Comparison of Color Light-Emitting Diode Corneal ...downloads.hindawi.com/journals/joph/2018/6764805.pdfcornealtopographerandthedualrotatingScheimpﬂug– Placidotopographer. 2. Methods

Research ArticleComparison of Color Light-Emitting Diode Corneal Topographerand Dual Rotating ScheimpflugndashPlacido Topographer

Jae Hyuck Lee1 Yong Woo Lee1 Jong Soo Lee2 Michael C Knorz3 Gerd U Auffarth 4

and Chul Young Choi 14

1Department of Ophthalmology Kangbuk Samsung Hospital Sungkyunkwan University School of MedicineSeoul Republic of Korea2Department of Ophthalmology Pusan National University HospitalPusan National University School of Medicine and Medical Research Institute Yangsan Republic of Korea3Medical Faculty Mannheim of the University of Heidelberg Mannheim Germany4International Vision Correction Research Centre (IVCRC) David J Apple International Laboratory on Ocular PathologyDepartment of Ophthalmology University of Heidelberg Heidelberg Germany

Correspondence should be addressed to Chul Young Choi sashimi0navercom

Received 14 July 2018 Revised 1 December 2018 Accepted 9 December 2018 Published 27 December 2018

Academic Editor Paulo Fernandes

Copyright copy 2018 Jae Hyuck Lee et al+is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Purpose To compare measurements of anterior and posterior keratometric values using a color light-emitting diode cornealtopographer and a dual rotating ScheimpflugndashPlacido topographer Methods Anterior and posterior corneal index mea-surements were performed using a color light-emitting diode corneal topographer (Cassini) and a dual rotatingScheimpflugndashPlacido topographer (Galilei G4) and then compared +e paired t-test intraclass correlation coefficients (ICCs)and BlandndashAltman plots were used to evaluate the agreement between measurements Results Sixty postrefractive surgery eyesand 60 normal eyes were evaluated Both the color light-emitting diode corneal topographer and the dual rotatingScheimpflugndashPlacido topographer provided highly repeatable corneal measurements (ICC gt 0969) +e agreement levelsbetween the 2 devices for anterior corneal power astigmatism magnitude and J0 and J45 values were ICC gt 0906 for the totalgroup However the ICC values for posterior corneal power astigmatism magnitude and J0 and J45 values were lower than0681 for the total group Conclusions +e anterior keratometric values obtained by the color light-emitting diode cornealtopographer and the dual rotating ScheimpflugndashPlacido topographer showed high agreement levels but the posterior ker-atometric values showed lower agreement levels

1 Background

Accurate evaluations of corneal biometry measurements areimportant in cataract and refractive surgery [1] As any errorin corneal power calculation can directly lead to post-operative refractive surprises the instruments used forkeratometric measurements are crucial [2]

Many devices for corneal power estimation are availablenowadays and the dual rotating ScheimpflugndashPlacido to-pographer (Ziemer Ophthalmic Systems AG) is a hybriddevice that combines dual rotating Scheimpflug cameraswith a Placido disk It is a widely used instrument because itcan provide not only anterior and posterior corneal power

measurements but also corneal curvature pachymetry andmaps

+e Cassini (i-Optics Corp v241) was recently re-leased as the first commercially available point-source colorlight-emitting diode (LED) topographer that obtains acorneal image based on the reflection of individualpoints of light [3] Although several studies have comparedthe color-LED corneal topographer with other devicesfew studies have compared it with the dual rotatingScheimpflugndashPlacido topographer and no studies to datehave considered posterior corneal evaluation Our purposein this study was to compare the measurements of anteriorand posterior corneal indices taken by the color-LED

HindawiJournal of OphthalmologyVolume 2018 Article ID 6764805 7 pageshttpsdoiorg10115520186764805

corneal topographer and the dual rotating ScheimpflugndashPlacido topographer

2 Methods

+is prospective cross-sectional study examined healthysubjects from the Department of Ophthalmology KangbukSamsung Hospital Seoul South Korea+e study adhered tothe tenets of the Declaration of Helsinki and was approvedby the Institutional Review Board of Kangbuk SamsungHospital Written informed consent was obtained from eachsubject before inclusion in the study In this study wefollowed the methods of Lee et al [4]

Inclusion criteria were healthy individuals aged 18 to40 years with a spherical equivalent ranging from +100 tominus600 diopters (D) to rule out high myopia which can causeextreme refractive errors +e best-corrected visual acuitywas 000 logMAR in all eyes Exclusion criteria included ahistory of ocular pathology ocular trauma contact lenswear pregnancy systemic or local medications and ocularsurgeries other than laser refractive surgery for myopia Inthe postrefractive surgery group we only included patientswho underwent surgery more than a year ago and who didnot have any subjective visual acuity change discomfort orhistory of ophthalmic treatment In addition patients withastigmatism of more than 250D K values higher than 472Din any axis or inferior-superior (I-S) values (differences inI-S keratometry) more than 14D were excluded from thisstudy to rule out keratoconus patients [5]

One eye from each subject was used for statisticalanalysis Eyes were divided into 2 groups according to theirhistory of myopic laser refractive surgery +e refractivegroup consisted of eyes with previous refractive surgerywhile the normal group consisted of eyes that had not re-ceived refractive surgery

