How to Determine Flatter Corneas From K Readings

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Enquiry Article

Evaluation of Equivalent Keratometry Readings Obtained by Pentacam HR (High Resolution)

• Yanjun Hua,
• Xiaolan Zhang,
• Tor Paaske Utheim,
• Jinhai Huang,
• Chao Pan,
• Weina Tan,
• Qinmei Wang

x

• Published: March 7, 2016
• https://doi.org/10.1371/periodical.pone.0150121

Figures

Abstract

Purpose

To appraise the repeatability of Equivalent Keratometry Readings (EKRs) obtained by the Pentacam Hr (high resolution) in untreated and mail-LASIK optics, and to compare them with the keratometry (K) values obtained past other algorithms.

Methods

In this prospective study, 100 untreated eyes and 71 post-LASIK eyes were included. In the untreated group, each center received iii consecutive scans using the Pentacam Hour, and EKR values in all key corneal zone, the true net power (K_net) and the imitation K (SimK) were obtained for each scan. In the post-LASIK group, each eye received subjective refraction and 3 consecutive scans with the Pentacam 60 minutes preoperatively. During the 3-month mail-surgery exam, the same examinations and the apply of an IOLMaster were conducted for each eye. The EKRs in all zone, the K_net, the mean Thou (Thousand_m) past IOLMaster and the K values by clinical history method (K_CHM) were obtained. The repeatability of the EKRs was assessed by the within-subject area standard deviation (Due south_{due west}), two.77S_w, coefficient of variation (CV_w) and intraclass correlation coefficient (ICC). The bonferroni corrected multiple comparisons were performed to clarify the differences among the EKRs and K values calculated by other algorithms inside the two groups. The 95% limits of agreement (LoA) were calculated.

Results

The EKR values in all primal corneal zone were repeatable in both the untreated group (S_w≦0.xix D, two.77S_w≦0.52 D, CV_w≦1%, ICC≧0.978) and the post-LASIK group (S_westward≦0.22 D, 2.77S_{due west}≦0.62 D, CV_westward≦1%, ICC≧0.980). In the untreated group, the EKR in 4mm zone was close to SimK (P = 1.000), and the 95% LoA was (-0.13 to 0.15 D). The difference between G_net and SimK was -1.30±0.13 D (95% LoA -1.55 to -i.55 D, P<0.001). In the post-LASIK group, all the EKRs were significantly higher than K_CHM (all P<0.001). The differences between the EKR in 4mm zone and Yard_CHM, the EKR in 7mm zone and K_CHM, K_net and Grand_CHM, One thousand_grand and Chiliad_CHM, SimK and K_net were 0.64±0.50 D (95% LoA, -0.33 to 1.62 D), 1.77±0.88 D (95% LoA, 0.04 to 3.51 D), -0.98±0.48 D (95% LoA, -i.92 to -0.04 D), 0.64±0.53 D (95% LoA, -0.40 to one.68 D), and 1.73±0.20 D (95% LoA, 1.33 to 2.thirteen D), respectively.

Conclusions

The EKRs obtained by the Pentacam HR were repeatable in both untreated optics and post-LASIK eyes. Compared to the total corneal ability obtained by the clinical history method, the EKR values more often than not overestimated the full corneal ability in post-LASIK eyes. So, further calibrations for the EKR values should be conducted, before they were used for the total corneal power cess in post-LASIK optics.

Commendation: Hua Y, Zhang X, Utheim TP, Huang J, Pan C, Tan Due west, et al. (2016) Evaluation of Equivalent Keratometry Readings Obtained by Pentacam Hr (High Resolution). PLoS ONE 11(three): e0150121. https://doi.org/10.1371/journal.pone.0150121

Editor: Gianni Virgili, University of Florence, ITALY

Received: September 3, 2015; Accepted: February ix, 2016; Published: March 7, 2016

Copyright: © 2016 Hua et al. This is an open access article distributed under the terms of the Creative Eatables Attribution License, which permits unrestricted apply, distribution, and reproduction in whatsoever medium, provided the original writer and source are credited.

