Accuracy Of Intraocular Lens Power Calculation Research Articles

Comparison of Intraocular Lens Power Estimation by Optical Biometry and Ultrasound Biometry in Cataract Surgery

Introduction: The evolution of modern technologies for cataract surgery has made it crucial for aiming emmetropia with highly defined vision. The key factor responsible for postoperative emmetropia is an accurate biometry, along with various other factors. Ultrasonic biometry is the gold standard method of Intraocular Lens (IOL) power calculation but the corneal indentation with the probe underestimate the axial length and result in a myopic shift which is overcome by the newer optical biometry devices, including swept source optical coherence biometry which uses infrared light to measure the ocular distances. Aim: To determine the precision and accuracy of IOL power calculation by ultrasound A-scan and optical IOL master and their refractive outcomes. Materials and Methods: This prospective, and observational study was conducted between September 2019 to February 2021 in 155 patients with cataract undergoing phacoemulsification in Kalinga Institute of Medical Sciences, KIIT University, Bhubaneswar, Odisha, India. All subjects underwent comprehensive ocular examination and biometry with two formulae {Sanders-RetzlaffKraff (SRK) and Holladay-I}. Biometry included corneal curvature (keratometry), axial length, anterior chamber depth, IOL power calculation, predicted refractive error. There were two broad groups. One group underwent biometry by ultrasound A-scan and the other group underwent optical biometry by IOL Master 700. The IOL power was calculated with the two formulae in both the groups. Comparisons between variables measured using the IOL master and A-scan were done using paired t-test. The p-values <0.05 were considered statistically significant. Results: In a 18 month period, 155 eyes were consecutively enrolled in the study. The mean age of all enrolled patients was 62.1±8.65 years (range 34-80 years) with male:female ratio of approximately 1.25:1. The mean axial length measured by IOL master was higher (23.15 ± 0.85) than that by A-scan (22.96±0.81 diopters) with a mean difference of 0.197±0.35 mm (p-value <0.001, paired t-test). The mean predicted IOL power was 20.81±1.84 diopters by IOL master and 21.13±1.62 by A-scan by SRK-II formula (p-value <0.001). While mean predicted IOL power with Holladay-I by IOL Master 700 was 20.61±1.92 and 21.44±1.98 diopters by A-scan with a mean difference (-0.82±0.76 diopters) with a significant p-value <0.001. Bland-Altman analysis plots showed almost perfect agreement between both methods regarding predicted IOL power. Conclusion: The swept source Optical Coherence Tomography (OCT) based IOL master 700 proved to be a faster non contact device to use with a shorter learning curve, higher accuracy in average axial length eye and less refractive surprises.

Intraocular lens power calculations in eyes with previous corneal refractive surgery: Challenges, approaches, and outcomes.

In eyes with previous corneal refractive surgery, difficulties in accurately determining corneal refractive power and in predicting the effective lens position create challenges in intraocular lens (IOL) power calculations. There are three categories of methods proposed based on the use of historical data acquired prior to the corneal refractive surgery. The American Society of Cataract and Refractive Surgery postrefractive IOL calculator incorporates many commonly used methods. Accuracy of refractive prediction errors within ± 0.5 D is achieved in 0% to 85% of eyes with previous myopic LASIK/photorefractive keratectomy (PRK), 38.1% to 71.9% of eyes with prior hyperopic LASIK/PRK, and 29% to 87.5% of eyes with previous radial keratotomy. IOLs with negative spherical aberration (SA) may reduce the positive corneal SA induced by myopic correction, and IOLs with zero SA best match corneal SA in eyes with prior hyperopic correction. Toric, extended-depth-of-focus, and multifocal IOLs may provide excellent outcomes in selected cases that meet certain corneal topographic criteria. Further advances are needed to improve the accuracy of IOL power calculation in eyes with previous corneal refractive surgery.

Нюансы предоперационной подготовки пациентов перед экстракцией катаракты. Что мы упускаем из виду при проведении биометрии, расчете ИОЛ и оценке состояния глаза?

