Intraocular Lens Calculation Formulas Research Articles

Long-term outcomes of intended undercorrection intraocular lens implantation in pediatric cataract.

PurposeTo evaluate the postoperative refraction of intended undercorrection after intraocular lens (IOL) implantation in pediatric cataract patients.DesignA cross-sectional study (data collected by retrospective chart review).Patients and methodsThe medical records of children aged under 10 years, who underwent cataract surgery with IOL implantation at the Ramathibodi Hospital between January 2000 and May 2018, were reviewed. IOL power calculations were 30%, 25%, 20%, 15% and 10% under-corrected if children were aged 6–12, 13–24, 25–36, 37–48 and 49–60 months, respectively. Two diopters (D) undercorrection was used in children aged between 5 and 8 years and one diopter undercorrection was used in children aged between 8 and 10 years. The main outcome measure was the postoperative refractive errors at the last follow-up visit.ResultsIn total, 50 children (21 females and 29 males, 16 unilateral and 34 bilateral, 84 eyes) met the inclusion criteria for this study. Mean age at the time of surgery was 77.82±31.24 months. Mean follow-up time was 56.56±45.83 months. The main outcome in this study was the postoperative refractive error in children aged 7 years or more. We found 74 eyes of 44 children who were aged 7 years or more at last follow-up visit. In total, 45 eyes were myopic (−0.25 to −8.25 D) with a mean refraction of −2.26±2.16 D. A further 21 eyes were hyperopic (+0.25 to +3.25 D), with a mean refraction of +1.05±0.79 D and eight eyes were emmetropic or having only astigmatism.ConclusionThe major postoperative refractive error at the last follow-up time was myopia. We have to adjust the IOL calculation formula to specify more undercorrection, with the aim of achieving more optimal refractive outcomes in adulthood.

Design and inspection of multifunctional intraocular lens calculation formula

Objective To establish a conventional intraocular lens (IOL) calculation formula which is applicable to eyeballs with abnormal data and laser in situ keratomileusis (LASIK) postoperative eyes. Methods A case-series study was adopted.According to the classical optical theory, a normal IOL implanted eye has the following characteristics: when light is refracted by cornea and arrives on the IOL plane, the value of refractive power (F1) + IOL refractive power (F2) = the value of refractive power which is suitable for vitreous body depth (F3). Thereafter, a mathematical model was built on the basis of theory, experience, and regression analysis data after IOL implantation surgeries.Furthermore, based on the new LASIK postoperative cornea curvature modified formula, the two kinds of IOL calculation programs of conventional and LASIK postoperative eyes were established.The test data was collected from 644 patients who had undergone the cataract extractions and IOL implantation surgeries (600 physiological cornea eyes, 7 radial keratotomy [RK] eyes and 37 LASIK postoperative eyes) at the Affiliated Drum Tower Hospital of Nanjing University Medical School.Through the analysis of these data, the new formulas were examined. Results With IOL refractive power of 607 eyes (including 7 RK postoperative eyes), the average error of XLQ formula (the tentative name of the established formula in this study)was 0.1 D, and the 95% limits of agreement range was -1.1 to + 1.2 D. The error range of IOL refractive power predicted by XLQ, SRK-T and Haigis formulas was -2.21 to + 2.25 D, -5.10 to + 5.63 D and -3.00 to + 3.18 D, respectively, the absolute average error of IOL refractive power predicted by the three formulas was (0.43±0.28), (0.74±0.53) and (0.79±0.49)D, respectively.Compared with SRK-T and Haigis formulas, the average error of IOL refractive power predicted by XLQ formula was Lower, with significant differences between them (both at P=0.000). The error value of IOL refractive power predicted by XLQ formula had no statistical correlations with axial length (AL), keratometry (K) and A constant respectively (all at P>0.05), while the error value predicted by SRK-T and Haigis formulas had statistical correlations with AL, K and A constant, respectively (all at P<0.05). Thirty-seven patients who had conducted LASIK for myopia (and whose IOL refractive power value were predicted by XLQ formula) had been undergone the postoperative examination.Comparing the predicted and actual value, the error range of IOL refractive power was -0.52 to + 1.18 D, and the absolute average error was (0.49±0.26)D. Conclusions The conventional mode of the XLQ formula established in this study can be used in the cases with broad values of axial length, corneal curvature and A constant, as well as various types of physiological cornea and RK postoperative eyes; the dedicated mode is suitable for LASIK postoperative eyes of myopia. Key words: Cataract; Intraocular lens; Formula; A constant; Cornea curvature; Axial length; Radial keratotomy; Laser in situ keratomileusis

