. This review aims to describe the pitfalls of IOL power calculation after LVC and give an overview of the current methods of IOL power calculation after LVC. REVIEW: Problems after LVC derive from the measurement of anterior corneal radii, central corneal thickness, asphericity, and the predicted effective lens position. A central issue is that most conventional 3rd generation formulas estimate lens position amongst other parameters on keratometry, which is altered in post-LVC eyes. CONCLUSION: An IOL power calculation results in eyes with prior LVC that are notably impaired in eyes without prior surgery. Effective corneal power including anterior corneal curvature, posterior corneal curvature, CCT (central corneal thickness), and asphericity is essential. Total keratometry in combination with the Barrett True-K, EVO (emmetropia verifiying optical formula), or Haigis formula is relatively uncomplicated and seems to provide good results, as does the Barrett True-K formula with anterior K values. The ASCRS ( American Society of Cataract and Refractive Surgery) calculator combines results of various formulae and averages results, which allows a direct comparison between the different methods. Tomography-based raytracing and the Kane and the Castrop formulae need to be evaluated by future studies.

A Review of Intraocular Lens Power Calculation Formulas Based on Artificial Intelligence.

PURPOSE: The proper selection of an intraocular lens power calculation formula is an essential aspect of cataract surgery. This study evaluated the accuracy of artificial intelligence-based formulas. DESIGN: Systematic review. METHODS: This review comprises articles evaluating the exactness of artificial intelligence-based formulas published from 2017 to July 2023. The papers were identified by a literature search of various databases (Pubmed/MEDLINE, Google Scholar, Crossref, Cochrane Library, Web of Science, and SciELO) using the terms "IOL formulas", "FullMonte", "Ladas", "Hill-RBF", "PEARL-DGS", "Kane", "Karmona", "Hoffer QST", and "Nallasamy". In total, 25 peer-reviewed articles in English with the maximum sample and the largest number of compared formulas were examined. RESULTS: The scores of the mean absolute error and percentage of patients within ±0.5 D and ±1.0 D were used to estimate the exactness of the formulas. In most studies the Kane formula obtained the smallest mean absolute error and the highest percentage of patients within ±0.5 D and ±1.0 D. Second place was typically achieved by the PEARL DGS formula. The limitations of the studies were also discussed. CONCLUSIONS: Kane seems to be the most accurate artificial intelligence-based formula. PEARL DGS also gives very good results. Hoffer QST, Karmona, and Nallasamy are the newest, and need further evaluation.

The E × B magnetized plasma device (EMPD).

A plasma device has been created to study dynamic plasma coupling in an E × B-drifting magnetized plasma. The E × B magnetized plasma device is a 1.2 m diameter by 2 m long cylindrical chamber with two sets of Helmholtz coils in a mirror configuration. A steady-state axial hollow cathode source injects a plasma discharge in electrical contact with a floating conductor at a range that forms a unique axisymmetric equipotential surface or Virtual Cathode Lightsaber (VCL). The VCL generates two plasma populations streaming relative to one another providing a suitable environment for the investigation of dynamic plasma coupling. The plasma density, radial electric field, and plasma rotational velocity outside the VCL are shown to be influenced by the current-voltage relationship of the cathode and applied magnetic field strength. A basic characterization of the device and plasma environment is presented with an emphasis on diagnostics systems and the analytical techniques utilized.

Impact of quality indicators on variability of keratometry measurements using a swept-source OCT based optical biometer.

PURPOSE: To characterize the variability of keratometry measurements on the IOLMaster 700, and relate it to device image quality indicators (QI). SETTING: Two academic centers and one private practice. DESIGN: Multicenter, retrospective consecutive case series. METHODS: Measurements from three sites, obtained between December, 2015 and July, 2023 were included. Surgery-naïve phakic eyes with same-day sequential measurements on the same eye were identified. Repeat measurement pairs were grouped by IOLMaster QIs (success vs. warning), and changes in mean standard (∆Kmean) and total (∆TKmean) keratometry as well as standard (∆Kastig) and total (∆TKastig) astigmatism vectors were calculated. RESULTS: Analysis was performed on 3,222 eyes of 1,890 patients. Measurement 'success' was associated with a smaller ΔKmean (0.09 ± 0.14 D) and ΔTKmean (0.11 ± 0.16 D) when compared to pairs in which both measurements had a 'warning' [0.25 ± 0.32 D and 0.14 ± 0.17 D, respectively; (p < 0.0001)]. A similarly smaller ∆Kastig (0.26 ± 0.28 D) and ∆TKastig (0.28 ± 0.30 D) was observed with measurement 'success' versus 'warning' [0.77 ± 0.79 D and 0.42 ± 0.41 D, respectively (p < 0.0001)]. Even when both measurements were successful, the proportion of measurement pairs that had a ∆Kastig > 0.50 D increased from 14% to 24% to 32% when Kmean standard deviation (SD) was ≥ 0.01, 0.05, and 0.10 D, respectively. CONCLUSIONS: When measurement quality is poor, total keratometry varies less than standard keratometry measurements. Clinicians may use the SD of Kmean/TKmean to estimate the repeatability of measurements and balance this against their tolerance for performing repeat measurements.