Modern cataract surgery is increasingly regarded as a refractive procedure. The focus has shifted from practicing and refining surgical steps towards personalized intraocular lens (IOL) choice based on the eye parameters of each individual. The best possible refractive outcome is now the priority. All components of biometry contribute to IOL power calculation accuracy. Therefore, any errors, a method of evaluating each parameter, and a technician’s experience are important. In addition, refraction, macular disorders, and prior surgical procedures affect IOL choice, preoperative care, and the extent of surgery. Moreover, subsequent changes in the IOL position that results in refractive errors after cataract surgery (this depends on the formula for IOL power calculation) should also be considered. The accuracy of IOL power calculation is affected by the inaccuracy of current biometry techniques and postoperative changes of the globe. Personalization of theoretical formulas provides better accuracy of IOL power calculations to meet modern trends in intraocular correction. Supplements containing macular pigments prevent macular degeneration and protect the macular zone. Keywords: cataract, refraction, cataract surgery, biometry, IOL power calculation, IOL power calculation formulas, retina, age-related macular degeneration. For citation: Movsisyan A.B., Egorov A.E. Nuances of preoperative care before cataract extraction. What do we overlook when performing biometry, calculating IOL power, and examining the eye? Russian Journal of Clinical Ophthalmology. 2021;21(3):159–163 (in Russ.). DOI: 10.32364/2311-7729-2021-21-3-159-163.

Comparison of Aphakic Refraction and Biometry-Based Formulae for Secondary In-The-Bag and Sulcus-Implanted Intraocular Lens Power Estimation in Children

Purpose: The aim of the study was to compare the accuracy of refractive outcomes in children undergoing secondary in-the-bag or cilliary sulcus intraocular lens (IOL) implantation, using aphakic refraction (AR)-based formulae (Hug and Khan) and biometry-based formulae (Holladay 1, Hoffer Q, SRK/T, and SRK II). Methods: In this retrospective study, a total of 65 eyes of 44 patients who underwent secondary in-the-bag or cilliary sulcus IOL implantation were included and divided into 2 groups: 39 eyes of the in-the-bag IOL group and the other 26 eyes of the sulcus-implanted IOL group. Holladay 1, Hoffer Q, SRK/T, and SRK II formulae were employed depending on the biometric data, while Hug and Khan formulae were used based on preoperative AR. The prediction error (PE) and the absolute value of predicted error (APE) were compared between the 2 groups and formulae. Results: In the in-the-bag IOL group, nonsignificant differences of APE were found among the 6 formulae, while the Holladay 1, Hoffer Q, SRK/T, and SRK II all demonstrated a significant hyperopic shift of median PE value compared to the Hug formula (p < 0.05, all), and Holladay 1 and SRK II also showed a significant hyperopic shift of PE compared to the Khan formula (p < 0.05, both). Higher percentages of eyes with PE <1 D were found using Hoffer Q and SRK/T. In the sulcus-implanted group, the Holladay 1, Hoffer Q, and SRK/T had a significantly smaller median value of APE than the Hug and Khan formulae (p < 0.05, all), and the SRK II had a significantly smaller median value of APE than the Hug formula (p < 0.05), while Holladay 1 had the lowest value of APE. Higher percentages of eyes within PE <1 D were found using Holladay 1, Hoffer Q, and SRK/T, while the highest one was SRK/T. Significantly larger hyperopic shifts of median PE value using all the 6 formulae were found in eyes with sulcus-implanted IOL than eyes with in-the-bag implanted IOL (p < 0.05, all). In the eyes of with in-the-bag implanted IOL, the Hug and Khan formulae had significantly smaller APE values when compared with the eyes with sulcus-implanted IOL (p < 0.05, both). Conclusions: Whether IOL was in the bag or implanted in the sulcus, almost all the formulae showed hyperopic shift, SRK/T showed the best accuracy. Biometry-based formulae were superior to AR-based formulae in accuracy of IOL power calculation, especially when IOL was implanted in the sulcus. In-the-bag IOL implantation should always be with higher priorities, especially when using AR-based formulae in IOL power calculation.