Accuracy of 8 intraocular lens calculation formulas in relation to anterior chamber depth in patients with normal axial lengths

To determine the effect of anterior chamber depth (ACD) on the accuracy of 8 intraocular lens calculation formulas in patients with normal axial lengths (ALs). Baylor College of Medicine, Alkek Eye center, Houston, Texas, USA. Retrospective case series. Patients having cataract surgery with ALs between 22.0mm and 25.0mm were divided into 3 groups based on their preoperative ACD measurement. The mean prediction errors, mean absolute errors (MAEs), and median absolute errors for each group were calculated. For the ACD of 3.0mm or less group and the ACD of 3.5mm or more group, the Barrett Universal II, Holladay 2, Haigis, and Olsen ray-tracing formulas had mean prediction error values that were not significantly different from zero. For the ACD of 3.01 to 3.49mm group, all formulas had mean prediction error values that were not significantly different from zero. For the ACD of 3.0mm or less group, the Barrett Universal II formula had a smaller median absolute error than the Haigis, Hoffer Q, and Olsen optical low-coherence reflectometry (OLCR) (Lenstar) formulas and a smaller MAE than the Hoffer Q, Hill-RBF, and Olsen OLCR (P<.05). In the ACD of 3.5mm or more group, the Barrett MAE was smaller than the Hoffer Q (P<.05); however, there were no significant differences between median absolute errors. In eyes with normal ALs, taking preoperative ACD values into consideration might improve refractive outcomes.

人工晶体计算公式在正常眼轴合并浅前房白内障患者中的准确性比较

人工晶体计算公式在正常眼轴合并浅前房白内障患者中的准确性比较

Visual Outcomes and Refractive Status after Combined Silicone Oil Removal/Cataract Surgery with Intraocular Lens Implantation.

Purpose:To evaluate refractive status and identify predictors of surgical success following a combined silicone oil removal/cataract surgery with intraocular lens (IOL) implantation procedure.Methods:In this single-armed, retrospective study, we reviewed patients who underwent vitreoretinal surgery followed by a combined silicone oil removal/cataract surgery procedure between 2009 and 2013. Preoperative data included patient demographics, refractive status, IOL power, and axial length (measured with the IOL Master). Postoperative data were obtained from the 8-week follow-up visit and from the last follow-up visit attended that included refractive error (RE) evaluation (e.g., myopic, hyperopic, and astigmatic). Associations between variables and refractive status were examined. Blindness was defined as a best-corrected visual acuity (BCVA) worse than 3/60.Results:Nighty-eight eyes were ultimately included in analyses. Following surgery, 37.0% of eyes achieved BCVA better than 6/18. The incidence of blindness (BCVA worse than 3/60) was reduced from 47.0% before surgery to 17.3% after surgery. Additionally, 33.7% of eyes did not require refractive correction. Forty-two percent of eyes were under-corrected (>0.5 D hyperopia) following surgery. Age, gender, silicone oil viscosity, axial length, IOL type, initial vitreoretinal pathology, surgeon, and IOL calculation formula were not significantly associated with surgical outcomes (all P > 0.05).Conclusion:A combined silicone oil removal/cataract surgery with IOL implantation procedure restored functional vision in approximately one-third of cases. However, nearly half of patients were under-corrected. Unfortunately, we did not identify any factors that predicted surgical success.

