Intraocular Lens Power Prediction Research Articles

Can the accuracy of multifocal intraocular lens power calculation be improved to make patients spectacle free?

To optimise intraocular lens (IOL) power calculation techniques for a segmental multifocal IOL, LENTIS™ MPlus(®) (Oculentis GmbH, Berlin, Germany) and assess outcomes. A retrospective consecutive non-randomised case series of patients receiving the MPlus(®) IOL following cataract surgery or clear lens extraction was performed at a privately owned ophthalmic hospital, Midland Eye, Solihull, UK. Analysis was undertaken of 116 eyes, with uncomplicated lens replacement surgery using the LENTIS™ MPlus(®) lenses. Pre-operative biometry data were stratified into short (<22.00 mm) and long axial lengths (ALs) (≥22.00 mm). IOL power predictions were calculated with SRK/T, Holladay I, Hoffer Q, Holladay II and Haigis formulae and compared to the final manifest refraction. These were compared with the OKULIX ray tracing method and the stratification technique suggested by the Royal College of Ophthalmologists (RCOphth). Using SRK/T for long eyes and Hoffer Q for short eyes, 64% achieved postoperative subjective refractions of ≤±0.25 D, 83%≤±0.50 D and 93%≤±0.75 D, with a maximum predictive error of 1.25D. No specific calculation method performed best across all ALs; however for ALs under 22 mm Hoffer Q and Holliday I methods performed best. Excellent but equivalent overall refractive results were found between all biometry methods used in this multifocal IOL study. For eyes with ALs under 22 mm Hoffer Q and Holliday I performed best. Current techniques mean that patients are still likely to need top up glasses for certain situations.

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.

Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis

To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Retrospective data analysis. The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. The study evaluated 25 patients. The mean and range of ERI values determined using post-LASIK data were similar to those determined from pre-LASIK data. Introducing individual or an average ERI in the ray-tracing IOL power calculation procedure resulted in mean IOL power errors that were not significantly different from zero. The ray-tracing procedure that includes an average ERI gave a greater percentage of eyes with an IOL power prediction error within ±0.5 diopter than the Haigis-L (84% versus 52%). For IOL power determination in post-LASIK patients, custom ray tracing including a modified ERI was an accurate procedure that exceeded the current standards for normal eyes.

Comparison of Intraoperative Aberrometry, OCT-Based IOL Formula, Haigis-L, and Masket Formulae for IOL Power Calculation after Laser Vision Correction

To compare the accuracy of intraoperative aberrometry technology and the Fourier-domain optical coherence tomography (OCT)-based intraocular lens (IOL) formula for IOL power calculation in eyes undergoing cataract surgery after previous laser vision correction (LVC) compared with established methods. Retrospective consecutive case series. Patients undergoing cataract surgery with a history of LASIK or photorefractive keratectomy. The IOL power was estimated preoperatively using the IOLMaster 500 (Carl Zeiss Meditec, Dublin, CA) to calculate the Haigis-L and Masket regression formulae (when prior data were available), and the Optovue RTVue (Optovue Inc, Fremont, CA) spectral domain OCT was used to obtain the Fourier-domain OCT-based IOL formula. The Optiwave Refractive Analysis (ORA) System (WaveTec Vision Systems Inc, Aliso Viejo, CA) wavefront aberrometer measured aphakic refractive measurements intraoperatively and calculated the IOL power with a modified vergence formula. Comparative analysis was done for predictive accuracy of IOL power determination using 2 conventional methods and 2 new technologies: the Haigis-L formula, Masket regression formula, ORA intraoperative aberrometry, and Optovue RTVue Fourier-domain OCT-based IOL formula. Patients without historical data (N = 39) were compared using 3 methods (Haigis-L, ORA, and Optovue), and patients with historical data (N = 20) were compared using all methods (Masket regression formula, Haigis-L, ORA, and Optovue). Median absolute error (MedAE), mean absolute error (MAE), and percentage of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 diopters (D) of refractive prediction error. A total of 39 eyes of 29 patients without historical data were analyzed separately from 20 eyes of 20 patients with historical data. In the group without historical data (N = 39), 49% of eyes were within ±0.25 D, 69% to 74% of eyes were within ±0.50 D, 87% to 97% of eyes were within ±0.75 D, and 92% to 97% of eyes were within ±1.00 D of targeted refractive IOL power prediction error. The MedAE was 0.26 D for Haigis-L, 0.29 D for ORA, and 0.28 D for Optovue. The MAE was 0.37 D for Haigis-L, 0.34 D for ORA, and 0.39 D for Optovue. In the group with historical data (N = 20), 35% to 70% of eyes were within ±0.25 D, 60% to 85% of eyes were within ±0.50 D, 80% to 95% of eyes were within ±0.75 D, and 90% to 95% of eyes were within ±1.00 D of targeted refractive IOL power prediction error. The MedAE was 0.21 D for the Masket regression formula, 0.22 D for the Haigis-L formula, 0.25 D for ORA, and 0.39 for Optovue. The MAE was 0.28 D for the Masket regression formula, 0.31 D for the Haigis-L formula, 0.37 D for ORA, and 0.44 D for Optovue. There was no statistically significant difference among the methods. Newer technology to estimate IOL power calculations in eyes after LVC shows promising results when compared with established methods.

