Refractive prediction by various intraocular lens formulas using optical biometry and effect of ocular parameters on their accuracy

Purpose: To assess the prediction accuracy of intraocular lens (IOL) formulas and study the effect of axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), and lens thickness (LT) on the accuracy of formulas using optic biometry. Methods: This study was performed on 164 eyes of 164 patients who underwent uneventful cataract surgery. Ocular biometry values were measured using Lenstar?900, and intraocular lens (IOL) power was calculated using the SRK/T, SRK II, Hoffer Q, Holladay 2, and Barrett Universal II formulas. We evaluated the extent of bias within each formula for different ocular biometric measurements and explored the relationship between the prediction error and the ocular parameters by using various IOL formulas. Results: The summarization of refractive prediction error and absolute prediction error for each IOL formulation was performed after adjusting the mean refractive error to zero. The deviation in the error values was minimum for SRK/T (0.265) followed by Holladay 2 (0.327) and Barret (0.382). Further, SRK/T had the lowest median (0.15) and mean (0.198) absolute error as compared to other formulations. For the above formulations, 100% of the eyes were in the diopter range of ±1.0. It was observed that the overall distribution of error was closer to zero for SRK/T, followed by Holladay 2 and then Barrett. Conclusion: In summary, we found that accuracy was better in SRK/T formula. We achieved a better understanding of how each variable in the formulas is relatively weighed and the influencing factors in the refraction prediction.

Analyze the effect of keratometry on the calculation accuracy of intraocular lens diopter in patients with normal axial cataract / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM:To evaluate the effect of keratometry on the calculation accuracy of intraocular lens(IOL)diopter in patients with normal axial cataract.METHODS:Totally 157 cases(157 eyes)with age related cataract were collected in Kaifeng Central Hospital from June 2020 to June 2021. Patients were divided into 3 groups according to keratometry: group A(53 eyes)(K<42D), group B(55 eyes)(42D≤K≤46D), group C(49 eyes)(K>46D). The IOL diopter was calculated by SRK/T, Hoffer Q, Holladay 2, Haigis, Kane and Barrett Ⅱ formulas respectively. Subjective optometry was performed after 1mo operation. The average refractive prediction error(RPE)and mean absolute error(MAE)were calculated, and their differences were compared and analyzed.RESULTS:There were significant difference between RPE of each formula and 0D in groups A and C(<i>P</i><0.05), and Barrett Ⅱ formula was significantly different with SRK/T, Hoffer Q, Holladay 2 and Haigis formula(<i>P</i><0.01), but was no significantly different with Kane formula in RPE(<i>P</i>>0.01). There was no significant difference in RPE between group B and 0D(<i>P</i>>0.05). The ratio of Barrett Ⅱ formula in MAE≤0.5D in group A was significantly higher than SRK/T, Hoffer Q, Holladay 2 and Haigis formula(all <i>P</i><0.01), but there was no significant difference compared with Kane formula(<i>P</i>>0.01). In group B, there was no significant difference among Barrett Ⅱ formula and the other formulas in the ratio of MAE≤0.5D and ≤1.0D(all <i>P</i> >0.01). In group C, the ratio of SRK/T and Hoff Q formula in MAE≤0.5D was lower than Barrett Ⅱ formula(all <i>P</i><0.01), and there were no significant difference among Barrett Ⅱ formula and the other formulas in the ratio of MAE≤1.0D(<i>P</i> >0.01).CONCLUSION:If K<42D or K>46D before operation, the commonly used formulas will produce refractive error, but the accuracy of Kane and Barrett Ⅱ formulas are still higher than other formulas.