Accuracy of Intraocular Lens Calculation Formulas

To compare the accuracy of intraocular lens (IOL) calculation formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, Olsen, and SRK/T) in the prediction of postoperative refraction using a single optical biometry device. Retrospective consecutive case series. A total of 13 301 cataract operations with an AcrySof SN60WF implant and 5200 operations with a SA60AT implant (Alcon Laboratories, Inc., Fort Worth, TX). All patients undergoing cataract surgery between July 1, 2014, and December 31, 2015, with Lenstar 900 optical biometry were eligible. A single eye per patient was included in the final analysis, resulting in a total of 18 501 cases. We compared the performance of each formula with respect to the error in predicted spherical equivalent and evaluated the effect of applying the Wang-Koch (WK) adjustment for eyes with axial length >25.0 mm on 4 of the formulas. For the SN60WF, the standard deviation of the prediction error, in order of lowest to highest, was the Barrett Universal II (0.404), Olsen (0.424), Haigis (0.437), Holladay 2 (0.450), Holladay 1 (0.453), SRK/T (0.463), and Hoffer Q (0.473), and the results for the SA60AT were similar. The Barrett formula was significantly better than the other formulas in postoperative refraction prediction (P < 0.01) for both IOL types. Application of the WK axial length modification generally resulted in a shift from hyperopic to myopic outcomes in long eyes. Overall, the Barrett Universal II formula had the lowest prediction error for the 2 IOL models studied.

Intraocular lens power calculations in short eyes using 7 formulas

To investigate the accuracy of 7 intraocular lens (IOL) calculation formulas in predicting refractive outcome in eyes with axial lengths (AL) equal to or less than 22.0mm and to evaluate factors contributing to prediction errors. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. Retrospective case series. Eighty-six eyes of 67 patients were included. Seven IOL calculation formulas were evaluated: Barrett Universal II, Haigis, Hill-RBF, Hoffer Q, Holladay 1, Holladay 2, and Olsen. The refractive prediction error was calculated as the difference between the postoperative refraction and the refraction predicted by each formula. The mean refractive prediction error and median absolute error were also calculated. The Hoffer Q and Holladay 2 formulas produced myopic refractive prediction errors of -0.22 diopter (D) and -0.23 D, respectively, and the Olsen formula produced a hyperopic refractive prediction error of +0.27 D (all P<.05). Without adjustment of the mean refractive prediction errors to zero, the only difference between formulas was that Hill-RBF had a statistically significantly smaller median absolute error than Hoffer Q (P<.05). With adjustment of the mean refractive prediction errors to zero, there were no statistically significant differences in the median absolute errors between the 7 formulas (P=.076). The Hoffer Q and Holladay 2 formulas produced slightly myopic refractive prediction errors, and the Olsen formula produced hyperopic refractive prediction errors. When the mean numerical refractive prediction error was adjusted to zero, no statistically significant differences in the median absolute error were found between the 7 formulas.

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.

The Enigmatic Cornea and Intraocular Lens Calculations: The LXXIII Edward Jackson Memorial Lecture

To review the progress and challenges in obtaining accurate corneal power measurements for intraocular lens (IOL) calculations. Personal perspective, review of literature, case presentations, and personal data. Through literature review findings, case presentations, and data from the author's center, the types of corneal measurement errors that can occur in IOL calculation are categorized and described, along with discussion of future options to improve accuracy. Advances in IOL calculation technology and formulas have greatly increased the accuracy of IOL calculations. Recent reports suggest that over 90% of normal eyes implanted with IOLs may achieve accuracy to within 0.5 diopter (D) of the refractive target. Though errors in estimation of corneal power can cause IOL calculation errors in eyes with normal corneas, greater difficulties in measuring corneal power are encountered in eyes with diseased, scarred, and postsurgical corneas. For these corneas, problematic issues are quantifying anterior corneal power and measuring posterior corneal power and astigmatism. Results in these eyes are improving, but 2 examples illustrate current limitations: (1) spherical accuracy within 0.5 D is achieved in only 70% of eyes with post-refractive surgery corneas, and (2) astigmatism accuracy within 0.5 D is achieved in only 80% of eyes implanted with toric IOLs. Corneal power measurements are a major source of error in IOL calculations. New corneal imaging technology and IOL calculation formulas have improved outcomes and hold the promise of ongoing progress.

