The effect of implantable collamer Lens V4c on ocular biometric measurements and intraocular lens power calculation based on Pentacam-AXL and IOLMaster 500
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Abstract Background To investigate the possible effect of implantable collamer lens (ICL) V4c on ocular biometric measurements by a new biometer Pentacam-AXL and partial coherence interferometry (PCI)-based IOLMaster 500 and intraocular lens power calculation using fourth-generation formula. Methods We retrospectively enrolled patients who underwent ICL (EVO-V4c, STAAR Surgical Co. Nidau, Switzerland) implantation surgery from September 2020 to November 2021. The Pentacam-AXL and IOLMaster 500 biometers were used to measure axial length (AL), anterior chamber depth (ACD), keratometry (K), white to white (WTW), and central corneal thickness (CCT) values before and at least 2 months after ICL V4c implantation. The IOL power was calculated using the Barrett Universal II formula. Results The study included 45 eyes in 28 patients. There was a significant increase in ALs (average 0.03 ± 0.07 mm, p = 0.01) and a significant decrease of ACDs (average 0.19 ± 0.17 mm, p < 0.001) based on Pentacam-AXL. Similar changes in ALs and ACDs were also found in IOLMaster 500. In addition, the difference in WTWs in the two devices and that of CCTs in Pentacam-AXL were statistically significant. However, the preoperative and postoperative K1 and K2 were separately comparable using either device. The IOL power calculated by the Barrett Universal II formula did not change significantly either by the software built in Pentacam-AXL or by manually putting the parameters of the IOLMaster 500 into the formula manually ( p = 0.058, p = 0.675, respectively). Conclusions Ocular parameters including ALs, ACDs, WTWs, and CCTs using a new Pentacam-AXL and standard PCI-based IOLMaster 500 changed significantly before and after the ICL V4c implantation, while IOL power prediction using the Barrett Universal II formula was little affected.In standard cataract surgery, one of the major goals is to reach target refraction. Based on keratometry measurements, axial length and anterior chamber depth, most of the intraocular lens calculation formulae are suitable to achieve this aim. Further evaluation of corneal refractive parameters like anterior and posterior corneal surface by Scheimpflug devices led to a significant enhancement of precision in astigmatic and post-refractive surgery cases.
Scheimpflug principle
Refractive Surgery
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Journal of Cataract & Refractive Surgery 21(2):p 114, March 1995. | DOI: 10.1016/S0886-3350(13)80494-4
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Abstract Background The accuracy of using total keratometry (TK) value in recent IOL power calculation formulas in highly myopic eyes remained unknown. Methods Highly myopic patients who underwent uneventful cataract surgery were prospectively enrolled in this prospective comparative study. At one month postoperatively, standard deviation (SD) of the prediction errors (PEs), mean and median absolute error (MedAE) of 103 highly myopic eyes were back-calculated and compared among ten formulas, including XGboost, RBF 3.0, Kane, Barrett Universal II, Emmetropia Verifying Optical 2.0, Cooke K6, Haigis, SRK/T, and Wang-Koch modifications of Haigis and SRK/T formulas, using either TK or standard keratometry (K) value. Results In highly myopic eyes, despite good agreement between TK and K ( P > 0.05), larger differences between the two were associated with smaller central corneal thickness ( P < 0.05). As to the refractive errors, TK method showed no differences compared to K method. The XGBoost, RBF 3.0 and Kane ranked top three when considering SDs of PEs. Using TK value, the XGboost calculator was comparable with the RBF 3.0 formula ( P > 0.05), which both presented smaller MedAEs than others (all P < 0.05). As for the percentage of eyes within ± 0.50 D or ± 0.75 D of PE, the XGBoost TK showed comparable percentages with the RBF 3.0 TK formula (74.76% vs. 66.99%, or 90.29% vs. 87.38%, P > 0.05), and statistically larger percentages than the other eight formulas ( P < 0.05). Conclusions Highly myopic eyes with thinner corneas tend to have larger differences between TK and K. The XGboost enhancement calculator and RBF 3.0 formula using TK showed the most promising outcomes in highly myopic eyes.