Information Availability: Data may compromise the privacy of study participants and may non be shared publicly. Information are available upon asking to the authors.

Funding: The authors have no support or funding to written report.

Competing interests: The authors have declared that no competing interests exist.

Introduction

The accurate assessment of the full corneal power in eyes later corneal refractive surgery is essential for the prediction of intraocular lens (IOL) ability[one–3]. Currently, there are several methods to assess full corneal power after corneal refractive surgery, which tin be divided into two categories. Ane requires preoperative data, including the clinical history method (Chiliad_CHM)[4] and double-K method[5, 6]. The other category does not require preoperative information and includes the rigid contact lens method[7], the Maloney method[8–x], Shammas formula[11, 12] and the BESSt formula[13].

The Holladay's Equivalent Keratometry Readings (EKRs) obtained by the Pentacam Hr belongs to the latter[14]. However, the precision of EKRs for the assessment of total corneal power afterwards corneal refractive surgery is still controversial. The repeatability of the EKR (4.v mm central corneal zone) from untreated optics has been shown to be suboptimal[xv]. Additionally, it was reported that the EKRs were not accurate for the prediction of IOL power in both untreated eyes and postoperative optics[sixteen].

The purpose of the nowadays study was to assess the repeatability of the EKR in all central corneal zones obtained by the Pentacam HR. In untreated eyes, nosotros compared the EKRs in all zones with the imitation keratometry (SimK) obtained past the Pentacam Hour, and in post-LASIK optics, we mainly compared the EKRs in all zones with Chiliad_CHM.

Subjects and Methods

The present study was conducted at the Heart Hospital of Wenzhou Medical University (Wenzhou, China) between August and December 2011. The study was performed in accordance with the principles stated in the Announcement of Helsinki and was approved by the Part of Research Ethical Committee, Heart Infirmary of Wenzhou Medical University. All subjects were informed of the purpose of the research and provided signed informed consent. Two groups were included in this study, the untreated group and the post-LASIK group. For the untreated group, inclusion criteria were healthy subjects aged eighteen to 40 years old, without advice or cooperation disorders. All the subjects had the following qualities: 1) a preoperative best corrected visual acuity of 1.0 or more, 2) a corneal astigmatism of less than 2.0 diopter (D), and 3) an intraocular pressure level range of 10 mmHg to 21 mmHg. The exclusion criteria included the following: i) history of ocular pathology, 2) history of corneal or intraocular trauma, three) previous ocular surgery, four) the wearing of hard contact lenses within four weeks or soft contact lenses within two weeks, and 5) astringent dry eye (tear moving-picture show break-up fourth dimension shorter than 5 seconds). For the mail service-LASIK grouping, besides the inclusion and exclusion criteria stated above, the postoperative uncorrected visual vigil was no less than ane.0 without corneal opacities.

In the untreated group, subjects received iii consecutive scans using the Pentacam Hr (Oculus, Federal republic of germany) afterward a routine ophthalmic examination (including subjective refraction, slit lamp exam, fundus examination and intraocular pressure). In add-on to the preoperative exams of the untreated group, the mail-LASIK group received exams more than than three months later the surgery, including the following: subjective refraction, the Pentacam 60 minutes (with three consecutive scans) and IOLMaster (Carl Zeiss). The Pentacam Hour was performed in a dark room. Subjects were told to place their mentum on the chinrest, focus on the indicator, and widely open their optics later blinking. The Pentacam HR would take pictures automatically within 2 seconds. When the quality specification screen displayed "OK", the issue was considered valid. Three valid scans for each eye were obtained. The hateful keratometry (Thou_m) from post-LASIK optics was obtained by the IOLMaster. In the mail service-LASIK group, the surgery was performed using the Allegretto laser system (Lumenis, Inc., United states). The diameters of optical zone ranged from six.0 mm to 7.0 mm during the surgery.