Comparison of 9 intraocular lens power calculation formulas

To evaluate the accuracy of 9 intraocular lens (IOL) calculation formulas using 2 optical biometers. Private practice, Saint Joseph, Michigan, USA. Retrospective consecutive case series. Nine IOL power formula predictions with observed refractions after cataract surgery were compared using 1 IOL platform. The performance of each formula was ranked for accuracy by machine and by axial length (AL). The Olsen was further divided by a preinstalled version (OlsenOLCR) and a purchased version (OlsenStandalone). The Holladay 2 was divided by whether a refraction was entered (Holladay 2PreSurgRef) or not (Holladay 2NoRef). The OLCR device used in the study was the Lenstar L5 900 and the PCI device, the IOLMaster. The formulas were ranked by the standard deviation of the prediction error (optical low-coherence reflectometry [OLCR], partial coherence interferometry [PCI]) as follows: OlsenStandalone (0.361, 0.446), Barrett Universal II (0.365, 0.387), OlsenOLCR (0.378, not applicable), Haigis (0.393, 0.401), T2 (0.397, 0.404), Super Formula (0.403, 0.410), Holladay 2NoRef (0.404, 0.417), Holladay 1(0.408, 0.414), Holladay 2PreSurgRef (0.423, 0.432), Hoffer Q (0.428, 0.432), and SRK/T (0.433, 0.44). The formulas gave different results depending on which machine measurements were used. The Olsen formula was the most accurate with OLCR measurements, significantly better than the best formula with PCI measurements. The Olsen was better, regardless of AL. If only PCI measurements (without lens thickness) were available, the Barrett Universal II performed the best and the Olsen formula performed the worst. The preinstalled version of Olsen was not as good as the standalone version. The Holladay 2 formula performed better when the preoperative refraction was excluded. Neither author has a financial or proprietary interest in any material or method mentioned.

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 Intraocular Lens Calculation Formulas Measured by Immersion-Type A-Scan Ultrasound and Partial Coherence Interferometry

Comparison of Intraocular Lens Calculation Formulas Measured by Immersion-Type A-Scan Ultrasound and Partial Coherence Interferometry

A 3-D "Super Surface" Combining Modern Intraocular Lens Formulas to Generate a "Super Formula" and Maximize Accuracy.

Cataract surgery is the most common eye surgery. Calculating the most accurate power of the intraocular lens (IOL) is a critical factor in optimizing patient outcomes. To develop a graphical method for displaying IOL calculation formulas in 3 dimensions, and to describe a method that uses the most accurate and current information on IOL formulas, adjustments, and lens design to create one "super surface" and develop an IOL "super formula." A numerical computing environment was used to create 3-D surfaces of IOL formulas: Hoffer Q, Holladay I, Holladay I with Koch adjustment, Haigis, and SRK/T. The surfaces were then analyzed to determine where the IOL powers calculated by each formula differed by more than 0.5, 1.0, and 1.5 diopters (D) from each of the other formulas. Next, based on the current literature and empirical knowledge, a super surface was rendered that incorporated the ideal portions from 4 of the 5 formulas to generate a super formula. Last, IOL power values of a set of 100 eyes from consecutive patients at an eye institute were calculated using the 5 formulas and super formula. The study was performed from December 11, 2014, to April 20, 2015. Analysis was conducted from February 18 to May 6, 2015. Intraocular lens power value in diopters and the magnitude of disparity between an existing individual IOL formula and our super formula. In the 100 eyes tested, the super formula localized to the correct portion of the super surface 100% of the time and thus chose the most appropriate IOL power value. The individual formulas deviated from the optimal super formula IOL power values by more than 0.5 D 30% of the time in Hoffer Q, 16% in Holladay I, 22% in Holladay I with Koch adjustment, 48% in Haigis, and 24% in SRK/T. A novel method was developed to represent IOL formulas in 3 dimensions. An IOL super formula was formulated that incorporates the ideal segments from each of the existing formulas and uses the ideal IOL formula for an individual eye. The expectation is that this method will broaden the conceptual understanding of IOL calculations, improve clinical outcomes for patients, and stimulate further progress in IOL formula research.

