Design and inspection of multifunctional intraocular lens calculation formula / 中华实验眼科杂志

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.

Personal A-constant in relation to axial length with various intraocular lenses.

Purpose: To study the relationship between the axial length and personal A‑constant for the 1‑piece Tecnis (Abbott ZCB00), AcrySof MA60AC (Alcon) and the Quatrix aspheric preloaded (CROMA) intraocular lenses (IOL). Materials and Methods: Patients matching the inclusion criteria were further subdivided according to the implanted IOL in this prospective comparative study. The obtained refractive outcomes were introduced into the formula installed in the biometry machine (Humphrey model 820 ultrasonic biometer) to obtain the personal A‑constant for each eye. Polynomial regression analysis was done to study the individualized A‑constant for each type of IOL in relation to preoperative axial length measurement. Results: Two hundred and forty five eyes of 186 patients were enrolled into this study, of whom 73 eyes with Tecnis 1‑piece, 116 eyes with MA60AC, and 56 eyes with Quatrix. The median of personalized A‑constant for Tecnis 1‑piece, MA60AC, and Quatrix were 119.21 (SD 1.3, Std. Mean error 0.15), 119 (SD 1.2, Std. Mean error 0.11) and 120.4 (SD 1.2, Std. Mean error 0.16) respectively. Regression plots for the same range of axial length among all the groups showed that the Tecnis1 group followed the same pattern of the Quatrix group in which there was a linear relationship of a trend towards myopia when the axial length had increased and a hyperopic shift when decreased. This relationship changed into a plateau when the axial length became in the range of 23.5 mm to 27 mm in the MA60AC group. Conclusions: Personal A‑constant follows different trends with different IOLs even for the same range of axial length.

Personalización de las constantes en las fórmulas de cálculo de la lente intraocular / Personalization of constants in the intraocular lens calculation formulas

Objetivo: personalizar las constantes A, factor cirujano y profundidad de la cámara anterior para las fórmulas de cálculo de la lente intraocular en la cirugía de catarata en el Instituto Cubano de Oftalmología Ramón Pando Ferrer de mayo de 2007 a enero de 2011...

Objective: to personalize the A, surgeon factor and anterior chamber depth constants for intraocular lens calculation formulas in the cataract surgery at the Ramón Pando Ferrer Cuban Ophthalmological Institute from May 2007 to January 2011...

The Evaluation of the Difference between the Calculated Estimated Post-operative Refraction and the Real Post-operative Refraction for Five Types Intraocular Lenses

PURPOSE: To evaluate and compare the difference of predictive post-operative refraction preoperatively and real post-operative refraction among five types of intraocular lens. METHODS: We reviewed retrospectively 567 cataractous eyes that had undergone phacoemulsification or ECCE with posterior chamber intraocular lens (IOL) implantation by the same surgeon. Applied IOLs were AMO(R) Phacoflex(R) II SI40NB, Acrysof(R) MA60BM, Sensar(TM) AR40e, CeeOn(TM) 811B and CeeOn(TM) 720A. Prediction of post-operative refraction (predictive refraction) was calculated by the SRK/T formula with manufactured A constant. Post-operative manifest refraction (real refraction) was done at least 2 months postoperatively. We compared the difference between the predictive refraction and the real refraction by paired t-test. RESULTS: Total studied eyes were 390 eyes. In all groups, more myopic shift were observed than predicted. In AMO(R) Phacoflex(R) II SI40NB group, statistically significant difference was seen in postoperative manifest refraction over the predictive refraction as much as mean 0.46 diopter myopically (p<0.05, paired t-test), but others were not. In the AR40e implanted group, the error of predictive refraction was the smallest among groups. CONCLUSIONS: Prediction of postoperative refractive state was influenced by various clinical factors. Using a revised A constant, predictive error would be decreased. We recommend that every cataract surgeon had better have one's original A constant over each IOL and A constant may be revised when major surgical or biomedical measurement settings were changed.

