To compare the intraocular pressure measurements as defined by the
      Pascal tonometer, the Goldmann tonometer and the pneumotonometer. METHODS: This
      was an observational clinical study, which included two hundred and five randomly
      selected subjects recruited from the Ophthalmology Department. The intraocular
      pressure measurements were performed with each tonometry technique in a
      randomized order. RESULTS: The Pascal's intraocular pressure measurement was
      significantly higher than that measured by the other two tonometers (p<0.05). The
      quality data of Pascal was: optimum in 27.3% (56 of 205 patients), acceptable in 
      42% (86 of 205 patients) and unacceptable in 23.4% (48 of 205 patients). In 7.3% 
      (15 of 205 patients) it was impossible to obtain any measurement using Pascal. A 
      weak correlation coefficient between the Pascal and the Goldmann, and between
      Pascal and the pneumotonometer was found. The Bland-Altman method of measurement 
      using these tonometers showed a high degree of discordance. CONCLUSION: As
      reported by others authors, the Pascal's intraocular pressure measurement is
      higher than that of the Goldmann tonometer. The measurement differs from 0.7 to
      4.4 mmHg. In corneas with pathology, it is very difficult or even unacceptable to
      measure the intraocular pressure using the Pascal tonometer

Heras-Mulero, H. (Henar)

Mendiluce, L. (Loreto)

Moreno-Montañes, J. (Javier)

Sadaba-Echarri, L.M. (Luis M.)

Universidad de Navarra

Comparison of dynamic contour tonometry (Pascal®) with pneumotonometry and Goldmann tonometry

