905129.pdf

7232019 905129pdf

httpslidepdfcomreaderfull905129pdf 17

Research Article Assessment of Corneal Biomechanical Properties andIntraocular Pressure in Myopic Spanish Healthy Population

Mariacutea A del Buey123 Laura Lavilla12 Francisco J Ascaso13 Elena Lanchares34

Valentiacuten Huerva5 and Joseacute A Cristoacutebal123

983089 Department of Ophthalmology Lozano Blesa University Clinic Hospital Zaragoza Spain983090 Department of Ophthalmology Quir on University Hospital Zaragoza Spain983091

Instituto Aragones de Ciencias de la Salud (IACS) Zaragoza Spain983092 Arag on Institute for Engineering Research (I983091A) University of Zaragoza CIBER on BioengineeringBiomaterials and Nanomedicine (CIBER-BBN) Zaragoza Spain

983093 Department of Ophthalmology Arnau de Vilanova University Hospital and IRB-Lleida Avenida Rovira Roure 983096983088 Lleida Spain

Correspondence should be addressed to Valentın Huerva vhuervagmailcom

Received 983089983091 November 983090983088983089983091 Accepted 983089983088 January 983090983088983089983092 Published 983090983093 February 983090983088983089983092

Academic Editor Cristina Peris-Martinez

Copyright copy 983090983088983089983092 Marıa A del Buey et al Tis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Purpose o examine biomechanical parameters o the cornea in myopic eyes and their relationship with the degree o myopia in awestern healthy population Methods Corneal hysteresis (CH) corneal resistance actor (CRF) Goldmann correlated intraocularpressure (IOP) and corneal compensated IOP (IOPcc) were measured using the ocular response analyzer (ORA) in 983091983089983090 eyes o 983089983095983095 Spanish subjects aged between 983090983088 and 983093983094 years Reraction was expressed as spherical equivalent (SE) which ranged rom 983088to minus983089983094983093983088 diopters (D) (mean minus388 plusmn 290 D) Subjects were divided into our groups according to their reractive status group983089 or control group emmetropia (minus050 le SE lt 050) group 983090 low myopia (minus075 le SE lt 300 D) group 983091 moderate myopia(minus300 le SE le minus600 D) and group 983091 high myopia (SE greater than minus983094983088983088 D) We analyzed the relationship between cornealbiomechanics measured with ORA and SE Results CH in the emmetropia low myopia moderate myopia and high myopia groupswas 1113plusmn 098 1149 plusmn 125 1052 plusmn 154 and 1035plusmn 133 mmHg respectively CH in the highly myopic group was signi1047297cantly lower than that in the emmetropic group ( = 007) and low myopic group ( = 0035) however there were no differences withthe moderate myopic group ( = 0872) Tere were no statistically signi1047297cant differences regarding IOP among the our groups( gt 005) nevertheless IOPcc was signi1047297cantly higher in the moderately myopic (1547plusmn247 mmHg) andhighly myopic (1614plusmn

259 mmHg) groups than in the emmetropia (1515 plusmn 206 mmHg) and low myopia groups (1453 plusmn 237 mmHg) No correlationbetween age and the measured parameters was ound CH and IOPcc were weakly but signi1047297cantly correlated with SE ( 1038389 = 0171 = 0002 and 1038389 = minus0131 = 0021 resp) Conclusions Present study showed only a very weak but signi1047297cant correlation

between CH andreractive error with CH being lower in both moderately and highly myopic eyes than that in the emmetropic andlow myopic eyes Tese changes in biomechanical properties o the cornea may have an impact on IOP measurement increasingthe risk o glaucoma

1 Introduction

Myopia is the most common ocular disorder Its worldwideprevalence is about 983091983088 and up to 983096983088 in certain Asian pop-ulations [983089ndash983092] Corneal hysteresis (CH) is a parameter whichmeasures the viscoelastic behaviour o the cornea indicatingits biomechanical integrity [983093] Some clinical conditions suchas keratoconus Fuchs corneal dystrophy glaucoma and

corneal reractive surgery may induce changes in cornealbiomechanical properties leading to a decrease in CH [983094ndash983089983088]Although several studies with the ocular response analyzer(ORA Reichert Inc NY USA) have reported a relationshipbetween the reractiveerrorand corneal biomechanical prop-erties it is still under debate [983092 983089983089] Tus whereas in severalstudies CH wasoundsigni1047297cantly lowerin patients with highmyopia [983089983090ndash983089983095] other authors did not 1047297nd any correlation

Hindawi Publishing CorporationJournal of Ophthalmology Volume 2014 Article ID 905129 6 pageshttpdxdoiorg1011552014905129

7232019 905129pdf


983090 Journal o Ophthalmology

[983089983096ndash983090983088] Most o the studies were perormed in myopicSingaporean and Chinese populations [983089983090 983089983092 983089983096 983090983088] andothers in Brazilian [983090983089] or urkish people [983089983093] withonly a ew ones in Caucasian individuals [983089983091 983089983094] Moreover sincebiomechanical properties o the cornea are known to changewith age [983090983090] some slightly mixed 1047297ndings in children may

not be applicable to adult populations [983089983094] Te aim o present study was to measure with the ORA device severalcorneal biomechanical parameters in an adult western heal-thy population containing emmetropes low myopes moder-ate myopes and highly myopic individuals and the relation-ship between these parameters and the values o intraocularpressure (IOP) determined with ORA including Goldmanncorrelated IOP (IOP) and corneal compensated IOP (IOPcc)

