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.

The Current Burden and Future Solutions for Preoperative Cataract-Refractive Evaluation Diagnostic Devices: A Modified Delphi Study.

Purpose: To obtain consensus on the key areas of burden associated with existing devices and to understand the requirements for a comprehensive next-generation diagnostic device to be able to solve current challenges and provide more accurate prediction of intraocular lens (IOL) power and presbyopia correction IOL success. Patients and Methods: Thirteen expert refractive cataract surgeons including three steering committee (SC) members constituted the voting panel. Three rounds of voting included a Round 1 structured electronic questionnaire, Round 2 virtual face-to-face meeting, and Round 3 electronic questionnaire to obtain consensus on topics related to current limitations and future solutions for preoperative cataract-refractive diagnostic devices. Results: Forty statements reached consensus including current limitations (n = 17) and potential solutions (n = 23) associated with preoperative diagnostic devices. Consistent with existing evidence, the panel reported unmet needs in measurement accuracy and validation, IOL power prediction, workflow, training, and surgical planning. A device that facilitates more accurate corneal measurement, effective IOL power prediction formulas for atypical eyes, simplified staff training, and improved decision-making process for surgeons regarding IOL selection is expected to help alleviate current burdens. Conclusion: Using a modified Delphi process, consensus was achieved on key unmet needs of existing preoperative diagnostic devices and requirements for a comprehensive next-generation device to provide better objective and subjective outcomes for surgeons, technicians, and patients.

Improving the second-eye refractive error in patients undergoing bilateral sequential cataract surgery.

PURPOSE: To assess the refractive error in the second eye to undergo surgery when the intraocular lens (IOL) power was modified to correct 50% of the error from the first eye when such an error exceeded 0.50 diopter (D). DESIGN: Prospective, observational case series. PARTICIPANTS: Two hundred fifty patients with bilateral, sequential cataract surgery. METHODS: Two hundred fifty consecutive patients who underwent the first-eye cataract operation 1 to 3 months earlier were scheduled for cataract surgery in the second eye. When choosing the IOL power for the second eye, the calculations were adjusted to correct 50% of the first-eye refractive error (FERE). The adjusted second-eye refractive error (aSERE) was evaluated 6 to 8 weeks after surgery. It was compared with the FERE, with a potential nonadjusted SERE, and with a potential fully adjusted SERE. MAIN OUTCOME MEASURES: Postoperative refractive error. RESULTS: The median aSERE was significantly lower in the second eye compared with the median FERE in the 47 cases in which the FERE ranged from -0.50 to -1.00 D (-0.12 vs. -0.66 D), in the 15 cases in which the FERE exceeded -1.00 D (-0.12 vs. -1.25 D), in the 24 cases in which the FERE ranged from 0.50 to 1.00 D (-0.03 vs. 0.65 D), and in the 11 cases in which the FERE exceeded 1.00 D (-0.29 vs. 1.19 D). The difference was statistically significant in all categories (P<0.00001). CONCLUSIONS: In patients undergoing bilateral sequential cataract surgery and in cases in which the FERE exceeded 0.50 D, the refractive error of the second eye can be improved by modifying the IOL power to correct up to 50% of the error from the first eye. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Accuracy of newer intraocular lens power formulas in short and long eyes using sum-of-segments biometry.

PURPOSE: To analyze the accuracy of newer intraocular lens power formulas in long and short eyes measured using the sum-of-segments biometry. SETTING: Private practice, Lynwood, California. DESIGN: Retrospective observational study. METHODS: 595 patients scheduled for cataract surgery had their eyes measured using the sum-of-segments biometry. The expected residual refractions were calculated using Barrett Universal II (B II), Barrett True Axial Length (BTAL), Emmetropia Verifying Optical (EVO), Hill-RBF, Hoffer QST, Holladay 2, Holladay 2-NLR, K6, Kane, Olsen, PEARL-DGS, T2, and VRF formulas and compared with the traditional Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. RESULTS: In the 102 long eyes, all new formulas had a mean absolute error (MAE) equal or lower than the traditional formulas, ranging from 0.29 to 0.32 diopter (D). In the 78 short eyes, BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas had the lowest MAE (0.33 D, 0.33 D, 0.31 D, 0.36 D, 0.32 D, and 0.32 D, respectively), whereas all traditional formulas exceeded 0.36 D. CONCLUSIONS: All new formulas performed equal or better than the traditional formulas with the sum-of-segments biometry. The best overall results in the short and long eyes as well as in the very short and very long eyes were noted with the BTAL, EVO, Hoffer QST, K6, Olsen, and PEARL-DGS formulas, closely followed by the B II and Kane formulas.

