Use of the Posterior/Anterior Corneal Curvature Radii Ratio to Improve the Accuracy of Intraocular Lens Power Calculation: Eom's Adjustment Method

Kim, Mingue; Eom, Youngsub; Lee, Hwa; Suh, Young Woo; Song, Jong Suk; Kim, Hyo Myung

doi:10.1167/iovs.17-22405

Cited by 24 publications

(18 citation statements)

References 30 publications

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“…Constant A = IOL + (REF × RF) + 2.5 × L + 0.9 × K – C (REF refers to the actual postoperative diopter, RF refers to the corneal refractive index, L refers to the AL, K refers to the corneal curvature, and C refers to the adjustment factor used according to the AL of the second-generation IOL calculation formula) [5, 6]. Regarding the fourth-generation formula, the Haigis formula is different from the SRK/T formula in that it takes preoperative ACD rather than the corneal curvature into account [11, 14]. The prediction of ELP by the Haigis formula is as follows: ELP = a0 + a1 × ACD + a2 × L, in which L refers to the AL of the eye, a0 is the specific constant of IOL, a1 is affected by the preoperative measurement of ACD, and a2 is affected by the preoperative measurement of the AL of the eye [14].…”

Section: Discussionmentioning

confidence: 99%

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Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

Zhang¹,

Wang²,

Zhao³

2020

Ophthalmic Res

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Objective: To evaluate the effect of constant C for ray tracing-assisted intraocular lens (IOL) power calculation in patients with different refractive power, we compared the refractive outcome of the ray tracing method based on constant C and conventional IOL calculation. Methods: 215 eyes which underwent phacoemulsification and IOL implantation were enrolled in the study. According to the average corneal power, patients were divided into 3 groups: high corneal power (K >45 D) group, medium corneal power (43 ≤ K ≤ 45 D) group, and low corneal power (K <43 D) group. The predicted sphero-equivalent refractive outcome for the IOL power implanted at surgery was calculated using the ray tracing method, SRK/T, and Haigis formulas. Results: On the basis of the corneal refractive power, there were 65 eyes of K >45 D (30.23%), 96 eyes of 43 ≤ K ≤ 45 D (44.65%), and 54 eyes of K <43 D (25.12%). In general, the ray tracing group had the smallest value of mean absolute error (MAE) and mean error, and the proportions of eyes with absolute error (AE) <0.50 and <0.75 D were significantly higher than those of the other 2 formulas (p = 0.010). In each group, the value of MAE was smallest in the ray tracing group; for the proportions of AEs <0.50 and <0.75 D, the values in the ray tracing group were higher than those in the SRK/T and Haigis groups. Especially in the high and low corneal refractive groups, the proportion of AE <0.25 D was also obviously higher, but only in the low corneal refractive power group, and the difference was statistically significant (p = 0.006). Conclusions: Compared with the conventional formulas, C constant of the ray tracing-assisted IOL power calculation has more accuracy for the patients with different corneal refractive powers. Ray tracing could provide better guidance for IOL selection clinically.

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Section: Discussionmentioning

confidence: 99%

“…When using the ray tracing method for calculation, we will consider factors such as pupil diameter, corneal irregularity, and IOL thickness to minimize the aberration. This is also one of the significant differences between the optical ray tracing system and the traditional IOL calculation formulas [9-11].…”

Section: Introductionmentioning

confidence: 99%

Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

Zhang¹,

Wang²,

Zhao³

2020

Ophthalmic Res

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“…In the clinical practice, DMEK surgeons have noticed this problem and aim to achieve a more myopic postoperative outcome by choosing a refractive target of − 0.5 to − 1D to compensate for this error [8]. In the future, IOL power calculation could be optimized for eyes with FECD undergoing triple DMEK surgery by using adjusted conventional keratometry to improve the predictability of IOL power calculation and account for the postoperative hyperopic shift [18,21,[29][30][31].…”

Section: Discussionmentioning

confidence: 99%

Assessing the validity of corneal power estimation using conventional keratometry for intraocular lens power calculation in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty

