Intraocular Lens Prediction Error Research Articles

IOL power calculations after LASIK or PRK: Barrett True-K biometer-only calculation strategy yields equivalent outcomes as a multiple formula approach.

To compare the accuracy of intraocular lens (IOL) power calculations performed using the biometer-embedded Barrett True-K formula vs a multiple formula approach using the ASCRS postrefractive calculator in eyes with previous myopic or hyperopic refractive surgery. Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio. Retrospective, consecutive case series. Patients who underwent cataract surgery with a history of corneal refractive surgery were included. For each formula, the IOL prediction error and refractive prediction error was calculated. Main outcome measures included mean absolute error (MAE) and the percentage of eyes within ±0.25 diopters (D), ±0.50 D, and ±1.00 D. 96 postmyopic eyes and 47 posthyperopic eyes were analyzed. In the postmyopic cohort, the Barrett True-K formula had the lowest MAE (0.36 D), followed by the Haigis-L formula (0.41 D). The Barrett True-K formula had a significantly higher percentage (44.8%) of eyes within ±0.25 D in comparison with the Haigis-L formula (34.4%), which had the second highest percentage ( P < .01). In the posthyperopic cohort, the Barrett True-K formula had the lowest MAE (0.41 D), followed by the ASCRS-mean (0.46). The Barrett True-K and ASCRS-mean formulas had the highest percentage of eyes within ±0.25 D (42.6% vs 38.3%, P = .16). The Barrett True-K formula built into the biometer performed equivalently to a multiple formula approach on the ASCRS online calculator in both postmyopic and posthyperopic eyes. This approach reduces the potential for transcription error from data entry for lens power calculation approaches that require manual data entry.

Comparison of intraocular lens calculation methods after myopic laser-assisted in situ keratomileusis and radial keratotomy without prior refractive data

AimTo compare intraocular lens (IOL) calculation methods not requiring refraction data prior to myopic laser-assisted in situ keratomileusis (LASIK) and radial keratotomy (RK).MethodsIn post-LASIK eyes, the methods not requiring prior...

Comparison of the accuracy of intraocular lens power calculation formulas for eyes after corneal refractive surgery.

In cataract surgery, calculating intraocular lens (IOL) power in patients who have previously received corneal refractive surgery on the same eye presents a clinical challenge. This study aims to compare the accuracy of the Haigis-L, Barrett True-K, and Shammas-PL formulas in predicting the IOL power in eyes following corneal refractive surgery. This study analyzed 32 eyes belonging to 28 patients who underwent cataract surgery and IOL implantation after previously undergoing myopic corneal refractive surgery. The IOL power was calculated using the Haigis-L, Barrett True-K, and Shammas-PL formulas, and the accuracy of the three formulas was compared. The Haigis-L, Barrett True-K, and Shammas-PL formulas had a mean arithmetic IOL prediction error of -0.65, -0.39, and -0.46, respectively. The mean numerical errors of the three formulas were significantly different from zero (P<0.001). The smallest median absolute refraction prediction error (median =0.40) belonged to the Barrett True-K formula, which was significantly smaller than that of the Haigis-L formula (median =0.57, P<0.05) but similar to that of the Shammas-PL formula (median =0.49, P>0.05). There was no significant difference in the percentage of eyes within either ±0.50 D or ±1.00 D of the predicted refraction error across the three formulas. The Barrett True-K formula can predict IOL power in eyes that have previously undergone myopic corneal refractive surgery better than the Haigis-L formula.

Effect of lens constants optimization on the accuracy of intraocular lens power calculation formulas for highly myopic eyes.