2 Methods

In this observational comparative study 983091983089983090 eyes o 983089983095983095healthy subjects were analyzed (983095983094 men and 983089983088983089 women)Tey were recruited sequentially among patients and healthy

volunteers in the Department o Ophthalmology at theLozano Blesa University Clinic Hospital and Quiron Univer-sity Hospital Zaragoza Spain Te average age o the patientswas 3327 plusmn 765 years (range 983090983088ndash983093983094) All subjects received acomplete ophthalmic examination including measurement o best-corrected visual acuity (BCVA) with EDRS chart slit-lamp anterior segment biomicroscopy undus examinationand corneal topography (Orbscan II) in order to discard theexistence o subclinical corneal pathology Automated andsubjective reractionswere perormed to determine reractiveerror in order to use it or the statistical analyses Teir spher-ical equivalent (SE) o reractive error ranged continuously rom983088to minus983089983094983093983088 D (mean minus388plusmn290 D) For the pur-pose o the study subjects were divided into our groups according totheir reractive status group 983089 or control group emmetropia(minus050 le SE lt 050) group 983090 low myopia (minus075 le SE ltminus300 D) group 983091 moderate myopia (minus300 le SE le minus600 D)and group 983092 high myopia (SE greater than minus983094983088983088 D) Allparticipants had monocular BCVA o 983090983088983091983090 (983088983090983088 logMarnotation) or better Subjects who had reractive errors suchas hyperopia gt 983088983093 D or astigmatism gt 983089 D IOP gt 983090983089 mmHgsigns o glaucomatous optic neuropathy amily history o glaucoma in a 1047297rst-degree relatives corneal dystrophy andmyopic macular degenerationthose who had undergonepre-

vious eye surgery or trauma eye inection diabetes mellitus

corticosteroid use or other acute or chronic diseases or usingany topical eye medication or subjects that did not meetnormal topographic criteria were excluded rom the study

Corneal biomechanical properties such as CH and CRFwere measured by the same masked technician with the Ocu-lar Response Analyzer (ORA sofware version 983090983088983092 ReichertOphthalmic Instruments Buffalo NY) using standard tech-nique [983093 983096 983090983091] Brie1047298y a rapid air puff deormed the corneaand the induced corneal deormation was detected withan electrooptical system Te air pulse induced inward andthen outward corneal movement which provided two appla-nation measurements CH resulted rom the damping o thecornea because o its biomechanical properties and was

derived rom the difference o the two measurements duringthe applanation process CRF also derived rom corneal hys-teresis is calculated as a linear unction o the pressurescorresponding to the two applanationsCRF is an indicator o the overall resistance o the cornea which according to pre-

vious data seems to be related to central corneal thickness

(CC) and GA determined IOP but not to IOPcc [983093] TeORA also determined the values o noncontact tonometerGoldmann correlated IOP and IOPcc IOPcc is a pressuremeasurement that utilizes the new inormation provided by the CH measurement to provide an IOP measurement lessaffected by corneal properties CC was measured ollowingcorneal biomechanical properties measurements by ultra-sound pachymetry (983090983088 MHz) using an ORA-integrated hand-held pachymeter Tree measurements o good quality wereobtained or each patient the signals with the highest Wave-orm Score (WS) were highlighted as the best score value(BSV) and were used or statistical evaluation Te study anddata accumulation were perormed with the approval o thelocal ethics committee inormed consent was obtained romeach subject participating in the study and the study protocolwas consistent with the tenets o the Declaration o Helsinki

3 Data Analysis

Values were presented as mean plusmn SD Statistical analyseswere conducted using a commercial sofware (SPSS sofware

version 983089983091983088 SPSS Inc Chicago IL) Te distribution o themeasured variables was estimated by the one-sample Kolmo-gorov-Smirnov test One-way analysis o variance (ANOVA)and post hoc tests were used or determining whether the

values o a particular variable differed between the three diag-

nostic groups We combined data rom both eyes using themixed model method [983090983092] which adjusts or the correlationbetween the two eyes in a unique person Multivariate mixed-model analysis adjusted by age and sex was used to determinethe relationship between two con-tinuous variables Pearsonrsquoscorrelation coefficient (1038389) was used to assess the relationshipbetween spherical equivalent power and the corneal biome-chanical properties (CH and CRF) as well as IOP (IOPcc andIOP) and CC Te level o statistical signi1047297cance was set to lt 005

