Comparison of Central Corneal Thickness measured by Standard Ultrasound Pachymetry, Corneal Topography, Tono-Pachymetry and Anterior Segment Optical Coherence Tomography

For Peer Review Only Comparison of Central Corneal Thickness measured by Standard Ultrasound Pachymetry, Corneal Topography, Tono-Pachymetry and Anterior Segment Optical Coherence Tomography. Journal: Current Eye Research Manuscript ID NCER-2018-0036 Manuscript Type: Original Articles Date Submitted by the Author: 12-Jan-2018 Complete List of Authors: Gonzalez-Perez, Javier; University of Santiago de Compostela, Applied Physiscs Queiruga Piñeiro, Juan ; University of Santiago de Compostela, Applied Physiscs; Instituto Oftalmológico Fernández-Vega Sánchez García, Angel; University of Santiago de Compostela, Applied Physiscs Gonzalez-Meijome, Jose; University of Minho, Keywords: Central corneal thickness, ultrasound pachymetry, non-contact tonopachymetry, Scheimpflug camera, anterior segment optical coherence tomography, interchangeability URL: http://mc.manuscriptcentral.com/ncer Current Eye Research For Peer Review Only Comparison of Central Corneal Thickness 1 measured by Standard Ultrasound 2 Pachymetry, Corneal Topography, Tono-3 Pachymetry and Anterior Segment Optical 4 Coherence Tomography. 5 6 Javier González-Pérez, OD, PhD, FIACLE,1 Juan Queiruga Piñeiro OD, MSc,1,2 7 Ángel Sánchez García OD, MSc,1 José Manuel González Méijome OD,1,3 PhD, 8 FIACLE. 9 10 1 Ocular Surface and Contact Lens Research Laboratory. Faculty of Optometry. 11 University of Santiago de Compostela, Spain. 12 2 Instituto Oftalmológico Fernández-Vega, Oviedo, Spain. 13 3 Clinical & Experimental Optometry Research Lab. Center of Physics (Optometry) - 14 School of Sciences. University of Minho, 4710-057 Gualtar – Braga, Portugal. 15 16 17 18 Running Head Title: Reliability of Ultrasound and 3 non-contact pachymeters 19 Corresponding Author: 20 Javier González-Pérez, OD, PhD 21 Lab. SOYLC – Applied Physics (Optometry) 22 Faculty of Optometry 23 University of Santiago de Compostela 24 15782 Santiago de Compostela (Spain) 25 Telephone: +34 881 813 537 / 881 813 504 26 e-mail: [email protected] 27 Key-words: Central corneal thickness, ultrasound pachymetry, non-contact tono28 pachymetry, Scheimpflug camera, anterior segment optical coherence tomography, 29 interchangeability. 30 Acknowledgement and Disclosure: 31 The authors declare that they do not have any proprietary or financial interest in any of 32 the materials mentioned in this article. 33 34 35 36 Page 1 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Abstract 37 38 Purpose: To compare central corneal thickness (CCT) measured by standard 39 ultrasound pachymetry (USP), and three non-contact devices in healthy eyes. 40 41 Methods: A cross-sectional study of CCT measurement in 52 eyes of 52 healthy 42 volunteers was done by a single examiner at Ocular Surface and Contact Lens 43 Laboratory. Three consecutive measurements were done by standard USP, non-44 contact tono-pachymeter, Pentacam corneal topographer, and Anterior Segment 45 Optical Coherence Tomography (AS-OCT). The mean values were used for 46 assessment. The results were compared using t-test, linear regression and Pearson 47 correlation. Agreement among the devices was analyzed using mean differences and 48 Bland-Altman analysis with 95% limits of agreement (LoA). Finally, reliability was 49 analyzed using intraclass correlation coefficient (ICC). 