Effect of pupil dilation on ocular biometry measurement and IOL power calculation in cataract patients with high myopia / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To evaluate the effect of pupil dilation on ocular biometry and IOL power in cataract patients with high myopia, and the difference between cataract patients with high myopia and cataract patients with normal axial length(AL).<p>METHODS:Measurements of AL, corneal curvature(K including K1 and K2), anterior chamber depth(ACD)were performed using IOLmaster in 22 cataract patients with high myopia(34 eyes)(group A)and 23 cataract patients with normal AL(39 eyes)(group B)before and after pupil dilation. SRK-T and Haigis were used to caculate pre- and post-cycloplegic IOL power.<p>RESULTS:ACD after dilation(3.84±0.58mm)significantly increased comparing with ACD before dilation(3.61±0.35mm)in group A(<i>P</i><0.01). ACD after dilation(3.30±0.70mm)also significantly increased comparing with ACD before dilation(3.13±0.63mm)in group B(<i>P</i><0.01). But the difference of pre- and post-cycloplegic ACD between the two groups was not statistically significant(<i>P</i>>0.05). Pre- and post-cycloplegic AL and K(including K1 and K2)were not significantly different in two groups(<i>P</i>>0.05). The differences between pre- and post-cycloplegic IOL power were not statistically significant using the SRK-T and Haigis formula(<i>P</i>>0.05), but the IOL power changed by over 1D after pupil dilation using the SRK-T and Haigis formula respectively in 15% and 27% of eyes in group A,in 3% and 5% in group B.<p>CONCLUSION:ACD increases after pupil dilation in cataract patients with high myopia, which is not different from cataract patients with normal AL. Pupil dilation does not affect AL, K and the IOL power(using SRK-T and Haigis)in cataract patients with high myopia. But the IOL power may change greater than in cataract patients with normal AL, so we suggest IOL power should be measured and calculated without mydriasis.

Observation on the effect of combined surgery in cataract patients with pterygium / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM:To observe the effect of combined surgery in cataract patients with pterygium.<p>METHODS:A prospective single centered study was performed on 22 patients(mean age: 59.05±8.70 years)of concurrent cataract and pterygium(size 2-5 mm in length), who attended the outpatient department during the study period of one year, and the minimum follow up was 3mo-1a for all patients. Mean keratometry(K_mean), mean astigmatism, best corrected visual acuity(LogMAR), preoperatively and 3mo postoperatively had been determined. The corneal curvature, pterygium size and the prediction error(PE)were observed.<p>RESULTS: The amount of PE was <±0.50 D in 18 patients(81.8%)and ±0.50 D to ±1.00 D in 4 patients(18.2%). None of the patients had PE of >1.00 D. The mean axial length did not change significantly(<i>P</i>=0.77)postoperatively. The mean keratometric reading increased from 42.994±1.536 preoperatively to 43.324±1.479 postoperatively but this was not significant(<i>P</i>=0.105). The corneal astigmatism decreased significantly from 2.09±0.789 D preoperatively to 0.523±0.277 D postoperatively(<i>P</i><0.05). BCVA(LogMAR)significantly improved from 1.007±0.402 preoperatively to 0.024±0.062 postoperatively(<i>P</i><0.05). No correlation was found between changes in keratometry and PE(<i>r</i>=-0.29, <i>P</i>=0.19). And, there was no correlation was found between pterygium size and PE(<i>r</i>=0.2997, <i>P</i>=0.17). <p>CONCLUSION: Combined phacoemulsification+foldable intraocular lens(IOL)implantation and conjuctival autograft(CAG)application was safe and effective procedure.

Accuracy of the refractive prediction determined by intraocular lens power calculation formulas in high myopia