4 Results

A total o 983089983095983095 patients (983091983089983090 eyes) were enrolled in this studyTe reraction among all included eyes ranged rom 983088to minus983089983094983093983088 D (SE) 983092983093 eyes corresponding to 983090983093 patients (983089983093women and 983089983088 men) were included as healthy controls (group983089) 983095983089 eyes o 983092983095 patients (983090983088 women and 983090983095 men) were in-cluded in group 983090 One hundred orty-1047297ve eyes o 983095983090 patientswere included in group 983091 And 1047297nally 983093983089 eyes o 983091983091 patients(983090983091 women and 983089983088 men) were included in group 983092 Signi1047297cantdifferences in reraction distribution were ound between theour diagnostic groups ( lt 005 able 983089) Te one-sampleKolmogorov-Smirnov test showed that CH CRF IOP IOPccand CC were normally distributed ( = 077 983088983095983096 983088983097983090983088983092983090 and 983088983093983089 resp) (Figure 983089) Parameters such as age

7232019 905129pdf


Journal o Ophthalmology 983091

983137983138983148983141 983089 Baseline data o the our diagnostic groups

Parameters Emmetropia(983092983093 eyes983090983093 patients)

Low myopia(983095983089 eyes983092983095 patients)

Moderate myopia(983089983092983093 eyes983095983090 patients)

High myopia(983093983089 eyes983091983091 patients)

SE (D) 025 plusmn 043 minus215 plusmn 069 minus423 plusmn 077 minus869 plusmn 288 lt983088983088983088983089a

Sex (MF) 983089983088983089983093 983090983095983090983088 983090983097983092983091 983089983088983090983091 983088983088983093983095b

Age (years) 3537 plusmn 773 3360 plusmn 712 3224 plusmn 668 3388 plusmn 985 983088983088983097983089

a

D diopters F emale M maleData were presented as mean plusmn SD o the indicated variablesaOne-way analysis o varianceb

-testSigni1047297cant differences in reraction were present among the our groups ( post hoc test 1038389 lt 005)

BCVA IOP and CC were not signi1047297cantly different amonggroups ( gt 005) (able 983090) CH in the emmetropia low myopia moderate myopia and highly myopic groups were1108plusmn098 1100plusmn125 1052plusmn154 mmHg and 1035plusmn133respectively (able 983090) CH in the moderately and highly myopic groups was signi1047297cantly lower than in the

emmetropic ( = 002 and = 001 resp Games-Howellpost hoc test) and low myopic group ( = 007 and = 004resp Games-Howell post hoc test) CRF o the emmetropicgroup was signi1047297cantly higher than that in the moderately and highly myopic groups ( lt 0001 and = 004 respGames-Howell post hoc test) Tere was no signi1047297cant di-erence in IOP ( = 0083 ANOVA test gt 005 leastsigni1047297cant difference post hoc test) however IOPcc wassigni1047297cantly higher in the moderate (1547plusmn247) and highly myopic (1614 plusmn 259) groups compared to the emmetropiagroup (1515plusmn206) ( = 0046 resp to highly myopic groupleast signi1047297cant difference post hoc test) and low myopiagroup (1453 plusmn 237) ( = 0008 and lt 0001 resp least

signi1047297cant difference post hoc test) (able 983090)No correlations were ound in the measured parameters

with the age CH and IOPcc were parameters signi1047297cantly correlated with SE (1038389 = 0171 = 0013 and 1038389 = minus0131 = 0021 resp Pearsonrsquos correlation coefficient) (Figure 983090)

5 Discussion

Corneal hysteresis is the result o viscoelastic properties o the cornea together with the combined effect o the cornealthickness and rigidity [983093] Low values o CH indicate a sof or1047298oppy cornea According to Reichert CRF is dominated by

the corneal elastic properties andappears to be an indicator o the overall resistance o the cornea [983093 983090983091 983090983093] Tere is strongevidence thatcorneal biomechanical properties are correlatedto the degree o myopia Tus the abnormal elongation o themyopic eye is associated with corneal 1047298attening and thinning[983089983089] resulting in a decreased CH and CRF [983089983090 983090983094] Moreovermyopic eyes have a lower ocular rigidity than emmetropicand hyperopic eyes [983090983095 983090983096] Tereore corneal rigidity aspart o the global rigidity is likely to be low in myopic eyesas suggested by the decreased CH Finally corneal biome-chanical properties re1047298ect viscoelastic characteristics o thecornea andthe mechanical strength o stromal collagen 1047297brilsinteracting with the extracellular proteoglycan matrix [983090983090]

CH (mmHg)

CRF (mmHg)IOPcc (mmHg)

IOP (mmHg)

E m m

e t r o p i a

L o w

m y o p i a

M o d e r a t e

m y o p i a

H i g h

m y o p i a

25

20

15

10

5

F983145983143983157983154983141 983089 Box-and-whisker plot or corneal hysteresis (CH) andcorneal resistance actor (CRF) and noncontact tonometer intraoc-ular pressure (IOP) and corneal compensated intraocular pressure(IOPcc) Average and standard deviation values are presented inmmHg

Several studies have used ORA to study the correlationbetween corneal biomechanics and the degree o myopiaNevertheless the results are contradictory Tus whereassome authors ound a signi1047297cantly lower CH in highly myopic patients compared with nonmyopic or low myopiasubjects [983089983090ndash983089983095] other studies did not show a correlationbetween CH and myopia [983089983096ndash983090983088]Tis could maybe be due tothe narrow range o myopia selected or the individuals [983090983088]We ound that CH in moderate andhighly myopic groupswassigni1047297cantly lower than that in the emmetropiclow myopicgroup However ourstudy differsin a ew aspects Most o thestudies were perormed in myopic Asian populationswhereas we measured corneal biomechanical characteristics