Effect of pupil dilation on biometry measurements with partial coherence interferometry and its effect on IOL power formula calculation.

To determine if there are any differences between eye parameters measured by the IOLMaster (Carl Zeiss Meditec AG, Jena, Germany) biometer before and after dilating the pupil. The effect of those changes on intraocular lens (IOL) power calculation is also analyzed. A prospective observational study was carried out including 107 right eyes of 107 patients with cataract and no other ocular morbidity. An IOLMaster baseline measurement included axial length (AL), mean keratometry (K), and anterior chamber depth (ACD) (corneal epithelium to lens). A second measurement was taken 45 minutes after instillation of topical tropicamide and phenylephrine. Biometric variation was analyzed and prediction for IOL power based on the Haigis and the Sanders/Retzlaff/Kraff Theoretical (SRK/T) formulas was calculated for both measurements. The ACD increased significantly after dilation (+0.12 ± 0.12 mm; p&lt;0.01). The AL and K variation was not significant: +0.00 ± 0.02 mm (p = 0.62) and +0.01 ± 0.22 D (p = 0.57), respectively. Pupil dilation did not affect IOL power calculation based on SRK/T formula either targeting emmetropia (-0.02 ± 0.26, p = 0.30) or the lowest myopic residual refraction (-0.03 ± 0.34, p = 0.30). However, using the Haigis formula significantly changed calculations for emmetropia (0.07 ± 0.34, p = 0.03) and for the lowest myopic refraction (0.10 ± 0.40, p = 0.01). Pupil pharmacologic dilation produces a significant increase in ACD when measured by the IOLMaster. This change results in a different IOL power prediction according to the Haigis formula, which calculates the effective lens position taking into account the ACD.

Accuracy of the Refractive Prediction Determined by Multiple Currently Available Intraocular Lens Power Calculation Formulas in Small Eyes

To observe the refractive outcomes of cataract surgery in small adult eyes, and to investigate the accuracy of different intraocular lens (IOL) power prediction formulas. Retrospective interventional case series. We included consecutive small eyes undergoing uneventful phacoemulsification cataract surgery with a single highly powerful IOL (Acrysof SA60AT) implanted in the capsular bag (range of powers+35.0 to+40.0 diopters [D]), at the Cataract Centre for Moorfields Eye Hospital. Exclusion criteria were combined or previous intraocular surgical procedures, and any type of intraoperative complications. Main outcome measures were mean prediction errors with Hoffer Q, Holladay 1, Holladay 2, Haigis, SRK-T, and SRK-II IOL power prediction formulas and proportions of eyes achieving absolute errors within the dioptric ranges of 0.5, 1.0, and 2.0 D of target and emmetropia, respectively. The ANOVA test was used to compare the refractive results among various formulas. Twenty-eight eyes were studied; the mean numerical error was 0.22 ± 1.22 D and the mean absolute error was 0.95 ± 0.78 D with the adopted Hoffer Q formula; 39%, 61%, and 89% of the eyes had a final refraction within 0.5 D, 1.0 D, and 2.0 D of target, respectively. None of the latest-generation formulas significantly outperformed the others (P= .245). The Hoffer Q formula led to good or fair refractive outcomes in less than two thirds of the cases. With Holladay 1 and 2 and Haigis formulas, outcomes would have not been significantly different. The SRK formulas yielded less accurate predictions. Possible reasons are discussed.