Purpose: Our study was conducted to evaluate and compare the accuracy of the refractive prediction determined by the calculation formulas for different intraocular lens (IOL) powers for high myopia. Methods: This study reviewed 217 eyes from 135 patients who had received cataract aspiration treatment and IOL implantation. The refractive mean numerical error (MNE) and mean absolute error (MAE) of the IOL power calculation formulas (SRK/T, Haigis, Holladay, Hoffer Q, and Barrett Universal II) were examined and compared. The MNE and MAE at different axial lengths (AL) were compared, and the percentage of every refractive error absolute value for each formula was calculated at ±0.25D, ±0.50D, ±1.00D, and ±2.00D. Results: In all, 98 patients were recruited into this study and 98 eyes of them were analyzed. We found that Barrett Universal II formula had the lowest MNE and MAE, SRK/T and Haigis formulas arrived at similar MNE and MAE, and the MNE and MAE calculated by Holladay and Hoffer Q formula were the highest. Barrett Universal II formulas have the lowest MAE among different AL patients, whereas it reached the highest percentage of refractive error absolute value within 0.5D in this study. The MAE of each formula is positively correlated with AL. Conclusion: Barrett Universal II formula rendered the lowest predictive error compared with SRK/T, Haigis, Holladay, and Hoffer Q formulas. Thus, Barrett Universal II formula may be regarded as a more reliable formula for high myopia.

Aplicación de un factor de corrección para el cálculo del lente intraocular en pacientes con cámara anterior / Application of a correction factor for intraocular lens power calculation in patients with a narrow anterior chamber and augmented crystalline lens thickness

Objetivo: evaluar la aplicación de un factor corrección en el cálculo del lente intraocular en pacientes con cámara anterior estrecha y grosor del cristalino aumentado. Métodos: se realizó un estudio experimental donde se aplicó un factor de corrección y se comparó con dos grupos de control. Resultados: predominó el sexo femenino con el 71 por ciento de los casos. La edad fue de 70 años y más. El 48,4 por ciento de los pacientes presentó una esfera posoperatoria entre ± 0,50 dioptrías; el 19,4 por ciento estuvo por debajo de -0,50 dioptrías y el 32,3 por ciento de los pacientes por encima de + 0,50 dioptrías. El grupo 3 (grosor del cristalino mayor que 4,60 mm si factor de corrección) tuvo el mayor porcentaje de esfera posoperatoria ± 0,50 dioptrías (58,3 por ciento). El grupo 2 tuvo el mayor porcentaje de pacientes con esfera obtenida mayor de 0,50 dioptrías (38,2 por ciento). Conclusiones: los pacientes a quienes se les aplica el factor de corrección obtienen una esfera posoperatoria cercana a la emetropía a pesar de que la muestra no es homogénea y no se obtienen esferas por encima de 1 dioptría(AU)

Objective: Evaluate the application of a correction factor for intraocular lens power calculation in patients with a narrow anterior chamber and augmented crystalline lens thickness. Methods: An experimental study was conducted in which a correction factor was applied and compared with two control groups. Results: Female sex prevailed with 71 percent of the cases. Age was 70 years and over. 48.4 percent of the patients had a postoperative sphere between ± 0.50 diopters; 19.4 percent were below - 0.50 diopters and 32.3 percent were above + 0.50 diopters. Group 3 (crystalline lens thickness above 4.60 mm without correction factor) had the highest postoperative sphere percentage of ± 0.50 diopters (58.3 percent). Group 2 had the highest percentage of patients with an achieved sphere above 0.50 diopters (38.2 percent). Conclusions: Patients to whom the correction factor was applied achieved a postoperative sphere close to emmetropia, despite the fact that the sample was not homogeneous and spheres above 1 diopter were not obtained(AU)

Principios para el cálculo de la lente intraocular tras cirugía refractiva corneal / Principles for the intraocular lens power calculation after corneal refractive surgery

Se estima que aproximadamente un millón o más de pacientes se realizan cirugía refractiva al año. Es por eso que con el envejecimiento son cada día más frecuentes los pacientes con catarata, a quienes previamente se les ha efectuado cirugía refractiva. El cálculo inexacto de la potencia dióptrica de la lente a implantar en la intervención de estos es también un problema de importancia creciente y con él la sorpresa refractiva. Este es mucho más complejo de lo normal, ya que existen dos fuentes de error: la incorrecta predicción de la posición efectiva de la lente por parte de la fórmula y la determinación errónea de la potencia de la córnea por parte de la queratometría. La corrección de estos dos factores permitirá realizar un cálculo correcto en estos ojos. De ahí la motivación para realizar una búsqueda actualizadas de los últimos diez años de diversos artículos publicados, con el objetivo de describir los principios para el cálculo de la lente intraocular tras cirugía refractiva corneal. Se utilizó la plataforma Infomed, específicamente la Biblioteca Virtual de Salud, con todos sus buscadores(AU)