7232019 905129pdf



983137983138983148983141 983090 Differences in corneal biomechanical parameters and CC in the our diagnostic groups

Parameters Emmetropia

(983092983093 eyes983090983093 patients)Low myopia

(983095983089 eyes983092983095 patients)Moderate myopia

(983089983092983092 eyes983095983090 patients)High myopia

(983093983089 eyes983091983091 patients)

CH (mmHg) 1108 plusmn 098 (951 plusmn 1370) 11 plusmn 125 (983096983095983088ndash983089983092983090983088) 1052 plusmn 154 (983093983088983090ndash983089983092983090983088) 1035 plusmn 133 (983095983092983096ndash983089983090983095)

CRF (mmHg) 1107 plusmn 106 (915 plusmn 1370) 1063 plusmn 139 (983096983092983088ndash983089983092983090983088) 1034 plusmn 164 (983093983092983094ndash983089983092983092983088) 1036 plusmn 146 (983095983090983091ndash983089983091983092983088)

CC (1103925m) 57382 plusmn 3803 (983093983089983091ndash983094983093983091) 55729 plusmn 3803 (983093983088983088ndash983094983093983096) 55322 plusmn 3421 (983092983094983094ndash983094983093983096) 55279 plusmn 2686 (983092983094983091ndash983093983097983093)IOP (mmHg) 1561 plusmn 223 (983089983089983097983094ndash983090983088983095) 1455 plusmn 252 (983089983088ndash983090983088983090) 1505 plusmn 253 (983097983095ndash983090983089983090) 1554 plusmn 278 (983096983091983094ndash983090983089983088983094)

IOPcc (mmHg) 1515 plusmn 206 (983089983088ndash983089983096983093983088) 1453 plusmn 237 (983089983088ndash983089983097983096983088) 1547 plusmn 247 (983097983089ndash983090983088983095) 1614 plusmn 259 (983089983088ndash983090983091)

CH corneal hysteresis CRF corneal resistance actor CC central corneal thickness IOP noncontact tonometer intraocular pressure IOPcc cornealcompensated IOPData were presented as mean plusmn SD o the indicated variables

S E ( D

)

CH (mmHg)

000

minus500

minus1000

minus1500

minus2000

600 800 1000 1200 1400

R2 linear = 0032

(a)

S E ( D

)

IOPcc (mmHg)

000

minus500

minus1000

minus1500

minus2000

900 1200 1500 1800 2100 2400

R2 linear = 0012

(b)

F983145983143983157983154983141 983090 Correlation between spherical equivalent (SE) and (a) corneal hysteresis (CH) and (b) corneal compensated intraocular pressure

(IOPcc)

in a western population Furthermore we analyzed these par-ameters in adults avoiding the possible in1047298uence o age i children would have been included We included notonly highly myopic eyes but also moderate myopes andemmetropeslow myopes Finally an exhaustive selection o the subjects was carried out or the present study excludingeyes with topographical patterns suspected or indicativeso keratoconus as well as signs o endothelial damage orglaucoma since these disorders would cause a decrease inCH

It has been suggested that the elastic properties o thecornea may in1047298uence the accuracy o IOP measurement [983090983090]In that case the ORA may be useul or the diagnosis andmanagement o glaucoma and ocular hypertension (OH)[983090983093] Several studies have reported that myopic subjects espe-cially in the highly myopic group showed higher IOP thancontrols [983089983090 983090983097ndash983091983090] Altan et al [983089983093] ound that IOPcc mea-sured by ORA but not IOP was signi1047297cantly higher in highly myopic eyes than in nonmyopia or low myopia group Addi-tionally we observed that IOPcc was signi1047297cantly higher inboth the moderately and highly myopic groups compared tothe emmetropialow myopia group Several studies [983089983093 983090983088]have revealed a signi1047297cant correlation between axial length

and IOPcc Te positive correlations between CC and CHhave also been con1047297rmed [983093 983090983091 983091983091] In accordance with Altanet al [983089983093] IOP and IOPcc were also signi1047297cantly correlatedwith CC However we ound a signi1047297cant relationship bet-ween IOP and IOPcc with CH but not with CC Te changesin CH with reraction are not related to the differences inCC[983089983094] CC in all ourmyopic patients was typically withinnormal limits and independent o the degree o myopia inagreement with previous studies which ound no signi1047297cantdifferences between myopes and emmetropes in terms o

corneal thickness [983091983092 983091983093]Unlike previous studies the present study showed thatnot only high myopic eyes but also moderately myopic oneshave a compromised corneal mechanical strength Teseinconsistent results could be justi1047297ed by differences related toother actors such as race range o age gender reractivestatus axial length corneal curvature and CC [983089983092 983089983097 983090983088]Although there is a higher prevalence o glaucoma amongmyopic eyes than that in nonmyopic eyes [983090983097 983091983090] it is stillunclear why myopia increases IOP Jiang et al [983089983092] attributedthese differences o corneal biomechanical properties to thedifference o age between groups Nevertheless in our study the variable age was not signi1047297cantly different among the ourgroups