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

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

Validating e-norms methodology in ophthalmic biometry.

OBJECTIVE: To validate the extrapolated norms or e-norms methodology in establishing a reference range for the biometric data used for intraocular lens power calculation. METHODS AND ANALYSIS: All measurements were performed with an optical low-coherence reflectometer. A novel technique, the e-norms methodology, was used to determine the normative values of measurements. RESULTS: Eyes (n=500) were measured to evaluate the axial length (AL), K readings (Ks), anterior chamber depth (ACD) and lens thickness (LT). Using the e-norms methodology, the normal AL ranged from 22.50 to 24.50 mm (mean=23.50 mm), with medium-long eyes between 24.51 and 24.99 mm and the long eyes measuring 25.00 mm and longer; the medium-short eyes ranged from 22.01 and 22.49 mm, with the short eyes measuring 22.00 mm and shorter. Normal values ranged from 2.50 to 3.50 mm for ACD (mean=3.00 mm), from 4.40 to 5.44 mm for LT (mean=4.92 mm), and from 42.50 to 44.82 dioptres for Ks (mean=43.66 dioptres). CONCLUSION: Measurements of the biometric mean values compared favourably with published data. The e-norms methodology assisted in establishing a biometric reference range. Furthermore, it allowed us to cluster patients into groups based on AL differences.

Effects on IOL Power Calculation and Expected Clinical Outcomes of Axial Length Measurements Based on Multiple vs Single Refractive Indices.

PURPOSE: To compare axial length measurements based on multiple specific refractive indices for each segment of the eye to those obtained using a single refractive index for the entire eye and to evaluate the subsequent effects on IOL power calculation. SETTING: One site in Lynwood, CA. DESIGN: Single-arm, non-interventional, non-randomized retrospective chart review. METHODS: Eyes undergoing cataract surgery where biometry and IOL power calculations were based on axial length calculated with multiple specific refractive indices (multiple) were evaluated. A simulated axial length based on using a single refractive index was calculated for each case (single). The expected residual refractions based on different IOL formulas were calculated for both single and multiple groups. Formulas were then optimized, and the mean prediction errors (MPE) and mean absolute prediction errors (MAE) were calculated, based on the difference between the (optimized) expected value and the actual refractive outcome. RESULTS: A total of 595 eligible eyes were evaluated. Differences between the axial lengths determined in the single and multiple groups ranged from +0.28 mm to -0.14 mm, with a significant correlation between the difference in AL and average AL (r2 = 0.73, p < 0.001). AL differences between groups were statistically significant in long and short eyes (p < 0.001) but not in average eyes or overall (p > 0.25). In nearly all cases, the average MPE in the multiple group was lower than that for the single group across all axial lengths and formulas. When larger differences in MAE were present, the multiple group results were more often lower (better). CONCLUSION: Differences were found between axial lengths calculated using a single refractive index and multiple refractive indices, mainly in the short and long eyes. Differences had some effect on IOL power calculation. Such effects may become increasingly important as the precision of formulas increases.

Variability of axial length, anterior chamber depth, and lens thickness in the cataractous eye.

PURPOSE: To review and evaluate the biometry measurements in 750 eyes (first eye developing cataract) of 750 consecutive patients with no retinal pathology. SETTING: Private practice, Lynwood, California, USA. METHODS: All measurements were performed with the I3 system A-scan (Innovative Imaging, Inc.) using an immersion technique. The axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) measurements were evaluated in relation to each other and in relation to age, sex, and keratometric readings. RESULTS: The mean AL was 23.46 mm +/- 1.03 (SD), the mean ACD was 2.96 +/- 0.45 mm, and the mean LT was 4.93 +/- 0.56 mm. Men presented for surgery at an earlier age than women (mean 73 +/- 9.41 years versus 75 +/- 8.55 years) with a longer AL (23.76 +/- 1.00 mm versus 23.27 +/- 1.01 mm). The AL tended to be longer in younger patients (r = -0.127; P<.001); the ACD tended to be deeper in younger patients (r = -0.250; P<.001) and in longer eyes (r = 0.423; P<.001). The LT tended to be thicker in older patients (r = 0.385; P<.001) and in shorter eyes (r = -0.179; P<.001), with large scatter in the distribution. CONCLUSIONS: There was a positive correlation between AL and ACD and an inverse correlation between AL and LT. Also, AL was inversely correlated with age and corneal power.