A Novel Method to Optimize Personal IOL Constants.

OBJECTIVE: To describe a novel method called "three variable optimization" that entails a process of doing just one calculation to zero out the mean prediction error of an entire dataset (regardless of size), using only 3 variables: (1) the constant used, (2) the average intraocular lens (IOL) power, and (3) the average prediction error (PE as actual refraction - predicted refraction). DESIGN: Development, evaluation, and testing of a method to optimize personal IOL constants. METHODS: A dataset of 876 eyes was used as a training set, and another dataset of 1,079 eyes was used to test the method. The Barrett Universal II, Cooke K6, Haigis, RBF 3.0, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2 were analyzed. The same dataset was also divided into 3 subgroups (short, medium, and long eyes). The three variable optimization process was applied to each dataset and subset, and the obtained optimized constants were then used to obtain the mean PE of each dataset. We then compared those results with those obtained by zeroing out the mean PE in the classical method. RESULTS: The three variable optimization showed similar results to classical optimization with less data needed to optimize and no clinically significant difference. Dividing the dataset into subsets of short, medium and long eyes, also shows that the method is useful even in those situations. Finally, the method was tested in multiple formulas and it was able to reduce the PE with no clinically significant difference from classical optimization. CONCLUSION: This method could then be applied by surgeons to optimize their constants by reducing the mean prediction error to zero without prior technical knowledge and it is available online for free at http://wwww.ioloptimization.com.

Modified intraocular lens power selection method according to biometric subgroups Eom IOL power calculator.

This study evaluates the accuracy of a newly developed intraocular lens (IOL) power calculation method that applies four different IOL power calculation formulas according to 768 biometric subgroups based on keratometry, anterior chamber depth, and axial length. This retrospective cross-sectional study was conducted in at Korea University Ansan Hospital. A total of 1600 eyes from 1600 patients who underwent phacoemulsification and a ZCB00 IOL in-the-bag implantation were divided into two datasets: a reference dataset (1200 eyes) and a validation dataset (400 eyes). Using the reference dataset and the results of previous studies, the Eom IOL power calculator was developed using 768 biometric subgroups. The median absolute errors (MedAEs) and IOL Formula Performance Indexes (FPIs) of the Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Ladas Super, SRK/T, and Eom formulas using the 400-eye validation dataset were compared. The MedAE of the Eom formula (0.22 D) was significantly smaller than that of the other four formulas, except for the Barrett Universal II and Ladas Super formulas (0.24 D and 0.23 D, respectively). The IOL FPI of the Eom formula was 0.553, which ranked first, followed by the Ladas Super (0.474), Barrett Universal II (0.470), Holladay 1 (0.444), Hoffer Q (0.396), Haigis (0.392), and SRK/T (0.361) formulas. In conclusion, the Eom IOL power calculator developed in this study demonstrated similar or slightly better accuracy than the Barrett Universal II and Ladas Super formulas and was superior to the four traditional IOL power calculation formulas.

Comparison of Pre- and Post-DMEK Keratometry and Total Keratometry Values for IOL Power Calculations in Eyes Undergoing Triple DMEK.