Dadun, University of Navarra

ARCH SOC ESP OFTALMOL 2007; 82: 337-342COMPARISON OF DYNAMIC CONTOUR TONOMETRY(PASCAL®) WITH PNEUMOTONOMETRY ANDGOLDMANN TONOMETRYCOMPARACIÓN DEL TONÓMETRO PASCAL® CON ELNEUMOTONÓMETRO Y EL TONÓMETRO GOLDMANNHERAS-MULERO H1, MORENO-MONTAÑÉS J2, SÁDABA ECHARRI LM2,MENDILUCE MARTÍN L3Received: 31/5/06. Accepted: 24/5/07.Department of Ophthalmology, University Clinic of Navarre. Pamplona (Navarre). Spain.1 Graduate in Medicine.2 Ph.D. in Medicine.3 Optometrist optician.Correspondence:Henar Heras Mulero Clínica Universitaria de Navarra Departamento de Oftalmología C/. Pío XII, 36 31008 Pamplona Spain E-mail: henarheras@yahoo.esABSTRACTPurpose: To compare the intraocular pressure mea-surements as defined by the Pascal® tonometer, theGoldmann tonometer and the pneumotonometer. Methods: This was an observational clinical study,which included two hundred and five randomlyselected subjects recruited from the OphthalmologyDepartment. The intraocular pressure measure-ments were performed with each tonometry techni-que in a randomized order.Results: The Pascal®’s intraocular pressure measure-ment was significantly higher than that measured bythe other two tonometers (p<0.05). The quality data ofPascal® was: optimum in 27.3% (56 of 205 patients),acceptable in 42% (86 of 205 patients) and unaccepta-ble in 23.4% (48 of 205 patients). In 7.3% (15 of 205patients) it was impossible to obtain any measurementusing Pascal®. A weak correlation coefficient betweenthe Pascal® and the Goldmann, and between Pascal®and the pneumotonometer was found. The Bland-Alt-man method of measurement using these tonometersshowed a high degree of discordance.Conclusion: As reported by others authors, the Pas-cal®’s intraocular pressure measurement is higherORIGINAL ARTICLERESUMENObjetivo: Comparar la medición de presión intrao-cular con el tonómetro de Pascal® en córneas nor-males frente al tonómetro de Goldmann y al pneu-motonómetro.Método: Estudio clínico observacional en el que sehan incluido 205 pacientes consecutivos y randomi-zados que han acudido a la consulta de oftalmolo-gía. Se realiza una medición con cada tonómetro enorden aleatorio.Resultados: El Pascal®, dio una medición de lapresión intraocular mayor que la del resto de tonó-metros. Se obtienen diferencias significativas delPascal® frente a los otros dos tonómetros (p<0,05).La fiabilidad del Pascal® fue: fiables en el 27,3%(56 de 205 pacientes), aceptable en el 42% (86 de205 pacientes) y en el 23,4% (48 de 205 pacientes)inaceptable. En el 7,3% (15 de 205 pacientes) res-tante no se obtuvo ninguna medición con el tonó-metro de Pascal®. Al comparar el tonómetro de Pas-cal® frente al de Goldmann y al neumotonómetro seobserva que el coeficiente de correlación es débil ypresenta alta discordancia con el método de Bland-Altman.338 ARCH SOC ESP OFTALMOL 2007; 82: 337-342 HERAS-MULERO H, et al.INTRODUCTIONThe Pascal® dynamic contour tonometer is adigital contact tonometer that measures intraocularpressure between 5 and 200 mmHg with a preci-sion of 0.2 mmHg (1-3). Together with the value ofintraocular pressure, it notes the level of reliabilityand quality of the measurement with Q1 being reli-able, Q2 and Q3 acceptable and Q4 and Q5 unac-ceptable, which requires repeating the measure-ment. The Pascal® tonometer is independent ofcorneal thickness and biomechanical cornea prop-erties such as elasticity, rigidity, level of cornealhydration or lamellar stroma configuration (1-3).The Goldmann tonometer is considered thegolden standard to measure intraocular pressure.However, it presents a series of limitations andsources of error since the value it provides is notdigital, heart beats make the semicircles changeposition, the amount of coloring varies the thick-ness of the semicircles, thus modifying the mea-surement and finally, corneal properties such asthickness and curvature can lead to a wrong mea-surement (1-3).The pneumatonometer (4) is an air pressure con-tact tonometer following the Mackay-Marg method.Compared to the Goldmann, it underestimates highpressures and overestimates low ones. This tonome-ter, as it is independent of cornea properties, is usefulin edematous, irregular corneas or with leucomas.The purpose of this study was to analyze the reli-ability of the Pascal® versus the Goldmann tonome-ter, the golden standard, and the pneumatonometer,which we know is not much influenced by theanatomical properties of the cornea.SUBJECTS, MATERIAL ANDMETHODAn observational clinical study was conductedwhich included 205 consecutive and randomizedpatients visiting the ophthalmology department. Ofthese 205 patients, 24 had glaucoma, 25 a corneatransplant and 156 patients