Differences Between Simulated Keratometry and Total Corneal Power in Eyes With Keratoconus and a Formula to Improve IOL Power Calculation Results.

PURPOSE: To compare simulated keratometry (SimK) and total corneal power (TCP) in keratoconic eyes, to determine whether the differences are systematic and predictable and to evaluate an adjusted TCP-based formula for intraocular lens (IOL) power calculation. METHODS: In a consecutive series of keratoconic eyes, measurements of SimK, TCP, posterior keratometry, and anterior and posterior corneal asphericities (Q-values) were retrospectively collected. The difference between SimK and TCP was linearly correlated to the biometric parameters. In a separate sample of keratoconic eyes that had undergone cataract surgery, IOL power was calculated with the Barrett Universal II, Hoffer QST, Holladay 1, Kane, and SRK/T formulas using the SimK and an adjusted TCP power. The respective prediction errors were calculated. RESULTS: A total of 382 keratoconic eyes (271 patients) were enrolled. An increasing overestimation of SimK by TCP was detected from stage I to III, with a significant correlation between the SimK and TCP difference and SimK in the whole sample (P < .0001, r2 = 0.1322). Approximately 7% of cases presented an underestimation of SimK by TCP. IOL power calculation with the adjusted TCP improved outcomes, achieving a maximum of 80% of eyes with a prediction error within ±0.50 diopters with the Hoffer QST, Holladay 1, and Kane formulas. CONCLUSIONS: Overall, SimK overestimated TCP. Such a difference could not be predicted by any variable. The proposed TCP-adjustment formula (TCPadj = TCP + 0.56 diopters) in keratoconic eyes for IOL power calculation might be valuable for improving refractive outcomes. [J Refract Surg. 2024;40(4):e253-e259.].

Meridional analysis for calculation of the toric power of phakic IOLs.

PURPOSE: To present a reproducible method to calculate the toricity needed at the intraocular lens (IOL) plane with toric phakic IOLs (ICL, Staar Surgical) and compare its results with those obtained with the online calculator provided by the manufacturer. DESIGN: Retrospective case series. SETTING: Private practice, Buenos Aires, Argentina. METHODS: The formula originally described by Holladay to calculate the IOL power in phakic eyes was used to calculate the required spherical power along the less refractive meridian and along the more refractive meridian. Meridional analysis was applied to calculate the required toricity at the IOL plane and the surgically induced corneal astigmatism was incorporated into the calculations. The refractive cylinder predicted by this method and by the online calculator of the manufacturer were compared to the postoperative refractive cylinder by means of vector analysis. The possible changes in the ratio of toricity in patients with different amounts of astigmatism and anterior chamber depth are assessed in a theoretical section. RESULTS: In 35 eyes, the measured mean postoperative refractive cylinder was 0.09 D @ 99°, the mean predicted postoperative refractive astigmatism was 0.04 D @ 102° according to the manufacturer's online calculator and 0.09 D @100° according to our method. With both methods, 91.43% of eyes had an absolute cylinder prediction error within ±0.50 diopters. CONCLUSIONS: The method described in this article to calculate the toricity of phakic IOLs has a refractive accuracy similar to that of the original calculator developed by the manufacturer.

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.

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.].

Accuracy of Nine Formulas to Calculate the Powers of an Extended Depth-of-Focus IOL Using Two SS-OCT Biometers.