It is considered that approximately one million or more patients undergo refractive surgery every year. Due to aging, the number of patients with cataract, who had previously undergone refractive surgery, is increasingly higher. The inaccurate calculation of the dioptric power of the lens to be implanted is also a growing significant problem and thus the refractive surprise. This is a much more complex situation since two error sources exist: the incorrect prediction of the effective position of the lens based on the formula and the wrong determination of the corneal power through keratometry. The correction of these two factors will allow making a suitable power calculation. Hence the motivation for updated search of several articles published in the last ten years, with the objective of describing the principles for intraocular lens power calculation after corneal refractive surgery. The Infomed platform, mainly the Virtual Library of Health, was fully used(AU)

Effect of pupillary dilation on intraocular lens power calculation / 国际眼科杂志(Guoji Yanke Zazhi)

Abstract?AIM: To investigate the effect of pupillary dilation on intraocular lens power calculation.?METHODS: This prospective study included 52 eyes of 45 patients diagnosed with cataract and indicated for phacoemulsification with intraocular lens ( IOL ) implantation at the Faculty of Medicine of Mersin University. For each patient, preoperative corneal topography, autokeratometric measurements and biometric measurements were performed before and after pupil dilation.?RESULTS: Kh ( horizontal ) values obtained through autokeratometry and anterior chamber depth measured by biometric ultrasonography were significantly greater when pupils were dilated compared with values obtained when pupils were undilated. Implanting IOLs with power calculated using measurements taken during pupillary dilation resulted in a significantly higher rate of emmetropia. Comparison of emmetropic eyes and ametropic eyes showed significantly larger anterior chamber depth in emmetropic eyes.? CONCLUSION: Keratometric and biometric measurements are more important in IOL power calculation than the formula used. If biometric ultrasonography is performed using contact technique, care must be taken to avoid corneal compression. Anterior chamber depth should be followed during measurement, and the margin of error can be minimized by using the highest value obtained in IOL power calculation.

Preliminary evaluation of an algorithm to minimize the power error selection of an aspheric intraocular lens by optimizing the estimation of the corneal power and the effective lens position / 国际眼科杂志(Guoji Yanke Zazhi)

?AIM: To evaluate the refractive predictability achieved with an aspheric intraocular lens ( IOL ) and to develop a preliminary optimized algorithm for the calculation of its power ( PIOL ) .?METHODS:This study included 65 eyes implanted with the aspheric IOL LENTIS L-313 ( Oculentis GmbH ) that were divided into 2 groups:12 eyes (8 patients) with PIOL≥23. 0 D (group A), and 53 eyes (35 patients) with PIOL<23. 0 D ( group B ). The refractive predictability was evaluated at 3mo postoperatively. An adjusted IOL power ( PIOLadj ) was calculated considering a variable refractive index for corneal power estimation, the refractive outcome obtained, and an adjusted effective lens position ( ELPadj ) according to age and anatomical factors.?RESULTS: Postoperative spherical equivalent ranged from -0. 75 to +0. 75 D and from -1. 38 to +0. 75 D in groups A and B, respectively. No statistically significant differences were found in groups A (P=0. 64) and B (P=0. 82 ) between PIOLadj and the IOL power implanted ( PIOLReal ) . The Bland and Altman analysis showed ranges of agreement between PIOLadj and PIOLReal of +1. 11 to -0. 96 D and +1. 14 to -1. 18 D in groups A and B, respectively. Clinically and statistically significant differences were found between PIOLadj and PIOL obtained with Hoffer Q and Holladay I formulas (P<0. 01).?CONCLUSION: The refractive predictability of cataract surgery with implantation of an aspheric IOL can be optimized using paraxial optics combined with linear algorithms to minimize the error associated to the estimation of corneal power and ELP.