7232019 905129pdf



Te main limitations o thisstudy would include that axiallength and corneal curvature were not measured Because o this the importance o both actors in the reraction-relatedmechanical changes o the cornea is unknown

Concluding the present study shows a very weak but sig-ni1047297cant correlation between CH and reractiveerror with CH

being lower in both moderately and highly myopic groupsthan that in the emmetropiclow myopic ones indicatingthat some aspects o corneal biomechanics may need to beinterpreted in light o the reraction especially in myopiaTese changes in biomechanical properties o the cornea may have an impact on IOP measurement increasing the risk o glaucoma Further studies with larger sample size should beperormed

Conflict of Interests

Te authors have neither con1047298ict o interests nor commercialinterest in the devices mentioned in the paper

References

[983089] M Feldkamper and F Schaeffel ldquoInteractions o genes andenvironment in myopiardquo Developments in Ophthalmology vol983091983095 pp 983091983092ndash983092983097 983090983088983088983091

[983090] V Choo ldquoA look at slowing progression o myopia solutionsor this common oculardisordermightcome rom cellular biol-ogyrdquo Te Lancet vol 983091983094983089 no 983097983091983094983097 pp 983089983094983090983090ndash983089983094983090983091 983090983088983088983091

[983091] C A McCarty and H R aylor ldquoMyopia and vision 983090983088983090983088rdquo American Journal of Ophthalmology vol 983089983090983097 no 983092 pp 983093983090983093ndash983093983090983095983090983088983088983088

[983092] D S Fan D S Lam R F Lam et al ldquoPrevalence incidence and

progression o myopia o school children in Hong Kongrdquo Inves-tigative Ophthalmology and Visual Science vol 983092983093 no 983092 pp983089983088983095983089ndash983089983088983095983093 983090983088983088983092

[983093] D A Luce ldquoDetermining in vivo biomechanical properties o the cornea with an ocular response analyzerrdquo Journalof Cataract and Refractive Surgery vol 983091983089 no 983089 pp 983089983093983094ndash983089983094983090 983090983088983088983093

[983094] M A Del Buey J A Cristobal F J Ascaso L Lavilla and ELanchares ldquoBiomechanical properties o the cornea in uchsrsquocorneal dystrophyrdquo Investigative Ophthalmology and Visual Sci-ence vol 983093983088 no 983095 pp 983091983089983097983097ndash983091983090983088983090 983090983088983088983097

[983095] M A Del Buey J A Cristobal F J Ascaso L Lavilla and ELanchares ldquoCorneal biomechanical properties in normal reg-ular astigmatic and keratoconic eyesrdquo Journal of Emmetropia vol 983090 pp 983091ndash983096 983090983088983089983089

[983096] S Shah M Laiquzzaman S Mantry and I Cunliffe ldquoOcularresponse analyser to assess hysteresis and corneal resistance ac-tor in low tension open angle glaucoma and ocular hyperten-sionrdquo Clinical and Experimental Ophthalmology vol 983091983094 no 983094pp 983093983088983096ndash983093983089983091 983090983088983088983096

[983097] F W De Medeiros A Sinha-Roy M R Alves S E Wilson andW J Dupps Jr ldquoDifferences in the early biomechanical effects o hyperopic and myopic laser in situ keratomileusisrdquo Journal of Cataractand Refractive Surgery vol 983091983094no 983094 pp 983097983092983095ndash983097983093983091 983090983088983089983088

[983089983088] M Detry-Morel J Jamart and S Pourjavan ldquoEvaluation o corneal biomechanical properties with the Reichert OcularResponse Analyzerrdquo European Journal of Ophthalmology vol983090983089no 983090 pp 983089983091983096ndash983089983092983096 983090983088983089983089

[983089983089] S W Chang I L sai F R Hu L L Lin and Y F Shih ldquoTecornea in young myopic adultsrdquo British Journal of Ophthalmol-ogy vol 983096983093 no 983096 pp 983097983089983094ndash983097983090983088 983090983088983088983089

[983089983090] M Shen F Fan A Xue J Wang X Zhou and F Lu ldquoBiome-chanical properties o the cornea in high myopiardquo VisionResearch vol 983092983096 no 983090983089 pp 983090983089983094983095ndash983090983089983095983089 983090983088983088983096

[983089983091] A Kotecha A Elsheikh C R Roberts H Zhu and D FGarway-Heath ldquoCorneal thickness- and age-related biome-chanical properties o the cornea measured with the ocularresponse analyzerrdquo Investigative Ophthalmology and Visual Sci-ence vol 983092983095 no 983089983090 pp 983093983091983091983095ndash983093983091983092983095 983090983088983088983094

[983089983092] Z Jiang M Shen G Mao et al ldquoAssociation between cornealbiomechanical properties and myopia in Chinese subjectsrdquo Eye vol 983090983093 no 983096 pp 983089983088983096983091ndash983089983088983096983097 983090983088983089983089