PURPOSE: To evaluate the accuracy of nine formulas to calculate the power of a new extended depth-of-focus intraocular lens (EDOF IOL), the AcrySof IQ Vivity (Alcon Laboratories, Inc), using measurements from two optical biometers, the IOLMaster 700 (Carl Zeiss Meditec AG) and Anterion (Heidelberg Engineering GmbH). METHODS: After constant optimization, the accuracy of these formulas was analyzed in 101 eyes: Barrett Universal II, EVO 2.0, Haigis, Hoffer Q, Holladay 1, Kane, Olsen, RBF 3.0, and SRK/T. Both standard and total keratometry from the IOLMaster 700 and standard keratometry from the Anterion were used for each formula. RESULTS: Constant optimization provided slightly different values for the A-constant, which ranged between 118.99 and 119.16, depending on the formula and the optical biometer. According to the heteroscedastic test, within each keratometry modality the standard deviation of the SRK/T was significantly higher compared to that of the Holladay 1, Kane, Olsen, and RBF 3.0 formulas. The SRK/T formula provided less accurate results also when the absolute prediction errors were compared by Friedman test. According to McNemar's test with Holm corrections, statistically significant differences were found within each keratometry modality between the percentage of eyes with a prediction error within ±0.25 diopters obtained with the Olsen formula compared to the Holladay 1 and Hoffer Q formulas. CONCLUSIONS: Constant optimization remains a mandatory step to achieve the best outcomes with the new EDOF IOL: the same constant should not be used for all formulas and for both optical biometers. Different statistical tests revealed that older IOL formulas have lower accuracy compared to newer formulas. [J Refract Surg. 2023;39(3):158-164.].

Comparison of the new Hoffer QST with 4 modern accurate formulas.

PURPOSE: To investigate the new Hoffer QST (Savini/Taroni) formula (HQST) and compare it with the original Hoffer Q (HQ) and 4 latest generation formulas. SETTING: I.R.C.C.S.-G.B. Bietti Foundation, Rome, Italy. DESIGN: Retrospective case series. METHODS: Refractive outcomes of the HQST, Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) 2.0, HQ, Kane, and Radial Basis Function (RBF) 3.0 formulas were compared. Subgroup analysis was performed in short (<22 mm) and long (>25 mm) axial length eyes. The SD of the prediction error (PE) was investigated using the heteroscedastic method. RESULTS: 1259 eyes of 1259 patients divided in a White group (n=696), implanted with the AcriSof SN60AT (Alcon Labs), and an Asian group (n=563), implanted with the SN60WF (Alcon Labs), were investigated. In the Asian group, the heteroscedastic method did not disclose any significant difference among the SD of the 4 modern formulas (range from 0.333 to 0.346 D), whereas the SD of the HQ formula (0.384 D) was significantly higher. Compared with the original HQ formula, in both White and Asian groups, the HQST formula avoided the mean myopic PE in short eyes and the mean hyperopic PE in long eyes. CONCLUSIONS: The new HQST formula was superior to the original HQ formula and reached statistical and clinical results comparable with those achieved by the BUII, EVO, Kane, and RBF formulas.

Optical Biometry and IOL Calculation in a Commercially Available Optical Coherence Tomography Device and Comparison With Pentacam AXL.

PURPOSE: Optical devices are the gold standard for ocular biometry; however, they are unable to obtain high-quality optical coherence tomography (OCT) images. The current study aimed to evaluate ocular measurements and intraocular lens (IOL) calculation used in an anterior/posterior segment OCT device and to compare the results with those of a validated biometer. DESIGN: Prospective evaluation of a diagnostic tool. METHODS: This study enrolled healthy subjects at the Hygeia Clinic, Gdansk, Poland, between October 2021 and November 2021. All individuals had ocular biometry measured with a validated biometer (Pentacam AXL) and with a new module of an anterior/posterior segment OCT device (Revo 80, Optopol Technologies). All IOL calculations were performed for the right eye with keratometric values from the Pentacam for one IOL: the Alcon AcrySof IQ SN60WF, with plano target setting. RESULTS: The mean age of the 144 participants was 25.23 ± 7.15 years. The axial length measured with Revo was longer than with Pentacam AXL (24.08 ± 1.13 vs 23.98 ± 1.13; P < .0001), a 0.10 ± 0.04 mm difference. This translated into a significantly lower IOL power to achieve emmetropia for all formulas (-0.34 ± 0.15, -0.32 ± 0.13, -0.34 ± 0.19, and -0.30 ± 0.15 for the Hoffer Q, Holladay I, Haigis, and SRK/T formulas, respectively). The study showed high agreement between the devices: nearly 90% of eyes were within ±0.50 diopters for all of the analyzed formulas (r > 0.99). CONCLUSIONS: The present study demonstrates that the results of IOL calculation with the OCT biometer have a very strong correlation with those obtained with the Pentacam AXL; however, axial length measurements and calculated IOL power cannot be considered interchangeable.