To evaluate the effect of different lens constant optimization methods on the accuracy of intraocular lens (IOL) power calculation formulas for highly myopic eyes. This study comprised 108 eyes of 94 consecutive patients with axial length (AL) over 26 mm undergoing phacoemulsification and implantation of a Rayner (Hove, UK) 920H IOL. Formulas were evaluated using the following lens constants: manufacturer's lens constant, User Group for Laser Interference Biometry (ULIB) constant, and optimized constant for long eyes. Results were compared with Barrett Universal II formula, original Wang-Koch AL adjustment method, and modified Wang-Koch AL adjustment method. The outcomes assessed were mean absolute error (MAE) and percentage of eyes with IOL prediction errors within ±0.25, ±0.50, and ±1.0 diopter (D). The nonparametric method, Friedman test, was used to compare MAE performance among constants. Optimized constants could significantly reduce the MAE of SRK/T, Hoffer Q, and Holladay 1 formulas compared with manufacturer's lens constant, whereas the percentage of eyes with IOL prediction errors within ±0.25, ±0.50, and ±1.0 D had no statistically significant differences. Optimized lens constant for long eyes alone showed non-significant refractive advantages over the ULIB constant. Barrett Universal II formula and formulas with AL adjustment showed significantly higher accuracy in highly myopic eyes (P<0.001). Lens constant optimization for the subset of long eyes reduces the refractive error only to a limited extent for highly myopic eyes.

Intraocular lens power calculations in eyes with previous hyperopic laser in situ keratomileusis or photorefractive keratectomy

To evaluate the accuracy of 7 intraocular lens (IOL) calculation formulas in patients with previous hyperopic laser in situ keratomileusis (LASIK) or excimer laser photorefractive keratectomy (PRK). Retrospective case series. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. The 7 formulas evaluated were the adjusted Atlas 0-3, Masket, Modified Masket, Haigis-L, Shammas-PL, Barrett True-K, and Barrett True-K No-History. The Masket and Modified Masket were calculated using the single-K version of Holladay 1 and Hoffer Q formulas; the adjusted Atlas 0-3 was calculated using the double-K version of Holladay 1 and Hoffer Q. The IOL power predicted by each formula was calculated by targeting the postoperative manifest refraction. The IOL prediction error was obtained by subtracting the predicted IOL power from the implanted IOL power. The mean IOL prediction error, median absolute refractive prediction error, and percentages of eyes within ±0.50 diopter (D) and ±1.00 D of the predicted refraction were calculated. Twenty-one eyes of 21 patients were evaluated. There were no significant differences in the median absolute refractive prediction error or percentages of eyes within ±0.50 D or ±1.00 D of the predicted refraction between formulas or methods. The IOL mean prediction errors were comparable between the Holladay 1 and Hoffer Q calculations for all formulas except for a greater error for the double-K version of the Hoffer Q of the adjusted Atlas 0-3. In eyes that had hyperopic LASIK or PRK, there were no significant differences in the accuracy between the 7 IOL calculation formulas.

Comparison of retropupillary fixated iris-claw lenses and sulcus placed intraocular lenses for the treatment of aphakia

Purpose: The purpose of this study is to compare the visual outcomes and safety profile of retropupillary fixated iris claw lenses (RPICLs) and sulcus placed posterior chamber intraocular lenses (SIPCIOL) in the management of aphakia. Materials and Methods: This was a comparative, observational study, which included 87 eyes of 84 patients who underwent RPICL or SIPCIOL for aphakia. BCVA at 6 weeks, mean prediction error, post-eperative complications were compared between the two groups. Results: Group 1 (RPICL group) consisted of 47 eyes of 45 patients and Group 2 (SIPCIOL group) consisted of 40 eyes of 39 patients. Mean age was 67.13 ± 9.33 years in Group 1 and 59.91 ± 16.62 years in Group 2. There was statistically significant difference between preoperative best-corrected visual acuity (BCVA) and post op BCVA at 6 weeks in Group 1 (P = 0.001, paired t-test) and Group 2 (P = 0.001, paired t-test). There was no significant difference in BCVA between the groups at 6 weeks (P = 0.54, unpaired t-test). There was no statistically significant difference in BCVA at 6 weeks between primary surgery and secondary surgery in Group 1 (P = 0.34, unpaired t-test) and Group 2 (P = 0.59, unpaired t-test). The mean prediction error in Group 1 was 0.41 ± 0.58 D and in Group 2 was 0.18 ± 0.20 and was not significant (P = 0.61, unpaired t-test). There was no significant difference between the two groups in mean intraocular pressure at 1 week (P = 0.43, paired t-test) and at 6 weeks (P = 0.83, paired t-test). There was no significant difference between the two groups in operative complications. Conclusion: RPICL was comparable with SIPCIOLs in terms of BCVA at 6 weeks, intraocular lens prediction error, and operative complications.