had neither.Measurements were always carried out by thesame person, only one eye per patient was includ-ed, and both the order of the tonometers and theeye selected for examination were random. Threemeasurements were conducted for the pneu-matonometer (Model 30 Classic Pneumatonome-ter, Medtronic Ophthalmics, Jacksonville, USA)and the Goldmann (Applanation Tonometer AT900 BQ, Haag-Streit, Köniz, Switzerland) notingdown the mean. With Pascal® (Pascal®, SMTSwiss Microtechnology AG, CH-2562 Port,Switzerland) three measurements were carried out,choosing whichever was equal or lower than Q3.For those patients with whom an acceptable mea-surement level was not achieved after three mea-surements, the pressure provided with the firstPascal® measurement was noted, together with itslevel of reliability.Analysis of methods was conducted by a non-parametric test using the Spearman coefficient forcorrelation and the Wilcoxon test to comparepaired samples. Consistency between tonometerswas achieved through the Bland-Altman method.We assessed the median and the interquantilerange (25-75%). The statistical suite used wasSPSS 11.0 (SPSS for Windows, SPSS Inc, Chica-go, USA).than that of the Goldmann tonometer. The measure-ment differs from 0.7 to 4.4 mmHg. In corneas withpathology, it is very difficult or even unacceptableto measure the intraocular pressure using the Pas-cal® tonometer (Arch Soc Esp Oftalmol 2007; 82:337-342).Key words: Pascal, pneumotonometry, Goldmanntonometer, dynamic contour tonometry, intraocularpressure.Conclusión: Diversos autores han comparado eltonómetro de Pascal® y el Goldmann coincidiendotodos en que el Pascal® ofrece una presión intrao-cular mayor que el Goldmann con unas diferenciasque van de 0,7 a 4,4 mmHg. En córneas patológi-cas es muy difícil realizar la medición y cuandoésto ocurre ésta suele ser informada como inacep-table.Palabras clave: Pascal, neumotonómetro, gold-mann, tonómetro dinámico de contorno, presiónintraocular.RESULTSThe pneumatonometer offered measurements in200 of the 205 patients, while the Goldmanntonometer did so in 198 patients and the Pascal®tonometer was only capable of conducting accept-able measurements in 190 of the 205 patients (Q1 toQ3). Pascal® provided a higher intraocular pressuremeasurement than that obtained with the othertonometers. When the measurements obtained withPascal® were compared to those of the other twotonometers, there were significant differences(p<0.001), the results of Pascal® being differentfrom those obtained with Goldmann or the pneu-matonometer (table I).When the level of reliability was analyzed with thePascal® measurement, we found that in 27.3% (56out of 205) of the patients, intraocular pressure fig-ures were reported as reliable, in 42% (86 out of 205)acceptable and in 23.4% (48 out of 205) unaccept-able, not reliable, and a new measurement wasrequired; when a new measurement was conducted, amore reliable value was not obtained. In the remain-ing 7.3% (15 out of 205) it was not possible to obtainany measurements with the Pascal® tonometer.When comparing the Pascal® tonometer to theGoldmann, we saw the Spearman correlation coef-ficient was weak, only 0.48 (p=0.01) (fig. 1a) andinconsistent with the Bland-Altman method(6.42%) (fig. 1b). When Pascal® was compared tothe pneumatonometer, results were similar with aweak Spearman coefficient of 0.44 (p=0.01)(fig. 2a) and variance of 6.25% (fig. 2b). This mightlead us to believe the results are due to the high per-centage (23.4%, 48 out of 205 patients) of patientswith low reliability with the Pascal® tonometer,however, when these patients were extracted andthe measurements reported with Pascal® as accept-able were compared to the other two tonometers,results did not vary much. So that the Spearmancoefficient of Pascal® versus that of Goldmann was0.38 (p=0.01) (fig. 3a) and 0.47 (p=0.01) with thepneumatonometer (fig. 3b) and discordancebetween Pascal® versus Goldmann and the pneu-matonometer was significant, 5.88% in both cases(fig. 4).339ARCH SOC ESP OFTALMOL 2007; 82: 337-342 Pascal Tonometer®Table I. Summary table of data obtained withtonometers Pascal®, Goldmann andpneumatonometerTonometer Cases Median IR (25-75) pWilcoxon*Pascal® 190 18.4 6.1Goldmann 198 14 4.2 <0.001Pneumatonometer 200 15 6.2 <0.001* Comparisons conducted with Pascal® versus Goldmann and Pascal®versus pneumatonometer.Fig. 1a: Linear regression and correlation coefficientfor Pascal® and Goldmann.Fig. 1b: Bland-Altman for Pascal® and Goldmann witha discordance coefficient of 6.42%.Fig. 2a: Linear regression and correlation coefficientfor Pascal® and pneumatonometer.DISCUSSIONSeveral authors (1-3,5-7) have compared the