Repeatability of new optical biometer and agreement with 2 validated optical biometers, all based on SS-OCT.

PURPOSE: To evaluate the repeatability of the measurements provided by a new optical biometer (EyeStar 900) based on swept-source optical coherence tomography (SS-OCT) and their agreement with the measurements given by 2 validated biometers based on the same technology, the IOLMaster 700 and Argos. SETTING: IRCCS G.B. Bietti Foundation, Rome, Italy. DESIGN: Prospective evaluation of diagnostic test. METHODS: In a series of unoperated eyes, 3 consecutive scans were acquired with the EyeStar 900, and 1 with the IOLMaster 700 and the Argos. The following biometry parameters were analyzed: axial length (AL), keratometry (K), corneal astigmatism, central corneal thickness, corneal diameter (CD), anterior chamber depth (ACD), lens thickness (LT), and lens tilting. Repeatability was assessed using test-retest variability, the coefficient of variation (CoV), and the intraclass correlation coefficient (ICC); agreement was based on the 95% limits of agreement. RESULTS: 56 eyes of 56 patients were analyzed. High repeatability was achieved for all measured parameters, as the CoV was <1% in most cases and ICC was >0.95 for all parameters. Good to high agreement was found among the measurements of the 3 optical biometers, although some statistically significant differences were detected between the EyeStar 900 and Argos (mean K, ACD, LT, and CD were higher with the Argos). The Argos measured a shorter AL in eyes >25 mm. CONCLUSIONS: The new generation SS-OCT EyeStar 900 optical biometer produces highly repeatable measurements that are in good agreement with those provided by 2 previously validated instruments.

IOL Power Calculation in Eyes Undergoing Combined Descemet Membrane Endothelial Keratoplasty and Cataract Surgery.

PURPOSE: To assess the accuracy of different corneal powers for intraocular (IOL) power calculation in combined Descemet membrane endothelial keratoplasty (DMEK) and cataract surgery and investigate whether preoperative parameters correlate to the prediction error (PE). METHODS: This prospective case series involved patients with Fuchs endothelial dystrophy receiving combined DMEK and cataract surgery. Preoperatively, patients underwent optical biometry and anterior segment OCT (AS-OCT). AS-OCT measurements were repeated 6 months postoperatively, when final refraction was assessed. The PE was calculated using the preoperative average keratometry (Kave) measured by the optical biometer and User Group for Laser Interference Biometry (ULIB) constants. It was also calculated, after constant optimization, using the preoperative Kave from both devices and the total corneal power (TCP) measured by AS-OCT, as well as the postoperative Kave and TCP measured by AS-OCT. RESULTS: ULIB constants resulted in the highest hyperopic PE (P < .0001). Constant optimization improved the results, because the PE was zeroed out and the absolute PEs decreased. No significant difference was found among the Barrett Universal II, Emmetropia Verifying Optical 2.0, Haigis, Hoffer Q, Holladay 1, Kane, and SRK/T formulas. Further improvement was achieved with the postoperative Kave and TCP, although the accuracy remained moderate. The PE based on preoperative corneal measurements was correlated to the amount of corneal flattening; the latter could be predicted by multiple linear regression accounting for anterior and posterior corneal radii (P = .0002) and was correlated to the preoperative anterior/posterior ratio. CONCLUSIONS: Constant optimization is beneficial for combined DMEK and phacoemulsification. Predicting postoperative corneal flattening may improve the results of IOL power accuracy. [J Refract Surg. 2022;38(7):435-442.].

Split-Window OCT biometry in pseudophakic eyes.