How to calculate toric intraocular lenses in clinical practice?

SummaryThere are several options for calculation of toric intraocular lenses, some are based on the classical intraocular lens calculation formulas and others utilize paraxial or numerical ray tracing techniques. Most online calculators use a two‐step system based on precalculated data for the equivalent monofocal lens. Other methods calculate intraocular lens power separately for both cardinal meridians. Advanced methods directly calculate spherocylindrical power by matrix or ray tracing techniques. Especially when considering superposition of regular and irregular astigmatic components, postoperative implant rotation or anisometropia and aniseikonia, the classical formula approach might be inadequate for estimating toric intraocular lens power. Therefore surgeons dealing with toric intraocular lenses require deeper knowledge on advanced calculation techniques to improve patient satisfaction.

Gender differences in biometry prediction error and intra-ocular lens power calculation formula.

To analyze changes over time in biometry prediction error (BPE) after cataract surgery with special reference to the impact of gender and the intra-ocular lens (IOL) calculation formula. About 65% of Swedish cataract surgery units participating in the outcome registration of the National Cataract Register (NCR) were included in this prospective register study. Data for planned and postoperative refraction and keratometry during the month of March 2004-2013 were analyzed, divided by gender. The newly introduced variables axial length and IOL calculation formula were analyzed for March 2013. Gender differences in BPE with correct sign (BPESign ) and absolute biometry prediction error (BPEAbs ) were compared for the Haigis' and Sanders-Retzlaff-Kraff T (SRK/T) formulas. The BPEAbs decreased throughout the study period. In 2004-2006, the BPEAbs was larger in women than in men (p < 0.05), but this difference disappeared from 2007. For 2004 through 2009, the mean BPESign was -0.105 ± 0.79D for women, but -0.003 ± 0.73D for men. After 2009, this myopic error for women gradually diminished. The Haigis' formula performed better in women than the SRK/T formula (p < 0.001); the SRK/T formula rendered a BPESign similar to that from 2004 to 2009 in women. Women had steeper corneas and shorter axial lengths than men (p < 0.001). The myopic BPE in women - associated with steeper corneas and shorter axial lengths - is decreasing, possibly owing to an increased use of the Haigis' formula. Using the Haigis' formula to a higher extent can potentially further reduce the BPEs after cataract surgery.

Evaluation of the Repeatability and the Reproducibility of AL-Scan Measurements Obtained by Residents.

Purpose. To assess the repeatability and reproducibility of ocular biometry and intraocular lens (IOL) power measurements obtained by ophthalmology residents using an AL-Scan device, a novel optical biometer. Methods. Two ophthalmology residents were instructed regarding the AL-Scan device. Both performed ocular biometry and IOL power measurements using AL-Scan, three times on each of 128 eyes, independently of one another. Corneal keratometry readings, horizontal iris width, central corneal thickness, anterior chamber depth, pupil size, and axial length values measured by both residents were recorded together with IOL power values calculated on the basis of four different IOL calculation formulas (SRK/T, Holladay, and HofferQ). Repeatability and reproducibility of the measurements obtained were analyzed using the intraclass correlation coefficient (ICC). Results. Repeatability (ICC, 0.872-0.999 for resident 1 versus 0.905-0.999 for resident 2) and reproducibility (ICC, 0.916-0.999) were high for all biometric measurements. Repeatability (ICC, 0.981-0.983 for resident 1 versus 0.995-0.996 for resident 2) and reproducibility were also high for all IOL power measurements (ICC, 0.996 for all). Conclusions. The AL-Scan device exhibits good repeatability and reproducibility in all biometric measurements and IOL power calculations, independent of the operator concerned.