PURPOSE: To evaluate prediction accuracy of pre- and post-DMEK keratometry (K) and total keratometry (TK) values for IOL power calculations in Fuchs endothelial corneal dystrophy (FECD) eyes undergoing DMEK with cataract surgery (triple DMEK). METHODS: Retrospective cross-sectional multicenter study of 55 FECD eyes (44 patients) that underwent triple DMEK between 2019 and 2022 between two centers in USA and Europe. Swept-source optical coherence tomography biometry (IOLMaster 700) was used for pre- and post-DMEK measurements. K and TK values were used for power calculations with ten formulae (Barrett Universal II (BUII), Castrop, Cooke K6, EVO 2.0, Haigis, Hoffer Q, Hoffer QST, Holladay I, Kane, and SRK/T). Mean error, mean absolute error (MAE), standard deviation, and percentage of eyes within ±0.50/±1.00 diopters (D) were calculated. Studied formulae were additionally adjusted using a method published previously (IOLup1D Method), which increases the IOL power by 1D. While both eyes from the same patient were considered for descriptive statistics, we restricted to one eye per individual (44 eyes for statistical comparisons. RESULTS: MAEs for all formulae were lower for post-DMEK K and TK than pre-DMEK K and TK by an average of 0.24 and 0.47 D, respectively. The lowest MAE was 0.49 D for Kane using post-DMEK TK, and the highest MAE was 1.05 D for BUII using pre-DMEK TK. Most IOLup1D formulae had lower MAEs than pre-DMEK K and TK formulae. CONCLUSIONS: The IOLup1D Method should be used instead of pre-DMEK K and TK values for triple DMEK in FECD eyes. Using post-DMEK TK values for cataract surgery after DMEK provides better refractive accuracy than any of the three studied methods used for triple DMEK procedures.

Updating the no-history method in intraocular lens power calculation after myopic laser vision correction.

PURPOSE: To describe the Shammas-Cooke formula, an updated no-history (NH) formula for IOL calculation in eyes with prior myopic laser vision correction (M-LVC), and to compare the results with the Shammas PL, Haigis-L, and Barrett True-K NH formulas. SETTING: Bascom Palmer Eye Institute (BPEI), The Lennar Foundation Medical Center, University of Miami, Miami, Florida; Dean A. McGee Eye Institute (DMEI), University of Oklahoma, Oklahoma City, Oklahoma; and private practice, Lynwood, California, and St Joseph, Michigan. DESIGN: Retrospective observational study. METHODS: We analyzed 2 large series of cataractous eyes with prior M-LVC. The training set (BPEI series of 330 eyes) was used to derive the new corneal power conversion equation to be used in the new Shammas-Cooke formula and the testing set (165 eyes of 165 patients in the DMEI series) to compare the updated formula with 3 other M-LVC NH formulas on the ASCRS calculator: Shammas PL, Haigis-L, and Barrett True-K NH. RESULTS: Mean prediction error was 0.09 ± 0.56 diopters (D), -0.44 ± 0.61 D, -0.47 ± 0.59 D, and -0.18 ± 0.56 D and the mean absolute error was 0.43 D, 0.60 D, 0.61 D, and 0.45 D for the Shammas-Cooke, Shammas PL, Haigis-L, and Barrett True-K NH, respectively. The percentage of eyes within ±0.50 D was 66.7% vs 47.9%, 48.5%, and 65.5%, respectively. CONCLUSIONS: The Shammas-Cooke formula performed better than the Shammas PL and Haigis-L (P < .001 for both) and as well as the Barrett True-K NH formula (P = .923).

Comparison of Legacy and New No-History IOL Power Calculation Formulas in Postmyopic Laser Vision Correction Eyes.

PURPOSE: To compare the refractive accuracy of legacy and new no-history formulas in eyes with previous myopic laser vision correction (M-LVC). DESIGN: Retrospective cohort study. METHODS: Setting: Two academic centers Study Population: 576 eyes (400 patients) with previous M-LVC that underwent cataract surgery between 2019-2023. A SS-OCT biometer was used to obtain biometric measurements, including standard (K), posterior (PK), and total keratometry values (TK). OBSERVATION PROCEDURES: Refractive prediction errors were calculated for 11 no-history formulas: two legacy M-LVC formulas, four new M-LVC formulas using K values only, and five new M-LVC formulas using K with PK or TK. MAIN OUTCOME MEASURES: Heteroscedastic testing was used to evaluate relative formula performance, and formulas were ranked by root mean square error (RMSE). RESULTS: New M-LVC formulas performed better than legacy M-LVC formulas. New M-LVC formulas with PK/TK values performed better than versions without PK/TK values. Among new M-LVC formulas with PK/TK values, EVO 2.0-PK was superior to Hoffer QST-PK (P < 0.005). Among new M-LVC formulas using K only, Pearl DGS-K and EVO 2.0-K were both superior to Hoffer QST-K and Barrett True K NH-K formulas (all P < 0.005). CONCLUSIONS: Surgeons should favor using new no-history post M-LVC formulas over legacy post M-LVC formulas whenever possible. The top-performing M-LVC formulas (EVO 2.0-PK, Pearl DGS-PK, and Barrett True K-TK) utilized posterior corneal power values. Among formulas utilizing K alone, the EVO 2.0-K and Pearl DGS-K performed best.