Intraocular Lens Power Calculations Using Dual Scheimpflug Analyzer

PURPOSE: To investigate the accuracy of intraocular lens power calculations using simulated keratometry (simK) of dual Scheimpflug analyzer and 5 types of formulas in cataract patients. METHODS: The keratometry (K), axial length (AXL) and anterior chamber depth (ACD) were measured using ultrasound biometry (USB) combined with auto-keratometry (Auto-K), parital coherence interferometry (PCI; IOL master®) and dual Scheimpflug analyzer (DSA; Galilei®) in 39 eyes of 39 patients. Predicted refraction was calculated using Auto-K, mean K of PCI, and simK and total corneal power (TCP) of DSA in the Sanders-Retzlaff-Kraff (SRK-T) formula. The SRK-II, SRK-T, Holladay II, Haigis, and Hoffer-Q formula were used to calculate predicted refraction with the simK of DSA and AXL of USB. Manifest refraction, mean numerical error (MNE) and mean absolute error were evaluated 1, 3 and 6 months after cataract surgery. RESULTS: TCP of DSA was lower compared with other keratometric values (p < 0.05). The MNE was not different among Auto-K, mean K and simK. The MNE using TCP was larger compared with Auto-K, mean K and simK at 1 month after surgery (p < 0.05). There was a difference in MNE between simK and TCP of DSA at 6 months after surgery (p < 0.05). The MNE of SRK-T formula was the smallest in the intraocular lens (IOL) power calculation using the simK of DSA. CONCLUSIONS: We suggest using IOL power calculations with simK of DSA and SRK-T formula rather than TCP of DSA in cataract patients with normal corneas.

The correlation study between the difference of equal IOL pre-and post Lasik and the degree of my-opia / 中国医师杂志

Objective The difference of the equivalent IOL powers before and after LASIK was calculated by using the Haigis-L formula and Sirius ray-tracing respectively.And study the correlation be-tween the intraocular lens power and the myopic before laser in situ keratomileusis.Methods Ninety-one patients undergoing myopic laser in situ keratomileusis were enrolled, they were divided into 3 groups ac-cording to myopic diopter, group I (-1.00D~-3.00D) 13cases, group II( -3.25D and -6.00D)60 cases, group III(-6.25D~-10.0D)18 cases.The equivalent IOL power before and after LASIK will be calculated using Haigis-L formula and Sirius ray-tracing.The data were analyzed using SPSS20.0.Results 80.2%of the cases calculated using Haigis-L formula were within ±0.50D of the predicted refraction , 94.5%were within ±1.00D, and 100%within ±1.50D.also, within ±0.50D of the predicted refrac-tion 13cases(100%),51cases(85%),9cases(50%) in group I, II, III respectively.74.7% of the eyes calculated using Sirius ray-tracing were within ±0.50D of the predicted refraction , 89.0%were within ± 1.00D, and 100%within ±1.50D.within ±0.50D of the predicted refraction 12cases(92.3%),48cases (80%),8cases(44.4%) in group I, II, III respectively.Conclusions Sirius ray-tracing and Haigis-L formula can calculate IOL power accurately in eyes with prior myopic LASIK, with no need for preoperative data.and there is positive correlation between the intraocular lens power aberration and the myopic diopter before LASIK.

Estimation of Intraocular Lens Power Calculation after Myopic Corneal Refractive Surgery: Using Corneal Height in Anterior Segment Optical Coherence Tomography