[983089983093] C AltanB Demirel E Azmanet al ldquoBiomechanical propertieso axially myopic corneardquo European Journal of Ophthalmology vol 983090983090 supplement 983095 pp 983090983092ndash983090983096 983090983088983089983090

[983089983094] A Plakitsi C OrsquoDonnell M A Miranda W N Charman andH Radhakrishnan ldquoCorneal biomechanical properties mea-sured with the Ocular Response Analyser in a myopic popu-

lationrdquo Ophthalmic and Physiological Optics vol 983091983089 no 983092 pp983092983088983092ndash983092983089983090 983090983088983089983089

[983089983095] Y Huang C Huang L Li et al ldquoCorneal biomechanics rerac-tive error andaxial length in Chinese primary school childrenrdquoInvestigative Ophthalmology amp Visual Science vol 983093983090 no 983095 pp983092983097983090983091ndash983092983097983090983096 983090983088983089983089

[983089983096] P Y Chang S W Chang and JYWang ldquoAssessmento cornealbiomechanical properties and intraocular pressure with theOcular Response Analyzer in childhood myopiardquo British Jour-nal of Ophthalmology vol 983097983092 no 983095 pp 983096983095983095ndash983096983096983089 983090983088983089983088

[983089983097] L Lim G Gazzard Y Chan et al ldquoCornea biomechanicalcharacteristics and their correlates with reractive error inSingaporean childrenrdquo Investigative Ophthalmology and Visual

Science vol 983092983097 no 983097 pp 983091983096983093983090ndash983091983096983093983095 983090983088983088983096[983090983088] Y Song N Congdon L Li et al ldquoCorneal hysteresis and axial

length among chinese secondary school children the Xichangpediatric reractive error study (X-PRES) report No 983092rdquo Ameri-can Journal of Ophthalmology vol 983089983092983093 no 983093 pp 983096983089983097ndash983096983090983094 983090983088983088983096

[983090983089] B M Fontes R Ambrosio Jr R S Alonso D Jardim G CVelarde and W Nose ldquoCorneal biomechanical metrics in eyeswith reraction o -983089983097983088983088 to +983097983088983088 D in healthy Brazilianpatientsrdquo Journal of Refractive Surgery vol 983090983092 no 983097 pp 983097983092983089ndash983097983092983093 983090983088983088983096

[983090983090] A Kotecha ldquoWhat biomechanical properties o the cornea arerelevant or the clinicianrdquo Survey of Ophthalmology vol 983093983090supplement 983094 pp S983089983088983097ndashS983089983089983092 983090983088983088983095

[983090983091] S Shah M Laiquzzaman I Cunliffe and S Mantry ldquoTe useo the Reichert ocular response analyser to establish the rela-tionship between ocular hysteresis corneal resistance actorand central corneal thickness in normal eyesrdquo Contact Lens and Anterior Eye vol 983090983097 no 983093 pp 983090983093983095ndash983090983094983090 983090983088983088983094

[983090983092] A Cnaan N M Laird and P Slasor ldquoUsing the general linearmixed model to analyse unbalanced repeated measures andlongitudinal datardquo Statistics in Medicine vol 983089983094 pp 983090983091983092983097ndash983090983091983096983088983089983097983097983095

[983090983093] S Shah M Laiquzzaman S Mantry and I Cunliffe ldquoOcularresponseanalyser to assess hysteresis and corneal resistance ac-tor in low tension open angle glaucoma and ocular hyperten-sionrdquo Clinical and Experimental Ophthalmology vol 983091983094 no 983094pp 983093983088983096ndash983093983089983091 983090983088983088983096

7232019 905129pdf



[983090983094] D Luce ldquoMethodology or corneal compensated IOP and cor-neal resistance actor or an ocular response analyzerrdquo Inves-tigative Ophthalmology amp Visual Science vol 983092983095 Article ID E-Abstract 983090983090983094983094 983090983088983088983094

[983090983095] F Berisha O Findl M Lasta B Kiss and L SchmettererldquoDependence o ocular rigidity on eye length a study compar-ing ocular pressure pulse and ocular undus pulse in healthy subjectsrdquo Investigative Ophthalmology amp Visual Science vol 983092983093Article ID E-Abstract 983090983094983089983091 983090983088983089983088

[983090983096] A K Lam S Wong C S Lam and C H o ldquoTe effect o myopic axial elongation and posture on the pulsatile ocularblood 1047298ow in young normal subjectsrdquo Optometry and VisionScience vol 983095983097 no 983093 pp 983091983088983088ndash983091983088983093 983090983088983088983090

[983090983097] S Xu A Xu A ao J Wang F Fan and F Lu ldquoCornealbiomechanical properties and intraocular pressure in highmyopic anisometropiardquo Eye and Contact Lens vol 983091983094 no 983092 pp983090983088983092ndash983090983088983097 983090983088983089983088

[983091983088] M H Edwards andB Brown ldquoIntraocular pressurein a selectedsample o myopicand nonmyopic Chinese childrenrdquo Optometry and Vision Science vol 983095983088 no 983089 pp 983089983093ndash983089983095 983089983097983097983091