50 51 Results: Mean CCT by ultrasound pachymeter, tono-pachymeter, corneal topographer 52 and AS-OCT were 558.9±31.2 µm, 525.8±43.1 µm, 550.4±30.5 µm and 545.9±30.5 µm 53 respectively. There was a significant positive correlation between AS-OCT and USP 54 (Pearson correlation = 0.957, p < 0.001), corneal topography and USP (Pearson 55 correlation = 0.965, p < 0.001) and corneal topography and AS-OCT (Pearson 56 correlation = 0.965, p < 0.001). There was a lower correlation between CT-1P tono-57 pachymeter and the other three modalities. Intraclass correlation coefficients shows an 58 excellent reliability between pairs except for CT-1P against the other three instruments 59 that were found moderate. 60 61 Conclusions: CT-1P tono-pachymeter underestimate CCT measurements compared 62 to Scheimpflug system, AS-OCT device, and USP. Mean CCT among USP, Pentacam 63 and AS-OCT were comparable and had significant linear correlations. In clinical 64 practice, these three modalities could be interchangeable in healthy patients. 65 66 67 Page 2 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Introduction 68 69 Central corneal thickness (CCT) is an important and sensitive indicator of corneal 70 health.1 It is necessary in monitoring corneal diseases such as corneal oedema, 71 keratoconus, Fuchs dystrophy, glaucoma and to evaluate corneal barrier and 72 endothelial pump function in several surgical conditions.2-4 In clinical practice, it is 73 useful in the evaluation of contact lens wear,5,6 selecting patients for refractive surgery 74 and posterior evaluation.7,8 75 76 CCT is also a predictive factor for glaucoma progression in patients with high baseline 77 intraocular pressure (IOP). Moreover, CCT is an important parameter in the risk 78 profiling of ocular hypertensives to glaucoma patients.9,10 Since IOP measurement by 79 applanation tonometry is influenced by CCT, it is important to obtain the reliable 80 corneal pachymetry for each patient and adjust the IOP for the measured CCT.1,11 81 82 There are numerous methods available to measure CCT. Ultrasound pachymetry 83 (USP) has been widely considered as the gold standard because it is very easy, fast 84 and convenient to repeat several measurements to minimize error.12,13 USP requires 85 contact with the cornea and uses the Doppler Effect to determine CCT. Disadvantages 86 of ultrasonic pachymetry include direct placement of the probe on the cornea, the risk 87 infection and corneal epithelial damage, the necessity for topical anesthesia (which 88 may influence by up 10 microns CCT measurements), and dependence on examiner 89 experience for reliable measurements.14-15 90 91 Optical Coherence Tomography (OCT), which was introduced in the early 1990s, is a 92 noncontact imaging method that provides detailed cross-sectional images of biological 93 tissues by measuring their optical reflections.16,17 OCT has been widely used clinically 94 Page 3 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only in ophthalmologic practice for the last two decades.18-19 In recent years, OCT 95 technology has experimented the incorporation of spectral-domain (SD) imaging that 96 offers significant advantages over the traditional time-domain (TD) techniques, which 97 include faster imaging speed, higher resolution, and better visualization.20 98 Simultaneously with these improvements, the utility of OCT in the ophthalmic practice 99 has become more extended. Particularly, anterior segment OCT (AS-OCT), which 100 provides high-resolution cross-sectional images of anterior segment structures, 101 including corneal thickness, anterior chamber angle, conjunctiva, and tear meniscus, 102 has recently gained popularity.21-24 There are very few studies giving comparative 103 accuracy of CCT measurements by AS-OCT versus USP.4,25 104 105 The Pentacam, developed in 2000s, uses a rotating Scheimpflug camera and a slit-106 light source that rotate together around the optical axes of the eye to calculate a three-107 dimensional model of the anterior segment. A total of 25 images are captured within 2 108 sg, with each slit image composed of 25,000 points including 500 true elevation points. 