Comparison of Newer IOL Power Calculation Methods for Eyes With Previous Radial Keratotomy.

PurposeTo evaluate the accuracy of the optical coherence tomography–based (OCT formula) and Barrett True K (True K) intraocular lens (IOL) calculation formulas in eyes with previous radial keratotomy (RK).MethodsIn 95 eyes of 65 patients, using the actual refraction following cataract surgery as target refraction, the predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the implanted IOL power. The arithmetic IOL PE and median refractive PE were calculated and compared.ResultsAll formulas except the True K produced hyperopic IOL PEs at 1 month, which decreased at ≥4 months (all P < 0.05). For the double-K Holladay 1, OCT formula, True K, and average of these three formulas (Average), the median absolute refractive PEs were, respectively, 0.78 diopters (D), 0.74 D, 0.60 D, and 0.59 D at 1 month; 0.69 D, 0.77 D, 0.77 D, and 0.61 D at 2 to 3 months; and 0.34 D, 0.65 D, 0.69 D, and 0.46 D at ≥4 months. The Average produced significantly smaller refractive PE than did the double-K Holladay 1 at 1 month (P < 0.05). There were no significant differences in refractive PEs among formulas at 4 months.ConclusionsThe OCT formula and True K were comparable to the double-K Holladay 1 method on the ASCRS (American Society of Cataract and Refractive Surgery) calculator. The Average IOL power on the ASCRS calculator may be considered when selecting the IOL power. Further improvements in the accuracy of IOL power calculation in RK eyes are desirable.

Comparison of Newer Intraocular Lens Power Calculation Methods for Eyes after Corneal Refractive Surgery

To compare the newer formulae, the optical coherence tomography (OCT)-based intraocular lens (IOL) power formula (OCT formula) and the Barrett True-K formula (True-K), with the methods on the American Society of Cataract and Refractive Surgery (ASCRS) calculator in eyes with previous myopic LASIK/photorefractive keratectomy (PRK). Prospective case series. A total of 104 eyes of 80 patients who had previous myopic LASIK/PRK and subsequent cataract surgery and IOL implantation. By using the actual refraction after cataract surgery as target refraction, predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the power of the IOL implanted. Arithmetic IOL PEs, variances of mean arithmetic IOL PE, median refractive PE, and percent of eyes within 0.5 diopters (D) and 1.0 D of refractive PE. Optical coherence tomography produced smaller variance of IOL PE than did Wang-Koch-Maloney (WKM) and Shammas (P < 0.05). With the OCT, True-K No History, WKM, Shammas, Haigis-L, and Average of these 5 formulas, the median refractive PEs were 0.35 D, 0.42 D, 0.51 D, 0.48 D, 0.39 D, and 0.35 D, respectively, the percentage of eyes within 0.5 D of refractive PE were 68.3%, 58.7%, 50.0%, 52.9%, 55.8%, and 67.3%, respectively, and the percentage of eyes within 1.0 D of refractive PE were 92.3%, 90.4%, 86.9%, 88.5%, 90.4%, and 94.2%, respectively. The OCT formula had smaller refractive PE compared with the WKM and Shammas, and the Average approach produced significantly smaller refractive PE than all methods except OCT (all P < 0.05). The OCT and True-K No History are promising formulas. The ASCRS IOL calculator has been updated to include the OCT and Barrett True K formulas. Intraocular Lens Power Calculation After Laser Refractive Surgery Based on Optical Coherence Tomography (OCT IOL); Identifier: NCT00532051; www.ClinicalTrials.gov.