PURPOSE: To investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery. METHODS: This study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELP(m)) was calculated. Intraocular lens power, which could achieve actual emmetropia (P(real)), was determined with medical records. Estimated ELP (ELP(est)) was back-calculated using P(real), axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELP(m) and ELP(est), converted ELP and intraocular lens power (ELP(conv), P(conv)) were obtained and then compared to ELP(est) and P(real), respectively. The proportion of eyes within a defined error was investigated. RESULTS: Mean CH, ELP(est), and ELP(m) were 3.71 +/- 0.23, 7.74 +/- 1.09, 5.78 +/- 0.26 mm, respectively. The ELP(m) and ELP(est) were linearly correlated (ELP(est) = 1.841 x ELP(m) - 2.018, p = 0.023, R = 0.410) and ELP(conv) and P(conv) agreed well with ELP(est) and P(real), respectively. Eyes within +/-0.5, +/-1.0, +/-1.5, and +/-2.0 diopters of the calculated P(conv), were 23.3%, 66.6%, 83.3%, and 100.0%, respectively. CONCLUSIONS: Intraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

Estimation of Intraocular Lens Power Calculation after Myopic Corneal Refractive Surgery: Using Corneal Height in Anterior Segment Optical Coherence Tomography

PURPOSE: To investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery. METHODS: This study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELP(m)) was calculated. Intraocular lens power, which could achieve actual emmetropia (P(real)), was determined with medical records. Estimated ELP (ELP(est)) was back-calculated using P(real), axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELP(m) and ELP(est), converted ELP and intraocular lens power (ELP(conv), P(conv)) were obtained and then compared to ELP(est) and P(real), respectively. The proportion of eyes within a defined error was investigated. RESULTS: Mean CH, ELP(est), and ELP(m) were 3.71 +/- 0.23, 7.74 +/- 1.09, 5.78 +/- 0.26 mm, respectively. The ELP(m) and ELP(est) were linearly correlated (ELP(est) = 1.841 x ELP(m) - 2.018, p = 0.023, R = 0.410) and ELP(conv) and P(conv) agreed well with ELP(est) and P(real), respectively. Eyes within +/-0.5, +/-1.0, +/-1.5, and +/-2.0 diopters of the calculated P(conv), were 23.3%, 66.6%, 83.3%, and 100.0%, respectively. CONCLUSIONS: Intraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

A study regarding efficacy of various intraocular lens power calculation formulas in a subset of Indian myopic population.

Efficacy of intraocular lens power calculation formulas in a subset of Indian myopic population. Retrospectively reviewed 43 patients who underwent phacoemulsification with high axial length (AL) (>24.5 mm, range 24.75‑32.35 mm). The power of the implanted intraocular lens (IOL) was used to calculate the predicted post‑operative refractive error by four formulas: Sanders‑Retzlaff‑Kraff (SRK II), SRK/T, Holladay 1, and Hoffer Q. The predictive accuracy of the formulas was analyzed by comparing the difference between the “actual” and “predicted” postoperative refractive errors. Repeated measures analysis of variance (ANOVA) tests were done to have pair‑wise comparisons between the formulas and P < 0.05 was considered significant. A subcategory of axial length 24.5‑26.5 mm was also tested. Holladay 1, Hoffer Q and SRK/T formulas showed a slight tendency toward resultant hyperopia, with mean error of +0.24 diopters (D), +0.58 D, and +0.92 D, respectively. The Holladay 1 formula provided the best predictive result overall.

Analysis of Factors that Influence on Accuracy of Intraocular Lens Power Calculation

PURPOSE: To investigate which factors primarily influence refractory errors between various formulas used to calculate intraocular lens (IOL) power. METHODS: Records of 266 eyes of 191 patients who underwent uneventful cataract surgery were reviewed retrospectively. IOL power was determined using SRK/T, HofferQ (H/Q), Master SRK/T (M/T), Master HofferQ (M/Q), Master Holladay (M/Hol), and Master Haigis (M/Hai). The mean absolute error (MAE) of each formula was compared; MAE was defined as the difference between the postoperative spherical equivalence (SE) determined 1 month after surgery and the predicted SE. Factors that could have influenced interformula refractive errors were analyzed. Patients were divided into 3 groups based on average keratometric value (Kavg) and the inter-group differences of the AE of each formula were analyzed. Effects of corneal curvature on changes in AE of each formula were evaluated by linear regression. RESULTS: The MAE was minimized in the M/T formula, followed by the M/Hol, M/Hai, SRK/T, H/Q, and M/Q formulas. Interformula MAE differences were not statistically significant. Kavg and AXL were significantly influenced by the different predictive values between formulas in univariate analysis, but only AXL was significant in multivariate analysis. The AE in each formula among the 3 groups according to keratometry was significantly different in SRK, M/Hol, and M/Hai. Linear regression analysis showed a significant negative correlation between Kavg, AE of SRK/T and the MHai formula. In particular, this effect was more pronounced in those with short AXL (<22.5 mm). CONCLUSIONS: There were no significant MAE differences between formulas. AXL was a significant factor that influenced the differences between formulas. SRK/T and M/Hai may be affected by outside the normal range of corneal curvatures.