Update on Intraocular Lens Power Calculation Study Protocols: The Better Way to Design and Report Clinical Trials

It was almost 40 years ago when one of the authors (K.J.H.) published an organized system to quantify the accuracy of intraocular lens (IOL) power calculation formulas, methods, and instruments. At the behest of the editor of the American Journal of Ophthalmology, the IOL Power Club (along with a statistician) published an editorial in 2015 modernizing and quantifying the proper protocols for these studies. Over the past decade, so many new optical biometers, formulas, and methods (whose accuracies have yet to be completely tested) have been introduced that we were asked to modernize and update these guidelines yet again to help others design and report correctly the results of clinical studies on IOL power calculation and biometry for 2020. We evaluated guidelines to enroll patients, including visual acuity minimums, exclusion of bilateral eyes, sample size issues, demographics (age, gender, and ethnicity), and whether such studies should not be performed using the same data that were used to develop the formula being tested. We showed the absolute need for constant optimization, which formulas should be tested for comparison, refraction measurement (testing distance), as well as the analysis of the prediction error (median and mean absolute errors; standard deviation; range of errors; percentage of eyes with a prediction within ±0.25 diopter [D], ±0.50 D, ±0.75 D, and ±1.00 D; and interquartile displays) and statistical methods of analyses. We present methods of ranking formula accuracy, including the new Haigis IOL Formula Performance Index. We also point out the issues of who programmed the formulas being tested, that all formulas used in the study must be referenced, and the software version number of all instruments used in the study should be stated clearly. The definition of anterior chamber depth should be stated as measured from the corneal epithelium to the lens. We hope that these recommendations will help researchers to improve the validity and accuracy of their studies with the ultimate goal to improve the accuracy of IOL power calculation.

Refractive outcomes and accuracy of IOL power calculation with the SRK/T formula for sutured, scleral-fixated Akreos AO60 intraocular lenses.

Scleral fixation of intraocular lenses has become a popular procedure for treating aphakia in the absence of capsular support. However, the lens formulas used to predict refractive outcomes were designed for in-the-bag lens placement. This study evaluates the accuracy of the SRK/T formula in predicting a target postoperative refraction when suturing a scleral-fixated intraocular lens (IOL) implant 3mm posterior to the limbus. This is a retrospective, case series including 20 eyes of 20 patients who underwent scleral fixation of Akreos AO60 IOLs (Bausch & Lomb, Rochester, NY) by a single surgeon at the OSU Wexner Medical Center. Preoperative measurements were performed with optical biometry, and IOL power was calculated with the SRK/T formula. Following surgery, the actual refractive spherical equivalent (SE) was performed and compared with the preoperative prediction. Prediction error (PE), defined as the deviation of actual postoperative SE refraction in diopters (D) from preoperative predicted SE refraction, was the primary outcome measure. The mean attempted (predicted) SE was - 1.12 D (± 0.87). Mean achieved SE was - 0.96 D (± 1.04). Mean PE (actual postoperative SE versus predicted preoperative SE) was 0.16 D (± 0.69). A total of 9 eyes (45%) were within ± 0.5 D of the predicted SE, 16 eyes (80%) were within ± 1.0 D, and all 20 eyes (100%) were within ± 1.5 D. IOL power calculation using the SRK/T formula with optical biometry demonstrates reliable postoperative refractive outcomes in patients undergoing scleral fixation of an IOL (Akreos AO60). Further studies are needed to refine the predictive value of the SRK/T and other formulas for application in scleral fixation of IOLs.