A Comparison of the American Society of Cataract and Refractive Surgery post-myopic LASIK/PRK Intraocular Lens (IOL) calculator and the Ocular MD IOL calculator

BackgroundTo compare the average values of the American Society of Cataract and Refractive Surgery (ASCRS) and Ocular MD intraocular lens (IOL) calculators to assess their accuracy in predicting IOL power in patients with prior laser-in-situ keratomileusis (LASIK) or photorefractive keratectomy.MethodsIn this retrospective study, data from 21 eyes with previous LASIK or photorefractive keratectomy for myopia and subsequent cataract surgery was used in an IOL calculator comparison. The predicted IOL powers of the Ocular MD SRK/T, Ocular MD Haigis, and ASCRS averages were compared. The Ocular MD average (composed of an average of Ocular MD SRK/T and Ocular MD Haigis) and the all calculator average (composed of an average of Ocular MD SRK/T, Ocular MD Haigis, and ASCRS) were also compared. Primary outcome measures were mean arithmetic and absolute IOL prediction error, variance in mean arithmetic IOL prediction error, and the percentage of eyes within ±0.50 and ±1.00 D.ResultsThe Ocular MD SRK/T and Ocular MD Haigis averages produced mean arithmetic IOL prediction errors of 0.57 and −0.61 diopters (D), respectively, which were significantly larger than errors from the ASCRS, Ocular MD, and all calculator averages (0.11, −0.02, and 0.02 D, respectively, all P < 0.05). There was no statistically significant difference between the methods in absolute IOL prediction error, variance, or the percentage of eyes with outcomes within ±0.50 and ±1.00 D.ConclusionThe ASCRS average was more accurate in predicting IOL power than the Ocular MD SRK/T and Ocular MD Haigis averages alone. Our methods using combinations of these averages which, when compared with the individual averages, showed a trend of decreased mean arithmetic IOL prediction error, mean absolute upper limit of IOL prediction error, and variance, while increasing the percentage of outcomes within ±0.50 D.

Evaluation of the American Society of Cataract and Refractive Surgery intraocular lens calculator for eyes with prior radial keratotomy

BackgroundThe purpose of this study was to evaluate the American Society of Cataract and Refractive Surgery (ASCRS) intraocular lens (IOL) calculator for eyes with prior radial keratotomy and assess the accuracy of its methods in predicting IOL power in patients with previous radial keratotomy.MethodsThis retrospective study included data from 15 eyes with previous radial keratotomy and subsequent cataract surgery. The average central power and Humphrey Atlas methods from the ASCRS IOL calculator, along with an average IOL power produced from an average of these two methods (ASCRS average), were compared. Primary outcome measures for each method were mean arithmetic and absolute IOL prediction error, variance in mean arithmetic IOL prediction error, and the percentage of refractive outcomes within ±0.50, ±1.00, ±1.50, and ±2.00 diopters (D).ResultsThe average central power method and the ASCRS average were significantly more accurate than the Humphrey Atlas method in terms of mean absolute IOL prediction error (1.03 D and 1.02 D versus 1.53; P = 0.04 and P = 0.01, respectively). In addition, the average central power method and ASCRS average produced a higher percentage of refractive outcomes within ±0.50 D when compared with the Humphrey Atlas method (60% and 46.67% versus 0%, respectively). A comparison of the average central power method and the ASCRS average demonstrated a smaller variance and higher percentage of patients within ±1.00 D when using the ASCRS average.ConclusionThe ASCRS calculator for eyes with prior radial keratotomy is an easily accessible and valuable online tool for calculating IOL power in patients with previous radial keratotomy. We found that the ASCRS average produced by the calculator provided the best IOL prediction. We recommend using it with the addition of 1.00 to 1.50 D to its IOL power prediction.

