Berta, András

Flaskó, Zsuzsanna

Módis, László

Németh, Gábor

Szalai, Eszter

Ziad, Hassan

International Journal of Ophthalmology

DEA University of Debrecen Electronic Archive

陨灶贼 允 韵责澡贼澡葬造皂燥造熏 灾燥造援 9熏 晕燥援 2熏 Feb.18, 圆园16 www. ijo. cn栽藻造押8629原愿圆圆源缘员苑圆 8629-82210956 耘皂葬蚤造押ijopress岳员远猿援糟燥皂窑Clinical Research窑Ocular biomechanical measurements on post -keratoplasty corneas using a Scheimpflug-basednoncontact device1Department of Ophthalmology, University of Debrecen,Debrecen H-4032, Hungary2Orbi-Dent Health and Laser Center, Debrecen H-4032,HungaryCorrespondence to: Gabor Nemeth. Department ofOphthalmology, University of Debrecen, Nagyerdei blvd. 98,Debrecen H-4012, Hungary. nemeth222@yahoo.comReceived: 2014-08-23 Accepted: 2015-02-03Abstract· AIM: To analyse ocular biomechanical properties,central corneal thickness (CCT) and intraocular pressure(IOP) in post-keratoplasty eyes, as compared to normalsubjects, with a new Scheimpflug -based technology.Moreover, biomechanical data were correlated with thesize and age of the donor and recipient corneas.·METHODS: Measurements were conducted on 46 eyesof 46 healthy patients without any corneal pathology(age: 53.83 依20.8y) and 30 eyes of 28 patients afterpenetrating keratoplasty (age: 49.43 依21.34y). Tenbiomechanical parameters, the CCT and IOP were recordedby corneal visualization Scheimpflug technology (CorVisST) using high-speed Scheimpflug imaging. Keratometryvalues were also recorded using Pentacam HR system.Scheimpflug measurements were performed after 43.41依40.17mo (range: 11 -128mo) after the keratoplasty andafter 7.64依2.34mo (range: 5-14mo) of suture removal.·RESULTS: Regarding the device-specific biomechanicalparameters, the highest concavity time and radius valuesshowed a significant decrease between these two groups( =0.01 and <0.001). None of other biomechanicalparameters disclosed a significant difference. The CCTshowed a significant difference between post -keratoplasty eyes as compared to normal subjects ( =0.003) using the CorVis ST device. The IOP was withinthe normal range in both groups ( =0.84). There were nosignificant relationships between the keratometric data,the size of the donor and recipient, age of the donor andrecipient and biomechanical properties obtained byCorVis ST.·CONCLUSION: The ocular biomechanics remain stableafter penetrating keratoplasty according to the CorVis STmeasurements. Only two from the ten device -specificparameters have importance in the follow-up period afterpenetrating keratoplasty.· KEYWORDS: corneal visualization Scheimpflugtechnology; ocular biomechanics; penetrating keratoplastyDOI:10.18240/ijo.2016.02.09Modis L Jr., Hassan Z, Szalai E, Flask佼 Z, Berta A, Nemeth G.Ocular biomechanical measurements on post-keratoplasty corneasusing a Scheimpflug-based noncontact device.2016;9(2):235-238INTRODUCTIONT he currently used diagnostic techniques are capable ofmeasuring only the static parameters of the anteriorsegment, however, the cornea also has viscoelastic properties[1].Up until recently, the only device used for conducting themeasurement of ocular biomechanical properties hasbeen the Ocular Response Analyzer (ORA, ReichertOphthalmic Instruments, Depew, New York, USA) whichbecame commercially available in 2005[2-3].With the introduction of ORA, an emphasis has been placedon the biomechanical measurements of the cornea in thediagnosis of keratoconus and glaucoma, and on theassessment of the outcomes of refractive surgeries andcorneal collagen cross-linking therapies[4-7].The initial publications have reported differences in theparameters measured with ORA in healthy and keratoconuseyes and in those subsequent to refractive surgeries[8-9].Recently, a new device, corneal visualization Scheimpflugtechnology (CorVis ST, Oculus Inc., Wetzlar, Germany), hasbeen introduced using a high intensity air impulse forbiomechanical measurements and applying anultra-high-speed Scheimpflug camera. The equipment has thepotential to measure the amplitude of maximal applanationand the time taken