Ratio of Axial Length to Corneal Radius in Japanese Patients and Accuracy of Intraocular Lens Power Calculation Based on Biometric Data

To evaluate the features of the axial length-to-corneal radius (AL/CR) ratio in Japanese patients with cataracts and to determine the accuracy of intraocular lens (IOL) power calculation formulas according to the AL/CR features and the axial length (AL). Retrospective observational case series. Setting was a clinical practice. Patient population was a total of 1,135 eyes (1,135 patients) with cataracts. Observation procedures included measurement of the AL and corenal radius (CR) by optical biometry and evaluation of the refractive outcomes by using the SRK/T, Holladay 1, Hoffer Q, Haigis, and Barrett Universal II formulas. Main outcome measurements were the features of the AL/CR ratio and the accuracy of IOL power calculations based on the AL/CR ratio and the AL. The mean AL/CR ratio was 3.15 ± 0.19. Significant weak negative correlations were observed between the spherical equivalent (SE) and AL (r=-0.7489; P < .001) and between the SE and AL/CR ratio (r=-0.8069; P < .001); no correlation was found between the SE and CR (r= 0.0208, P= .483). For medium ALs and high AL/CR ratios, the SRK/T formula performed less accurately. For long ALs and high AL/CR ratios, the Holladay 1 and Hoffer Q formulas performed less accurately. The Barrett Universal II formula performed well across a range of ALs and AL/CR ratios. The AL/CR ratio explained the total variation in the SE better than the AL alone. Surgeons should pay attention to the selection of IOL power calculation formulas in eyes with high AL/CR ratios.

Accuracy of Refractive Outcome Using Optical Low Coherence Reflectometry in Silicone Oil-Filled Eyes Undergoing Intraocular Lens Implantation with Silicone Oil Removal

Aim: To assess the accuracy and consistency of intraocular lens (IOL) power calculation using optical low coherence reflectometry device (OLCR), LENSTAR LS-900, in silicone oil-filled eyes undergoing combined IOL implantation and silicone oil removal (SOR). Setting: Sankara Eye Hospital, Bangalore, Karnataka, India. Design: Retrospective study. Method: This study comprised 49 silicone oil-filled eyes of 47 patients who underwent combined IOL implantation with SOR. All patients were measured with OLCR before performing phacoemulsification and IOL implantation in silicone oil mode. The predicted refraction as calculated with OLCR was correlated with the postoperative spherical equivalent. Results: The mean deviation of the spherical equivalent was −0.74 diopters (D). The mean difference between predicted refraction and postoperative spherical equivalent was −0.34 D. The mean axial length of the eyes was 23.53+1.86 (range 21.49–30.03 mm). Conclusion: OLCR is a safe device that provides precise biometry and accurate IOL power calculation in silicone oil-filled eyes.

Calculation of intraocular lens power in surgical treatment of extreme hyperopia

To assess the accuracy of power calculation for IOL used to correct extreme hyperopia and to compare available formulas based on their predictive capacity. Results of 13 implantations involving IOLs of at least 40 Diopters (D) in power were retrospectively evaluated. IOL power was calculated using five formulas: Haigis, Hoffer Q, HolladayI, SRKII, SRK/T. Mean numerical refractive prediction error (RPE) and mean absolute refractive prediction error (ARPE) were calculated. Mean and median ARPE were computed after optimizing the A0 constant. Proportions of eyes within certain RPE limits were compared between the formulas. Mean RPE ranged from 1.43 to 11.71 D before adjustment and from 1.08 to 5.34 D after adjustment (p<0.0001). Haigis formula produced the least RPE, and SRKII - the most. Pairwise comparison by mean ARPE after adjustment revealed no statistically significant difference between Haigis and Hoffer Q formulas. Comparison of formulas by percentage of eyes with minimal RPE identified Haigis and Hoffer Q as the most accurate, while the difference between the two was not statistically significant. The difference between the most accurate formulas (Haigis and Hoffer Q) and the least accurate (SRKII) was statistically significant. In eyes with extremely short anterior-posterior axis, prediction errors in IOL power calculations are relatively frequent (only 31-46% of eyes are within ±0.5 D) and warrant reduction. Among the evaluated formulas, Haigis and Hoffer Q are the most accurate. In order to improve the accuracy of IOL power calculations, it is necessary to employ personalized constants.