Emmetropia
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Cataract extraction
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Purpose: To investigate the relationship between corneal powers measured by simulated keratometry (Sim-K) and ray tracing and understand whether their difference influences intraocular lens (IOL) power calculation. Methods: In a first sample of healthy eyes, corneal curvature was measured using a rotating Scheimpflug camera (Sirius, CSO). Sim-K was obtained from anterior corneal curvature using the 1.3375 keratometric index. Ray tracing was performed through both corneal surfaces to calculate the total corneal power (TCP). The difference between Sim-K and TCP was correlated with various parameters. In a second sample of patients undergoing cataract surgery, IOL power was subsequently calculated using both Sim-K and TCP. Results: In the first sample (114 eyes), Sim-K (43.64 ± 1.44 D) was higher than TCP (43.07 ± 1.41 D, P < 0.0001); the difference ranged between 0.07 and 1.95 D and correlated with the anterior/posterior (A/P) ratio (r = 0.7292, P < 0.0001), which ranged between 1.10 and 1.30. In the second sample (107 eyes), the A/P ratio influenced the outcomes of the Holladay 1 and SRK/T, but not Haigis and Hoffer Q formulas. However, using TCP, which takes the A/P ratio into account, did not improve the prediction error of any formula. Conclusions: Sim-K provides a higher corneal power compared with TCP. This difference is not constant but depends on the A/P ratio and can influence the refractive outcome of IOL power calculation by theoretical formulas. However, TCP values do not improve the results of these formulas, as they were developed for keratometric values such as Sim-K.
Scheimpflug principle
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Purpose: To compare the accuracy of standard keratometry and computerized videokeratography (CVK) in determining intraocular lens (IOL) power calculations. Methods: Using the EyeSys Corneal Analysis SystemTM, we prospectively obtained CVK maps on 75 eyes of 69 patients scheduled to have phacoemulsification with implantation of a posterior chamber intraocular lens. Using manifest refraction obtained at 6 weeks postoperatively, we optimized the calculations for the Hoffer Q, Holladay, and SRK/T formulas for standard keratometric and the following six CVK values: average curvatures at the 1 mm, 2 mm, and 3 mm zones, the keratometric equivalent at the 3 mm zone, and the Stiles-Crawford weighted averages over the 3 mm and 6 mm zones. The accuracy of these parameters was determined by calculating the mean absolute error and percentage of patients with accuracy within ≤ 0.5 diopter (D), ≤ 1.0 D, and ≤ 2.0 D. Results: Keratometrically derived data were slightly more accurate than the CVK-derived values. The average difference in mean absolute error between the keratometric and CVK values was 0.13 D for the Hoffer Q formula, 0.11 D for the Holladay, and 0.08 D for the SRK/T. Conclusions: In this population of patients, we found the CVK-derived corneal curvature values to be slightly less accurate than standard keratometry in predicting IOL power. However, CVK provides important corneal curvature data for IOL calculations in patients with abnormal or surgically altered corneal surfaces.
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Purpose: To compare and analyze the accuracy of the refractive outcomes obtained in intraocular lens power calculation using the classical calculation method with mean keratometry (K) and the calculation method with both K meridians presented in this article. Methods: A total of 62 eyes of 62 subjects who were undergoing cataract surgery were included in this study. Optical biometry was performed using mean K and Haigis formula for classical intraocular lens calculation methods to achieve intraocular lens power; 4 weeks after surgery, prior to medical discharge, subjective refraction was made. Alternatively, intraocular lens power was calculated with bicylindric method using both keratometry readings, obtaining spherocylindrical refractive expected outcomes. Finally, results obtained with intraocular lens calculation methods, bicylindric method, and Haigis formula were compared. Results: Spherical equivalent calculated by classical intraocular lens calculation methods using Haigis formula (H-SE) was −0.027 ± 0.115 D and using bicylindric method (B-SE) was −0.080 ± 0.222 D. Achieved spherical equivalent obtained 4 weeks after surgery (A-SE) was −0.144 ± 0.268 D. Difference between H-SE and A-SE was −0.117 D (p = 0.002). Difference between B-SE and A-SE was not significant (−0.054 D, p = 0.109). Analysis in refraction groups showed a positive correlation between A-SE confronted to B-SE and H-SE (r = 0.313; p = 0.013 and r = 0.562; p < 0.001, respectively). This indicated a reliability in ametropic group prediction of 0.767 in H-SE and 0.843 in B-SE. Conclusion: Intraocular lens calculation with bicylindric method could be more accurate and had more reliability than classical intraocular lens calculation method. Bicylindric method adds astigmatism control and provides a reliable expected spherocylindrical refraction.
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We compared the accuracy of keratometry and computerized videokeratography (CVK) for use in intraocular lens calculations. We studied 48 eyes of 45 patients having phacoemulsification and posterior chamber lens implantation. Computerized videokeratography was performed with the EyeSys Corneal Analysis System™ (ECAS™). Using the SRK II, SRK/T, and Holladay formulas, we evaluated predictive accuracy calculated with keratometric values and four values derived from ECAS measurements. For each formula, the use of one of the CVK parameters resulted in lower mean absolute errors between actual and predicted postoperative refractive errors and higher percentages of cases with power prediction errors <0.5 and <1.0 diopters. Computerized videokeratography may provide a more accurate corneal curvature value than keratometry for use in intraocular lens calculations.
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