No-history method of intraocular lens power calculation for cataract surgery after myopic laser in situ keratomileusis.

PURPOSE: To prospectively evaluate the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available. SETTING: Private practice, Lynwood, California, USA. METHODS: The predicted IOL power was calculated in each case. Also calculated were the mean arithmetic and absolute IOL predictor errors, range of the prediction errors, and number of eyes in which the error was within +/-1.00 diopter (D). RESULTS: The mean arithmetic IOL prediction error was -0.003 D +/- 0.63 (SD), and the mean absolute IOL prediction error was 0.55 +/- 0.31 D (range -0.89 to +1.05 D). Fourteen eyes (93.3%) were within +/-1.00 D. The results of the Shammas post-LASIK formula compared favorably to the results obtained with the optimized Holladay 1 (P = .42), Hoffer Q (P = .25), Haigis (P = .30), and Holladay 2 (P = .19) formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005). CONCLUSION: The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.

Accuracy of a New Swept-Source Optical Coherence Tomography Biometer for IOL Power Calculation and Comparison to IOLMaster.

PURPOSE: To investigate the accuracy of the measurements provided by a new optical biometer (OA-2000, Tomey Corporation, Nagoya, Japan) for calculating the intraocular lens (IOL) power and to compare the refractive outcomes to those obtained with the IOLMaster 500 (Carl Zeiss Meditec, Jena, Germany). METHODS: In this interventional multicenter study, consecutive patients having cataract surgery were enrolled. Only the IOL model used in the largest sample of patients was selected and the eyes implanted with that IOL were subsequently analyzed. The OA-2000, an optical biometer based on swept-source optical coherence tomography (SS-OCT), was used to measure axial length and corneal power in all eyes. IOL power was calculated with the Hoffer Q, Holladay 1, and SRK/T formulas. In a subsample of eyes, the IOL power was also calculated with measurements obtained by partial coherence interferometry (IOLMaster 500). The median absolute error and percentage of eyes with a prediction error of ±0.50 diopters (D) or less were calculated. RESULTS: Two hundred forty-nine eyes were analyzed. Using SS-OCT, the median absolute error ranged between 0.33 (Holladay 1) and 0.35 (SRK/T) D. The rate of eyes with a prediction error of ±0.50 D or less ranged between 71.5% (Hoffer Q) and 67.1% (SRK/T). In the subsample of 87 eyes with measurements by both devices, the median absolute error was lower with the OA-2000 (Hoffer Q: P = .0377; Holladay 1: P = .0191; SRK/T: P = .0087). CONCLUSIONS: The SS-OCT-based optical biometer investigated in the current study provides accurate measurements for IOL power calculation and seems to offer more predictable refractive results compared to the partial coherence interferometry IOLMaster. [J Refract Surg. 2017;33(10):690-695.].

Multicenter study of optical low-coherence interferometry and partial-coherence interferometry optical biometers with patients from the United States and China.

PURPOSE: To evaluate the agreement between the measurements provided by a new optical biometer, the Aladdin, based on optical low-coherence interferometry (OLCI), and those provided by the most commonly used optical biometer (IOLMaster 500), based on partial-coherence interferometry (PCI). SETTING: Multicenter clinical trial. DESIGN: Prospective evaluation of diagnostic test. METHODS: In this study, 2 samples of adult patients were enrolled, 1 in the United States and the other in China. The U.S. group included a sample of consecutive patients scheduled for cataract surgery. The China group included a sample of healthy subjects with no cataracts. In both cases, only 1 eye of each patient was analyzed. Axial length (AL), corneal power (in diopters [D]) (K), anterior chamber depth (ACD) (corneal epithelium to lens), and corneal astigmatism were measured. All values were analyzed using a paired t test, the Pearson product-moment correlation coefficient (r), and Bland-Altman plots. RESULTS: In the U.S. and China groups, the OLCI mean AL values did not show a statistically significant difference from PCI values and showed excellent agreement and correlation. On the contrary, OLCI measured a lower mean K (-0.14 D) and a deeper ACD measurements (U.S. +0.16 mm and China +0.05 mm). These differences were statistically significant (P < .0001). Vector analysis did not show a statistically significant difference in astigmatism measurements. CONCLUSIONS: Agreement between OLCI and PCI was good. However, the small but statistically significant differences in K and ACD measurements make constant optimization necessary when calculating the intraocular lens power using theoretical formulas. FINANCIAL DISCLOSURE: Dr. Hoffer licenses the registered trademark name Hoffer to Carl Zeiss-Meditec (PCI), Haag-Streit (Lenstar), Movu (Argos), Oculus (Pentacam, AXL), Nidek (AL-Scan), Tomey (OA-2000), Topcon EU Visia Imaging (Aladdin), Ziemer (Galilei G6), and all A-scan biometer manufacturers. Dr. Shammas licenses his formulas to Carl Zeiss-Meditec (PCI), Haag-Streit (Lenstar), Nidek (AL-Scan), and Topcon EU (Visia Imaging) (Aladdin). None of the other authors has a financial or proprietary interest in any material or method mentioned.