Intraocular lens power calculation in 2019: The cutting edge

In today's world, with the developments in technology to measure ocular biometric parameters more accurately and the availability of sophisticated methods for intraocular lens (IOL) power calculation, cataract surgery has become no less than a refractive surgery. This along with free and easy access to information regarding the latest technology has heightened patient expectations. The demand for a spectacle-free life after cataract surgery is higher than ever. Newer advances in optical biometry, including swept-source optical coherence tomography technology, supplemented by the availability of highly accurate IOL power calculation formulae including ones that use artificial intelligence have the potential to enable surgeons to achieve near-perfect outcomes in majority of their patients. To hit the bull's eye as far as target refraction is concerned, it is necessary to understand the benefits and limitations of currently available cutting edge technology and formulae and apply them to the cataract surgery practice.

Refractive outcomes of phacoemulsification after pars plana vitrectomy using traditional and new intraocular lens calculation formulas

To evaluate refractive outcomes of cataract surgery in previously vitrectomized eyes and compare the accuracy of intraocular lens (IOL) calculation formulas in this population. Stony Brook University Hospital, Stony Brook, New York, USA. Retrospective case series. All electronic medical records of patients who had phacoemulsification from 2013 to 2017 were reviewed. Patients who had previously had pars plana vitrectomy in the same eye were selected. Patients with a history of refractive surgery, silicone oil in the eye, or other factors preventing accurate IOL power calculation were excluded. The mean postoperative spherical equivalent was -0.16 diopter (D)±0.81 (SD) (n=61). The mean prediction errors were 0.30±0.82 D, -0.09±0.76 D, 0.23±0.76 D, 0.25±0.81 D, 0.04±0.85 D, 0.30±0.82 D, 0.33±0.79 D, and 0.45±0.80D with the Holladay 1, Wang/Koch (WKA) adjusted Holladay 1 (n=14), Holladay 2 (n=48), SRK/T, WKA SRK/T (n=14), Hill-Radial Basis Function (n=50), and Ladas formulas, respectively. The formula with the highest percentage of predictions within ±0.50 D of the postoperative outcome was the Holladay 2 (60.42%). Statistically significant differences between the predicted and actual refractive outcomes were found with all formulas (P<.05) except the WKA Holladay and WKA SRK/T. Intraclass correlation showed low repeatability (<0.50) for all formulas. Refractive outcomes after cataract extraction in vitrectomized patients can be variable and more hyperopic than the predicted outcomes using traditional and newer IOL calculation methods. Thus, predicting refractive outcomes in this population is challenging, and patients should be counseled accordingly.

Intraocular lens power calculation using a Placido disk–Scheimpflug tomographer in eyes that had previous myopic corneal excimer laser surgery

To assess the accuracy of different methods to calculate the intraocular lens (IOL) power from measurements obtained with an optical biometer combined with a Placido disk-Scheimpflug tomographer (Galilei G6) in eyes that had previous myopic excimer laser surgery. G.B. Bietti Foundation, Rome, Italy. Prospective case series. When prerefractive surgery data were available, the following methods were evaluated: the Barrett True-K, total corneal power 1 (TCP 1) with double-K SRK/T, TCP with double-K Holladay 1, as well as the Masket and Savini methods. In all eyes, these "no-history" methods were studied: Barrett True-K No-History, TCP 1 using the American Society of Cataract and Refractive Surgery calculator, a ray-tracing program, and the Shammas No-History formula. In eyes with historical data (n=15), the Masket method, Savini method, and TCP 1 with double-K SRK/T produced the highest percentage of cases with an absolute prediction error in refraction of 0.50 diopters (D) or less and the lowest median absolute error (0.32 D, 0.28 D, and 0.25 D, respectively). In the whole cohort (N=22), the most accurate no-history method was paraxial ray tracing, which had the highest percentage of eyes with an absolute prediction error of 0.50 D or less and the lowest median absolute error of 0.31 D. Different solutions can provide accurate IOL power calculations when using the measurements obtained with the optical biometer combined with a Placido-dual Scheimpflug tomographer.