Parameters for cess of corneal ability in the Pentacam HR

The anterior and posterior primal corneal curvature, within a sure diameter (in meter), were defined every bit r_inductive and r_posterior, respectively. The refractive index of air (n₀) is 1.000. The standard corneal refractive index (n) is 1.3375. The real corneal refractive alphabetize (north₁) is 1.376. The aqueous refractive index (n₂) is 1.336. The ratio of posterior and inductive curvature from an untreated cornea (R_one) is 0.822[17–nineteen]. The ratio of fake keratometry and anterior corneal power (R₂) is (i.3375–1.000)/(ane.376–1.000) = 0.8976.

The SimK was calculated based on the anterior cardinal corneal curvature within certain range and the standard corneal refractive index equally follows:

The true cyberspace ability (K_net)[20] represents the sum of the inductive and posterior corneal power and is calculated using the following formula:

The EKR[xiv] was advanced by Holladay and his colleagues specifically for the evaluation of full corneal ability after corneal refractive surgery and has been obtained in Pentacam Hr since 2006. In the Pentacam Hr'south software interface "Holladay EKR Detail Report" values are given within 1 mm, 2 mm, three mm, 4 mm, four.v mm, v mm, six mm and seven mm of the central corneal bore, respectively. The values were calculated using the following formula:

This formula higher up, notwithstanding, can be simplified to:

In this study, the mean EKR within one mm, 2 mm, 3 mm, iv mm, 4.5 mm, five mm, 6 mm and 7 mm zones were calculated and were abbreviated every bit EKR1, EKR2, EKR3, EKR4, EKR4.five, EKR5, EKR6 and EKR7, respectively.

The following 3 parameters are needed for the calculation of Thousand_CHM[4]: i) the preoperative spherical equivalent (SEQ_pre) at corneal airplane, 2) the postoperative spherical equivalent (SEQ_post) at the corneal airplane and 3) the preoperative faux keratometry (preK). Start, the amount of refraction change in diopters before and after the surgery is calculated using this formula:

2d, the 1000_CHM is calculated based on the post-obit formula:

In this written report, preK was obtained by the Pentacam Hr, and we regarded the K_CHM as the criterion to appraise the EKR, SimK and K_cyberspace obtained by the Pentacam 60 minutes in the post-LASIK grouping.

Statistical assay

All data were entered into an Excel spreadsheet (Microsoft Excel 2010 Crop.), and MedCalc Software (Vision11.iv.two.0, MedCalc, Inc.) was used for statistical assay. The results were expressed as the mean ± standard deviation (SD). A P value less than 0.05 was considered statistically significant. The normality of all data distributions was confirmed by the Kolmogorov-Smirnov exam (all P>0.05), and parametric statistical tests were used for data analysis. Repeated measures ANOVA was applied to analyze the repeatability of EKR in different zones and the SimK and K_cyberspace in both the untreated and post-LASIK groups_. The within-subject SD (S_west) of three consecutive measurements were calculated. The repeatability limit was defined every bit two.77S_w, which means an interval within which 95% of the differences between measurements are expected to prevarication. The within-subject coefficient of variance (CV_w) was calculated every bit the ratio of the S_w to the overall hateful. Using the CV_w, information with different means can be compared with each other. A lower CV_w is associated with college repeatability. The intraclass correlation coefficients (ICCs) were based on the assay of variance for a two-mode mixed-effects model with an absolute understanding for consistency of individual measurements and the 95% confidence interval (CI) was calculated. The ICC (ranging from 0 to 1) assesses the consistency for data sets of repeated measurements. Every bit the ICC nears a value of ane, the measurement consistency increases, and a value more 0.9 indicates adequate clinical reliability[21]. The repeated measures analysis of variance with the Bonferroni corrected multiple comparisons was applied to compare the EKRs, SimK and K_net in the untreated group, and the EKRs, SimK, G_net and K_CHM in mail-LASIK group. The 95% limits of understanding (LoA) were calculated.