to reach this applanation. CorVis ST alsomonitors the corneal velocity between the first and secondapplanation and the distance of the two apexes at highestconcavity in time. In addition, the images of the Scheimpflugcamera, capturing 4330 frames/s, are also recorded on avideo throughout an examination period of 30ms.235Our aim was to investigate the device-specific biomechanicalparameters of eyes after penetrating keratoplasty (PK) ascompared to normal subjects with CorVis ST and to assesspossible correlations between postoperative keratometricdata, size of the donor and recipient, age of the donor andrecipient cornea and biomechanical properties using aScheimpflug-based noncontact device.SUBJECTS AND METHODSOur patient was informed about the measurements andwritten informed consent was obtained from all of oursubjects. The research protocol of this retrospective studyadhered to the tenets of the Declaration of Helsinki.Subjects Measurements were conducted in 46 eyes of 46healthy patients without any corneal pathology or anteriorsegment disease (age: 53.83 依20.8y) and 30 eyes of 28patients after penetrating keratoplasty (age: 49.43依21.34y).The male/female ratio was 20/26 in the normal group and14/14 in the post-keratoplasty group. The preoperativediagnoses included keratoconus ( =10), corneal dystrophy( =10), pseudophakic bullous keratopathy ( =5), cornealleucoma ( =3), keratoglobus ( =1) and rekeratoplasty afterherpetic keratitis ( =1). CorVis ST measurements wereperformed after 43.41依40.17mo (range: 11-128mo) after thekeratoplasty and 7.64依2.34mo (range: 5-14mo) after sutureremoval. In addition, keratometry values were recorded byPentacam HR imaging system. The size of the donor andrecipient and age of the donor and recipient corneas weretaken from medical and eye bank records.Penetrating Keratoplasty Technique The conventionalMoria trephination system (Anthony, France) was used totrephine the donor and recipient corneas in each case.Corneal buttons (age of donor: 58.00 依11.24y) between6.5-7.5 mm in diameter were fixed with 16 bites 10/0 nylonrunning sutures. Local corticosteroid therapy (Maxidex,Alcon Laboratories, Forth Worth, Texas, USA) wascontinued for six month in all patients. All the corneas wereclear and transparent at the time of evaluation, without thepresence of inflammation or neovascularisation.Measurements The measurements were carried out usingthe CorVis ST device, software version 1.00r24 rev. 772. CorVisST is a non-contact tonometer and pachymeter measuring tenspecific ocular biomechanical parameters as well. This deviceuses an ultra-high-speed Scheimpflug camera (4330 frames/s)with a light source of a blue LED light at a wavelength of455 nm. The air impulse employs a metered, symmetricaland fixed maximal internal pump pressure of 25 kPa.Due to the air impulse, the cornea goes through three distinctphases: first applanation, highest concavity (HC) and secondapplanation. During these phases, a number of specificparameters are recorded: the maximum deformationamplitude (HC of the cornea), the time taken to reach it, thefirst and second applanation times, the length of the flattenedcornea, the maximum corneal velocity at the first and secondapplanations, the peak distance, which is the distance of thetwo apexes at HC, and a radius value which represents theradius of the curvature of a circle that fits with the centralconcave curvature at the HC. The central corneal thickness(CCT) and intraocular pressure (IOP) were also determinedby the device.The patient is in sitting position with his or her chin on thechinrest and their forehead against the equipment. Theexaminer targets the centre of the cornea with a joystick,enabling the patients to see a red fixating light. The adjustingdirection needed to centre on the corneal apex is seen on thedisplay. With an accurate setting, the air puff automaticallystarts, after which the data are exported to a computer.Statistical analysis was performed with the MedCalc 10.0software. Descriptive statistical results