Evaluation of intraocular lens power prediction methods using the American Society of Cataract and Refractive Surgeons Post-Keratorefractive Intraocular Lens Power Calculator

To evaluate the accuracy of methods of intraocular lens (IOL) power prediction after previous laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) using the American Society of Cataract and Refractive Surgery IOL power calculator. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. The following methods were evaluated: methods using pre-LASIK/PRK keratometry (K) and surgically induced change in refraction, methods using surgically induced change in refraction, and methods using no previous data. The predicted IOL power was calculated with each method using the actual refraction after cataract surgery as the target. The IOL prediction error was calculated as the implanted IOL power minus the predicted IOL power. Arithmetic and absolute IOL prediction errors, variances in mean arithmetic IOL prediction error, and percentage of eyes within +/-0.50 diopter (D) and +/-1.00 D of refractive prediction errors were calculated. Methods using surgically induced change in refraction or no previous data had significantly smaller mean absolute IOL prediction errors, smaller variances, and a greater percentage of eyes within +/-0.50 D and +/-1.00 D of refractive prediction errors than methods using pre-LASIK/PRK keratometry (K) values and surgically induced change in refraction (all P<.05 with Bonferroni correction). There were no statistically significant differences between methods using surgically induced change in refraction and methods using no previous data. Methods using surgically induced change in refraction and methods using no previous data gave better results than methods using pre-LASIK/PRK K values and surgically induced change in refraction.

Comparison of 2 laser instruments for measuring axial length

To compare axial length (AL), anterior chamber depth (ACD), and keratometric (K) measurements of 2 laser biometers. Private practices, Lynwood and Santa Monica, California, USA. In this prospective comparative observational study of eyes with cataract and eyes with a clear lens, AL, ACD, and K measurements were performed using an IOLMaster biometer, which uses partial coherence interferometry (PCI), and a Lenstar LS 900 biometer, which uses optical low-coherence reflectometry (OLCR). Intraocular lens (IOL) power calculation was performed using the Haigis formula. The IOL prediction error was calculated for each eye. The study evaluated 50 eyes with cataract and 50 eyes with a clear lens. There was a good correlation between AL, ACD, and K measurements in the cataractous eyes (r = 0.9993, 0.9667, and 0.9959, respectively) and in eyes with a clear lens (r = 0.9995, 0.8211, and 0.9959, respectively). The OLCR unit measured a slightly longer AL in the cataract group and clear lens group (mean difference 0.026 mm and 0.023 mm, respectively), a deeper ACD (0.128 mm and 0.146 mm, respectively), and a flatter K (-0.107 diopter [D] and -0.121 D, respectively). The differences were statistically significant (P<.0001). The mean absolute error in IOL power prediction was 0.455 D +/- 0.32 (SD) with the OLCR unit and 0.461 +/- 0.31 D with the PCI unit (P>.1). Measurements were comparable between the OLCR device and the PCI device. A slight decrease (0.050) in the a(0) constant is recommended if the Haigis formula is used.

Estimation of the effective lens position using a rotating Scheimpflug camera

To describe a no-history method of estimating the effective lens position (ELP) for double-K intraocular lens (IOL) power calculation in eyes that had previous refractive surgery. Departments of Ophthalmology, Taipei Medical University Hospital and Taipei City Hospital, Taipei, Taiwan. The corneal height (H(m)) and anterior chamber diameter (AG(m)) in 106 unoperated eyes were measured using a rotating Scheimpflug camera. The theoretical anterior corneal radius (R(rt)) was then derived from H(m) and AG(m) by regression and rearrangement of the Fyodorov equation. The ELP estimate was then calculated from R(rt). The performance of this ELP estimation method in double-K IOL power calculation and the performance of other methods were compared retrospectively in 11 eyes having cataract surgery that had previous refractive surgery. The refractive results 9 to 12 weeks after cataract surgery were selected for data analysis. The new ELP estimation method, combined with the BESSt formula or the Savini et al. method for estimating post refractive-surgery corneal power (K(post)) in the double-K SRK/T formula, provided the best IOL power prediction results. The mean arithmetic and absolute IOL prediction errors were -0.05+/-0.62 diopters (D) and 0.49+/-0.34 D, respectively, when combined with the BESSt formula and 0.03+/-0.73 D and 0.60+/-0.36 D, respectively, when combined with the Savini et al. method. With either combination, all 11 eyes were within+/-1.00 D of the refractive prediction error. This ELP estimation method may be helpful for IOL power calculation in post refractive-surgery eyes when historical data are unavailable.