109 As a pachymeter, Pentacam provides a corneal thickness map and determines the 110 thinnest point as well. Previous studies have shown that Pentacam has high agreement 111 compared with USP,12 high intraoperator repeatability and reproducibility for CCT 112 measurements.26,27 113 114 In recent years, several units of non-contact tonometry and pachymetry have been 115 developed. Tono-pachymetry simultaneously measures CCT using the principle of the 116 Scheimpflug camera system and IOP using a conventional non-contact tonometry 117 method. Tono-pachymetry is patient-friendly and time-saving, but it has not been well 118 documented whether the CCT values obtained from tono-pachymetry are comparable 119 to those derived from conventional USP as the gold standard for measuring CCT.28,29 120 To the best knowledge of the authors, this was one of the few studies that was 121 designed to compare the correlation and agreement between CCT measurements 122 Page 4 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only obtained using recently marketed, CT-1P tono-pachymetry, 3D OCT-2000 and 123 Pentacam with USP in young myopic healthy eyes. 124 125 Materials and Methods 126 127 Study Design and subjects: This prospective cross-sectional comparative study 128 includes 52 eyes of 52 healthy subjects voluntarily enrolled at the Ocular Surface and 129 Contact Lens Laboratory (LSOYLC) from the University of Santiago de Compostela. All 130 subjects after CCT measurement were subjected to a full ophthalmic examination. This 131 examination included routine evaluation of visual acuity, refractive error and slit lamp 132 biomicroscopy with particular attention to the presence of ocular adverse events. The 133 inclusion criteria were age between 18-30 years, normal corneal topographic pattern, 134 myopia between -6.00 D and -0.75 D, no more than -1.75 D of astigmatism, correctable 135 to 20/20 and also included emmetropic eyes achieving 20/20 or better visual acuity. 136 Exclusion criteria included previous refractive surgery, corneal diseases, recent use of 137 contact lenses, no other systemic or ocular diseases, and use of topical medications. 138 139 The study was performed according to the renewed and revised rules of Helsinki 140 Declaration and was approved by the Ethics Committee of the University of Santiago 141 de Compostela. 142 143 Technologies used to measure CCT: Three consecutive measurements were done 144 by standard USP, non-contact tono-pachymeter, corneal topography, and anterior 145 segment optical coherence tomography (AS-OCT). In order to eliminate effects of 146 diurnal variation on thickness, all measurements were taken between 2 PM and 6 147 PM.30 148 149 Page 5 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Automatic analysis by Scheimpflug camera Pentacam (Oculus Optikgerate GmbH, 150 Wetzlar, Germany) was performed for all eyes. Multiple slit images of the anterior 151 segment with 500 true elevation points are captured by the rotating camera. CCT was 152 recorded only when the examination quality specification reading was satisfactory; 153 otherwise it was excluded and reanalyzed until three valid readings were obtained. 154 155 Spectral-domain optical coherence tomographic 3D OCT-2000 (Topcon, Tokyo, Japan) 156 equipment was used for anterior segment analysis using the headrest attachment. It 157 captures high resolution images of the cornea using non-contact OCT, allowing for 158 topographical mapping of the cornea including corneal thickness. The system obtained 159 different images, separated by 0.25 mm with 5-6 micron of axial resolution and 20 160 microns of transverse resolution. The corneal thickness was measured by an 161 automated algorithm, that detects epithelium and endothelium limits on the cross-162 sectional images of the cornea. The mean value from three consecutive measurements 163 was taken as the CCT value. 