E valuation for the Differences of Predictive Refraction Among Three Types of Intraocular Lenses with Manufactu red A constant and Revised A constant

To compare the difference of predictive refraction among three types of PC-IOLs, we reviewed retrospectively 180 cataractous eyes that had undergone phacoemulsification and PC-IOL implantation by the same surgeon at 2 months postoperatively. The inclusion criteria consisted of the axial length ranging from 22 mmto 24.5 mm, the best corrected visual acuity better than 0.9 in Snellen chart and the astigmatism within+/-1 diopter at the time of postoperative 2 months. Patients were divided into 3 groups according to PCIOL types. Group 1 comprised of AMO(r) PhacoFlex SI30NB(71 eyes), group 2 of Acylsof(r) MA60BM(58 eyes), and group 3 of CILCO(r) PMMA single-piece MZ60BD(50 eyes).IOL power calculations were processed by SRKII with manufactured A constant and with revised A constant. There were no significant differences in predictive error within+/-1 diopter among different groups(P>0.05).With manufactured A constant, SI30NB with polypropylen haptics showed hyperopic shift in relative error. MZ60BD with a single-piece and narrowing haptic angle showed more myopic shift than MA60BM(P<0.05). But with revised A constant, there were no significant differences in myopic or hyperopic shift and showed more enhancement in the accuracy of predictive refraction than with manufactured A constant.

Clinical Evaluation of AMO Phacoflex SI-30NB in the Aspect of A-constant

We inspected reliability of A-constant of AMO SI-30NB by comparing target diopter and actual postoperative refractive status. Group 1 comprised 191 eyes which were implanted AMO PhacoFlex SI-30NB with corneal incision. Group 2 comprised 45 eyes implanted Pharmacia 812C with scleral incisions. Group 3 comprised 17 eyes implanted AMO OgaciFlex SI-30NB with corneal incision. Refraction was performed on post operative day 1, day 5, day 14, 1 month, and 3 month. It revealed hyperopic shift of 0.31 to 0.40 diopter compared to the target diopters in both Group 1 and Group 3 and no statistical difference was found between two groups(p value>0.05). On the other hand, Group 2 were statistically significant(p value<0.01). We attempted mathematical modelling of this phenomenon and the cause of hyperopylene haptics, structural weakness of haptic-optic junction, and the structure of SI-30NB itself.

Evaluation for the Accuracy of the SRK/T Formula in PCL Implanted Patients(II): Optimizing, A-Constant

To evaluate the efficacy of optimizing of A-constant, the error in prediction was analyzed in three groups of eyes after posterior chamber lens implantation ; 102 eyes with bag placed, 66 eyes with simple sulcus places, and 25 eyes with sulcus placed with transscleral fixation suture. We compared the predictive accuracy of the SRK/T formula using optimized A-constant (bag-placed, sulcus-placed) derived from the 300 eyes with Holladay and SRK/T using original surgeon factor and A-constant. The SRK/T formula with optimized A-constant has a better mean relative, absolut, and standard error and has a better range of IOL prediction error, which was more accurate than other formulas without optimizing. In this study it is our recommendation that each surgeon use a different optimized A-constants for sulcus or bag placement to enhance the predictability of the postoperative refraction.

Comparison of the SRK and SRKII Formulas with Revision of Constant A in Intraocular Lens Power Calculation

The predictive accuracy of the SRK and SRKII formulas were compared in 113 pseudophakic eyes who had extracapsular cataract extraction with implantation of same type of posterior chamber IOL from Feburary 1990 to March 1991. These patients were folio we red up for at least 2 months postoperatively. Their best corrected visual acuities were above 0.5 and their astigmatisms were below 3 diopters by spectacles correction at the time of the last refraction. The results were as follows. 1. Overall, there were no significant differences in predictive accuracy between SRK and SRKII formulas. 2. The revised constant A for same type of implatnts, which constant A was 118.8. was 117.4 The SRK and SRKII formulas with revised constant A were more accurate than conventional formulas(p<0.001). 3. Our results suggested the constant A was to be revised appropriately according to the surgeon's individual regression analysis when using SRK or SRKII formulas for the calculation of intraocular lens power in Koreans.

Evaluation for the Accuracy of the SRK/T Formula in PCL Implanted Patients(I)

The 1224 cataractous patients who had extracapsular cataract extraction and posterior chamber lens implantations were evaluated retrospectively irrespective of style, postoperative position of intraocular lens and surgeon. The 100 cataractous patients who had extracapsular cataract extraction and posterior chamber lens implantations in the bag accurately using single lens style by one surgeon(E.H.L) were evaluated prospectively. And then the predictive accuracy of the SRK/T intraocular lens power calculation formula was compared with other formulas (SRK, SRKII and Holladay) without consideration of individual A constant. The SRK/T formula was more accurate than other 3 formulas in all axial length, but there were no significant differences statistically. Especially for short and long eyes, SRK/T formula was more accurate than other 3 formulas.