Results

In the untreated grouping, 100 eyes (47 men and 53 women) were included, and the mean manifest spherical equivalent refraction was -iii.23±1.76 D. In the post-LASIK group, 71 eyes (24 men and 19 women) were included. The hateful manifest spherical equivalent refraction before the surgery and at least three months afterward surgery were -5.01±i.91 D (range -9.l D to -i.fifty D) and 0.03±0.38 D (range -1.50 D to 0.88 D), respectively. The mean amount of refraction change in diopters before and after the surgery was 5.05±ane.81 D (range 1.25 to eight.88 D).

The repeatability of the EKRs in dissimilar zones, SimK and K_net (Tabular array i)

In both the untreated grouping and the post-LASIK grouping, all the S_w, 2.77S_w and CV_w values were less than 0.22 D, 0.62 D and i%, respectively, and all ICCs were higher than 0.978. The Pentacam HR performed high repeatability of all the EKRs, SimK and Grand_cyberspace values from both untreated eyes and postal service-LASIK eyes.

Comparison of the EKRs, SimK, M_internet and K_CHM (Table two)

In the untreated group, amid all the EKRs, EKR2 (43.39±1.28 D) was the smallest, but non significantly smaller than EKR1 (43.40±one.28 D, P = one.000). EKR2 was, however, significantly lower than all the other EKR (P<0.05) and SimK (P<0.001), and significantly college than One thousand_net (P<0.001). SimK was 43.48±1.28 D. Comparing all the EKR to SimK, EKR1, EKR2 and EKR3 were significantly lower than SimK. EKR4.five, EKR5, EKR6 and EKR7 were significantly higher than SimK. EKR4 was close to SimK (P = 1.000), and the 95% LoA was -0.13 to 0.15 D (Fig i). The divergence betwixt Yard_internet and SimK was -i.30±0.13 D (95% LoA, -one.55 to -1.04 D).

Fig ane. Multiple variables graph in the untreated grouping.

EKR1/2/3/iv/4.5/5/6/7, Equivalent Keratometry Readings in 1 mm /2 mm/3 mm/4 mm/4.5 mm/five mm/half dozen mm/7 mm zone; SimK, mean Simulated Keratometry obtained past Pentacam HR; Grand_net, the true net power obtained past Pentacam HR.

https://doi.org/x.1371/journal.pone.0150121.g001

In the post-LASIK group, it indicated that the trend from EKR1 to EKR7 gradually decreased to EKR4 (39.04±1.67 D) as the minimum, then increased to EKR7 (Fig two). There was no statistical significance between EKR4 and EKR4.5 (P = 0.396), EKR3 and EKR4.5 (P = 0.559). M_CHM was 38.40±one.86 D. The differences betwixt EKR4 and K_CHM, EKR7 and One thousand_CHM, K_net and 1000_CHM, K_m and K_CHM, SimK and K_net were 0.64±0.50 D (95% LoA, -0.33 to one.62 D), ane.77±0.88 D (95% LoA, 0.04 to iii.51 D), -0.98±0.48 D (95% LoA, -1.92 to -0.04 D), 0.64±0.53 D (95% LoA, -0.forty to 1.68 D), and one.73±0.20 D (95% LoA, 1.33 to 2.13 D), respectively. SimK was equal to K_yard (95% LoA -0.51 to 0.73 D, P = 0.324, Fig 2).

Fig 2. Multiple variables graph in the mail-LASIK grouping.