The Accuracy of the Double-K Adjustment for Third-Generation Intraocular Lens Calculation Formulas in Previous Keratorefractive Surgery Eyes

To evaluate the effect of the double-K (DK) modification on third-generation formulas. Thirty-eight previously myopic and 24 previously hyperopic eyes that underwent phacoemulsification with intraocular lens (IOL) insertion after Laser in situ keratomileusis (LASIK) were evaluated. Pre-LASIK refraction and keratometry, post-LASIK topography, axial length (AL), IOL type and power, and 1-month postphacoemulsification refraction were recorded spherical equivalent after phacoemulsification (SE(postphaco)). Measured corneal power was adjusted using published and validated methods for postmyopic and posthyperopic LASIK. For each eye, and using SE(postphaco), different DK-IOL formulas were used to calculate the corresponding IOL power, the outcome measure, which was compared with the implanted IOL. DK-Holladay 1 yielded the highest Pearson correlation coefficient (PCC), 0.955 for myopes and 0.943 for high myopes (AL>26 mm). Mean error (ME) and mean absolute error (MAE) for myopes for DK Sanders-Retzlaff-Kraff theoretical formula [DK-SRK/T] were 0.44±0.84 D and 0.75±0.61 D for DK-SRK/T compared with -0.04±0.67 D and 0.52±0.40 D for DK-Holladay 1 (P<0.001 and P=0.016, respectively), and 0.03±0.88 and 0.64±0.58 for DK-Hoffer Q. For high myopes, ME and MAE were 0.75±0.81 D and 0.84±0.69 D for DK-SRK/T, and -0.05±0.74 D (P<0.0001) and 0.57±0.45 D (P=0.019) for DK-Holladay 1. About 29% of DK-SRK/T eyes with large AL had MAE>1.5 D, compared with 0% for DK-Holladay 1 and 14% for DK-Hoffer-Q. Eyes with previous hyperopic LASIK faired similarly for all formulas, with similar PCCs, and only 8% in each category with MAE>1.5 D. DK-SRK/T overestimates IOL power in eyes with large AL, especially with concomitant steep pre-lasik keratometry. Among third-generation formulas, DK-Holladay 1 seems more accurate to use in postmyopic LASIK eyes.

A new central–peripheral corneal curvature method for intraocular lens power calculation after excimer laser refractive surgery

To propose the central-peripheral (C-P) method, which requires no data history to calculate intraocular lens (IOL) powers for eyes that underwent laser in situ keratomileusis (LASIK), and compare the accuracy of the C-P method with other IOL formulas for eyes after LASIK. Sixteen patients with cataract (25 eyes) who underwent myopic LASIK were analysed retrospectively. The C-P method is a modified double-K method using the SRK/T formula, in which the estimated pre-LASIK keratometric power calculated from the post-LASIK peripheral anterior sagittal power (also called the axial power) is used for the Kpre in the double-K method using the SRK/T formula, and the post-LASIK anterior sagittal power is used for the Kpost. We compared the accuracy of the C-P method with other popular IOL calculation formulas for use in eyes after LASIK. The median values of the arithmetic and absolute prediction errors with the C-P method were 0.11 diopter (D) (range, -1.67 to 1.97 D) and 0.55 D (range, 0.02-1.97 D), respectively. The prediction error using the C-P method was within ±0.5 D in 48% of eyes, within -1.0 to +0.5 D in 60% of eyes, and within ±1.0 D in 68% of eyes. The C-P method resulted in a significantly higher percentage of eyes within ±0.5 D than the BESSt formula, Shammas-PL formula, true net power method, double-K method using 43.5 D for Kpre, and Feiz-Mannis method. The C-P method may be a good option for calculating IOL powers in eyes undergoing cataract surgery after LASIK when the preoperative LASIK data are unavailable.