Intraocular Lens Power Calculation After Automated Lamellar Keratoplasty for High Myopia

To report intraocular lens (IOL) power calculation in 2 eyes that were highly undercorrected by previous myopic automated lamellar keratoplasty (ALK). A 35-year-old man underwent bilateral myopic ALK, which caused high residual myopia (-9.0 -4.0 x 171 and -9.5 -4.5 x 74). The patient then underwent cataract surgery with IOL implantation for cataract development. The double-K clinical history method was utilized, and satisfactory IOL power prediction results were obtained. Two no-history IOL power calculation methods (Rosa correcting factor method and Ferrara theoretical variable refractive index method), which involved axial length-dependent modification of the keratometer-measured corneal radius, and 1 no-history IOL power calculation method (Shammas' method), which involved axial length-independent modification of the keratometer-measured corneal power, were tested on these 2 eyes. In both eyes, the double-K SRK-T clinical history method gave small IOL prediction errors (-0.66 and -0.81 D). The Shammas' no-history method gave a slightly higher IOL prediction error in the right eye (-1.67 D) and a small IOL prediction error in the left eye (-0.74 D). Unacceptable IOL power prediction errors would have resulted if Rosa's correcting factor method (-8.07 and -8.35 D) or Ferrara's theoretical variable refractive index method (-17.56 and -18.51 D) had been applied. When we utilized Rosa's method for the IOL power calculation by assuming that the previous ALK had fully corrected the refractive error, the predicted IOL powers were very close to the benchmark IOL powers (IOL power prediction errors: 1.16 and 0.37 D). When we utilized Ferrara's method with the same assumption, the IOL power prediction errors remained high (-6.32 and -7.16 D). For patients who have had previous myopic ALK (and whose eyes are highly undercorrected) and who require cataract surgery and for whom the pre-ALK history is available, the double-K method appears to yield excellent predictive results. However, if the pre-ALK history is not available, the Shammas' no-history method appears to yield better results than the Rosa's or the Ferrara's method. High undercorrection by the previous ALK might have been one of the major reasons why Rosa's method resulted in a high IOL prediction error in these 2 eyes. The cause for the marked IOL prediction error by Ferrara's method in this case, however, remains to be determined.

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

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. Private practice, Lynwood, California, USA. 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). 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). The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.

Improved accuracy of intraocular lens power calculation with the Zeiss IOLMaster

This study aimed to demonstrate how the level of accuracy in intraocular lens (IOL) power calculation can be improved with optical biometry using partial optical coherence interferometry (PCI) (Zeiss IOLMaster) and current anterior chamber depth (ACD) prediction algorithms. Intraocular lens power in 461 consecutive cataract operations was calculated using both PCI and ultrasound and the accuracy of the results of each technique were compared. To illustrate the importance of ACD prediction per se, predictions were calculated using both a recently published 5-variable method and the Haigis 2-variable method and the results compared. All calculations were optimized in retrospect to account for systematic errors, including IOL constants and other off-set errors. The average absolute IOL prediction error (observed minus expected refraction) was 0.65 dioptres with ultrasound and 0.43 D with PCI using the 5-variable ACD prediction method (p < 0.00001). The number of predictions within +/- 0.5 D, +/- 1.0 D and +/- 2.0 D of the expected outcome was 62.5%, 92.4% and 99.9% with PCI, compared with 45.5%, 77.3% and 98.4% with ultrasound, respectively (p < 0.00001). The 2-variable ACD method resulted in an average error in PCI predictions of 0.46 D, which was significantly higher than the error in the 5-variable method (p < 0.001). The accuracy of IOL power calculation can be significantly improved using calibrated axial length readings obtained with PCI and modern IOL power calculation formulas incorporating the latest generation ACD prediction algorithms.