EKR1/two/3/4/four.5/five/6/seven, Equivalent Keratometry Readings in 1 mm/2 mm/3 mm/4 mm/iv.five mm/5 mm/6 mm/7 mm zone; SimK, mean Imitation Keratometry obtained past Pentacam Hr; K_net, the true net power obtained by Pentacam HR; Thousand_CHM, total corneal power obtained by clinical history method.

https://doi.org/10.1371/periodical.pone.0150121.g002

Discussion

The EKR assessment, advanced by Holladay and co-workers, was used to assess the total corneal ability after corneal refractive surgery. In the written report past Holladay et al[xiv], the Pentacam was used to obtain the inductive and posterior corneal ability of 100 post-LASIK optics and the formula (EKR(D) = 0.376/r_anterior − 0.03165/r_posterior) was used to summate EKR from different central corneal zones (from 0.5 mm to eight mm bore, each 0.5 mm to an lodge). Holladay et al observed that the EKR of the 4.5 mm diameter zone was close to the total corneal power obtained past the clinical history method. Comparing the EKR4.v to the back calculated total corneal ability in 41 eyes that received both RK and cataract surgery, minor errors were found. Based on these results, Holladay et al recommended EKR4.5 to exist used for the assessment of corneal ability afterward corneal refractive surgery.

Thus far, in that location have been very few studies concerning the repeatability of the EKRs. McAlinden et al[15] used the Pentacam Hr to measure out 100 untreated eyes and institute that the repeatability of EKR maps and the Holladay report Equivalent K1, K2 and Km (EKR4.five) were poor. In dissimilarity, in the present study, EKRs in all zones from untreated eyes were repeatable. According to McAlinden et al, merely the EKR in iv.5 mm was evaluated, and we evaluated the EKRs in all central corneal zones. Moreover, this written report was the first to study the repeatability of EKRs in all zones in postal service-LASIK optics, and the results for the EKRs were repeated in all central corneal zones.

Interestingly, in the mail service-LASIK group, it indicated that the trend from EKR1 to EKR7 gradually decreased to EKR4 as the minimum, then increased to EKR7 (Fig 2). This issue was unlike from the studies by Falavarlani et al[22] (35 eyes after PRK) and Savini et al[23] (sixteen eyes afterwards myopic laser correction) in which the values gradually increased from EKR1 to EKR4.v. According to Falavarlani et al, the EKR values increased from twoscore.43±ii.04 D to twoscore.91±ane.82 D, and co-ordinate to Savini et al, they increased from 37.46±1.77 D to 38.forty±one.13 D. The difference might be explained past the use of the different surgical approaches and laser systems used during surgery. In our study, just post-LASIK eyes were included, while Falavarlani et al only included post-PRK optics. Savini et al included eyes later on LASIK, PRK and LASEK.

Currently, there is no more often than not accustomed device that can exactly measure and calculate the total corneal power after corneal refractive surgery. The clinical history method, which was presented in 1989 by Holladay et al, has been regarded as the gold standard in several published studies[13, 14, 22–24]. In our study, K_CHM was smaller than all the EKRs, and compared to EKR4 (the smallest among all the EKRs), the difference was 0.64±0.50 D (P<0.001). The K_{one thousand} obtained by the IOLMaster was equal to EKR4 and similar to SimK. Nosotros compared our study with Falavarjani et al[22] and Savini et al[23]. The Thou_CHM, SimK and EKR in our report were higher than in Savini et al, but lower than in Falavarjani et al. I possibility may be due to the different preoperative refraction of the subjects. In our study, the hateful preoperative spherical equivalent was -5.01±1.91 D (range -9.fifty D to -one.50 D). According to Savini et al and Falavarjani et al, the values were -five.10±ane.forty D, and -three.46±ane.xvi D (range -6.00 D to -1.50 D), respectively. In the issue of similar mean corneal power, a higher refractive error will lead to a larger corporeality of surgical correction. This leads to a flatter cornea with smaller postoperative corneal ability. Based on all 3 studies, we speculate that the EKR overestimates the corneal power in post-LASIK optics. Two observations support this notion. First, in our written report the EKR4 (the smallest among all the EKRs) was 0.half-dozen to 0.7 D higher than the gilt standard K_CHM. Second, the SimK, K_chiliad, EKR4 and EKR4.5 in our written report were very close to each other (the same results were shown by Savini et al and Falavajani et al). As SimK and K_thou were calculated by the same formula (SimK = 1.3375/r_inductive), which explains why no statistical significance was observed between SimK and K_m. For untreated eyes, we could obtain accurate results using this formula; however, for eyes after corneal refractive surgery, because of the change of ratio between the posterior and inductive corneal curvature, the corneal power was overestimated[25, 26]. And in our study, EKR4 (the minimum of EKRs) was equal to K_yard, and similar to SimK. Therefore, we conclude that EKR4 too overestimates the corneal ability in mail service-LASIK eyes.