Biometry measurements using a new large-coherence-length swept-source optical coherence tomographer.

PURPOSE: To evaluate the repeatability and reproducibility of the measurements obtained with the Argos, a new biometer with swept-source optical coherence tomography (SS-OCT), and to compare them with the results obtained with the IOLMaster 500 (partial-coherence interferometry [PCI]) and the Lenstar LS 900 (optical low-coherence reflectometry [OLCR]) biometers. SETTING: Private practice, Lynwood, California, USA. DESIGN: Prospective observational study. METHODS: All measurements were performed with the SS-OCT tomographer, the PCI biometer, and the OLCR biometer. RESULTS: Eyes (n = 107) were measured to evaluate the axial length (AL), central corneal thickness (CCT), aqueous depth, anterior chamber depth (ACD), lens thickness, pupil size, corneal diameter, and anterior corneal radius of curvature (RAV). Repeatability and reproducibility of the SS-OCT measurements showed comparable values and a low variation rate, with an interset mean difference of 0.01 mm for AL, 0.01 mm for CCT, 0.01 mm for aqueous depth and ACD, 0.03 mm for lens thickness, 0.10 mm for pupil size, 0.14 mm for corneal diameter, and 0.02 mm for RAV. The SS-OCT device correctly measured the AL in 96% of the cases compared with 79% for the OLCR device and 77% for the PCI device. Comparisons between the PCI device and SS-OCT device were -0.01 ± 0.05 mm for AL, -0.17 ± 0.20 mm for ACD, and -0.01 ± 0.05 mm for RAV. Comparison between the OLCR device and the SS-OCT device was 0.01 ± 0.06 mm for AL, 0.08 ± 0.15 mm for ACD, 0.00 ± 0.05 mm for RAV, 0.00 ± 0.01 mm for CCT, 0.07 ± 0.14 mm for aqueous depth, -0.23 ± 0.22 mm for lens thickness, -0.29 ± 0.53 mm for pupil size, and -0.34 ± 0.76 mm for corneal diameter. CONCLUSION: Axial length measurements with the new SS-OCT biometer were comparable to the PCI and OLCR measurements with a higher AL acquisition rate. FINANCIAL DISCLOSURE: Dr. Shammas is a consultant to Movu, Inc. Drs. Ortiz, Kim, and Chong have proprietary interest in the new technology.

Measuring the cataractous lens.

PURPOSE: To evaluate the lens thickness, anterior cortex space, nucleus thickness, and posterior cortex space in cataractous eyes and compare them with those in eyes of younger patients with clear lenses. SETTING: Private practice, Lynwood, California, USA. DESIGN: Retrospective observational study. METHODS: The study evaluated a group of cataractous eyes and compared them with a group of eyes of younger patients with clear lenses. All measurements were performed with a biometer (Lenstar LS 900). RESULTS: The cataractous group (200 eyes) had a greater mean lens thickness (4.65 mm ± 0.41 [SD]) than the control group (80 eyes) (4.09 ± 0.33 mm). The mean measured values for the cataractous groups and control groups were 0.84 ± 0.21 mm and 0.35 ± 0.11 mm for anterior cortex space, 3.31 ± 0.25 mm and 3.27 ± 0.27 mm for mean nucleus thickness, and 0.51 ± 0.16 mm and 0.48 ± 0.13 mm for mean posterior cortex space, respectively. Anterior cortex space, nucleus thickness, and posterior cortex space correlated positively with lens thickness (r = 0.69, r = 0.69, and r = 0.59, respectively). Lens thickness, anterior cortex space, nucleus thickness, and posterior cortex space showed a weak inverse correlation with axial length (r = 0.06, r = 0.08, r = 0.10, and r = 0.10, respectively) and an inverse correlation with anterior chamber depth (r = 0.57, r = 0.43, r = 0.42, and r = 0.22, respectively). Lens thickness showed a positive correlation with age (r = 0.28), as did the anterior cortex space (r = 0.32) and posterior cortex space (r = 0.26), but nucleus thickness did not show a positive correlation (r = 0.02). CONCLUSION: Lens thickness increased with age and with cataract formation and was mostly attributable to an increase in the anterior cortex space. FINANCIAL DISCLOSURE: Neither author has a financial or proprietary interest in any material or method mentioned.