were described asmean and standard deviation (SD). Independent-samples -testwas used for comparing the data of the two groups. Multipleregression analyses were performed with the ten specificCorVis ST data in combination as independent variables andkeratometric data, the size of the donor and recipient, and ageof the donor and recipient as dependent variable. A valuebelow 0.05 was considered to be statistically significant.RESULTSThe specific parameters measured with the CorVis ST areshown in detail in Table 1. Regarding the device-specificbiomechanical parameters, only the highest concavity timeand radius value disclosed a significant decrease between thetwo groups ( =0.01 and <0.001). None of the otherbiomechanical parameters showed a significant difference.Multiple regression analyses showed that there were nosignificant relationship between horizontal radius ofcurvature of the cornea, vertical radius of curvature of thecornea, size of the donor, size of the recipient, age of thedonor, age of the recipient and CorVis ST specific parameters( =0.68, =0.22; =0.64, =0.36; =0.61, =0.49; =0.61,=0.51; =0.54, =0.46; =0.51, =0.73, respectively).After surgery, pachymetry showed significantly thickercorneas in the PK group as compared to normal eyesmeasured with CorVis ST ( =0.003). The IOP was withinthe normal range in both groups ( =0.84).DISCUSSIONRecently, a novel piece of equipment has been introduced formeasuring ocular biomechanical properties . CorVisST measures ten specific biomechanical parameters and inaddition CCT, IOP using an air impulse. Our aim was toassess these new biomechanical data following PK ascompared to a normal group. Moreover, the present studycorrelated the obtained biomechanical parameters withkeratometry readings and the size and age of the donor andrecipient corneas.Ocular biomechanics after keratoplasty236陨灶贼 允 韵责澡贼澡葬造皂燥造熏 灾燥造援 9熏 晕燥援 2熏 Feb.18, 圆园16 www. ijo. cn栽藻造押8629原愿圆圆源缘员苑圆 8629-82210956 耘皂葬蚤造押ijopress岳员远猿援糟燥皂Table 1 Corneal biomechanical measurements obtained with the CorVis ST Subjects1 Parameters   Normal Postkeratoplasty P2 Applanation 1    Time (ms) 7.24±0.22 (7.17-7.30) 7.25±0.47 (7.08-7.42) 0.86 Length (mm) 1.79±0.25 (1.72-1.87) 1.81±0.23 (1.72-1.89) 0.79 Velocity (m/s) 0.15±0.03 (0.15-0.16) 0.14±0.03 (0.13-0.15) 0.08 Applanation 2    Time (ms) 21.58±0.40 (21.45-21.7) 21.52±0.50 (21.34-21.70) 0.61 Length (mm) 1.90±0.46 (1.76-2.04) 1.92±0.50 (1.73-2.11) 0.86 Velocity (m/s) -0.36±0.06 (-0.38- -0.34) -0.37±0.10 (-0.40- -0.33) 0.74 Highest concavity    Time (ms) 16.89±0.49 (16.74-17.03) 16.48±0.77 (16.19-16.76)  0.01 Peak distance (mm) 3.23±1.10 (2.91-3.56) 3.64±1.22 (3.18-4.10) 0.14 Radius (mm) 7.55±0.72 (7.34-7.77) 6.42±0.89 (6.09-6.75) <0.001 Def. ampl. max. (mm) 1.08±0.09 (1.06-1.11) 1.14±0.18 (1.07-1.20)  0.12 IOP (mm Hg) 14.66±1.90 (14.10-15.23) 14.50±4.39 (12.86-16.14)  0.84 Pachymetry (μm) 545.57±31.97 (536.07-555.06) 585.2±58.25 (561.15-609.25) 0.003 Def. ampl. max.: Maximal deformation amplitude; IOP: Intraocular pressure. 1Mean±standard deviation (95% confidence interval); 2Independent-samples t-test. In biomechanical measurements, the cornea is considered tobe a viscoelastic substance [1]. Up until recently, the onlyequipment applied in the measurement of ocularbiomechanical properties was the ORA. Biomechanicalmeasurements are applied in the diagnosis of keratoconus[8-10],but the two main parameters showed low sensitivity andspecificity in distinguishing between normal and keratoconusgroups [10-11]. Yenerel [12] found correlations between theseverity of keratoconus and the viscoelastic properties of thecornea.Investigating the biomechanics has a role in the effect ofstudies of refractive surgeries[4], corneal collagen crosslinking(CXL) [6-7], and also in glaucoma diagnosis [5]. CXL causessignificant biomechanical differences, but only whenapplying the latest parameters of the ORA software[7].The measurement and evaluation of IOP after PK is achallenging task because of the irregularities of the donorsurface [13-14]. There