Biometry and intraocular lens power calculation results with a new optical biometry device: Comparison with the gold standard

To evaluate the agreement in axial length (AL), keratometry (K), anterior chamber depth (ACD) measurements; intraocular lens (IOL) power calculations; and predictability using a new partial coherence interferometry (PCI) optical biometer (AL-Scan) and a reference (gold standard) PCI optical biometer (IOLMaster 500). Service d'Ophtalmologie, Hopital Bicêtre, APHP Université, Paris, France. Evaluation of a diagnostic device. One eye of consecutive patients scheduled for cataract surgery was measured. Biometry was performed with the new biometer and the reference biometer. Comparisons were performed for AL, average K at 2.4 mm, ACD, IOL power calculations with the Haigis and SRK/T formulas, and postoperative predictability of the devices. A P value less than 0.05 was statistically significant. The study enrolled 50 patients (mean age 72.6 years±4.2 SEM). There was a good correlation between biometers for AL, K, and ACD measurements (r=0.999, r=0.933, and r=0.701, respectively) and between IOL power calculation with the Haigis formula (r=0.972) and the SRK/T formula (r=0.981). The mean absolute error (MAE) in IOL power prediction was 0.42±0.08 diopter (D) with the new biometer and 0.44±0.08 D with the reference biometer. The MAE was 0.20 D with the Haigis formula and 0.19 with the SRK/T formula (P=.36). The new PCI biometer provided valid measurements compared with the current gold standard, indicating that the new device can be used for IOL power calculations for routine cataract surgery. No author has a financial or proprietary interest in any material or method mentioned.

Comparison of intraocular lens power calculation methods after myopic laser refractive surgery without previous refractive surgery data

To compare the accuracy of intraocular lens (IOL) power calculation methods for post-myopic excimer laser surgery patients without previous refractive surgery data using the Holladay IOL Consultant Program and the American Society of Cataract and Refractive Surgery (ASCRS) IOL Power Calculator. Wang Vision Cataract and LASIK Center, Nashville, Tennessee, USA. Case series. Eight methods were used to calculate IOL power: Holladay 2 partial coherence interferometry (PCI)-K, Holladay 2 FlatK, Wang-Koch-Maloney, Shammas No-History, Haigis-L, ASCRS-Average, ASCRS-Min, and ASCRS-Max. The optimum IOL power corresponding to the target refraction was back-calculated using the stable post-cataract surgery refraction and implanted IOL power. Using the optimum IOL power, the predicted IOL power error and the resultant refractive error with each method were calculated and compared. The Holladay 2 FlatK method was most accurate for IOL power calculation, followed by the Holladay 2 PCI-K, ASCRS-Min, Wang-Koch-Maloney, ASCRS-Average, Shammas No-History, Haigis-L, and ASCRS-Max. Statistically significant differences were observed between Holladay 2 FlatK and Holladay 2 PCI-K (P<.05), Wang-Koch-Maloney and ASCRS-Average (P<.05), and Haigis-L and ASCRS-Max (P<.01). No statistically significant differences were observed between the Holladay 2 PCI-K, ASCRS-Min, and Wang-Koch-Maloney or between the ASCRS-Average, Shammas No-History, and Haigis-L (both P>.05). The Holladay 2 FlatK method provided the most accurate IOL power in eyes without previous myopic laser surgery data. If the Holladay IOL Consultant Program is unavailable, the ASCRS methods can be used; the ASCRS-Min represents the most accurate method.

Comparison of IOL Power Calculation Methods and Intraoperative Wavefront Aberrometer in Eyes After Refractive Surgery