Spherotoric bag-in-the-lens intraocular lens: Power calculation and predictive misalignment nomogram

To propose a method of calculating the power of the 1-sided posterior chamber toric bag-in-the-lens (BIL) intraocular lens (IOL) and propose a misalignment nomogram to calculate the postoperative rotational misalignment or predict the effect of preoperative existing irregular corneal astigmatism. Antwerp University Hospital, Department of Ophthalmology, Antwerp, Belgium. Cohort study. The new IOL calculation formula uses the steepest corneal meridian and flattest corneal meridian separately (regular spherical IOL formula) followed by a customized A-constant approach based on the changes in the IOL principal plane depending on the spherical and cylindrical powers (thickness) of the IOL. The calculation of the remaining astigmatism (power and axis) in cases of postoperative rotational misalignment resulted in a nomogram that can also be used to predict the degree of tolerance for irregular corneal astigmatism correction at the lenticular plane. The calculation is performed using a worksheet. Because 10 degrees of misalignment would result in 35% refractive inaccuracy, it is the maximum acceptable corneal astigmatic irregularity for correction at the lenticular plane. Calculation of spherocylindrical power is specific to each toric IOL. Because the surgeon must fully understand the optical properties of the toric IOL that is going to be implanted, a comprehensive outline of a new calculation method specific to the toric BIL IOL is proposed. Primary rotational misalignment of the toric BIL IOL can be fine tuned postoperatively. Drs. Gobin and Mathysen have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Accuracy of intraocular lens power calculation in high myopia

PurposeTo study the accuracy of different recent intraocular lens (IOL) calculation formulas in predicting a target postoperative refraction ± 1.0D (Diopters) in patients with long eyes (axial length ≥ 26.0 mm) undergoing phacoemulsification.Materials and MethodsThis study comprised 127 eyes of 87 patients who presented with cataract and axial eye length ≥ 26 mm. Before phacoemulsification and IOL implantation; axial length measurement using immersion ultrasound A-scan technique, and autokeratometry with or without computerized corneal topography for K readings were done. The IOL power was calculated using four formulas, namely the SRK-T, Hoffer-Q, Holladay-2, and Haigis formulas. Four months after surgery, refraction was done. Differences between actual postoperative refraction and assumed target refraction using the different formulas were analyzed. P < 0.05 was considered statistically significant.ResultsIn all 127 eyes, the mean axial length was 31.71 mm (range, 26.06–37.11 mm) and the mean K was 44.68 D (range, 40.05–55.14D). The mean preoperative spherical equivalent (SE) was −17.52D (range, −12.25 to −30.50D). After surgery, the mean spherical equivalent was −0.8 ± 0.83D (range, +1.25 to −3.75D). The mean postoperative refractive SE when implanting a plus power IOLs was −0.3 ± 0.51D (P < 0.001) while the mean postoperative refractive SE when implanting a minus power IOLs was +1.21 ± 0.11D denoting a highly significant tendency toward hyperopia (P < 0.001). Concerning the minus power group, most postoperative refractive error was within +1.0 to +2.0D in the actual implanted IOL and in all other formula calculated IOL power. However, Haigis formula showed the least deviation while SRK-T and other formulas showed a greater tendency toward hyperopia.ConclusionsIn eyes with high axial myopia, the performance of SRK-T, Hoffer-Q, Holladay-2 and Haigis formulas are comparable in low plus-powered IOL implantation. Haigis formula is the best formula when minus power IOL is implanted.