are only a few papers analysingbiomechanical properties after PK with ORA [12,15-21], and mostof these studies conclude that the corneal biomechanicsweaken after PK [18,20], whereas deep anterior lamellarkeratoplasty (DALK) did not affect these values [18]. Hosny[18] concluded that corneas after PK have weakerbiomechanical properties than normal corneas, whereasDALK preserves the biomechanical strength of the corneasdue to the intact Descemet's membrane. In contrast,Jafarinasab [17] stated that no significant difference canbe measured between PK and DALK in terms of IOP andbiomechanical properties. Improved corneal biomechanicswere observed after PK compared to keratoconus eyes, yetthey did not reach a normal level [12]. Yenerel [12] foundsignificantly lower corneal hysteresis (CH) and cornealresistance factor (CRF) values in keratoconus andpost-keratoplasty eyes when compared to normal eyes. Hosny[18] found the same, with decreased biomechanical dataafter PK. Shin [16] found that CH decreased but CRFincreased after PK, however this was without any significantdifference.The biomechanical data were lower after one year of PK, andthe difference in the biomechanical properties measured withORA was statistically significant between normal andpost-keratoplasty eyes [20]. They could not observe differencesaccording to the preoperative diagnosis [20] or the follow-upperiod [17]. John [19] found lower ORA data afterdescemetorhexis and endokeratoplasty compared to thenormal group.We found that the HC time and radius values of CorVis STshowed a significant decrease between post-keratoplasty andnormal eyes. According to our hypothesis, these twoparameters are sensitive enough to show difference betweenthese two patient groups. None of the other 8 device-specificparameters showed significant differences between the twogroups. We think that there can be two possible explanationsbehind these results. First, there are really no significantdifferences in these new biomechanical parameters (obtainedby CorVis ST) between the two groups. Second, it is possiblethat this device or its measured parameters are not sensitiveenough to differentiate between these two groups. In a recentpaper of Maeda [21], the deformation amplitude, measuredwith CorVis ST, in PK eyes was significantly higher thanthose of the control eyes. Maybe this is explainable bydifferent population sample and different population ages.237Another reason for the difference can be the follow-up timeafter keratoplasty (a mean of 43.41mo in our study) orpresence of sutures (in our study: only after suture removal).The mean CCT was higher after PK measured by ORA [20].We found the same alteration using the CorVis ST. Inaddition, the present study showed no correlations betweenspecific CorVis ST parameters and radii of curvature of thecornea, size of the donor, size of the recipient, age of thedonor or age of the recipient after perforating keratoplasty.According to our data with a new device measuring ocularbiomechanics, only the time of HC, the radius value and theCCT showed differences in the PK group as compared to thenormal group. There was no statistical difference regardingall other specific parameters of CorVis ST. In this study, theeyes after suture removal were the inclusion criteria. Therewas no difference in the IOP or biomechanics betweenpostkeratoplasty eyes with or without sutures according to aprevious paper that used ORA [15]. We did not find anyproblem with keratoplasty wounds after CorVis STmeasurements and so, similar to the study of Jafarinasab[17], we also propose that biomechanical measurementswith high-intensity air-puff are safe after PK.In conclusion, the ocular biomechanics are stable after PKaccording to the Corvis ST measurements. The highestconcavity time and radius value of CorVis ST can beimportant in follow-up studies after PK. The role of the otherdevice-specific parameters of CorVis ST in PK needs furtherclarification and investigation.ACKNOWLEDGEMENTSConflicts of Interest: Modis L Jr., None; Hassan Z,None; Szalai E, None; Flask佼 Z, None; Berta A, None;Nemeth G, None.REFERENCES1 Soergel F, Jean B, Seiler T, Bende T, M俟cke S, Pechhold W, Pels L.Dynamic mechanical spectroscopy of the cornea for measurement of itsviscoelastic properties in vitro. 