164 165 The non-contact tono-pachymeter CT-1P (Topcon, Tokyo, Japan), also was used for 166 pachymetric analysis by a specular microscope method. The patient was seated and 167 asked to look at a fixation target. The emitted light from a narrow slit in the cornea is 168 reflected by the front and backside of the cornea and CCT was measured according to 169 the interval between both reflection images on the line sensor. The operator visualized 170 a real-time image of the patient’s eye on the screen. Although the operator manually 171 focused the image to the center of the pupil, CT-1P tono-pachymeter automatically 172 measured CCT three times and calculated the average value. 173 174 These non-contact measurements were followed by USP (Paxis, Biovision Inc, 175 Clermont-Ferrand, France). The subject was seated on the chair and asked to look at 176 fixation light located straight ahead. The examiner placed the pachymeter probe on the 177 Page 6 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only central cornea as perpendicular as possible. Measurements were obtained 5 times and 178 the average reading was recorded for each patient. USP was performed by one 179 experienced operator on all patients under topical anesthesia with tetracaine 180 hydrochloride 0,5% (Colircusí Anestésico, Alcon Cusí, Barcelona, Spain). 181 182 Data Analysis: Data were analyzed by SPSS version 20 (SPSS Inc., Chicago, Illinois, 183 USA) using descriptive statistics, linear regression and Pearson correlation coefficient. 184 The CCT measured by USP and the three non-contact devices was compared by 185 paired t-test. A p-value of less than 0.05 was considered statistically significant. Bland-186 Altman plot was used to evaluate the agreement between the four techniques. Finally, 187 reliability was analyzed using intraclass correlation coefficient (ICC). Based on the 95% 188 confident interval of the ICC estimate, values less than 0.5, between 0.5 and 0.75, 189 between 0.75 and 0.9, and greater than 0.90 are indicative of poor, moderate, good, 190 and excellent reliability, respectively.31-32 191 192 Results 193 194 A total of 52 eyes in 52 healthy subjects (only right eyes) were studied (32 females and 195 20 males). The mean age was 23.52±3.78 years (range 20 to 28 years) and a mean 196 spherical equivalent of -1.56±1.78 D (range -0.50 to -5.75 D). 197 198 The highest CCT mean value was obtained with the USP (558.9 ± 31.2 µm; range from 199 476 to 614 µm), followed by the Pentacam (550.4±30.5 µm; range from 465 to 615 200 µm), then by the 3D OCT (545.9±30.5 µm; range from 457 to 602 µm), and finally, the 201 lowest value was obtained with the tono-pachymeter (525.8±43.1 µm; range from 431 202 to 674 µm). 203 204 Page 7 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Figures 1 shows a significant positive correlation between the CCT readings obtained 205 by USP and by the non-contact devices. There was a significant strong correlation 206 between AS-OCT and USP (Pearson correlation = 0.979, p < 0.001), Pentacam and 207 USP (Pearson correlation = 0.946, p < 0.001) and Pentacam versus AS-OCT (Pearson 208 correlation = 0.951, p < 0.001). The correlation coefficient between tono-pachymeter 209 and the other three modalities was significantly lower than between USP, Pentacam 210 and OCT with each other. 