21 Repeatability Twenty participants (20 eyes) were in-cluded in the assessment of device repeatability and 10 eyeshad a history of refractive surgery for myopia +ree con-secutive measurements were performed and intraclasscorrelation coefficients (ICCs) were calculated for eachmeasurement for anterior and posterior K and astigmatismvalues +e ICC is the ratio of between-subjects variance tothe sum of the pooled within-subject variance and between-subjects variance It expresses the consistency of repeatedmeasurements and ranges from 0 to 1 An ICC smaller than075 indicates poor repeatability from 075 to 089 repre-sents moderate repeatability and greater than 090 corre-sponds to high repeatability [6] All measurements in thisstudy were performed by the same person experienced inophthalmic examinations

3 Measurements

All eyes were measured using both a dual rotatingScheimpflugndashPlacido corneal topographer and a color-LEDcorneal topographer Table 1 shows the characteristics andmeasurement settings used for each system All measure-ments were performed continuously in individual subject

between 10 am and 1 pm to avoid the effects of diurnalvariation in corneal indices [7]

31 Dual Rotating ScheimpflugndashPlacido System +e GalileiG4 uses 2 cameras in opposite positions in combination witha Placido disk with 20 Placido rings to analyze the shape ofthe cornea Double rotating systems prevent and compen-sate for errors with oblique angle imaging By detecting theedge in the dual-Scheimpflug images the shape of theposterior cornea can be assessed +e total acquisition timewas approximately 075 seconds and more than 122000points were scanned +e simulated K (simK) values werecalculated based on the anterior corneal curvatures in the 10to 40mm central zone A keratometric index of 13375 wasused to calculate the powers of the steep and flat meridians+e posterior simK was derived from the posterior axialcurvature map as the arithmetic mean of the pair of or-thogonal meridians with the greatest difference in averagepower in the 05 to 20mm zone+e refractive indices of thecornea (1376) and aqueous humor (1336) were used tocalculate the powers of the steep and flat meridians

32 Color Light-Emitting Diode Corneal Topographer +eCassini v241 has approximately 700 red yellow and greenLEDs arranged in a specific pattern to ensure a 1-to-1correspondence between the source and image pointswhich potentially decreases source-image mismatch andartifacts caused by the shadow +e color-LED topographerevaluates the keratometric values in the 30mm central zoneAdditionally the Cassini analyzes the reflections (2ndPurkinje images) of infrared LEDs on the posterior surfaceto calculate the posterior curvature To calculate the anteriorcorneal surface astigmatism using the Cassini we convertedthe anterior radii of curvature to meridional power using akeratometric index of 13375 Posterior corneal astigmatismwas calculated using ray tracing in which Snellrsquos law isapplied to calculate the refraction of a large number of lightrays incident on the anterior and posterior corneal surface

33 Statistical Analysis Data analysis was performed usingSPSS software (version 240 SPSS Inc) andMicrosoft OfficeExcel (Microsoft Corp) +e results of the quantitativevariables were expressed by their minimum and maximumvalues means and standard deviations (SDs) +e meananterior and posterior corneal powers were calculated foreach measurement on each device as the arithmetic averageof the anterior and posterior corneal steep K and flat K +e

Table 1 Characteristics and measurement settings for each system

Parameter Dual rotatingScheimpflugndashPlacido

Colorlight-emitting diode

Acquisition time (s) 075 2K index 13375lowast 13375lowastKmeasurement zone(mm)

1ndash4 (anterior) 305ndash2 (posterior)K keratometry lowastConfigurable or selectable option

2 Journal of Ophthalmology

magnitude of corneal astigmatism was the measured dif-ference between the steepest and flattest meridians with itslocation along the steepest corneal meridian Additionallycorneal astigmatism was expressed and compared usingpower vector analysis [8] Each astigmatism value wasconverted to a Jackson (J) cross-cylinder notation repre-sented by the rectangular vectors J0 and J45 using thefollowing equations

J0 C

21113874 1113875cos(2empty)

J45 C

21113874 1113875sin(2empty)

(1)

where J0 is themagnitude of a Jackson cross-cylinder with itsaxis at 0 degrees J45 is the magnitude of a Jackson cross-cylinder with its axis at 45 degrees C is the magnitude of thecorneal astigmatism (the steepest K minus the flattest K)and empty is the axis of the steepest meridian [8]

To compare the measurements between the 2 devices weperformed paired sample t-tests +e ICC was calculated toanalyze the repeatability and agreement of the results A p

value less than 005 was considered statistically significantand ICC values higher than 0900 were regarded as in-dicating a high degree of agreement BlandndashAltman plotsmade with Stata software (version 92 Stata Corp LP) wereused to evaluate the agreement in corneal power andastigmatism between the dual rotating ScheimpflugndashPlacidoand color-LED corneal topographers [9]

34 Sample Size Calculation Based on the previous studythe standard deviation of the differences in corneal powermeasurements between devices was estimated to be 025D[10] +e smallest difference that may be clinically relevantwas defined as 0125D With a significance level of 5 and atest power of 90 at least 44 eyes were required in eachgroup