The Prediction of Changes in Mean Corneal Refractive Power by Pterygium Size after Pterygium Surgery

PURPOSE: To assess the changes in mean corneal refractive power (DeltaK) following pterygium surgery and to predict DeltaK in cases of combined cataract and pterygium surgery. METHODS: Thirty-seven eyes of unilateral pterygium patients who underwent pterygium surgery were analyzed retrospectively with at least more than 1 month of follow-up. Preoperative and postoperative 1 month corneal refractive power was measured using auto-keratometer (RK-F1, Canon, Tokyo, Japan). Pterygium horizontal extension, width, and area were measured and correlation with DeltaK before and after surgery analyzed. We also compared DeltaK of the contralateral normal eye. RESULTS: The mean corneal refractive (Km) power measured before and 1 month after surgery was 43.30 +/- 1.66 D and 44.07 +/- 1.42 D, respectively. The Km significantly increased at 4 weeks after surgery (p < 0.001). However, postoperative Km was not significantly different when compared with the contralateral normal eye (43.86 +/- 1.34 D; p = 0.59). All parameters of pterygium size including horizontal extension, width, and area were positively correlated with the mean DeltaK. Among parameters, horizontal extension was best correlated with mean DeltaK (p < 0.001). The mean DeltaK with horizontal extension was predicted using linear regression (2.5 mm to 1 D, 4.0 mm to 1.8 D). CONCLUSIONS: We recommend contralateral corneal refractive power or prediction of corneal refractive power using linear regression with pterygium horizontal extension for determining intraocular lens power in cases of combined cataract and pterygium surgery.

Formula Comparison for Intraocular Lens Power Calculation Using IOL Master and Ultrasound for the ZCB00 IOL

PURPOSE: To evaluation the accuracy of the IOL power calculation formulae measured by IOL Master(R) and applanation ultrasonography for the Tecnis ZCB00 IOL. METHODS: We performed a retrospective study of 170 eyes in 121 patients who underwent cataract surgery in our hospital with AMO Tecnis ZCB00 IOL.s. The SRK/T formula was used to predict the patient's implanted IOL power. Differences in the predicted refractive errors between IOL Master(R) and ultrasonography were analyzed and factors attributed to the differences were also analyzed. Three months after cataract surgery, mean numeric error and mean absolute error were analyzed. RESULTS: SRK/II and SRK/T formulas calculated using ultrasonography showed differences compared to the same formulas calculated using IOL Master(R), in which hyperopic shift was also demonstrated. No definite factor was attributed to the differences between the 2 methods. Although the 3 formulas of IOL Master(R) showed no significant difference in refractive errors, the SRK/T formula calculated using IOL Master(R) showed the least mean absolute and numeric errors. CONCLUSIONS: IOL Master(R) is considered more suitable when determining proper AMO Tecnis ZCB00 IOL power in cataract surgery. The hyperopic shift should be considered when calculating the IOL power using only ultrasonography.