Differences Between Keratometry and Total Keratometry Measurements in a Large Dataset Obtained With a Modern Swept Source Optical Coherence Tomography Biometer.

PURPOSE: This study aimed to explore the concept of total keratometry (TK) by analyzing extensive international datasets representing diverse ethnic backgrounds. The primary objective was to quantify the disparities between traditional keratometry (K) and TK values in normal eyes and assess their impact on intraocular lens (IOL) power calculations using various formulas. DESIGN: Retrospective multicenter intra-instrument reliability analysis. METHODS: The study involved the analysis of biometry data collected from ten international centers across Europe, the United States, and Asia. Corneal power was expressed as equivalent power and astigmatic vector components for both K and TK values. The study assessed the influence of these differences on IOL power calculations using different formulas. The results were analyzed and plotted using Bland-Altman and double angle plots. RESULTS: The study encompassed a total of 116,982 measurements from 57,862 right eyes and 59,120 left eyes. The analysis revealed a high level of agreement between K and TK values, with 93.98% of eyes exhibiting an absolute difference of 0.25 D or less. Astigmatism vector differences exceeding 0.25 D and 0.50 D were observed in 39.43% and 1.08% of eyes, respectively. CONCLUSIONS: This large-scale study underscores the similarity between mean K and TK values in healthy eyes, with rare clinical implications for IOL power calculation. Noteworthy differences were observed in astigmatism values between K and TK. Future investigations should delve into the practicality of TK values for astigmatism correction and their implications for surgical outcomes.

Determining specified intraocular lens powers when silicone oil is to be used in the vitreous chamber.

PURPOSE: To apply a theoretical approach to determining how specified intraocular lens (IOL) powers should change when vitreous oil substitution is combined with IOL implantation. SETTING: University laboratory, private Ophthalmological practice. DESIGN: Theoretical raytracing. METHODS: Raytracing was done backwards from the retina with equi-convex 20 diopters (D) and 25 D IOLs, of refractive index 1.5332, to the object side of the anterior IOL surface. The 1.336 vitreous index was replaced with a high index 1.405 silicone oil. Raytracing was repeated with increase in specified power, that power as if 1.336 index was still surrounding the IOL, so that the object reduced vergence on the anterior side of the lens matched that of the original IOL power. This was done for a range of lens shapes from plano-convex (front surface flat), through equi-convex, to plano-convex (back surface flat), and for a range of axial lengths. The true power, the power with 1.336 index on the object side and silicone oil on the image side, was also determined. RESULTS: Replacing vitreous by silicone oil increases the necessary specified IOL power. This increase varies from approximately 14% for flat back surfaces, to 40% for equi-convex lenses, to 80% for flat front surface IOLs. True powers increase by about 15% across the range of IOL shapes. In terms of percentages, effects of changing the original IOL power and the axial length are small. CONCLUSIONS: When silicone oil is to remain in an eye after cataract surgery, biconvex IOLs require much higher specified powers than convex-plano IOLs.

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.].

Surgeons need to know more about intraocular lens design for accurate power calculation.

Improvement in biometry and formulas has raised the bar for accurate intraocular lens (IOL) power calculation. However, when we look closely at the performance of a specific IOL model, we often find that the prediction error varies with the implant power. This phenomenon has no explanation other than that the optic design of the IOL has shifted over the power range, thereby disrupting the assumptions of the calculations. By this report, we call the industry to be more transparent and disclose the basic information about the IOL design that is important for accurate IOL power calculation. The relevant information concerns the refractive index, the central optic thickness, the anterior and posterior curvature radii, the toricity location, the spherical aberration, and haptic angulation. The goal is to predict possible shifts in principal planes or IOL position over the power range causing a refractive surprise if not corrected for.