Multifocal Intraocular Lenses Clinical Assessment. Patient Selection for Multifocal Intraocular Correction

There are some multufocal intraocular corrections particular qualities compared to monofocal correction. Therefore, the patient’s careful selection, detail preoperative diagnosis, accurate intraocular lens power calculation are necessary to get the optimal clinical results. There are some disadvantages in the postoperative period, such as the contrast sensitivities reduction, dysphotopsia, neuroadaptation. In addition multifocal IOLs are expensive. The clinical studies include evaluating of visual acuity for different distances, defocus curve, spectacle independence, contrast sensitivity, aberrometry data. Additionally, complications after multifocal IOLs implantation and the reasons of explantation are analyzed. This review includes 36 articles (34 clinical studies and 2 meta-analysis) of the following aspects of multifocal intraocular correction: contrast sensitivity, aberrometry analysis, pupil influence on the visual outcomes, postoperative complications, analysis of explantation reasons, preoperative patient’s selection for multifocal correction.

Sustained accuracy improvement in intraocular lens power calculation with the application of quality control circle

Accurate intraocular lens (IOL) power calculation is always a challenge in ophthalmology, and unoptimized process may lead to inaccurate refractive outcomes. Quality control circle (QCC) has shown its success in many fields as a process management tool. However, its efficacy in ophthalmology remains unclear. Here we utilized the QCC method to optimize the process and evaluate its efficacy in improving the accuracy of IOL power calculation. After the QCC application, the percentage of eyes with achieved refractive outcomes within 0.5 diopter significantly increased from 63.2% to 80.8% calculated by Haigis formula and 59.2% to 75.8% by SRK/T formula in patients with normal axial length (AL) (22 mm ≤ AL < 26 mm). Although there were no statistically significant differences in patients with long AL by the two formulas (p = 0.886 and 0.726), we achieved an accuracy of 75% with the application of the PhacoOptics software, which was significantly higher than that using the other two formulas (p < 0.001). Our findings indicated that QCC optimized and standardized the process of IOL power calculation, thus improved the accuracy of IOL power calculation in patients who underwent cataract surgery.

Predicting the refractive outcome and accuracy of IOL power calculation after phacoemulsification using the SRK/T formula with ultrasound biometry in medium axial lengths.

PurposeTo evaluate the accuracy of the SRK/T formula using ultrasound (US) biometry in predicting a target postoperative refraction of ±1.00D in eyes with medium axial length (AL) that underwent phacoemulsification.MethodsThe present study was a retrospective analysis, which included 538 eyes with an AL from 22.0 to 24.60 mm that underwent phacoemulsification and foldable intraocular lens (IOL) implantation (six different IOLs) in the bag. Preoperative AL was measured by US biometry and IOL power (IOLp) was calculated with the SRK/T formula. Patients had a complete ophthalmic examination, preoperatively and 1, 7, and 30 days after surgery. The achieved spherical equivalent (SE) and the prediction error (PE) were calculated. The prediction error was defined as the difference between attempted predicted target refraction and the achieved postoperative SE refraction. Statistical analysis was performed with SPSS V21.ResultsThe mean age of the patients was 66.96±9.67 years, the mean AL was 23.29±0.62 mm, the mean K1 was 43.62±1.49D, the mean K2 was 43.69±1.53D, the mean IOL power was 21.066±1.464D, the mean attempted (predicted) SE was −0.178±0.266D, and the mean achieved SE was −0.252±0.562D. The mean PE (difference between predicted and achieved SE) showed a relatively hyperopic shift (mean ± standard deviation: 0.074±0.542D, ranging from −1.855 to 2.170D, P=0.001). A total of 93.87% of eyes were within ±1.00D of the PE and 92.75% of eyes within ±1.00D of achieved postoperative refraction. A total of 39 eyes (7.25%) had a refractive surprise. A total of 32 of 39 eyes were more myopic than −1.00D and 7 of them were more hypermetropic than +1.00D. There was no correlation between the mean PE and IOL type, AL, K1, K2, and IOLp. There were a positive statistically significant correlation between PE and age (r=0.095; P=0.028) and a negative statistically significant correlation between achieved SE and AL (Spearman’s r=−0.125; P=0.04), and age (r=−0.141; P=0.01).ConclusionThe IOLp calculation using the SRK/T formula with US biometry may demonstrate very good postoperative refractive outcomes in medium eyes with a few refractive surprises.