4 Results

+e study enrolled 120 eyes from 120 subjects Sixty eyeswere in the normal group and 60 in the refractive group+ere was no statistical difference in sex or age between thetwo groups As expected refractive errors were statisticallysignificantly smaller in the refractive group (Table 2)

41 Repeatability +e repeatability of both the dual rotatingScheimpflugndashPlacido system and the color-LED cornealtopographer was excellent for anterior simK (ICC 0998and ICC 0992 respectively) anterior astigmatism mag-nitude (ICC 0980 and ICC 0984 respectively) anteriorJ0 (ICC 0991 and ICC 0988 respectively) anterior J45(ICC 0993 and ICC 0996 respectively) posterior simK(ICC 0985 and ICC 0983 respectively) posteriorastigmatism magnitude (ICC 0971 and ICC 0973respectively) posterior J0 (ICC 0969 and ICC 0976respectively) and posterior J45 (ICC 0977 and ICC

0972 respectively)

42 Anterior Corneal Indices Tables 3 and 4 compare themeasurements of the anterior corneal indices between thedual rotating ScheimpflugndashPlacido and color-LED cornealtopographers+emeasurements for anterior simK anteriorastigmatism magnitude anterior J0 and anterior J45 did notdiffer significantly between the two devices in either group(pgt 005) with the exception of anterior simK in the normalgroup (p 0001) and anterior J45 in the postrefractivegroup (p 0000) +e ICC values between the two deviceswere high for anterior simK anterior astigmatism magni-tude anterior J0 and anterior J45 in both the groups (ICC gt0900)

43 Posterior Corneal Indices Tables 3 and 4 also comparethe measurements of the posterior corneal indices betweenthe two instruments +e measurements for posterior simKand posterior astigmatism magnitude in the normal groupand posterior simK and posterior J0 in the postrefractivegroup differed significantly between the 2 devices (plt 005)+e values for posterior J0 (p 0274) and posterior J45(p 0977) in the normal group and posterior astigmatismmagnitude (p 0216) and posterior J45 (p 0655) in thepostrefractive group did not differ significantly +e ICCvalues between the two devices were low for posterior simKposterior astigmatismmagnitude posterior J0 and posteriorJ45 in both the groups (ICC lt 0900) with the exception ofposterior simK in the normal group (ICC 0944)BlandndashAltman plots showed poor agreement between thedevices in the posterior corneal indices (Figure 1)

5 Discussion

+e cornea is one of the most important refractive ele-ments of the eye thus a precise evaluation of its char-acteristics is mandatory and requires the use of reliablemeasurement devices Generally it is essential to compareand evaluate new measurement instruments to determinewhether there is an adequate agreement among differentmodalities [9] Estimating and comparing the repeatabilityof different instruments is basic research for data reliabilityand determination of a better system An agreement in

Table 2 Demographics and refractive error by group

Parameter Refractivegroup (n 60)

Normal group(n 60) p value

Mean age(y) plusmn SD 3230 plusmn 805 3278 plusmn 698 0684lowast

Sex n () 0133dagger

Male 24 (400) 32 (533)Female 36 (600) 28 (467)

Mean SE (D) plusmn SD(range)

minus042 plusmn 046(minus175ndash050)

minus228 plusmn 225(minus550ndash075) lt0001

lowast

Surgery n ()LASEK 48 (800) LASIK 12 (200)

LASEK laser-assisted subepithelial keratectomy LASIK laser in situkeratomileusis SE spherical equivalent lowastIndependent sample t-test daggerchi-square test

Journal of Ophthalmology 3

measurements assesses the exchangeability of devicesand serves as an indirect indicator of accuracy [11] +isstudy was designed to evaluate the repeatability andagreement of anterior and posterior corneal power andastigmatism measurements acquired from a dual rotat-ing ScheimpflugndashPlacido topographer and a color-LEDtopographer

Traditionally the total corneal power calculation is basedon the anterior corneal surface measurements assuming afixed anterior and posterior curvature ratio to estimate theposterior corneal power [12] +e standardized keratometricindex (13375 for most cases) has been used when converting

anterior corneal measurements into total corneal power andastigmatism However this reasoning has reportedly led toerrors [13 14] Although diverse technologies such asScheimpflug imaging slit-scanning technology and opticalcoherence tomography enable measurement of the poste-rior corneal surface various levels of repeatability andagreement among measurement systems have been re-ported therefore the need to develop more accurate in-struments remains high To our knowledge this is the firststudy to report the comparability and repeatability of arecently introduced device the Cassini point-source color-LED topographer for posterior corneal assessment

Table 3 Comparison of corneal index measurements using dual rotating ScheimpflugndashPlacido and color light-emitting diode cornealtopographers

Parameter DRSP (mean plusmn SD) Color LED (mean plusmn SD)Difference

p valuelowast ICCMean plusmn SD 95 CI

Postrefractive groupAnterior corneal indices (D)simK 3878 plusmn 180 3871 plusmn 188 minus008 plusmn 044 minus019 004 0186 0986Astigmatism magnitude 083 plusmn 047 084 plusmn 053 001 plusmn 037 minus009 010 0904 0938J0 minus032 plusmn 028 minus029 plusmn 032 003 plusmn 020 minus002 008 0267 0925J45 006 plusmn 022 minus004 plusmn 025 minus010 plusmn 015 minus014 minus006 0000 0905

