Evaluation of Barrett universal II formula for intraocular lens power calculation in Asian Indian population

Purpose: Barrett Universal II (BU-II) is considered as one of the most accurate intraocular lens (IOL) power calculation formulas; however, there is no literature studying the same in Indian population. The aim of this study was to evaluate the accuracy of BU-II formula in prediction of IOL power for cataract surgery in Asian Indian population. This was an institutional, prospective, observational study. Methods: Patients with senile cataract who underwent phacoemulsification with posterior chamber IOL implantation were enrolled in the study. Biometry data from Lenstar-LS900 was used and IOL power was calculated using four IOL formulas: modified SRK-II, SRK/T, Olsen, and BU-II. Primary outcome was measured as the prediction error in postoperative refraction for each formula and secondary outcome was measured as the difference in mean absolute errors between the four formulas. SPSS Version-21 with P < 0.05 considered significant. Results: A total of 244 eyes were included in the study and were divided into three groups in accordance to axial length (AL): Group 1 (AL: 22�.5 mm; N = 135), Group 2 (AL <22 mm; N = 53), and Group 3 (AL >24.5 mm; N = 56). BU-II formula gave the lowest mean absolute error (0.37 � 0.27D) and median absolute error (0.34) in predicted postoperative refraction in the entire study population. When compared with the other formulas, mean absolute error was significantly lower in all three groups (P < 0.0005) as well, except for Olsen formula in the normal AL group, where the results were comparable (P = 0.742). Conclusion: BU-II performed as the most accurate formula in the prediction of postoperative refraction over a wide range of ALs.

Comparison of Three Formulas for Intraocular Lens Power Formula Accuracy

PURPOSE: To compare the accuracy of three intraocular lens (IOL) power calculation formulas (SRK/T, Barrett Universal II, and T2) in cataract surgery patients.METHODS: In total, 73 eyes of 73 patients who underwent uneventful cataract surgery were retrospectively reviewed. IOL power was determined using SRK/T, Barrett Universal II, and T2 preoperatively. The findings were compared with the actual refractive outcome to obtain the prediction error. The mean prediction error (ME) and mean absolute error (MAE) of each formula were compared. The MAE was defined as the difference between the postoperative spherical equivalence (SE) and the preoperatively predicted SE. The ME and MAE of each formula 3 months after surgery were compared with preoperatively predicted SE. Eyes were classified into subgroups based on axial length (AL) and average keratometry (K).RESULTS: The ME and MAE for the three formulas were SRK/T [−0.08 ± 0.45 diopters (D) and 0.35 ± 0.40 D, respectively], Barrett Universal II (−0.01 ± 0.44 D and 0.33 ± 0.30 D, respectively), and T2 (0.04 ± 0.45 D and −0.34 ± 0.30 D, respectively), but no statistically significant differences were detected. Similar results were obtained in groups with a long AL or a large average K. In groups with an AL ≥ 26 mm or with an average K ≥ 47 D, the Barrett Universal II formula yielded the smallest standard deviation and a ME closest to zero, but these differences were not statistically significant.CONCLUSIONS: No significant differences were observed between the three formulas regarding ME or MAE. However, recent formulas such as the Barrett Universal II could provide certain benefits in predicting IOL power for patients with a long AL (> 26 mm) or larger average K. Further research with a larger sample size is recommended for more evaluation.

Postoperative Refractive Error by Using A-scan in Cataract Surgery After Vitrectomy

PURPOSE: To investigate the difference between target refraction and actual refraction of intraocular lens implantation when cataract surgery was performed after vitrectomy. METHODS: This study evaluated 28 eyes of 28 patients who had undergone vitrectomy without gas tamponade and 25 eyes of 25 patients who had undergone vitrectomy with gas tamponade. A-scans were performed before the respective cataract and vitrectomy surgeries. Three months after cataract surgery, the actual refraction was measured. To compare the difference between the actual and the target refraction calculated by each A-scan, the refractive prediction error was calculated. It is determined by subtracting the target refraction from the actual refraction. RESULTS: In 28 eyes, the mean refractive prediction error calculated by the A-scan performed before vitrectomy was -0.146+/- 0.901D (diopter, D), and the mean refractive prediction error calculated by an A-scan performed just prior to cataract surgery was -0.228+/-1.011D. The two values were not statistically significant (p=0.653). In 25 eyes, the mean refractive prediction errors calculated by A-scans performed before vitrectomy and cataract surgery were -0.171+/-1.079D, and -0.227+/-0.798D, respectively. There was no statistically significant difference between the two values (p=0.563). CONCLUSIONS: When a cataract surgery was performed after vitrectomy, a precise target refraction could be obtained.

Refractive Predictability of Partial Coherence Interferometry and Factors that can Affect It

PURPOSE: To evaluate the refractive predictability of a partial coherence interferometry (PCI) biometry device (IOL Master(R)) for cataract surgery and to investigate factors that may affect it. METHODS: Retrospective review of 209 eyes from 151 patients that had undergone preoperative PCI biometry and an uneventful phacoemulsification cataract surgery with posterior chamber intraocular lens (IOL) implantation was conducted. Prediction error defined as the intended refraction minus the postoperative refraction in spherical equivalent (SE) and the absolute error were analyzed according to IOL calculation formulas, patient characteristics, preoperative visual acuity (VA) and refraction, posterior subcapsular cataract (PSC), signal-to-noise ratio (SNR), and axial length (AL). RESULTS: The overall refractive predictability of the PCI device was good. Generally, the SRK/T formula performed better than the SRK-II formula. Refractive predictability was slightly worse in eyes with > or =+2.0 diopters (D) of preoperative SE (with both SRK-II and SRK/T) and in eyes with an AL or =+2.0D was related to a significantly greater hyperopic shift in postoperative refraction. With proper verification of measured data and a suitable IOL calculation formula, good refractive predictability is expected from PCI biometry regardless of patient characteristics, preoperative VA, SNR, PSC, and AL.