Comparison on the application of five formulas in cataract patients with short axial length

Objective To compare the predicating accuracy of intraocular lens(IOL)power calculations by using five formulas(SRK-T, SRK-Ⅱ, Holladay-1, Haigis and Hoffer Q)in eyes of age-related cataract with short axial length before surgery. Methods Sixty-three eyes of 63 cases of age-related cataract with short axial length(<22.0mm) were collected and their optical biometry were performed by the Zeiss IOL Master before operation. All patients underwent regular phacoemulsification and posterior chamber IOL implantation by the same surgeon. No complication occurred. The actual postoperative refraction was measured with the methods of phoropter and subjective optometry at 3 months after surgery. The differences of actual postoperative refraction predicted and measured with the five formulas among the short axial lengths cases were compared. Results In the short axial lengths cases, the differences between Haigis formula and SRK-T、Holladay-1、Hoffer Q were statistically significant (P 0.05). The difference among the five formulas of the number of cases which forecast error was 0.05). Conclusion In the short axial lengths cases, the accuracy of intraocular lens power calculations by using SRK-Ⅱ、SRK-T、Holladay-1 and Hoffer Q is high. Key words: Cataract, short axial lengths; Phacoemulsification; Lens, intraocular; Formula, calculating

A Comparative Study to Assess the Predictability of Different IOL Power Calculation Formulas in Eyes of Short and Long Axial Length.

Accurate Intraocular Lens (IOL) power calculation in cataract surgery is very important for providing postoperative precise vision. Selection of most appropriate formula is difficult in high myopic and hypermetropic patients. To investigate the predictability of different IOL (Intra Ocular Lens) power calculation formulae in eyes with short and long Axial Length (AL) and to find out most accurate IOL power calculation formula in both groups. A prospective study was conducted on 80 consecutive patients who underwent phacoemulsification with monofocal IOL implantation after obtaining an informed and written consent. Preoperative keratometry was done by IOL Master. Axial length and anterior chamber depth was measured using A-scan machine ECHORULE 2 (BIOMEDIX). Patients were divided into two groups based on AL. (40 in each group). Group A with AL<22 mm and Group B with AL>24.5 mm. The IOL power calculation in each group was done by Haigis, Hoffer Q, Holladay-I, SRK/T formulae using the software of ECHORULE 2. The actual postoperative Spherical Equivalent (SE), Estimation error (E) and Absolute Error (AE) were calculated at one and half months and were used in data analysis. The predictive accuracy of each formula in each group was analyzed by comparing the Absolute Error (AE). The Kruskal Wallis test was used to compare differences in the (AE) of the formulae. A statistically significant difference was defined as p-value<0.05. In Group A, Hoffer Q, Holladay 1 and SRK/T formulae were equally accurate in predicting the postoperative refraction after cataract surgery (IOL power calculation) in eyes with AL less than 22.0 mm and accuracy of these three formulae was significantly higher than Haigis formula. Whereas in Group B, Hoffer Q, Holladay 1, SRK/T and Haigis formulae were equally accurate in predicting the postoperative refraction after cataract surgery (IOL power calculation) in eyes with AL more than 24.5 mm. Hoffer Q, Holladay 1 and SRK/T formulae were showing significantly higher accuracy than Haigis formula in predicting the postoperative refraction after cataract surgery (IOL power calculation) in eyes with AL less than 22.0 mm. In eyes with AL more than 24.5 mm Hoffer Q, Holladay 1, SRK/T and Haigis formulae were equally accurate.