To compare preoperative methods for calculating intraocular lens (IOL) power versus the intraoperative wavefront aberrometer in eyes with a history of refractive surgery. A retrospective study of 46 eyes (33 patients) with previous refractive surgery that underwent subsequent cataract surgery was conducted. Suggested IOL power predicted by ORange intraoperative wavefront aberrometer (WaveTec Vision Systems, Inc., Aliso Viejo, CA) was compared to power predicted by the (1) SRK-T formula using keratometry and axial length measurements from the IOLMaster (Carl Zeiss Meditec, Dublin, CA), (2) average central keratometry (Avg K) from corneal topography, and (3) average IOL power predicted by the American Society of Cataract and Refractive Surgery (ASCRS) web site. No historical information was used for the calculations. IOL power required for emmetropia was back-calculated using manifest refraction and implanted IOL power after cataract surgery. Mean age was 60 ± 7.9 years. Fifteen percent had a history of myopic photorefractive keratectomy (n = 7), 57% myopic LASIK (n = 26), 13% hyperopic LASIK (n = 6), and 22% radial keratectomy (RK) (n = 10). In 37% of cases, ORange predicted IOL power to within ±0.50 diopters (D) of emmetropia, compared to 30% for IOLMaster keratometry, 26% for Avg K, and 17% for ASCRS web site. In eyes after myopic treatment, ORange, IOLMaster, Avg K, and ASCRS web site predicted within ±0.50 D of emmetropia in 39%, 27%, 24%, and 18%, respectively, and within ±1.0 D in 60%, 39%, 39%, and 51%, respectively. In eyes after RK, ORange, Avg K, and ASCRS web site predicted to within ±0.50 D of emmetropia in 14% and the IOLMaster in 43% cases. Although the ORange most often predicted to within ±0.5 D of emmetropia, no method was able to achieve this accuracy more than 50% of the time. Predictions for eyes after RK were worse than for other types of refractive procedures.

Effect of Pharmacologic Pupil Dilation on OLCR Optical Biometry Measurements for IOL Predictions

To determine the possible influence of pupil dilation on intraocular lens (IOL) power predictions made using optical biometry with Lenstar LS 900® (Haag-Streit AG, Koeniz, Switzerland). A total of 72 eyes of 72 patients scheduled to undergo cataract surgery were prospectively examined using the optical low-coherence reflectometry (OLCR) optical biometer before and after pupil dilation with tropicamide 1%. The measurements made were axial length, central corneal thickness, anterior chamber depth (ACD), lens thickness, mean keratometry, corneal diameter (CD), and pupil diameter. Holladay II and SRK/T formulas were used to calculate IOL power. Agreement between the 2 measurement modes (with and without dilation) was assessed by calculating intraclass correlation coefficients (ICC) and constructing Bland-Altman plots. The mean age of the patients was 74.71 ± 7.53 years (range 56-90). Among the variables determined, only ACD varied significantly according to pupil dilation (p<0.001). The ICC data revealed excellent intraobserver correlation between measurements made with and without dilation, except for CD. The IOL power predictions were unmodified. The use of pupil dilation does not seem to influence measurements and IOL predictions made using this OLCR optical biometer.

Power prediction for one‐piece and three‐piece intraocular lens implantation after cataract surgery in patients with chronic angle‐closure glaucoma: a prospective, randomized clinical trial

To assess the accuracy of intraocular lens (IOL) power prediction for cataract surgery in chronic angle-closure glaucoma (CACG) patients with different IOLs' implantation. This prospective randomized clinical trial included 45 eyes with CACG and 48 eyes with normal controls undergoing cataract surgery. In the CACG group, 23 eyes (51%) had three-piece IOL implantation and 22 eyes (49%) had one-piece IOL implantation. In the normal control group, 25 eyes (52%) had three-piece IOL implantation and 23 eyes (48%) had one-piece IOL implantation. Using the SRK/T formula, the mean difference between the predicted and actual postoperative spherical equivalent [mean absolute error (MAE)] was obtained and converted to natural logarithm (ln) for statistical analysis. The power of the implanted IOL was calculated to predict postoperative SE using three formulas: SRK II, Holladay II and Hoffer Q by post hoc analysis in each group. The predictive accuracy of each formula was analysed by comparing the lnMAE. In the one-piece IOL group, there was no difference in lnMAE between the CACG and normal control group (p = 0.314). In the three-piece IOL group, the lnMAE of the CACG group was larger than that of the normal control group (p < 0.001). The lnMAEs calculated by the SRK/T formula were more accurate than the Holladay II (p = 0.045) and Hoffer Q (p = 0.042) formula in the CACG one-piece IOL group. Implantation of one-piece IOLs provides similar power prediction accuracy comparable to normal cataract patients; this result may be explained by the IOL haptic configuration or design.