PURPOSE: To determine the utility of Split-Window optical coherence tomography OCT (SW-OCT) biometry in measuring ocular axial dimensions as well as imaging the intraocular lens (IOL) and posterior capsule in pseudophakic eyes. METHODS: Sixty-nine pseudophakic eyes of 69 subjects were enrolled in the study. The results of SW-OCT biometry implemented in the SD OCT device for posterior and anterior segment imaging (REVO NX, Optopol Technology) were compared with those obtained with the SS-OCT-based biometer IOLMaster 700 (Carl Zeiss Meditec). Differences in measurement values between the two biometers were determined using the paired t-test. Agreement was assessed through intraclass correlation coefficients (ICC) and Bland-Altman plots. RESULTS: The correlation between measurements obtained with SW-OCT and SS-OCT was very high (ICC for: axial length (AL) = 1.000; anterior chamber depth (ACD) = 0.997; IOL thickness (IOL LT) = 0.997; central corneal thickness (CCT) = 0.987). The mean AL measurement difference was 0.003 ± 0.021 mm (the 95% LoA ranged from -0.04 to 0.05); the mean ACD difference was -0.009 ± 0.025 mm (95% LoA, -0.06 to 0.04); mean LT difference was 0.001 ± 0.021 mm (95% LoA, -0.04 to 0.04); and mean CCT difference was 1.4 ± 5.4 µm (95% LoA, -9 to 12). CONCLUSION: The study shows small, non-significant differences between the biometric measurements obtained with REVO NX SW-OCT and IOLMaster 700 SS-OCT in pseudophakic eyes. However, SW-OCT offered significantly lower ACD and LT measurement failure rates. With high-resolution imaging, SW-OCT enables accurate assessment of IOL position relative to the posterior capsule and visualization of capsular fibrosis.

Corneal diameter measurements by 3 optical biometers and their effect on phakic intraocular lens sizing.

PURPOSE: To compare phakic intraocular lens size calculations based on corneal diameter (CD) measurements by 3 instruments. SETTING: G.B. Bietti Foundation I.R.C.C.S., Rome, Italy. DESIGN: Retrospective interventional case series. METHODS: Preoperatively, CD was measured with the Aladdin, IOLMaster 700, and Pentacam AXL Wave. The simulated ICL size was computed by entering CD measurements into the manufacturer's calculator. Postoperatively, vaulting was measured by anterior segment optical coherence tomography. The optimal ICL size (OIS) was calculated and compared with the commercially available OIS (CAOIS). RESULTS: 54 eyes (29 patients) with the implantable collamer lens (ICL) were enrolled. The mean CD was 12.02 ± 0.36 mm with the Aladdin, 12.35 ± 0.39 mm with the IOLMaster 700, and 12.22 ± 0.41 mm with the Pentacam AXL Wave ( P &lt; .0001), with the closest agreement between the Pentacam AXL Wave and IOLMaster 700 (95% limits of agreement: -0.43 to +0.17 mm). Vaulting (mean: 558 ± 261 µm) was within 251 and 1000 µm in 49 eyes (83.3%). The mean difference between the simulated ICL size and OIS ranged between -0.11 ± 0.35 mm and 0.10 ± 0.30 mm ( P &lt; .0001), with no statistically significant difference between the IOLMaster 700 and Pentacam AXL Wave. The simulated ICL size was equal to CAOIS in 38 eyes (70.37%) with the Aladdin, 37 eyes (68.52%) with the IOLMaster 700, and 39 eyes (72.22%) with the Pentacam AXL Wave, without any statistically significant difference. CONCLUSIONS: CD measurements by the 3 devices lead to similar percentages of eyes with an ICL size equal to the OIS. Agreement is closer between the IOLMaster 700 and Pentacam AXL Wave.

Intraocular lens power calculation with ray tracing based on AS-OCT and adjusted axial length after myopic excimer laser surgery.