Pas-cal® tonometer to the Goldmann one and all agreethat the Pascal® provides greater intraocular pres-sure than Goldmann. Kotecha (2) has found theleast differences, only an increase in favor of Pas-cal® of 0.7 mmHg, compared to our study, whichhas found that Pascal® overestimates intraocularpressure by 4.4 mmHg when compared to Gold-mann. When we analyzed the existing correlationbetween Pascal® and Goldmann we found very dis-parate data in literature, ranging from the weakestcorrelation by Kotecha (2) with a coefficient of0.22, and the present study (spearman r=0.48p=0.01) up to reaching the almost perfect correla-tion by Kamppeter (1) of 0.95.Doyle (3) analyzed the existing relation betweenthe Goldmann and the Pascal® tonometers in vari-ous corneal thicknesses, noting that before a normalor thick cornea there were no significant differencesin the intraocular pressure measurements, whilewhen the cornea was thin there were differences(p=0.009) in the intraocular pressure measured withGoldmann and Pascal®.340 ARCH SOC ESP OFTALMOL 2007; 82: 337-342 HERAS-MULERO H, et al.Fig. 2b: Bland-Altman for Pascal® and pneumatonome-ter with a discordance coefficient of 6.25%.Fig. 3a: Linear regression and correlation coefficientfor Pascal® and Goldmann only for values measured asacceptable for Pascal.Fig. 3b: Linear regression and correlation coefficient forPascal® and pneumatonometer only for values measuredas acceptable for Pascal.Fig. 4a: Bland-Altman for Pascal® and Goldmann witha discordance coefficient of 5.88%, only for values mea-sured as acceptable for Pascal.Fig. 4b: Bland-Altman for Pascal® and pneumatonome-ter with a variance coefficient of 5.88% only for valuesmeasured as acceptable for Pascal.In literature there is only one paper comparingPascal®, Goldmann and the pneumatonometer andit was published by Kniestedt (4) in 2005. As allother authors have found, Pascal® provided an aver-age intraocular pressure of 18.3 mmHg, higher thanthat obtained with the pneumatonometer(17.1 mmHg) and Goldmann (16 mmHg). Also, heanalyzed the correlation of each one of the threetonometers with the corneal thickness, finding therewas only correlation with the Goldmann tonometer(r=0.24 p<0.01), the pneumatonometer (r=17.1p=0.1) and the Pascal® tonometer (r<0.1 p=0.80)being independent of corneal thickness.It has struck us that Pascal® conducts, in manycases, not very reliable measurements or that it is notable to measure intraocular pressure. To conduct themeasurement, this tonometer requires a round tearfilm contour not found in patients with lachrymaldryness, high astigmatism or keratoplasty. Althoughthis tonometer can be very useful in healthy eyes, inpatients with glaucoma under chronic treatment orelderly patients with ocular dryness, this low relia-bility can be clinically significant. Although Pascal®has become popular as a system to measure intraoc-ular pressure following LASIK, its use should beassessed with all type of patients as a tonometer notaffected by corneal thickness.In this study, as in all other literature, the Pascal®tonometer overestimates intraocular pressure. Mea-surements were not reliable in 23.4% (48 out of205) of patients, and it was impossible to conductmeasurements in 7.3% (15 out of 205).BIBLIOGRAFÍA1. Kamppeter BA, Jonas JB. Dynamic contour tonometry forintraocular pressure measurement. Am J Ophthalmol2005; 140: 318-320.2. Kotecha A, White ET, Shewry JM, Garway-Heath DF. Therelative effects of corneal thickness and age on Goldmannapplanation tonometry and dynamic contour tonometry.Br J Ophthalmol 2005; 89: 1572-1575.3. Doyle A, Lachkar Y. Comparison of dynamic contourtonometry with goldmann applanation tonometry over awide range of central corneal thickness. J Glaucoma2005; 14: 288-292.4. Kniestedt C, Lin S, Choe J, Bostrom A, Nee M, StamperRL. Clinical comparison of contour and applanation tono-metry and their relationship to pachymetry. Arch Opht-halmol 2005; 123: 1532-1537.5. Schneider E, Grehn F. Intraocular pressure measurement-comparison of dynamic contour tonometry and goldmannapplanation tonometry. J Glaucoma 2006; 15: 2-6.6. Kaufmann C, Bachmann LM, Thiel MA. Comparison ofdynamic contour tonometry with goldmann applanationtonometry. Invest Ophthalmol Vis Sci 2004; 45: 3118-3121.7. Pache M, Wilmsmeyer S, Lautebach S, Funk J. Dynamiccontour tonometry versus goldmann applanation tono-metry: a comparative study. Graefes Arch Exp Ophthal-mol 2005; 243: 763-767.341ARCH SOC ESP OFTALMOL 2007; 82: 337-342 Pascal Tonometer®

Comparison of dynamic contour tonometry (Pascal®) with pneumotonometry and Goldmann tonometry

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Dadun, University of Navarra