Clinical Efficacy and Complications of Intraocular Lens Exchange for Opacified Intraocular Lenses

PURPOSE: To evaluate the clinical efficacy and complications of intraocular lens (IOL) exchange. METHODS: A review of medical records was performed for 52 eyes that had undergone an IOL exchange due to IOL opacification. Surgical complications and their incidences were analyzed. The mean best corrected visual acuity (BCVA) after the IOL exchange was compared with the mean pre-exchange BCVA and with the mean BCVA after the initial IOL implantation. Prediction error of refraction and biometric data obtained for the IOL exchange were, if available, compared with those obtained for the initial IOL implantation. The prediction error for the IOL exchange, calculated from the biometric data obtained before the IOL exchange, was compared with that calculated from the measurements obtained before the initial IOL implantation. RESULTS: The overall complication rates were low and no serious complications were found. The mean BCVA improved significantly after the IOL exchange and was not significantly different from that obtained after the initial IOL implantation. However, the refractive prediction for the IOL exchange was not as good as it was for the initial IOL implantation, which was thought to be related with difficulties in axial length (AL) measurements. Biometric data taken before the initial IOL implantation was associated with a significantly better refractive prediction than those taken before the IOL exchange. CONCLUSIONS: IOL exchange was both efficacious and safe for visual recovery. However, IOL exchange was related with increased difficulty of predicting postoperative refraction; difficulties in AL measurements are the suggested cause.

Early prediction of birth weight percentile and large for gestational age fetuses using gestation-adjusted projection of estimated fetal weight / 대한산부인과학회잡지

OBJECTIVE: To evaluate the accuracy of predicted birth weight percentile and large for gestational age(LGA) fetuses by the gestation-adjusted projection method using estimated fetal weight. METHODS: From 462 low-risk pregnancies with singleton fetus, fetal biometry including fetal biparietal diameter(BPD), head circumference(HC), abdominal circumference(AC), and femur length(FL) was made from 30 weeks of gestation until term. Estimated fetal weight(EFW) by combinations of fetal biometry were made by Campbell, Hadlock1, Hadlock2, and Shepard formulas respectively. The diagnostic accuracy according to 4 formulas was assessed by correlation between EFW percentile and birth weight percentile, prediction of LGA fetuses, and prediction error(percentile difference between birth weight and EFW). RESULTS: The mean gestational age on ultrasound and on birth, and birth weight were 33.21 +/- 2.08(30-40) weeks, 38.43 +/- 1.72(30-42) weeks, and 3.14 +/- 0.47(0.99-4.38) Kg, respectively. The diagnostic accuracies of gestation-projection method using EFW were similar result to predict birth weight percentile and LGA fetuses according to 4 formulas. Correlation between EFW percentile and birth weight percentile(correlation coefficient, r) were Campbell: 0.644(p <0.001), Hadlock 1: 0.682(p <0.001), Hadlock 2: 0.681(p <0.001), Shepard: 0.638(p <0.001), respectively. Youden's index(sensitivity + specificity - 1) in prediction of LGA fetuses were Campbell: 0.532, Hadlock1: 0.525, Hadlock2: 0.520, Shepard: 0.549, respectively. Prediction error were Campbell: 18.14+/-16.56, Hadlock1: 16.19+/-14.35, Hadlock2: 16.10+/-14.29, Shepard: 19.68+/-17.00, respectively. The prediction error was increased according to increasing of lapse time(p <0.001), gestational weeks on ultrasound, and estimated fetal weight percentile, and decreasing birth weight percentile(p <0.001)(R square=0.411, (p <0.001). But, amniotic fluid index did not affect to prediction error(p=0.199). CONCLUSION: Our study presented relatively accurate prediction for birth weight percentile and LGA fetuses from remote sonographic examination. If LGA fetuses was suspected by antenatal ultrasound, adequate therapy and periodic observation are recommended for good perinatal outcome.

Predicting the Progression of Chronic Renal Failure Using Serum Creatinine Factored for Height

PURPOSE: Efforts to predict the progression of chronic renal failure (CRF) in children, using mathematical models based on transformations of serum creatinine (Scr) concentration, have failed. Error may be introduced by age-related variations in creatinine production rate. Height (Ht) is a reliable reference for creatinine production in children. Thus, Scr, factored for Ht, could provide a more accurate predictive model. We examined this hypothesis. METHODS: The progression of CRF was detected in 63 children who proceeded to end-stage renal disease. Derivatives of Scr, including 1/Scr, log Scr and Ht/Scr, were defined for the period Scr was between 2 and 5 mg/dl. Regression equation were used to predict the time, in months, to Scr > 10 mg/dl. The prediction error (PE) was defined as the predicted time minus actual time for each Scr transformation. RESULT: The PE for Ht/Scr was lower than the PE for either 1/Scr or log Scr (median: -0.01, -2.0 and +10.6 mos respectively; p < 0.0001). For children with congenital renal diseases, the PE for Ht/Scr was also lower than for the other two transformations (median: -1.2, -3.2 and +8.2 mos respectively; p < 0.0001). However, the PE's for children with glomerular diseases was not as clearly different (median: +0.9, +0.5 and +9.9 respectively). In children <13 yrs, PE for Ht/Scr was the lowest, while in older children, 1/Scr provided the lowest PE, but not significantly different from that for Ht/Scr. The logarithmic transformation tended to predict a slower progression of CRF than actually occurred. CONCLUSION: Scr, factored for Ht, appears to be a useful model to predict the rate of progression of CRF, particularly in the prepubertal child with congenital renal disease.