Assessments of total corneal power and intraocular lens power in post-LASIK eyes

To compare the different evaluations of corneal power in post-laser-assisted in situ keratomileusis (LASIK) eyes and assess the accuracy and differences of intraocular lens (IOL) power prediction with corneal powers through different calculation methods. For this prospective study, 71 eyes of 39 candidates undergoing LASIK and 3 months later returning for reexamination were included. All subjects were divided into 2 groups according to the axial length: Group A (23.46 - 25.97 mm) 44 eyes, Group B (26.00 - 28.52 mm) 27 eyes. The ranges of spherical equivalents were -1.75 - -9.50 D with an average of (-4.82 ± 1.98) D. Subjective refraction and Pentacam Scheimpflug analyzer were performed at pre-operation and subjective refraction, IOLMaster and Galilei II dual Scheimpflug analyzer at over 3 months post-operation. The following values were obtained: SimK by Galilei II dual Scheimpflug analyzer, Kn calculated with Gaussion thick lens formula, Kray with ray tracing method, Kchm calculated with clinical history method and Km by IOLMaster. Repeated measures analysis of variance analyze the differences between SimK, Kn, Kray, Km and Kchm. Repeated measurement analysis of variance was employed to analyze the differences between SimK, Kn, Kray, Km combining intraocular lens power formula and Kchm combining intraocular lens power formula. Pearson's analysis was performed to analyze the correlations between SimK, Kn, Kray, Km and Kchm. Those combining with formulas for IOL power calculations were also analyzed. P < 0.05 indicated statistical significance. The values of SimK, Kn, Kray, Km and Kchm were (39.02 ± 1.8), (37.8 ± 1.51), (36.8 ± 1.84), (39.18 ± 1.75) and (38.55 ± 1.83) D respectively. The differences between SimK, Kn, Kray, Km and Kchm had statistical significances (P < 0.01). High correlations existed between SimK, Kn, Kray, Km and Kchm (r > 0.9, P < 0.01). In the same IOL formula, Kray had the highest IOL power value, Kn followed, Kchm the third, SimK and Km the smallest. Among the IOL formulas, Haigis-L and Haigis predicted the highest IOL power, HofferQ followed, Holladay the third and SRK/T the smallest. Kn/Kray combining with Haigis formula may be a new and effective method for predicting the IOL power in post-LASIK eyes.

Effect of corneal aberrations on intraocular lens power calculations

To use ray tracing to determine the influence of corneal aberrations on the prediction of the optimum intraocular lens (IOL) power for implantation in normal eyes and eyes with previous laser in situ keratomileusis (LASIK). Hospital Universitario Virgen de la Arrixaca, Murcia, Spain. Case series. The optimum IOL power was calculated by ray tracing using a patient-customized eye model in cataract surgery cases. The calculation can be performed with or without inclusion of the patient's corneal aberrations. Standard predictions were also generated using current state-of-the-art IOL power calculation techniques. The results for all predictions were compared with the optimum IOL power after cataract surgery. For patients without previous LASIK (n = 18), the standard approaches and the ray-tracing procedure gave a similar mean absolute residual error and variance. The incorporation of corneal aberrations did not improve the accuracy of the ray-tracing prediction in these cases. For post-LASIK patients (n = 10), the ray-tracing prediction incorporating corneal aberrations generated the most accurate results. The difference between the prediction with and without considering corneal aberrations correlated with the amount of corneal spherical aberration (r(2) = 0.82), resulting in a difference of up to 3.00 diopters in IOL power in some cases. Ray tracing using patient-customized eye models was a robust procedure for IOL power calculation. The incorporation of corneal aberrations is crucial in post-LASIK eyes, primarily because of the elevated corneal spherical aberration. Mrs. Canovas and Dr. Artal hold a provisional patent application on the ray-tracing procedure. Mrs. Canovas is an employee of Abbott Medical Optics Groningen B.V. No other author has a financial or proprietary interest in any material or method mentioned.