Refractive Changes after Removal of Anterior IOLs in Temporary Piggyback IOL Implantation for Congenital Cataracts

PURPOSE: To assess the refractive change and prediction error after temporary intraocular lens (IOL) removal in temporary polypseudophakic eyes using IOL power calculation formulas and Gills' formula. METHODS: Four consecutive patients (7 eyes) who underwent temporary IOL explantation were enrolled. Postoperative refractions calculated using IOL power calculation formulas (SRK-II, SRK-T, Hoffer-Q, Holladay, and the modified Gills' formula for residual myopia and residual hyperopia) were compared to the manifest spherical equivalents checked at 1 month postoperatively. RESULTS: The mean ages of temporary piggyback IOL implantation and IOL removal were 6.71 +/- 3.68 months (range, 3 to 12 months) and 51.14 +/- 18.38 months (range, 29 to 74 months), respectively. The average refractive error was -13.11 +/- 3.10 diopters (D) just before IOL removal, and improved to -1.99 +/- 1.04 D after surgery. SRK-T showed the best prediction error of 1.17 +/- 1.00 D. The modified Gills' formula for myopia yielded a relatively good result of 1.47 +/- 1.27 D, with only the variable being axial length. CONCLUSIONS: Formulas to predict refractive change after temporary IOL removal in pediatric polypseudophakia were not as accurate as those used for single IOL implantation in adult eyes. Nonetheless, this study will be helpful in predicting postoperative refraction after temporary IOL removal.

Refractive Changes after Removal of Anterior IOLs in Temporary Piggyback IOL Implantation for Congenital Cataracts

PURPOSE: To assess the refractive change and prediction error after temporary intraocular lens (IOL) removal in temporary polypseudophakic eyes using IOL power calculation formulas and Gills' formula. METHODS: Four consecutive patients (7 eyes) who underwent temporary IOL explantation were enrolled. Postoperative refractions calculated using IOL power calculation formulas (SRK-II, SRK-T, Hoffer-Q, Holladay, and the modified Gills' formula for residual myopia and residual hyperopia) were compared to the manifest spherical equivalents checked at 1 month postoperatively. RESULTS: The mean ages of temporary piggyback IOL implantation and IOL removal were 6.71 +/- 3.68 months (range, 3 to 12 months) and 51.14 +/- 18.38 months (range, 29 to 74 months), respectively. The average refractive error was -13.11 +/- 3.10 diopters (D) just before IOL removal, and improved to -1.99 +/- 1.04 D after surgery. SRK-T showed the best prediction error of 1.17 +/- 1.00 D. The modified Gills' formula for myopia yielded a relatively good result of 1.47 +/- 1.27 D, with only the variable being axial length. CONCLUSIONS: Formulas to predict refractive change after temporary IOL removal in pediatric polypseudophakia were not as accurate as those used for single IOL implantation in adult eyes. Nonetheless, this study will be helpful in predicting postoperative refraction after temporary IOL removal.

Refractive Eerror According to the Anterior Chamber Depth and Corneal Refractive Power in Short Eyes

PURPOSE: To evaluate the accuracy of the chosen formula in short eyes and the effect of the anterior chamber depth (ACD) and corneal refractive power on the accuracy. METHODS: A total of 251 eyes out of 185 patients (axial length below 22.0 mm) who underwent cataract surgery in our hospital were retrospectively studied. Introcular lens (IOL) power was calculated with the Hoffer Q, SRK II, SRK-T and Holladay 1 formulas and refractive outcome was measured. Patients were divided into 2 groups based on ACD. The accuracy of the 4 formulas was compared and the errors according to the ACD were also evaluated. RESULTS: In eyes with short axial lengths, all formulas showed a tendency for hyperopic shifts. The Hoffer Q formula showed significantly high predictive accuracy. This tendency for hyperopic shifts was similar in the eyes with extremely short axial length, but a large refractive error deviation was observed. The 2 groups based on ACD showed no significant difference in the refractive error, but the group with deep ACD had a tendency for hyperopic shifts. The difference of the calculated IOL power between the 4 formulas was more pronounced in eyes with lower corneal refractive power. CONCLUSIONS: In eyes with short axial lengths, preoperative ACD and corneal refractive power had an influence on the accuracies of predicted IOL power. Therefore, these factors should be considered in IOL power determination.