Improving the preoperative prediction of the anterior pseudophakic distance for intraocular lens power calculation.

PURPOSE: To establish a new formula for intraocular (IOL) power calculation. SETTING: Private practice, Lynwood, California, USA. DESIGN: Retrospective observational and prospective evaluation. METHODS: In this 2-part retrospective observational study followed by a prospective evaluation, the postoperative anterior pseudophakic distance (APD) was correlated with the ante-nucleus distance (AND), the nucleus thickness (NT) of the cataractous lens, and the axial length. An estimated APD (EAPD) equation was established and used prospectively in a new formula on eyes scheduled for cataract surgery. RESULTS: Correlations were made in 90 operated eyes, and the EAPD equation was used in a new formula on 110 eyes scheduled for cataract surgery. Using the new IOL power formula, the median absolute error was 0.28 D with 82.7% of the eyes within ±0.50 D and 100% within ±1.00 D. CONCLUSIONS: The new IOL power formula with its incorporated EAPD equation performed well. FINANCIAL DISCLOSURE: H.J.S. has a pending patent on this system and method for determining IOL lens power.

New mode for measuring axial length with an optical low-coherence reflectometer in eyes with dense cataract.

PURPOSE: To evaluate a new algorithm for measuring eyes with dense cataract using a biometer based on optical low-coherence reflectometry (OLCR). SETTING: Shammas Eye Medical Center, Lynwood, California, USA, and Augenarztpraxis EYEC, Bern, Switzerland. DESIGN: Cross-sectional retrospective study. METHODS: Data were collected from 2 sites where the new Dense Cataract Measurement mode for the OLCR optical biometer (Lenstar LS 900) had been implemented. Related ultrasound (US) data for patients whose eyes could not be measured with optical biometry were also collected where available. The percentage of eyes that were measurable in the new mode that were not measurable in the standard mode was calculated. The quality of the measurements by the new mode was evaluated using postoperative axial length measurements and/or concurrent US measurements, where available. RESULTS: Data for 4791 eyes were available for analysis. Axial length measurement was possible using the standard algorithm in 94.4% of cases. The use of the new mode allowed for measurement of an additional 4.0% of cases, a statistically significant increase (P < .001). Comparisons of AL measurements with concurrent US or postoperative optical biometry showed high correlations, with the 95% limits of agreement of -0.47 to +0.29 mm, similar to results for standard measurements. CONCLUSIONS: The new measurement mode of the OLCR system provided a significant increase in the number of eyes that could be measured with optical biometry. Axial length measurements using the new mode appeared as reliable as those made using the standard measurement mode. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis.

PURPOSE: To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method. DESIGN: Interventional case series. METHODS: Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre - CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost -0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost -6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results. RESULTS: Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram (P <.001), and there was no statistically significant difference between the mean keratometric values (P >.5). CONCLUSIONS: The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.

Intraocular lens power calculation in eyes with previous hyperopic laser in situ keratomileusis.

PURPOSE: To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data. SETTING: Private practices, Lynwood, California, and Mesa, Arizona, USA. DESIGN: Retrospective comparative observational study. METHODS: The corrected corneal power (Kc) was calculated in each eye by adding the refractive change at the corneal level to the pre-LASIK keratometric (K) readings. By comparing Kc with the measured post-LASIK K readings (Kpost), the following equation was derived: Kc = 1.0457 Kpost-1.9538. This equation was combined with the Shammas original formula to obtain the Shammas-PHL formula. RESULTS: The new formula was evaluated in 18 eyes with previous LASIK data and in 24 eyes with no previous LASIK data. Using the Shammas-PHL formula, the mean arithmetic prediction error was -0.03 diopter (D) ± 0.72 (SD) (range -1.57 to +1.54 D) and the median absolute error was 0.38 D in 18 eyes with available pre-LASIK data and 0.05 ± 0.58 D (range -0.56 to +1.40 D) and 0.43 D, respectively, in the 24 eyes with no pre-LASIK data. CONCLUSION: The Shammas-PHL formula can be used in post-hyperopic LASIK cases whether or not the pre-LASIK data are available.