Comparison of intraocular lens power prediction using immersion ultrasound and optical biometry with and without formula optimization

Comparison of postoperative refraction results using ultrasound biometry with closed immersion shell and optical biometry. Three hundred and sixty-four eyes of 306 patients (age: 70.6 ± 12.8 years) underwent cataract surgery where intraocular lenses calculated by SRK/T formula were implanted. In 159 cases immersion ultrasonic biometry, in 205 eyes optical biometry was used. Differences between predicted and actual postoperative refractions were calculated both prior to and after optimization with the SRK/T formula, after which we analysed the similar data in the case of Holladay, Haigis, and Hoffer-Q formulas. Mean absolute error (MAE) and the percentage rate of patients within ±0.5 and ±1.0 D difference in the predicted error were calculated with these four formulas. MAE was 0.5-0.7 D in cases of both methods with SRK/T, Holladay, and Hoffer-Q formula, but higher with Haigis formula. With no optimization, 60-65 % of the patients were under 0.5 D error in the immersion group (except for Haigis formula). Using the optical method, this value was slightly higher (62-67 %), however, in this case, Haigis formula also did not perform so well (45 %). Refraction results significantly improved with Holladay, Hoffer-Q, and Haigis formulas in both groups. The rate of patients under 0.5 D error increased to 65 % by the immersion technique, and up to 80 % by the optical one. According to our results, optical biometry offers only slightly better outcomes compared to those of immersion shell with no optimized formulas. However, in case of new generation formulas with both methods, the optimization of IOL-constants give significantly better results.

Predictability of intraocular lens power calculations based on formulas on the ASCRS website after myopic laser refractive surgery

PurposeThis work was conducted in order to study the intraocular lens (IOL) power predictability of formulas provided by the American Society of Cataract and Refractive Surgery (ASCRS) website for patients who had undergone myopic laser refractive surgery. MethodsIn this retrospective study, we analyzed 11 eyes (from nine patients) that had previously undergone myopic laser-assisted in situ keratomileusis or photorefractive keratectomy and experienced subsequent phacoemulsification and posterior-chamber IOL implantation. Using the adjusted central K (keratometry), axial length, and the SRK/T formula, we compared the original desired refraction to the manifest refraction 1 month after cataract surgery. According to the postoperative manifest refraction, we compared the IOL power calculated using the different methods on the ASCRS website. ResultsBefore cataract surgery, the mean adjusted central K reading was 35.90 diopters (D) (range 29.24–41.58 D), and the mean axial length was 28.53 mm (range 25.77–32.79 mm). Postoperatively, the mean arithmetic refractive prediction error was 0.50 D (range −1.72 D to 2.33 D), and the mean absolute error was 1.07 D (range 0.01–2.33 D). The most reliable method was the Masket method in combination with the double K Holladay I formula. The predictability of the adjusted central K method and the Masket method in combination with the single-K SRK/T formula was as precise as that of the modified Masket method in combination with the double K Holladay I formula and the Shammas method in combination with the Shammas-PL formula. ConclusionASCRS offers the use of a postrefractive IOL calculator online, free of charge. The Masket method in combination with the double K Holladay I formula is the best choice for IOL power prediction after laser-assisted in situ keratomileusis or photorefractive keratectomy surgery. The adjusted central K method is a convenient and effective strategy with which to correct central corneal power. However, double K formulas designed for adjusted central K should be used for more accurate predictions of lens position.

Clinically relevant biometry

Obtaining precise postoperative target refraction is of utmost importance in today's modern cataract and refractive surgery. Given the growing number of patients undergoing premium intraocular lens (IOL) implantations, patient expectation continues to rise. In order to meet heightened patient expectations, it is crucial to pay utmost attention to patient selection, accurate keratometry and biometry readings, as well as to the application of correct IOL power formula with optimized lens constants. This article reviews recent advances in the field of clinical biometry and IOL power calculations. Recently developed low-coherence reflectometry optical biometry is comparable to older ultrasonic biometric and keratometric techniques. In addition, the new IOLMaster software upgrade has improved reproducibility and enhanced signal acquisition. Further, the modern lens power formulas currently determine the effective lens position and the shape of the intraocular lens power prediction curve more accurately. In order to reach target refraction, precise biometric measurements are imperative. Understanding the strengths and limitations of the currently available biometry devices allows prevention of high variability and inaccuracy, ultimately determining the refractive outcomes.