In our study, SimK was 1.thirty±0.thirteen D higher than M_net in the untreated group, and in the mail service-LASIK grouping the difference increased to ane.68±0.42 D. The divergence was attributed to two factors. First, the ii parameters were calculated using a unlike corneal refractive index based on dissimilar assumptions. For SimK, the standard corneal refractive index (1.3375) was adopted considering the cornea every bit a thin lens; for K_net, the real corneal refractive index (1.376) and aqueous refractive alphabetize (one.336) were adopted. Savini et al[27] used the Pentacam to measure 71 preoperative eyes, and establish that SimK was 1.25 D higher than M_internet, which was very close to our study (ane.thirty±0.thirteen D). Thus, we believe that this factor might cause the deviation of 1.2 to 1.3 D. Information technology should be noted that One thousand_internet, which is the sum of anterior and posterior corneal ability (without consideration of CCT), was different from the total corneal power based on the Gaussian thick lens formula (with consideration of CCT). The difference, which was betwixt 0.12 to 0.25 D[20], could exist regarded as acceptable in the clinic. 2nd, for post-LASIK optics the ratio of the posterior and inductive corneal curvature is considerably unlike from of the Gullstrand model eye value of 0.883. Therefore, the standard corneal refractive index based on the Gullstrand model eye caused the incorrect adding, explaining the deviation of approximately 0.4 D.

There were two limitations to our study. First, we simply studied untreated eyes and myopic post-LASIK eyes, the eyes after RK and hyperopia corneal refractive surgery were non involved. Second, the repeatability of the clinical history method was not confirmed. The clinical history method has been suggested not to be the near authentic for the prediction of IOL power after corneal refractive surgery[28].

In conclusion, the EKR obtained past the Pentacam Hour were repeatable in both untreated eyes and post-LASIK eyes. Compared to the clinical history method, EKRs generally overestimated the corneal power in mail-LASIK optics. EKR4 and EKR4.5 were closest to the clinical history method, but were still overestimated by 0.6 to 0.7 D.

Supporting Information

Author Contributions

Conceived and designed the experiments: YH QW. Performed the experiments: CP WT. Analyzed the data: YH JH. Contributed reagents/materials/analysis tools: TPU. Wrote the paper: YH XZ TPU.