[983091983089] M H Edwards and B Brown ldquoIOP in myopic children therelationship between increases in IOP and the development o myopiardquo Ophthalmic and Physiological Optics vol 983089983094 no 983091 pp983090983092983091ndash983090983092983094 983089983097983097983094

[983091983090] Y Wong BE K Klein R Klein M Knudtson and K E LeeldquoReractive errors intraocular pressure and glaucoma in awhite populationrdquo Ophthalmology vol 983089983089983088 no 983089 pp 983090983089983089ndash983090983089983095983090983088983088983091

[983091983091] Kida J H K Liu and R N Weinreb ldquoEffects o aging oncorneal biomechanical properties and their impact on 983090983092-hourmeasurement o intraocular pressurerdquo American Journal of Ophthalmology vol 983089983092983094 no 983092 pp 983093983094983095ndash983093983095983090 983090983088983088983096

[983091983092] P Cho and C Lam ldquoFactors affecting the central corneal thick-ness o Hong Kong-Chineserdquo Current Eye Research vol 983089983096 no

983093 pp 983091983094983096ndash983091983095983092 983089983097983097983097[983091983093] H-B Fam A C S How M Baskaran K-L Lim Y-H Chan

and Aung ldquoCentral corneal thickness and its relationship tomyopia in Chinese adultsrdquo British Journal of Ophthalmology vol 983097983088 no 983089983090 pp 983089983092983093983089ndash983089983092983093983091 983090983088983088983094

7232019 905129pdf


Submit your manuscripts at

httpwwwhindawicom

7232019 905129pdf



[983089983096ndash983090983088] Most o the studies were perormed in myopicSingaporean and Chinese populations [983089983090 983089983092 983089983096 983090983088] andothers in Brazilian [983090983089] or urkish people [983089983093] withonly a ew ones in Caucasian individuals [983089983091 983089983094] Moreover sincebiomechanical properties o the cornea are known to changewith age [983090983090] some slightly mixed 1047297ndings in children may

not be applicable to adult populations [983089983094] Te aim o present study was to measure with the ORA device severalcorneal biomechanical parameters in an adult western heal-thy population containing emmetropes low myopes moder-ate myopes and highly myopic individuals and the relation-ship between these parameters and the values o intraocularpressure (IOP) determined with ORA including Goldmanncorrelated IOP (IOP) and corneal compensated IOP (IOPcc)

2 Methods

In this observational comparative study 983091983089983090 eyes o 983089983095983095healthy subjects were analyzed (983095983094 men and 983089983088983089 women)Tey were recruited sequentially among patients and healthy

volunteers in the Department o Ophthalmology at theLozano Blesa University Clinic Hospital and Quiron Univer-sity Hospital Zaragoza Spain Te average age o the patientswas 3327 plusmn 765 years (range 983090983088ndash983093983094) All subjects received acomplete ophthalmic examination including measurement o best-corrected visual acuity (BCVA) with EDRS chart slit-lamp anterior segment biomicroscopy undus examinationand corneal topography (Orbscan II) in order to discard theexistence o subclinical corneal pathology Automated andsubjective reractionswere perormed to determine reractiveerror in order to use it or the statistical analyses Teir spher-ical equivalent (SE) o reractive error ranged continuously rom983088to minus983089983094983093983088 D (mean minus388plusmn290 D) For the pur-pose o the study subjects were divided into our groups according totheir reractive status group 983089 or control group emmetropia(minus050 le SE lt 050) group 983090 low myopia (minus075 le SE ltminus300 D) group 983091 moderate myopia (minus300 le SE le minus600 D)and group 983092 high myopia (SE greater than minus983094983088983088 D) Allparticipants had monocular BCVA o 983090983088983091983090 (983088983090983088 logMarnotation) or better Subjects who had reractive errors suchas hyperopia gt 983088983093 D or astigmatism gt 983089 D IOP gt 983090983089 mmHgsigns o glaucomatous optic neuropathy amily history o glaucoma in a 1047297rst-degree relatives corneal dystrophy andmyopic macular degenerationthose who had undergonepre-

vious eye surgery or trauma eye inection diabetes mellitus

corticosteroid use or other acute or chronic diseases or usingany topical eye medication or subjects that did not meetnormal topographic criteria were excluded rom the study

Corneal biomechanical properties such as CH and CRFwere measured by the same masked technician with the Ocu-lar Response Analyzer (ORA sofware version 983090983088983092 ReichertOphthalmic Instruments Buffalo NY) using standard tech-nique [983093 983096 983090983091] Brie1047298y a rapid air puff deormed the corneaand the induced corneal deormation was detected withan electrooptical system Te air pulse induced inward andthen outward corneal movement which provided two appla-nation measurements CH resulted rom the damping o thecornea because o its biomechanical properties and was

derived rom the difference o the two measurements duringthe applanation process CRF also derived rom corneal hys-teresis is calculated as a linear unction o the pressurescorresponding to the two applanationsCRF is an indicator o the overall resistance o the cornea which according to pre-

vious data seems to be related to central corneal thickness

(CC) and GA determined IOP but not to IOPcc [983093] TeORA also determined the values o noncontact tonometerGoldmann correlated IOP and IOPcc IOPcc is a pressuremeasurement that utilizes the new inormation provided by the CH measurement to provide an IOP measurement lessaffected by corneal properties CC was measured ollowingcorneal biomechanical properties measurements by ultra-sound pachymetry (983090983088 MHz) using an ORA-integrated hand-held pachymeter Tree measurements o good quality wereobtained or each patient the signals with the highest Wave-orm Score (WS) were highlighted as the best score value(BSV) and were used or statistical evaluation Te study anddata accumulation were perormed with the approval o thelocal ethics committee inormed consent was obtained romeach subject participating in the study and the study protocolwas consistent with the tenets o the Declaration o Helsinki