1995;4(3):151-156.2 Kynigopoulos M, Schlote T, Kotecha A, Tzamalis A, Pajic B, Haefliger I.Repeatability of intraocular pressure and corneal biomechanical propertiesmeasurements by the ocular response analyser.2008;225(5):357-360.3 Moreno-Montanes J, Maldonado MJ, Garcia N, Mendiluce L,Garcia-Gomez PJ, Segui-Gomez M. Reproducibility and clinical relevanceof the ocular response analyzer in nonoperated eyes: corneal biomechanicaland tonometric implications. 2008;49(3):968-974.4 Chen S, Chen D, Wang J, Lu F, Wang Q, Qu J. Changes in ocularresponse analyzer parameters after LASIK. 2010;26 (4):279-288.5 Ayala M. Corneal hysteresis in normal subjects and in patients withprimary open-angle glaucoma and pseudoexfoliation Glaucoma.2011;46(4):187-191.6 Greenstein SA, Fry KL, Hersh PS. In vivo biomechanical changes aftercorneal collagen cross-linking for keratoconus and corneal ectasia: 1-yearanalysis of a randomized, controlled, clinical trial. 2012;31 (1):21-25.7 Spoerl E, Terai N, Scholz F, Raiskup F, Pillunat LE. Detection ofbiomechanical changes after corneal cross-linking using Ocular ResponseAnalyzer software. 2011;27(6):452-457.8 Shah S, Laiquzzaman M, Bhojwani R, Mantry S, Cunliffe I. Assessment ofthe biomechanical properties of the cornea with the ocular responseanalyzer in normal and keratoconic eyes. 2007;48(7):3026-3031.9 Saad A, Lteif Y, Azan E, Gatinel D. Biomechanical properties ofkeratoconus suspect eyes. 2010;51(6):2912-2916.10 Fontes BM, Ambr佼sio R Jr, Jardim D, Velarde GC, Nos佴 W. Cornealbiomechanical metrics and anterior segment parameters in mildkeratoconus. 2010;117(4):673-679.11 Fontes BM, Ambr佼sio R Jr, Velarde GC, Nos佴 W. Ocular responseanalyzer measurements in keratoconus with normal central cornealthickness compared with matched normal control eyes.2011;27(3):209-215.12 Yenerel NM, Kucumen RB, Gorgun E. Changes in cornealbiomechanics in patients with keratoconus after penetrating keratoplasty.2010;29(11):1247-1251.13 Irvine AR, Kaufman HE. Intraocular pressure following penetratingkeratoplasty. 1969;68(5):835-844.14 Ayyala RS. Penetrating keratoplasty and glaucoma.2000;45(2):91-105.15 Fabian ID, Barequet IS, Skaat A, Rechtman E, Goldenfeld M, RobertsCJ, Melamed S. Intraocular pressure measurements and biomechanicalproperties of the cornea in eyes after penetrating keratoplasty.2011;151(5):774-781.16 Shin JY, Choi JS, Oh JY, Kim MK, Lee JH, Wee WR. Evaluation ofcorneal biomechanical properties following penetrating keratoplasty usingthe ocular response analyzer. 2010;24(3):139-142.17 Jafarinasab MR, Feizi S, Javadi MA, Hashemloo A. Graft biomechanicalproperties after penetrating keratoplasty versus deep anterior lamellarkeratoplasty. 2011;36(5):417-421.18 Hosny M, Hassaballa MA, Shalaby A. Changes in corneal biomechanicsfollowing different keratoplasty techniques. 2011;5:767-770.19 John T, Taylor DA, Shimmyo M, Siskowski BE. Corneal hysteresisfollowing descemetorhexis with endokeratoplasty: early results.2007;39(1):9-14.20 Laiquzzaman M, Tambe K, Shah S. Comparison of biomechanicalparameters in penetrating keratoplasty and normal eyes using the OcularResponse Analyser. 2010;38(8):758-763.21 Maeda N, Ueki R, Fuchihata M, Fujimoto H, Koh S, Nishida K. Cornealbiomechanical properties in 3 corneal transplantation techniques with adynamic Scheimpflug analyzer. 2014;58(6):483-489.Ocular biomechanics after keratoplasty238

Ocular biomechanical measurements on post-keratoplasty corneas using a Scheimpflug-based noncontact device

https://dea.lib.unideb.hu/dea/bitstream/2437/222460/1/file_up_20160209.pdf

Ocular biomechanical measurements on post-keratoplasty corneas using a Scheimpflug-based noncontact device

Abstract

Similar works

Full text

Available Versions

DEA University of Debrecen Electronic Archive