Diener¹,

Treder²,

Lauermann³

et al. 2020

Graefes Arch Clin Exp Ophthalmol

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Purpose The present retrospective study was designed to test the hypothesis that the postoperative posterior to preoperative anterior corneal curvature radii (PPPA) ratio in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty (DMEK) is significantly different to the posterior to anterior corneal curvature radii (PA) ratio in virgin eyes and therefore renders conventional keratometry (K) and the corneal power derived by it invalid for intraocular lens (IOL) power calculation. Methods Measurement of corneal parameters was performed using Scheimpflug imaging (Pentacam HR, Oculus, Germany). In 125 eyes with Fuch’s dystrophy undergoing DMEK, a fictitious keratometer index was calculated based on the PPPA ratio. The preoperative and postoperative keratometer indices and PA ratios were also determined. Results were compared to those obtained in a control group consisting of 125 eyes without corneal pathologies. Calculated mean ratios and keratometer indices were then used to convert the anterior corneal radius in each eye before DMEK to postoperative posterior and total corneal power. To assess the most appropriate ratio and keratometer index, predicted and measured powers were compared using Bland-Altman plots. Results The PPPA ratio determined in eyes with Fuch’s dystrophy undergoing DMEK was significantly different (P < 0.001) to the PA ratio in eyes without corneal pathologies. Using the mean PA ratio (0.822) and keratometer index (1.3283), calculated with the control group data to convert the anterior corneal radius before DMEK to power, leads to a significant (P < 0.001) underestimation of postoperative posterior negative corneal power (mean difference (∆ = − 0.14D ± 0.30) and overestimation of total corneal power (∆ = − 0.45D ± 1.08). The lowest prediction errors were found using the geometric mean PPPA ratio (0.806) and corresponding keratometer index (1.3273) to predict the postoperative posterior (∆ = − 0.01 ± 0.30) and total corneal powers (∆ = − 0.32D ± 1.08). Conclusions Corneal power estimation using conventional K for IOL power calculation is invalid in eyes with Fuch’s dystrophy undergoing DMEK. To avoid an overestimation of corneal power and minimize the risk of a postoperative hyperopic shift, conventional K for IOL power calculation should be adjusted in eyes with Fuch’s dystrophy undergoing cataract surgery combined with DMEK. The fictitious PPPA ratio and keratometer index may guide further IOL power calculation methods to achieve this.

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“…Assessment of the corneal curvature plays an important role in refractive surgery planning, intraocular lens power calculation and early diagnosis of keratoconus 6,[11][12][13] . In traditional keratometry, the cornea is assumed to have a xed ratio between the anterior and poster corneal curvature, and the anterior corneal curvature is used to calculate the total corneal curvature.…”

Section: Discussionmentioning

confidence: 99%

A Multicenter Study of the Correlations of Anterior and Posterior Corneal Parameters in Chinese Myopic Patients

Hu¹,

Wang²,

Zhu³

et al. 2020

Preprint

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In this observational cross-sectional study consisting of 8365 Chinese myopic patients from five different ophthalmic centers, we investigated the correlations between anterior and posterior corneal parameters. Strongly negative anterior-posterior correlations of the mean corneal curvature were observed, with similar correlation coefficients in all myopic groups (R: -0.85 to -0.88). The anterior-posterior correlations of corneal astigmatism (R: 0.65 to 0.75), eccentricity (R: 0.27 to 0.38) and asphericity (R: 0.29 to 0.41) were all positive, with slightly different correlation coefficients between the myopic groups. The anterior-posterior correlations of mean corneal curvature were strongly negative with similar correlation coefficients in all quantile groups of six corneal and anterior chamber parameters (R: -0.84 to -0.91), except Sim Km (R: -0.36 to -0.64). The anterior-posterior correlations of corneal astigmatism were all positive with slightly different correlation coefficients between the quantile groups of SimKm (R: 0.66 to 0.74). The anterior-posterior correlations of corneal eccentricity (R: 0.30 to 0.44) and asphericity (R: 0.33 to 0.45) were positive and slightly different between the quantile groups of SimKm, pachy apex and corneal volume. In conclusion, anterior-posterior correlations of corneal curvature, astigmatism, eccentricity and asphericity can be affected by the severity of myopia and some other corneal parameters.

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Use of the Posterior/Anterior Corneal Curvature Radii Ratio to Improve the Accuracy of Intraocular Lens Power Calculation: Eom's Adjustment Method

Abstract: IOL power calculation using adjusted corneal power according to the posterior/anterior corneal curvature radii ratio provided more accurate refractive outcomes than calculation using conventional K.

Cited by 24 publications

References 30 publications

Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

Assessing the validity of corneal power estimation using conventional keratometry for intraocular lens power calculation in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty

A Multicenter Study of the Correlations of Anterior and Posterior Corneal Parameters in Chinese Myopic Patients

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