Posterior corneal indices (D)simK minus639 plusmn 016 minus597 plusmn 032 042 plusmn 032 034 051 0000 0327Astigmatism magnitude minus036 plusmn 011 minus039 plusmn 021 minus004 plusmn 023 minus009 002 0216 0183J0 017 plusmn 006 008 plusmn 016 minus009 plusmn 016 minus013 minus005 0000 0016J45 minus002 plusmn 015 minus001 plusmn 006 minus001 plusmn 016 minus005 003 0655 0000

Normal groupAnterior corneal indices (D)simK 4328 plusmn 137 4340 plusmn 138 012 plusmn 026 006 019 0001 0991Astigmatism magnitude 134 plusmn 083 141 plusmn 088 007 plusmn 035 minus002 015 0133 0956J0 minus061 plusmn 044 minus064 plusmn 047 minus003 plusmn 017 minus008 001 0135 0963J45 001 plusmn 025 000 plusmn 024 minus001 plusmn 014 minus004 003 0740 0916

Posterior corneal indices (D)simK minus643 plusmn 027 minus626 plusmn 025 016 plusmn 012 013 019 0000 0944Astigmatism magnitude minus037 plusmn 011 minus041 plusmn 017 minus004 plusmn 016 minus008 minus000 0043 0499J0 017 plusmn 007 018 plusmn 009 001 plusmn 009 minus001 004 0274 0469J45 000 plusmn 006 000 plusmn 009 minus000 plusmn 010 minus003 003 0977 0175

CI confidence interval color LED color light-emitting diode corneal topographer DRSP dual rotating ScheimpflugndashPlacido corneal topographer ICCintraclass correlation coefficient K keratometry lowastPaired sample t-test

Table 4 Comparison of corneal index measurements using dual rotating ScheimpflugndashPlacido and color light-emitting diode cornealtopographers in total group

ParameterTotal group

DRSP (mean plusmn SD) Color LED (mean plusmn SD)Difference


Anterior corneal indices (D)simK 4107 plusmn 276 4109 plusmn 287 003 plusmn 037 -004 009 0451 0996Astigmatism magnitude 109 plusmn 072 113 plusmn 078 004 plusmn 036 minus003 010 0256 0938J0 minus046 plusmn 039 minus047 plusmn 044 minus000 plusmn 019 minus004 003 0874 0947J45 004 plusmn 024 minus002 plusmn 025 minus005 plusmn 015 minus008 003 0000 0906

Posterior corneal indices (D)simK minus641 plusmn 022 minus612 plusmn 032 029 plusmn 027 024 034 0000 0681Astigmatism magnitude minus036 plusmn 011 minus040 plusmn 019 minus004 plusmn 020 minus007 minus000 0027 0334J0 017 plusmn 006 013 plusmn 013 minus004 plusmn 014 minus006 minus001 0004 0180J45 minus001 plusmn 006 minus001 plusmn 012 minus000 plusmn 013 minus003 002 0695 0000



0

10

15

ndash05

05

Diff

eren

ce

Averagendash70 ndash68 ndash66 ndash64 ndash62 ndash58 ndash56ndash60

0164 (95 CI 0134 to 0195)

ndash0077

0406

(a)

0

10

15

ndash05

05

Diff

eren

ce


0424 (95 CI 0342to 0507)

ndash0215

1064

(b)

ndash0043 (95 CI ndash0084 to ndash0001)

ndash0370

0284

Averagendash09 ndash08 ndash07 ndash05 ndash03 0ndash01ndash06 ndash04 ndash02

10

ndash08ndash06ndash04ndash02

0204

ndash10

0

0608

Diff

eren

ce

(c)


10


0204

ndash10

0

0608

Diff

eren

ce

ndash0036 (95 CI ndash0095 to 0022)

ndash0488

0415

(d)05


0102

ndash05

0

0304

Averagendash01 0 01 02 0403

0013 (95 CI ndash0010to 0036)

ndash0171

0196

Diff

eren

ce

(e)

05


0102

ndash05

0

0304


Diff

eren

ce

ndash0089 (95 CI ndash0131to ndash0048)

ndash0412

0233

(f )08

ndash04

ndash02

0

02

04

06

ndash06

Averagendash02 ndash01 0 01 0302

ndash0000 (95 CI ndash0027to 0026)

ndash0206

0205

Diff

eren

ce

(g)

08

ndash04

ndash02

0

02

04

06

ndash06


Diff

eren

ce


ndash0330

0312

(h)

Figure 1 BlandndashAltman plots showing the agreement between the posterior corneal indexmeasurements from the 2 systemse bold linesrepresent the mean dierence between the 2 methods e broken lines represent the 95 limits of agreement (a) Normal group posteriorsimK (b) refractive group posterior simK (c) normal group posterior astigmatism magnitude (d) refractive group posterior astigmatismmagnitude (e) normal group posterior J0 (f ) refractive group posterior J0 (g) normal group posterior J45 and (h) refractive groupposterior J45 (color LED color light-emitting diode corneal topographer DRSP dual rotating ScheimpugndashPlacido corneal topographer)