Comparison of intraocular lens power calculation methods in eyes that have undergone LASIK

Objective To compare methods of calculating intraocular lens (IOL) power for cataract surgery in eyes that have undergone myopic LASIK. Design Noncomparative case series. Participants Eleven eyes of 8 patients who had previously undergone myopic LASIK (amount of LASIK correction [±standard deviation], −5.50±2.61 diopters [D]; range, −8.78 to −2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs (Alcon Surgical, Inc., Fort Worth, TX) were included (refractive error after cataract surgery, −0.61 ± 0.79 D; range, −2.0 to 1.0 D). Methods We evaluated the accuracy of various combinations of: (1) single-K versus double-K (in which pre-LASIK keratometry is used to estimate effective lens position) versions of the IOL formulas; the Feiz–Mannis method was also evaluated; (2) 4 methods for calculating corneal refractive power (clinical history, contact lens overrefraction, adjusted effective refractive power [EffRP adj], and Maloney methods); and (3) 4 IOL formulas (SRK/T, Hoffer Q, Holladay 1, and Holladay 2). The IOL prediction error was obtained by subtracting the IOL power calculated using various methods from the power of the implanted IOL, and the F test for variances was performed to assess the consistency of the prediction performance by different methods. Main outcome measures Mean arithmetic IOL prediction error, mean absolute IOL prediction error, and variance of the IOL prediction error. Results Compared with double-K formulas, single-K formulas predicted lower IOL powers than the power implanted and would have left patients hyperopic in most cases; the Feiz–Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRP adj were significantly smaller than those for the clinical history method (0.43 D 2 vs. 1.74 D 2, P = 0.018 for Hoffer Q; 0.75 D 2 vs. 2.35 D 2, P = 0.043 for Holladay 1). The Maloney method consistently underestimated the IOL power but had significantly smaller variances (0.19–0.55 D 2) than those for the clinical history method (1.09–2.35 D 2; P<0.015). There were no significant differences among the variances for the 4 formulas when using each corneal power calculation method. Conclusions The most accurate method was the combination of a double-K formula and corneal values derived from EffRP adj. The variances in IOL prediction error were smaller with the Maloney and EffRP adj methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.

The Hoffer Q formula: A comparison of theoretic and regression formulas

A new formula, the Hoffer Q, was developed to predict the pseudophakic anterior chamber depth (ACD) for theoretic intraocular lens (IOL) power formulas. It relies on a personalized ACD, axial length, and corneal curvature. In 180 eyes, the Q formula proved more accurate than those using a constant ACD (P < .0001) and equal (P = .63) to those using the actual postoperative measured ACD (which is not possible clinically). In 450 eyes of one style IOL implanted by one surgeon, the Hoffer Q formula was equal to the Holladay (P =.65) and SRK/T (P =.63) and more accurate than the SRK (P <.0001) and SRK II (P =.004) regression formulas using optimized personalization constants. The Hoffer Q formula may be clinically more accurate than the Holladay and SRK/T formulas in eyes shorter than 22.0 mm. Even the original nonpersonalized constant ACD Hoffer formula compared with SRK I (using the most valid possible optimized personal A-constant) has a better mean absolute error (0.56 versus 0.59) and a significantly better range of IOL prediction error (3.44 diopters [D] versus 7.31 D). The range of error of the Hoffer Q formula (3.59 D) was half that of SRK 1(7.31 D). The highest IOL power errors in the 450 eyes were in the SRK II (3.14 D) and SRK I (6.14 D); the power error was 2.08 D using the Hoffer Q formula. The series using overall personalized ACD was more accurate than using an axial length subgroup personalized ACD in each axial length subgroup. The results strongly support replacing regression formulas with third-generation personalized theoretic formulas and carefully evaluating the Holladay, SRK/T, and Hoffer Q formulas.