211 212 The t-Student analysis (Table 1) showed statistically significant differences between 213 CCT mean values from all paired instruments (p < 0.001 in all cases). The highest 214 difference between pairs was found between tono-pachymeter and USP (-33.1 ± 33.3 215 µm; CI 23,8 to 42,3 µm; p < 0.001), while the lowest difference was found between 216 OCT and Pentacam (-4.5 ± 9.5 µm; CI 1.9 to 7.2; p = 0.001) but followed too close by 217 difference between Pentacam and USP (-8.5 ± 10.2 µm; CI 5,7 to 11.3; p < 0.001) or 218 between OCT and USP (-13.0 ± 6.4 µm; CI 11.2 to 14.8; p < 0.001). 219 220 Bland-Altman analysis confirmed these results, CCT obtained by Pentacam, 3D OCT-221 2000 and USP pairs showed excellent agreement, with the mean difference centered 222 close to zero, and 95% of the points were accurately located between the predicted 223 95% limits of agreement (Figure 2ABC). Conversely, tono-pachymeter CT-1P showed 224 the lowest concordance when compared with USP, Pentacam or OCT (Figure 2DEF), 225 with the higher differences (mean ± 1.96 SD). The limits of agreement 95% (LoA = 226 mean of the difference ± 1.96 × SD of the differences) indicates that the values on the 227 error between the pairs of measurement have exceeded the limits of concordance. 228 Particularly, tono-pachimetry underestimated CCT by 33.1 µm when compared with 229 USP, with 95% LoA ranging between 23.8 and 42.3 µm (Figure 2DEF). 230 231 Page 8 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only measurements and agreement with Stratus optical coherence tomography 396 measurements. Am J Ophthalmol 2009;147:1067–1074. 397 19. Kashani AH, Chen CL, Gahm JK, Zheng F, Richter GM, Rosenfeld PJ, et al. Optical 398 coherence tomography angiography: A comprehensive review of current methods 399 and clinical applications. Prog Retin Eye Res 2017;60:66-100. 400 20. Leitgeb R, Hitzenberger CK, Fercher AF. Performance of Fourier-domain vs. time-401 domain optical coherence tomography. Opt Express 2003;11:889–894. 402 21. Sakata LM, Lavanya R, Friedman DS, Aung HT, Gao H, Kumar RS, et al. 403 Comparison of gonioscopy and anterior segment ocular coherence tomography in 404 detecting angle closure in different quadrants of the anterior chamber angle. 405 Ophthalmology 2008;115:769–774. 406 22. Doors M, Tahzib NG, Eggink FA, Berendschot TT, Webers CA, Nuijts RM. Use of 407 anterior segment optical coherence tomography to study corneal changes after 408 collagen cross-linking. Am J Ophthalmol 2009;148:844–851. 409 23. Chen Q, Wang J, Shen M, Cai C, Li J, Cui L, et al. Lower volumes of tear menisci in 410 contact lens wearers with dry eye symptoms. Invest Ophthalmol Vis Sci 411 2009;50:3159–3163. 412 24. Ang M, Cai Y, Tan AC. Swept Source Optical Coherence Tomography Angiography 413 for Contact Lens-Related Corneal Vascularization. J Ophthalmol 2016;2016:1-3. 414 25. Ramesh PV, Jha KN, Srikanth K. Comparison of Central Corneal Thickness using 415 Anterior Segment Optical Coherence Tomography Versus Ultrasound Pachymetry. 416 J Clin Diagn Res 2017;11:NC08-NC11. 417 26. Huang J, Ding X, Savini G, Pan C, Feng Y, Cheng D, et al. A comparison between 418 scheimpflug imaging and optical coherence tomography in measuring corneal 419 thickness. Ophthalmology 2013;120:1951–1958. 420 27. Al-Mezaine HS, Al-Amro SA, Kangave D, Sadaawy A, Wehaib TA, Al-Obeidan S. 421 Comparison between central corneal thickness measurements by oculus pentacam 422 and ultrasonic pachymetry. Int Ophthalmol. 2008;28:333-8. 423 Page 15 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only 28. Barkana Y, Gerber Y, Elbaz U, Schwartz S, Ken-Dror G, Avni I, et al. Central 424 corneal thickness measurement with the Pentacam Scheimpflug system, optical 425 low-coherence reflectometry pachymeter, and ultrasound pachymetry. J Cataract 426 Refract Surg 2005;31:1729–1735. 