Previous studies have reported various repeatabilityoutcomes for the corneal power and astigmatism mea-surements from the dual rotating ScheimpflugndashPlacidosystem (Galilei G4) and the Cassini color-LED corneal to-pographer Ventura et al found that the ICCs for cornealpower from the color-LED topographer the Placido to-pographer and a reflectometer were all greater than 0960although the ICC for the color-LED topographer was thelowest [15] And they also found that while the astigmatismmeasurements from the 3 devices were all highly repeatablethe color-LED topographer had statistically lower re-peatability than the others [15] Klijn et al reported that therepeatability of the Cassini corneal powermeasurements wasnot statistically different from that of the Keratron but it waslower than those of the Lenstar and Pentacam suggestingthat the discrepancy might result from Cassinirsquos high sen-sitivity to misalignment of the cornea [16] And they alsodemonstrated that Cassinirsquos repeatability for cylindermeasurements was significantly higher than those of theKeratron and Pentacam [16] However in this study thedual rotating ScheimpflugndashPlacido and color-LED cornealtopographers both provided highly repeatable corneal powerand astigmatism measurements achieving ICCs of greaterthan 0968 and 0952 in the normal and postrefractivegroups respectively +e previous studies were performedusing an earlier version of the Cassini which could explainthe differences to our results

+e anterior corneal power and astigmatism measure-ments provided by the color-LED corneal topographer didnot differ significantly from those of the dual rotatingScheimpflugndashPlacido system in either the normal or post-refractive group with the exception of the anterior simK inthe normal group and the anterior J45 in the postrefractivegroup +e anterior corneal simK measurement was sig-nificantly higher with the Cassini topographer than with theGalilei topographer with a mean difference of 012DHowever that value is smaller than the diurnal corneavariation [17] or the minimum measurement scale Fur-thermore as there is no sufficient standard reference forkeratometry measurements it is difficult to determine theaccuracy of the devices [9 18] +erefore we evaluated andcompared the quantitative agreement by calculating the ICCbetween the two devices [18] Agreement was high for all theanterior corneal power and astigmatismmeasurements withICCs greater than 0905 in both the normal and post-refractive groups Previously Ventura et al reported nostatistically significant differences in corneal power mea-surements in normal or postrefractive surgery eyes orastigmatism in postrefractive surgery eyes between thecolor-LED device and the Placido or dual-Scheimpflugdevices [15] which accords with our study

In this study we found statistically significant differencesin all posterior parameters except for the posterior J45 of thetotal group (120 eyes with and without a history of refractivesurgery) the posterior simK and posterior astigmatismmagnitude of the normal group and the posterior simK andposterior J0 of the postrefractive group Furthermoreagreement ICCs were lower than 0681 in all parameters forthe total group and the subgroups except only the posterior

simK of the normal group (ICC 0944) But more spe-cifically as shown in Figure 1 there was a greater variabilityin the group of patients who underwent refractive surgeryPrevious studies also reported greater differences of theestimated values in the postrefractive group than in thenormal group because refractive surgeries change thecorneal centration and eccentricity and assumed the ratio ofanterior-to-posterior radius of the curvature +is maypotentially have an influence on the estimated values of thetwo devices

+e first explanation for the low ICCs in the posteriorparameters is the differences in the measurement principles+e dual rotating ScheimpflugndashPlacido topographer derivesthemean posterior corneal power from the Scheimpflug data[19] whereas the color-LED topographer analyzes the re-flections of 7 infrared LEDs on the posterior surface And themeasurement zone of the Galilei topographer is from 05 to20mm from the center while the Cassini topographerevaluates keratometry values in the 30mm central zoneFurthermore the acquisition time with the Cassini (v241) isabout 2 seconds with 20 instantaneous frame acquisitionsthe Galilei in contrast requires 075 seconds Within ourknowledge more recent version of the Cassini (v25) isexpected to have shorter acquisition time since it only needs3 individual instantaneous acquisitions As there is noreference system to confirm which system comes closer tothe real values we cannot conclude which system providesthe correct values of the posterior cornea

A major limitation of this study was that the keratometrymeasurement zones for the Cassini and Galilei are differentDifferent optical zones of the two different devices made itimpossible for us to compare values exactly under the sameconditions however as a characteristic of the comparativestudy this difference of the result should be noticed andappreciated as well Nevertheless we unified all configurablesettings as the keratometric index to ensure the comparabilityof corneal parameters Also most studies including this oneenroll young healthy patients who can cooperate well withthe tests however older patients with poorer cooperation canproduce different outcomes Moreover a larger number ofparticipants are needed to clarify the various tendencies ofeach parameter Finally the clinical relevance of this studysuch as postoperative results warrants further studies

6 Conclusion

+is study is the first to compare both anterior andposterior keratometries between the dual rotatingScheimpflugndashPlacido and color-LED corneal topographers+e color-LED corneal topographer and dual rotatingScheimpflugndashPlacido topographer showed high agreementfor anterior corneal measurements however the agreementwas low for posterior corneal indices +ese results weresimilar in both the normal and the postrefractive groups