References

1. ane. Feiz Five. Intraocular lens ability calculation after corneal refractive surgery. Center East Afr J Ophthalmol. 2010;17(1):63–8. pmid:20543939.
   • View Article
   • PubMed/NCBI
   • Google Scholar
2. two. Jin H, Holzer MP, Rabsilber T, Borkenstein AF, Limberger IJ, Guo H, et al. Intraocular lens ability adding after laser refractive surgery: cosmetic algorithm for corneal power estimation. J Cataract Refract Surg. 2010;36(1):87–96. pmid:20117710.
   • View Commodity
   • PubMed/NCBI
   • Google Scholar
3. three. Kalyani SD, Kim A, Ladas JG. Intraocular lens power calculation after corneal refractive surgery. Curr Opin Ophthalmol. 2008;19(4):357–62. pmid:18545021.
   • View Article
   • PubMed/NCBI
   • Google Scholar
4. iv. Holladay JT, Van Gent S, Ting AC, Portney 5, Willis TR. Silicone intraocular lens power vs temperature. Am J Ophthalmol. 1989;107(iv):428–9. pmid:2929713.
   • View Commodity
   • PubMed/NCBI
   • Google Scholar
5. 5. Saiki Grand, Negishi K, Kato N, Ogino R, Arai H, Toda I, et al. Modified double-K method for intraocular lens power calculation after excimer laser corneal refractive surgery. J Cataract Refract Surg. 2013;39(four):556–62. pmid:23415780.
   • View Commodity
   • PubMed/NCBI
   • Google Scholar
6. six. Aramberri J. Intraocular lens power calculation afterward corneal refractive surgery: double-K method. J Cataract Refract Surg. 2003;29(xi):2063–viii. S088633500300957X. pmid:14670413.
   • View Article
   • PubMed/NCBI
   • Google Scholar
7. seven. Haigis W. Corneal power subsequently refractive surgery for myopia: contact lens method. J Cataract Refract Surg. 2003;29(7):1397–411. S0886335002020448. pmid:12900252.
   • View Article
   • PubMed/NCBI
   • Google Scholar
8. 8. Maloney RK, Smith RJ. Measuring corneal refractive ability after LASIK. J Refract Surg. 2000;16(half dozen):756–7. pmid:11110321.
   • View Article
   • PubMed/NCBI
   • Google Scholar
9. 9. Wang L, Booth MA, Koch DD. Comparison of intraocular lens power calculation methods in optics that have undergone LASIK. Ophthalmology. 2004;111(10):1825–31. S0161-6420(04)00818-8. pmid:15465542.
   • View Commodity
   • PubMed/NCBI
   • Google Scholar
10. x. Jin H, Auffarth GU, Guo H, Zhao P. Corneal ability estimation for intraocular lens power calculation after corneal laser refractive surgery in Chinese optics. J Cataract Refract Surg. 2012;38(ten):1749–57. pmid:22925179.
    • View Article
    • PubMed/NCBI
    • Google Scholar
11. 11. Shammas HJ, Shammas MC, Garabet A, Kim JH, Shammas A, LaBree 50. Correcting the corneal ability measurements for intraocular lens ability calculations after myopic light amplification by stimulated emission of radiation in situ keratomileusis. Am J Ophthalmol. 2003;136(three):426–32. S0002939403002757. pmid:12967794.
    • View Article
    • PubMed/NCBI
    • Google Scholar
12. 12. Shammas HJ, Shammas MC. No-history method of intraocular lens ability adding for cataract surgery after myopic laser in situ keratomileusis. J Cataract Refract Surg. 2007;33(1):31–half-dozen. S0886-3350(06)01221-ane. pmid:17189790.
    • View Article
    • PubMed/NCBI
    • Google Scholar
13. thirteen. Borasio E, Stevens J, Smith GT. Estimation of true corneal ability after keratorefractive surgery in optics requiring cataract surgery: BESSt formula. J Cataract Refract Surg. 2006;32(12):2004–fourteen. S0886-3350(06)01183-7. pmid:17137976.
    • View Commodity
    • PubMed/NCBI
    • Google Scholar
14. xiv. Holladay JT, Hill We, Steinmueller A. Corneal power measurements using scheimpflug imaging in eyes with prior corneal refractive surgery. J Refract Surg. 2009;25(10):862–eight. pmid:19835326.