PURPOSE: To report the results of intraocular lens (IOL) power calculation by ray tracing in eyes with previous myopic excimer laser surgery. SETTING: G.B. Bietti Foundation I.R.C.C.S., Rome, Italy. DESIGN: Retrospective interventional case series. METHODS: A series of consecutive patients undergoing phacoemulsification and IOL implantation after myopic excimer laser was investigated. IOL power was calculated using ray-tracing software available on the anterior segment optical coherence tomographer MS-39. Axial length (AL) was measured by optical biometry, and 4 values were investigated: (1) that from the printout, (2) the modified Wang/Koch formula, and (3) the polynomial equation for the Holladay 1 and (4) for the Holladay 2 formulas. The mean prediction error (PE), median absolute error (MedAE), and percentage of eyes with a PE within ±0.50 diopters (D) were reported. RESULTS: The study enrolled 39 eyes. Entering the original AL into ray tracing led to a mean hyperopic PE (+0.56 ±0.54 D), whereas with the Wang/Koch formula, a mean myopic PE (-0.41 ±0.53 D) was obtained. The Holladay 1 and 2 polynomial equations lead to the lowest PEs (-0.10 ±0.49 D and +0.08 ±0.49 D, respectively), lowest MedAE (0.37 D and 0.25 D), and highest percentages of eyes with a PE within ±0.50 D (71.79% and 76.92%). Calculations based on the Holladay 2 polynomial equation showed a statistically significant difference compared with other methods used (including Barrett-True K formula), with the only exception of the Holladay 1 polynomial equation. CONCLUSIONS: IOL power was accurately calculated by ray tracing with adjusted AL according to the Holladay 2 polynomial equation.

Agreement of intraocular lens power calculation between 2 SS-OCT-based biometers.

PURPOSE: To assess agreement of measurements by 2 swept-source optical coherence tomography biometers and to evaluate the prediction error (PE) in intraocular lens power calculation with 7 formulas. SETTING: Tertiary public eye hospital. DESIGN: Consecutive observational. METHODS: Axial length (AL), keratometry (K), anterior chamber depth (ACD), lens thickness (LT), and corneal diameter (CD) were measured with the IOLMaster 700 (Biometer A) and Anterion (Biometer B). Agreement was quantified by the limits of agreement and concordance correlation coefficient (CCC). The PE, the median absolute error, and the mean absolute error of the Barrett Universal II, EVO 2.0, Haigis, Hoffer Q, Holladay 1, Kane, and SRK/T formulas were investigated after constant optimization. RESULTS: In 78 eyes from 78 patients, excellent agreement was obtained for AL (CCC >0.99), very good agreement for K, ACD, and LT (CCC >0.95), and strong agreement for CD (CCC >0.72). An additive offset of 0.07 mm was measured for ACD and LT whose mean values were higher with Biometer B (P < .001). No statistically significant difference was found between the PEs and their absolute values when comparing the results of each formula between the 2 biometers. CONCLUSIONS: Agreement of biometric measurements by the 2 biometers was high, although Biometer B provided higher mean values of ACD and LT by 0.07 mm. In cataract patients with normal eye length, measurements by the 2 biometers did not lead to different refractive outcomes with the 7 formulas investigated.

Comparison of different methods to calculate the axial length measured by optical biometry.

PURPOSE: To compare axial length (AL) measurements in long eyes by 2 swept-source optical coherence tomography (SS-OCT) biometers, one based on the group refractive index (IOLMaster 700, Zeiss) and the other based on sum of segments (Argos, Movu Inc.), and compare these measurements with previously published methods to optimize AL. SETTING: G.B. Bietti Foundation I.R.C.C.S., Rome, Italy. DESIGN: Prospective case series. METHODS: AL was measured with both optical biometers in patients with myopia (AL > 24.0 mm) and compared with the values obtained with Wang-Koch adjustment, polynomial equations for the Holladay 1 and 2 formulas, and Cooke-modified AL (CMAL). RESULTS: In 102 eyes of 55 subjects, a statistically significant difference (P < .0001) was found among the 6 AL values. Posttest revealed that Argos measurements (26.90 ± 1.61 mm) were significantly lower compared with those provided by all methods (P < .001) but CMAL, whereas IOLMaster 700 measurements (27.01 ± 1.65) were higher (P < .001). No difference was found between the 2 Holladay equations. CMAL values did not reveal any difference compared with those of the Argos, but a proportional bias showed that in longer eyes, CMAL provided smaller values (P < .0001, r = -0.7221). AL overestimation by the IOLMaster 700 AL compared with the Argos was higher, the longer the eye was (P < .0001, r = 0.6959, r2 = 0.4842). CONCLUSIONS: The SS-OCT optical biometer based on the group refractive index overestimates AL compared with the device using segmented AL. CMAL provides the measurements closest to those of the device using segmented AL.