List of abbreviations

ICC Intraclass correlation coefficientLED Light-emitting diode


D DioptersI-S Inferior-superiorsimK Simulated KSD Standard deviationsJ JacksonLASEK Laser-assisted subepithelial keratectomyLASIK Laser in situ keratomileusisSE Spherical equivalentCI Confidence intervalColorLED

Color light-emitting diode cornealtopographer

DRSP Dual rotating ScheimpflugndashPlacido cornealtopographer

K Keratometry

Data Availability

+e data used to support the findings of this study areavailable from the corresponding author upon request

Disclosure

+is work was approved by the Institutional Review Board ofKangbuk Samsung Hospital

Conflicts of Interest

+e authors declare that they have no conflicts of interests

Acknowledgments

+is work was supported by the Medical Research Fundsfrom Kangbuk Samsung Hospital presented in 2017 Con-gress of ESCRS and 2018 ASCRSmiddotASOA Annual Meeting

References

[1] S Y Jung H S Chin N R Kim et al ldquoComparison ofrepeatability and agreement between swept-source opticalbiometry and dual-Scheimpflug topographyrdquo Journal ofOphthalmology vol 2017 Article ID 1516395 5 pages 2017

[2] P D Chamberlain I Montes de Oca R Shah et al ldquoPre-operative prediction of the optimal toric intraocular lensalignment meridianrdquo Journal of Refractive Surgery vol 34no 8 pp 515ndash520 2018

[3] A C L Vrijling B Braaf J J Snellenburg et al ldquoClinicalvalidation of point-source corneal topography in kerato-plastyrdquo Optometry and Vision Science vol 88 no 7pp E837ndashE842 2011

[4] Y W Lee C Y Choi and G Y Yoon ldquoComparison of dualrotating Scheimpflug-Placido swept-source optical coherencetomography and Placido-scanning-slit systemsrdquo Journal ofCataract and Refractive Surgery vol 41 no 5 pp 1018ndash10292015

[5] M Romero-Jimenez J Santodomingo-Rubido andJ S Wolffsohn ldquoKeratoconus a reviewrdquo Contact Lens andAnterior Eye vol 33 no 4 pp 157ndash166 2010

[6] K O McGraw and S P Wong ldquoForming inferences aboutsome intraclass correlation coefficientsrdquo PsychologicalMethods vol 1 no 1 pp 30ndash46 1996

[7] M R Lattimore Jr S Kaupp S Schallhorn and R LewisldquoOrbscan pachymetryrdquo Ophthalmology vol 106 pp 977ndash9811999

[8] L N +ibos W Wheeler and D Horner ldquoPower vectors anapplication of Fourier analysis to the description and statis-tical analysis of refractive errorrdquo Optometry and Vision Sci-ence vol 74 no 6 pp 367ndash375 1997

[9] J M Bland and D G Altman ldquoStatistical methods forassessing agreement between two methods of clinical mea-surementrdquo Lancet vol 8 no 1 pp 307ndash10 1986

[10] M Shirayama L Wang M P Weikert and D D KochldquoComparison of corneal powers obtained from 4 differentdevicesrdquo American Journal of Ophthalmology vol 148pp 528ndash535e1 2009

[11] D Z Reinstein M Gobbe and T J Archer ldquoAnterior seg-ment biometry a study and review of resolution and re-peatability datardquo Journal of Refractive Surgery vol 28 no 7pp 509ndash527 2012

[12] T B Ferreira and F J Ribeiro ldquoComparability and re-peatability of different methods of corneal astigmatism as-sessmentrdquo Clinical Ophthalmology vol 12 pp 29ndash34 2018

[13] G Savini F Versaci G Vestri P Ducoli and K NaeligserldquoInfluence of posterior corneal astigmatism on total cornealastigmatism in eyes with moderate to high astigmatismrdquoJournal of Cataract and Refractive Surgery vol 40 no 10pp 1645ndash1653 2014

[14] D D Koch S F Ali M P Weikert M Shirayama R Jenkinsand L Wang ldquoContribution of posterior corneal astigmatismto total corneal astigmatismrdquo Journal of Cataract and Re-fractive Surgery vol 38 no 12 pp 2080ndash2087 2012

[15] B V Ventura Z Al-Mohtaseb L Wang D D Koch andM P Weikert ldquoRepeatability and comparability of cornealpower and corneal astigmatism obtained from a point-sourcecolor light-emitting diode topographer a Placido-basedcorneal topographer and a low-coherence reflectometerrdquoJournal of Cataract and Refractive Surgery vol 41 no 10pp 2242ndash2250 2015

[16] S Klijn N J Reus and V A D P Sicam ldquoEvaluation ofkeratometry with a novel color-LED corneal topographerrdquoJournal of Refractive Surgery vol 31 no 4 pp 249ndash256 2015

[17] S A Read M J Collins and L G Carney ldquo+e diurnalvariation of corneal topography and aberrationsrdquo Corneavol 24 no 6 pp 678ndash687 2005

[18] C Costa-Santos J Bernardes D Ayres-de-Campos A Costaand C Costa ldquo+e limits of agreement and the intraclasscorrelation coefficient may be inconsistent in the in-terpretation of agreementrdquo Journal of Clinical Epidemiologyvol 64 no 3 pp 264ndash269 2011