427 29. Fujimura F, Kamiya K, Fujiwara K, Shoji N, Shimizu K. Repeatability and 428 reproducibility of measurements using a NT-530P noncontact tono/pachymeter and 429 correlation of central corneal thickness with intraocular pressure. Biomed Res 430 Int 2013;2013:1-5. 431 30. Du Toit R, Vega JA, Fonn D, Simpson T. Diurnal variation of corneal sensitivity and 432 thickness. Cornea 2003;22:205–209. 433 31. Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. 434 Psychol Bull 1979;86:420-8. 435 32. Bland JM, Altman DG. Statistical methods for assessing agreement between two 436 methods of clinical measurement. Lancet 1986;1:307–310. 437 33. Ho T, Cheng AC, Rao SK, Lau S, Leung CK, Lam DS. Central corneal thickness 438 measurements using Orbscan II, Visante, ultrasound, and Pentacam pachymetry 439 after laser in situ keratomileusis for myopia. J Cataract Refract Surg 2007;33:1177–440 82. 441 34. Hashemi H, Mehravaran S. Central corneal thickness measurement with 442 Pentacam, Orbscan II, and ultrasound devices before and after laser refractive 443 surgery for myopia. J Cataract Refract Surg 2007;33:1701–7. 444 35. Al-Mezaine HS, Al-Amro SA, Kangave D, Al-Obeidan S, Al-Jubair KM. Comparison 445 of central corneal thickness measurements using Pentacam and ultrasonic 446 pachymetry in post-LASIK eyes for myopia. Eur J Ophthal 2010;20:852–7. 447 36. Tai LY, Khaw KW, Ng CM, Subrayan V. Central corneal thickness measurements 448 with different imaging devices and ultrasound pachymetry. Cornea 2013;32:766–1. 449 Page 16 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only 37. Rao HL, Kumar AU, Kumar A, Chary S, Senthil S, Vaddavalli PK, et al. Evaluation 450 of central corneal thickness measurement with RTVue spectral domain optical 451 coherence tomography in normal subjects. Cornea 2011;30:121-126. 452 38. Kanellopoulos AJ, Asimellis G. Comparison of high-resolution Scheimpflug and 453 high-frequency ultrasound biomicroscopy to anterior-segment OCT corneal 454 thickness measurements. Clin Ophthalmol 2013;7:2239-2247. 455 39. Northey LC, Gifford P, Boneham GC. Comparison of Topcon optical coherence 456 tomography and ultrasound pachymetry. Optom Vis Sci 2012;89:1708-1714. 457 40. Lee YG, Kim JH, Kim NR, Kim CY, Lee ES. Comparison between Tonopachy and 458 other tonometric and pachymetric devices. Optom Vis Sci 2011;88:843-9. 459 41. Lomoriello DS, Lombardo M, Tranchina L, Oddone F, Serrao S, Ducoli P. 460 Repeatability of intra-ocular pressure and central corneal thickness measurements 461 provided by a non-contact method of tonometry and pachymetry. Graefe's Arch Clin 462 Exp Ophthalmol 2011;249:429-34. 463 42. Garcia-Resua C, Blanco A, Miñones M, Yebra-Pimentel E, Jesus Giraldez M. 464 Accuracy and repeatability of a new tono-pachymeter for measuring central corneal 465 thickness. Eye Contact Lens 2012;38:158-63. 466 43. Sagdik HM, Aktas S, Tetikoglu M, Ozcura F. Comparison of ultrasonic pachymetry, 467 with a new optical biometry and tono-pachymetry. Medicine Science 2017;6:225. 468 44. Lackner B, Schmidinger G, Pieh S, Funovics MA, Skorpik C. Repeatability and 469 reproducibility of central corneal thickness measurement with Pentacam, Orbscan, 470 and ultrasound. Optom Vis Sci 2005;82:892-899. 471 45. Bayhan HA, Aslan Bayhan S, Can I. Comparison of central corneal thickness 472 measurements with three new optical devices and a standard ultrasonic 473 pachymeter. Int J Ophthalmol 2014;7:302-308. 474 46. Ciolino JB, Khachikian SS, Belin MW. Comparison of corneal thickness 475 measurements by ultrasound and Scheimpflug photography in eyes that have 476 undergone laser in situ keratomileusis. Am J Ophthalmol 2008;145:75–80. 