    • View Commodity
    • PubMed/NCBI
    • Google Scholar
15. xv. McAlinden C, Khadka J, Pesudovs G. A comprehensive evaluation of the precision (repeatability and reproducibility) of the Oculus Pentacam HR. Invest Ophthalmol Vis Sci. 2011;52(10):7731–7. pmid:21810981.
    • View Article
    • PubMed/NCBI
    • Google Scholar
16. 16. Tang Q, Hoffer KJ, Olson MD, Miller KM. Accurateness of Scheimpflug Holladay equivalent keratometry readings afterwards corneal refractive surgery. J Cataract Refract Surg. 2009;35(seven):1198–203. pmid:19545808.
    • View Article
    • PubMed/NCBI
    • Google Scholar
17. 17. Tang M, Chen A, Li Y, Huang D. Corneal power measurement with Fourier-domain optical coherence tomography. J Cataract Refract Surg. 2010;36(12):2115–22. pmid:21111315.
    • View Article
    • PubMed/NCBI
    • Google Scholar
18. 18. Goss DA, W RW. Introduction to the Optics of the Eye. Butterworth-Heinemann. 2002. pp. 113–135.
19. 19. Ho JD, Tsai CY, Tsai RJ, Kuo LL, Tsai IL, Liou SW. Validity of the keratometric index: evaluation by the Pentacam rotating Scheimpflug camera. J Cataract Refract Surg. 2008;34(i):137–45. pmid:18165094.
    • View Article
    • PubMed/NCBI
    • Google Scholar
20. twenty. Savini G, Hoffer KJ. Pentacam 60 minutes equivalent Grand-reading. J Refract Surg. 2010; 26(6): author reply 389–391. pmid:20677725
    • View Article
    • PubMed/NCBI
    • Google Scholar
21. 21. Bland JM, Altman DG. Measurement mistake. BMJ. 1996;313(7059):744. pmid:8819450.
    • View Article
    • PubMed/NCBI
    • Google Scholar
22. 22. Falavarjani KG, Hashemi M, Joshaghani G, Azadi P, Ghaempanah MJ, Aghai GH. Determining corneal ability using Pentacam after myopic photorefractive keratectomy. Clin Experiment Ophthalmol. 2010;38(iv):341–5. pmid:20491804.
    • View Article
    • PubMed/NCBI
    • Google Scholar
23. 23. Savini M, Barboni P, Profazio Five, Zanini Chiliad, Hoffer KJ. Corneal power measurements with the Pentacam Scheimpflug photographic camera later myopic excimer laser surgery. J Cataract Refract Surg. 2008;34(5):809–13. pmid:18471637.
    • View Article
    • PubMed/NCBI
    • Google Scholar
24. 24. Holladay JT. Accuracy of Scheimpflug Holladay equivalent keratometry readings after corneal refractive surgery. J Cataract Refract Surg. 2010;36(1):182–four. pmid:20117729.
    • View Commodity
    • PubMed/NCBI
    • Google Scholar
25. 25. Seitz B, Langenbucher A, Nguyen NX, Kus MM, Kuchle M. Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy. Ophthalmology. 1999;106(4):693–702. S0161-6420(99)90153-7. pmid:10201589.
    • View Article
    • PubMed/NCBI
    • Google Scholar
26. 26. Seitz B, Langenbucher A. Intraocular lens power calculation in eyes after corneal refractive surgery. J Refract Surg. 2000;sixteen(3):349–61. pmid:10832985.
    • View Article
    • PubMed/NCBI
    • Google Scholar
27. 27. Savini Chiliad, Barboni P, Carbonelli K, Hoffer KJ. Agreement between Pentacam and videokeratography in corneal power assessment. J Refract Surg. 2009;25(six):534–8. pmid:19603621.
    • View Article
    • PubMed/NCBI
    • Google Scholar
28. 28. McCarthy M, Gavanski GM, Paton KE, Kingdom of the netherlands SP. Intraocular lens power calculations subsequently myopic laser refractive surgery: a comparison of methods in 173 optics. Ophthalmology. 2011;118(v):940–4. pmid:21131054.
    • View Commodity
    • PubMed/NCBI
    • Google Scholar

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Source: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0150121

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