[19] E J Kim I Montes de Oca L Wang M P WeikertD D Koch and S S Khandelwal ldquoRepeatability of posteriorand total corneal curvature measurements with a dualScheimpflug-Placido tomographerrdquo Journal of Cataract andRefractive Surgery vol 41 no 12 pp 2731ndash2738 2015


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corneal topographer and the dual rotating ScheimpflugndashPlacido topographer

2 Methods

+is prospective cross-sectional study examined healthysubjects from the Department of Ophthalmology KangbukSamsung Hospital Seoul South Korea+e study adhered tothe tenets of the Declaration of Helsinki and was approvedby the Institutional Review Board of Kangbuk SamsungHospital Written informed consent was obtained from eachsubject before inclusion in the study In this study wefollowed the methods of Lee et al [4]

Inclusion criteria were healthy individuals aged 18 to40 years with a spherical equivalent ranging from +100 tominus600 diopters (D) to rule out high myopia which can causeextreme refractive errors +e best-corrected visual acuitywas 000 logMAR in all eyes Exclusion criteria included ahistory of ocular pathology ocular trauma contact lenswear pregnancy systemic or local medications and ocularsurgeries other than laser refractive surgery for myopia Inthe postrefractive surgery group we only included patientswho underwent surgery more than a year ago and who didnot have any subjective visual acuity change discomfort orhistory of ophthalmic treatment In addition patients withastigmatism of more than 250D K values higher than 472Din any axis or inferior-superior (I-S) values (differences inI-S keratometry) more than 14D were excluded from thisstudy to rule out keratoconus patients [5]

One eye from each subject was used for statisticalanalysis Eyes were divided into 2 groups according to theirhistory of myopic laser refractive surgery +e refractivegroup consisted of eyes with previous refractive surgerywhile the normal group consisted of eyes that had not re-ceived refractive surgery

21 Repeatability Twenty participants (20 eyes) were in-cluded in the assessment of device repeatability and 10 eyeshad a history of refractive surgery for myopia +ree con-secutive measurements were performed and intraclasscorrelation coefficients (ICCs) were calculated for eachmeasurement for anterior and posterior K and astigmatismvalues +e ICC is the ratio of between-subjects variance tothe sum of the pooled within-subject variance and between-subjects variance It expresses the consistency of repeatedmeasurements and ranges from 0 to 1 An ICC smaller than075 indicates poor repeatability from 075 to 089 repre-sents moderate repeatability and greater than 090 corre-sponds to high repeatability [6] All measurements in thisstudy were performed by the same person experienced inophthalmic examinations

3 Measurements

All eyes were measured using both a dual rotatingScheimpflugndashPlacido corneal topographer and a color-LEDcorneal topographer Table 1 shows the characteristics andmeasurement settings used for each system All measure-ments were performed continuously in individual subject

between 10 am and 1 pm to avoid the effects of diurnalvariation in corneal indices [7]

31 Dual Rotating ScheimpflugndashPlacido System +e GalileiG4 uses 2 cameras in opposite positions in combination witha Placido disk with 20 Placido rings to analyze the shape ofthe cornea Double rotating systems prevent and compen-sate for errors with oblique angle imaging By detecting theedge in the dual-Scheimpflug images the shape of theposterior cornea can be assessed +e total acquisition timewas approximately 075 seconds and more than 122000points were scanned +e simulated K (simK) values werecalculated based on the anterior corneal curvatures in the 10to 40mm central zone A keratometric index of 13375 wasused to calculate the powers of the steep and flat meridians+e posterior simK was derived from the posterior axialcurvature map as the arithmetic mean of the pair of or-thogonal meridians with the greatest difference in averagepower in the 05 to 20mm zone+e refractive indices of thecornea (1376) and aqueous humor (1336) were used tocalculate the powers of the steep and flat meridians

32 Color Light-Emitting Diode Corneal Topographer +eCassini v241 has approximately 700 red yellow and greenLEDs arranged in a specific pattern to ensure a 1-to-1correspondence between the source and image pointswhich potentially decreases source-image mismatch andartifacts caused by the shadow +e color-LED topographerevaluates the keratometric values in the 30mm central zoneAdditionally the Cassini analyzes the reflections (2ndPurkinje images) of infrared LEDs on the posterior surfaceto calculate the posterior curvature To calculate the anteriorcorneal surface astigmatism using the Cassini we convertedthe anterior radii of curvature to meridional power using akeratometric index of 13375 Posterior corneal astigmatismwas calculated using ray tracing in which Snellrsquos law isapplied to calculate the refraction of a large number of lightrays incident on the anterior and posterior corneal surface

33 Statistical Analysis Data analysis was performed usingSPSS software (version 240 SPSS Inc) andMicrosoft OfficeExcel (Microsoft Corp) +e results of the quantitativevariables were expressed by their minimum and maximumvalues means and standard deviations (SDs) +e meananterior and posterior corneal powers were calculated foreach measurement on each device as the arithmetic averageof the anterior and posterior corneal steep K and flat K +e