477 Page 17 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only 47. Sedaghat MR, Daneshvar R, Kargozar A, Derakhshan A, Daraei M. Comparison of 478 central corneal thickness measurement using ultrasonic pachymetry, rotating 479 Scheimpflug camera, and scanning-slit topography. Am J 480 Ophthalmol 2010;150:780–9. 481 48. Sadoughi MM, Einollahi B, Einollahi N, Rezaei J, Roshandel D, Feizi S. 482 Measurement of Central Corneal Thickness Using Ultrasound Pachymetry and 483 Orbscan II in Normal Eyes. J Ophthalmic Vis Res 2015;10:4–9. 484 49. Calvo-Sanz JA, Ruiz-Alcocer J, Sánchez-Tena MA. Accuracy of Cirrus HD-OCT 485 and Topcon SP-3000P for measuring central corneal thickness. J Optom 2017;18: 486 S1888-4296(17)30002-X. doi: 10.1016/j.optom. 487 50. Ramesh PV, Jha KN, Srikanth K. Comparison of Central Corneal Thickness using 488 Anterior Segment Optical Coherence Tomography Versus Ultrasound Pachymetry. 489 J Clin Diagn Res 2017;11:NC08-NC11. 490 51. Brown BW, Jr., Lucero RJ, Foss AB. A situation where the Pearson correlation 491 coefficient leads to erroneous assessment of reliability. J Clin Psychol 1962;18:95–492 97. 493 52. Landis JR, Koch GG. The measurement of observer agreement for categorical 494 data. Biometrics 1977;33:159-174. 495 496 497 498 499 500 501 502 503 504 505 Page 18 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Figure 1. Scattered plot analysis of CCT showing a significant positive strong correlation between CCT measured by: A) USP and Pentacam (slope=0.946, R2=0.895); B) USP and 3D OCT-2000 (slope=0.979, R2=0.957); C) Pentacam and 3D OCT-2000 (slope=0.951, R2=0.905); D) USP (slope=0.640, R2=0.409); E) Pentacam (slope=0.700, R2=0.490); F) 3D OCT-2000 (slope=0.687, R2=0.471). 237x305mm (72 x 72 DPI) Page 19 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Figure 2. Bland-Altman analysis. Mean difference (solid line) and 95% limits of agreementLoA (dashed line) for CCT. Mean differences were: A) 8.5 µm with 95% LoA from - 11.4 to 28.4 µm for the USP/Pentacam pair; B) 13.0 µm with 95% LoA from 0.4 to 25.6 µm for the USP/AS-OCT pair; C) 4.5 µm with 95% LoA from - 14.1 to 23.2 µm for the Pentacam/AS-OCT pair; D) 33.1 µm with 95% LoA from -32.2 to 98.3 µm for the USP/CT-1P pair; E) 20.0 µm with 95% LoA from -41.4 to 81.5 µm for the AS-OCT/ CT-1P pair; F) 24.6 µm with 95% LoA from -35.7 to 84.9 µm for the Pentacam/ CT-1P pair. 205x216mm (72 x 72 DPI) Page 20 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Pairs-Parameter Mean Diff. 95% Confidence Interval Range Sig (p-value) Correlation Pearson USP vs Pentacam 8.5±10.2 -11.4 to 28.4 39.8 <0.001 0.946 US P vs 3D OCT 13.0±8.4 -1.1 to 25.6 26.7 <0.001 0.979 US P vs CT - 1P 33.1±33.3 -32.2 to 98.3 130.5 <0.001 0.640 Pentacam vs 3D OCT 4.5±9.5 -14.1 to 23.2 37.3 0.001 0.951 Penta cam vs CT - 1P 24.6±30.8 -35.7 to 84.9 120.6 <0.001 0.700 3D OCT vs CT - 1P 20.0±31.3 -41.4 to 81.5 122.9 <0.001 0.687 Table 1. Comparisons among pairs of instruments, average difference, upper and lower 95% confidence limits and statistical significance. Values are in microns. Page 21 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Only Pairs-Parameter ICC 95% Confidence Interval Sig (p-value) USP vs Pentacam 0.946 0.807 to 0.968 < 0.001 USP vs 3D OCT 0.978 0.863 to 0.987 < 0.001 USP vs CT - 1P 0.608 0.303 to 0.759 < 0.001 Pentacam vs 3D OCT 0.951 0.839 to 0.972 < 0.001 Penta cam vs CT - 1P 0.660 0.375 to 0.790 < 0.001 3D OCT vs CT - 1P 0.648 0.347 to 0.781 < 0.001 Table 2. Results of intraclass correlation coefficient (ICC), upper and lower 95% confidence limits and statistical significance. Calculation in SPSS using two-way random model. Page 22 of 22 URL: http://mc.manuscriptcentral.com/ncer Current Eye Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60