Accuracy of intraocular lens power calculation using partial coherence interferometry and OKULIX ray tracing software in high myopic cataract patients

Purpose The aim of the study was to evaluate the accuracy of intraocular lens (IOL) power calculation using partial coherence interferometry and OKULIX ray tracing software in high myopic cataract patients. Patients and methods This retrospective study was conducted on 60 consecutive myopic eyes with an axial length of at least 26.5 mm (60 patients, 20 men and 40 women, mean age 62.27±7.74 years). The patients underwent uneventful phacoemulsification and IOL implantation following IOL power calculation using the OA-1000 optical biometer and OKULIX ray tracing software for lens power calculation. All patients were recruited from the Department of Ophthalmology, Faculty of Medicine, Alexandria University (Alexandria, Egypt). All surgeries were performed by the same surgeon (K.M.N.). The accuracy of IOL power calculation was evaluated by subtracting attempted and achieved spherical refraction 1 month postoperatively and was recorded as mean absolute error. Results Fifty-three (88.33%) eyes yielded a postoperative spherical refraction that differed 1.00 D or less from predicted. In 42 (70%) eyes, the postoperative refractive error was within ±0.50 D. The mean absolute error was 0.45±0.40 D. Conclusion Optical biometry combined with OKULIX ray tracing software for calculation of IOL power provides accurate results for highly myopic cataract patients.

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.

Pilot study on dry eye affecting the accuracy of intraocular lens power measurement in age-related cataract

Background The incidence of dry eye is gradually increasing, and the aging of population is one of factors. Researches showed that the change of tear film stability leads to shift of corneal refractive power, which probably affects the measurement of intraocular lens (IOL) power. The influence of dry eye on the calculation of IOL power is worth paying close attention. Objective This study was to investigate the influence of dry eye on the accuracy of IOL power calculation in age-related cataractous patients. Methods A non-randomized controlled clinical study was performed. Two hundred and sixteen eyes of 216 cataract patients were enrolled in Yanbian Eye Ear Nose and Throat Hospital from May 2013 to February 2014. The visual acuity, intraocular pressure, break up time of tear film (BUT), SchirmerⅠtest (SⅠt) and corneal fluorescein staining were examined in all the eyes, and then the patients were assigned to mild dry eye group (73 eyes), severe dry eye group (68 eyes) and non-dry eye control group (75 eyes). The axial length (AL) and anterior chamber depth (ACD) were measured using IOL Master for the calculation of IOL power and K value (corneal curvature). Phacoemulsification with IOL implantation was performed on all the eyes, and the refractive power was measured with KR 8100 automatic optometry 2 months after operation. The mean absolute refractive error (MARE) between actual refraction and predicted refraction was calculated, and percentage of eyes in different refractive error ranges was compared between the dry eye group and non-dry eye control group. The correlations of dry eye-related parameters with peroperative K value and refractive error were analyzed. This study was approved by the Ethics of Yanbian University, and written informed consent was obtained from each subject prior to entering the cohort. Results No significant differences were found in age, gender, AL, ACD and MARE among the mild dry eye group, severe dry eye group and non-dry eye control group (all at P>0.05), and significant differences in BUT, SⅠt and corneal fluorescein staining scores were found among these three groups (F=5.460, 4.521, 3.572, all at P<0.05). The K values were (43.59±1.39), (44.66±1.53) and (43.42± 1.32)D in the mild dry eye group, severe dry eye group and non-dry eye control group, and the K value in the severe dry eye group was significantly higher than that in the non-dry eye control group (P=0.012). The percentage of eyes with + 0.50-+ 0.75 D deviation was significantly elevated(28.8% versus 13.3%), and that with -0.50--0.75 D deviation was significantly declined (17.3% versus 28.0%)in the dry eye group compared with non-dry eye control group (χ2=4.513, P=0.032; χ2=4.236, P=0.037). A negative correlation was found between BUT and K value (r=-0.204, P=0.011). Conclusions Dry eye affects the accuracy of the determination of IOL power. Compared with the preoperative refraction predictive value, the postoperative refraction shift toward hyperopia. Key words: [Key words] Biometry; Dry eye; Cataract; Refractive error; Intraocular lens power