Table 1 Characteristics and measurement settings for each system

Parameter Dual rotatingScheimpflugndashPlacido

Colorlight-emitting diode

Acquisition time (s) 075 2K index 13375lowast 13375lowastKmeasurement zone(mm)

1ndash4 (anterior) 305ndash2 (posterior)K keratometry lowastConfigurable or selectable option



J0 C

21113874 1113875cos(2empty)

J45 C

21113874 1113875sin(2empty)

(1)





4 Results



0972 respectively)



5 Discussion






Sex n () 0133dagger

Male 24 (400) 32 (533)Female 36 (600) 28 (467)




lowast























0

10

15

ndash05

05

Diff

eren

ce


0164 (95 CI 0134 to 0195)

ndash0077

0406

(a)

0

10

15

ndash05

05

Diff

eren

ce


0424 (95 CI 0342to 0507)

ndash0215

1064

(b)


ndash0370

0284


10


0204

ndash10

0

0608

Diff

eren

ce

(c)


10


0204

ndash10

0

0608

Diff

eren

ce


ndash0488

0415

(d)05


0102

ndash05

0

0304


0013 (95 CI ndash0010to 0036)

ndash0171

0196

Diff

eren

ce

(e)

05


0102

ndash05

0

0304


Diff

eren

ce


ndash0412

0233

(f )08

ndash04

ndash02

0

02

04

06

ndash06



ndash0206

0205

Diff

eren

ce

(g)

08

ndash04

ndash02

0

02

04

06

ndash06


Diff

eren

ce


ndash0330

0312

(h)









6 Conclusion








K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of




















J0 C

21113874 1113875cos(2empty)

J45 C

21113874 1113875sin(2empty)

(1)





4 Results



0972 respectively)



5 Discussion






Sex n () 0133dagger

Male 24 (400) 32 (533)Female 36 (600) 28 (467)




lowast























0

10

15

ndash05

05

Diff

eren

ce


0164 (95 CI 0134 to 0195)

ndash0077

0406

(a)

0

10

15

ndash05

05

Diff

eren

ce


0424 (95 CI 0342to 0507)

ndash0215

1064

(b)


ndash0370

0284


10


0204

ndash10

0

0608

Diff

eren

ce

(c)


10


0204

ndash10

0

0608

Diff

eren

ce


ndash0488

0415

(d)05


0102

ndash05

0

0304


0013 (95 CI ndash0010to 0036)

ndash0171

0196

Diff

eren

ce

(e)

05


0102

ndash05

0

0304


Diff

eren

ce


ndash0412

0233

(f )08

ndash04

ndash02

0

02

04

06

ndash06



ndash0206

0205

Diff

eren

ce

(g)

08

ndash04

ndash02

0

02

04

06

ndash06


Diff

eren

ce


ndash0330

0312

(h)









6 Conclusion








K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of






































0

10

15

ndash05

05

Diff

eren

ce


0164 (95 CI 0134 to 0195)

ndash0077

0406

(a)

0

10

15

ndash05

05

Diff

eren

ce


0424 (95 CI 0342to 0507)

ndash0215

1064

(b)


ndash0370

0284


10


0204

ndash10

0

0608

Diff

eren

ce

(c)


10


0204

ndash10

0

0608

Diff

eren

ce


ndash0488

0415

(d)05


0102

ndash05

0

0304


0013 (95 CI ndash0010to 0036)

ndash0171

0196

Diff

eren

ce

(e)

05


0102

ndash05

0

0304


Diff

eren

ce


ndash0412

0233

(f )08

ndash04

ndash02

0

02

04

06

ndash06



ndash0206

0205

Diff

eren

ce

(g)

08

ndash04

ndash02

0

02

04

06

ndash06


Diff

eren

ce


ndash0330

0312

(h)









6 Conclusion








K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of



















0

10

15

ndash05

05

Diff

eren

ce


0164 (95 CI 0134 to 0195)

ndash0077

0406

(a)

0

10

15

ndash05

05

Diff

eren

ce


0424 (95 CI 0342to 0507)

ndash0215

1064

(b)


ndash0370

0284


10


0204

ndash10

0

0608

Diff

eren

ce

(c)


10


0204

ndash10

0

0608

Diff

eren

ce


ndash0488

0415

(d)05


0102

ndash05

0

0304


0013 (95 CI ndash0010to 0036)

ndash0171

0196

Diff

eren

ce

(e)

05


0102

ndash05

0

0304


Diff

eren

ce


ndash0412

0233

(f )08

ndash04

ndash02

0

02

04

06

ndash06



ndash0206

0205

Diff

eren

ce

(g)

08

ndash04

ndash02

0

02

04

06

ndash06


Diff

eren

ce


ndash0330

0312

(h)









6 Conclusion








K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of

























6 Conclusion








K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of






















K Keratometry

Data Availability


Disclosure




Acknowledgments


References

























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of























of




Disease Markers



OncologyJournal of





PPAR Research



Volume 2018


Journal of

ObesityJournal of



















Comparison of Color Light-Emitting Diode Corneal ...downloads.hindawi.com/journals/joph/2018/6764805.pdfcornealtopographerandthedualrotatingScheimpﬂug– Placidotopographer. 2. Methods

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