Improved Refractive Outcome for Ciliary Sulcus-Implanted Intraocular Lenses

To investigate the ideal correction of intraocular lens (IOL) power for sulcus implantation. Retrospective, comparative case series. The records of 679 patients undergoing cataract surgery from June 2007 to June 2008 were reviewed. Eyes in this series underwent phacoemulsification and IOL implantation with local anesthesia. Patients in our study population had their IOL power reduced by 0.5 or 1 diopter (D) from that calculated by the SRK-T formula for in-the-bag implantation. The IOL implanted was the foldable 3-piece acrylic Acrysof MA60AC (Alcon Laboratories Inc., Fort Worth, TX). In each case, the difference between actual spherical equivalent (SE) refraction and that predicted by biometry using the SRK-T formula was calculated. Posterior capsule tears requiring implantation of IOL in the ciliary sulcus occurred in 36 eyes. When comparing eyes in which the power was reduced by 0.5 D with those in which the reduction was 1.0 D, those with a power reduction of 1.0 D had significantly less unexpected error (0.49 vs. 1.01 D SE). After stratifying eyes by axial length (AL), we found higher unexpected refractive error in short eyes (<22 mm AL). Likewise, eyes with a predicted IOL power >25 D had a greater postoperative refractive error. This is the first comparative clinical review examining adjustment of power of the sulcus-implanted IOL. We found that the IOL power should be adjusted according to the measured AL and predicted IOL power. For patients with a predicted IOL power from 18 to 25 D, power should be reduced by at least 1 D; for lenses >25 D, power should be reduced by 1.5 to 2 D.

Secondary in-the-Bag Implantation of Intraocular Lenses in Aphakic Eyes after Vitreoretinal Surgeries

Background/Aims: To report the accuracy of intraocular lens (IOL) power calculations and refractive outcomes in aphakic eyes after secondary in-the-bag IOL implantation. Method: We retrospectively reviewed a consecutive case series of secondary in-the-bag IOL implantations in aphakic patients with intact capsular bag without severe capsular fibrosis between October 2006 and October 2010. Single-piece foldable lenses were secondarily implanted in 21 eyes of 20 patients. Postoperative best-corrected visual acuity (BCVA) and refraction were measured approximately 1 month after surgery. The accuracy of IOL power prediction was evaluated using the mean error (ME) and mean absolute error (MAE). Results: Successful in-the-bag IOL implantation without capsular tear or defect was achieved in all eyes. The mean interval between phacoemulsification and IOL implantation was 5.4 months (range, 1.5–19 months). The ME was +0.06 dpt and the MAE was +0.24 dpt. The BCVA significantly improved from 0.66 logMAR at the pre-IOL implantation examination to 0.38 logMAR at the postoperative examination (p < 0.0001). Conclusions: The postoperative refractive results are comparable with those of routine cataract surgery. Among the selected aphakic patients who underwent simultaneous phacoemulsification and vitreoretinal surgery, successful in-the-bag IOL implantation and satisfactory refraction were achieved after secondary IOL implantation.

Comparison of aphakic refraction formulas for secondary in-the-bag intraocular lens power estimation in children

Intraocular lens (IOL) formulas based on aphakic refraction alone have been proposed as an alternative to biometry-based formulas. The purpose of this study was to determine the relative accuracy of these simplified formulas. Records of patients who received secondary in-the-bag (IOL) implants and for whom aphakic refraction was obtainable were retrospectively studied. The formulas for IOL power calculation by Hug (J Pediatr Ophthalmol Strabismus 2004;41;209-11) and Khan and by AlGaeed (Br J Ophthalmol 2006;90:1458-60; modified to account for greater K values in our population) were compared with the biometry-based Holladay 1 formula by calculating the absolute prediction error for each. Twenty eyes met the inclusion criteria. The average age at IOL implantation was 4.8 ± 3.4 years. The mean of the absolute value of the prediction error when we used the Hug's formula was 2.4 ± 2.1 D; with Khan's formula, 2.4 ± 2.0 D; and with biometry, 1.6 ± 1.4 D. None of these differences was statistically significant (paired t test: Hug vs Khan, P = 0.9; biometry vs Hug, P = 0.3; biometry vs Khan, P = 0.2). The absolute prediction error was more than 2 D in 8 of 20 eyes (40%) when we used Hug's formula, 11 of 20 eyes (55%) with Khan's formula, and 5 of 20 eyes (25%) with biometry. Although the 0.8 D reduction in accuracy of the refraction-based formulas was not statistically significant, we recommend continued use of biometry-based formulas for IOL power calculation. Aphakic refraction may be used to confirm IOL power prediction when biometry is difficult.

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.