3 Data Analysis

Values were presented as mean plusmn SD Statistical analyseswere conducted using a commercial sofware (SPSS sofware

version 983089983091983088 SPSS Inc Chicago IL) Te distribution o themeasured variables was estimated by the one-sample Kolmo-gorov-Smirnov test One-way analysis o variance (ANOVA)and post hoc tests were used or determining whether the

values o a particular variable differed between the three diag-

nostic groups We combined data rom both eyes using themixed model method [983090983092] which adjusts or the correlationbetween the two eyes in a unique person Multivariate mixed-model analysis adjusted by age and sex was used to determinethe relationship between two con-tinuous variables Pearsonrsquoscorrelation coefficient (1038389) was used to assess the relationshipbetween spherical equivalent power and the corneal biome-chanical properties (CH and CRF) as well as IOP (IOPcc andIOP) and CC Te level o statistical signi1047297cance was set to lt 005

4 Results

A total o 983089983095983095 patients (983091983089983090 eyes) were enrolled in this studyTe reraction among all included eyes ranged rom 983088to minus983089983094983093983088 D (SE) 983092983093 eyes corresponding to 983090983093 patients (983089983093women and 983089983088 men) were included as healthy controls (group983089) 983095983089 eyes o 983092983095 patients (983090983088 women and 983090983095 men) were in-cluded in group 983090 One hundred orty-1047297ve eyes o 983095983090 patientswere included in group 983091 And 1047297nally 983093983089 eyes o 983091983091 patients(983090983091 women and 983089983088 men) were included in group 983092 Signi1047297cantdifferences in reraction distribution were ound between theour diagnostic groups ( lt 005 able 983089) Te one-sampleKolmogorov-Smirnov test showed that CH CRF IOP IOPccand CC were normally distributed ( = 077 983088983095983096 983088983097983090983088983092983090 and 983088983093983089 resp) (Figure 983089) Parameters such as age

7232019 905129pdf









Sex (MF) 983089983088983089983093 983090983095983090983088 983090983097983092983091 983089983088983090983091 983088983088983093983095b


a







5 Discussion



CH (mmHg)


IOP (mmHg)

E m m

e t r o p i a

L o w

m y o p i a

M o d e r a t e

m y o p i a

H i g h

m y o p i a

25

20

15

10

5



7232019 905129pdf








(983093983089 eyes983091983091 patients)






S E ( D

)

CH (mmHg)

000

minus500

minus1000

minus1500

minus2000

600 800 1000 1200 1400

R2 linear = 0032

(a)

S E ( D

)

IOPcc (mmHg)

000

minus500

minus1000

minus1500

minus2000

900 1200 1500 1800 2100 2400

R2 linear = 0012

(b)


(IOPcc)





7232019 905129pdf








References





























7232019 905129pdf














7232019 905129pdf



httpwwwhindawicom

7232019 905129pdf









Sex (MF) 983089983088983089983093 983090983095983090983088 983090983097983092983091 983089983088983090983091 983088983088983093983095b


a







5 Discussion



CH (mmHg)


IOP (mmHg)

E m m

e t r o p i a

L o w

m y o p i a

M o d e r a t e

m y o p i a

H i g h

m y o p i a

25

20

15

10

5



7232019 905129pdf








(983093983089 eyes983091983091 patients)






S E ( D

)

CH (mmHg)

000

minus500

minus1000

minus1500

minus2000

600 800 1000 1200 1400

R2 linear = 0032

(a)

S E ( D

)

IOPcc (mmHg)

000

minus500

minus1000

minus1500

minus2000

900 1200 1500 1800 2100 2400

R2 linear = 0012

(b)


(IOPcc)





7232019 905129pdf








References





























7232019 905129pdf














7232019 905129pdf



httpwwwhindawicom

7232019 905129pdf








(983093983089 eyes983091983091 patients)






S E ( D

)

CH (mmHg)

000

minus500

minus1000

minus1500

minus2000

600 800 1000 1200 1400

R2 linear = 0032

(a)

S E ( D

)

IOPcc (mmHg)

000

minus500

minus1000

minus1500

minus2000

900 1200 1500 1800 2100 2400

R2 linear = 0012

(b)


(IOPcc)





7232019 905129pdf








References





























7232019 905129pdf














7232019 905129pdf



httpwwwhindawicom

7232019 905129pdf








References





























7232019 905129pdf














7232019 905129pdf



httpwwwhindawicom

7232019 905129pdf














7232019 905129pdf



httpwwwhindawicom

7232019 905129pdf



httpwwwhindawicom

905129.pdf

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