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Intraocular pressure measurement after DSAEK by iCare, Goldmann applanation and dynamic contour tonometry: A comparative study
Journal français d’ophtalmologie (2016) 39, 822—828
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ORIGINAL ARTICLE
Intraocular pressure measurement after DSAEK by iCare, Goldmann applanation and dynamic contour tonometry: A comparative study Mesure de la pression intraoculaire après DSAEK par iCare, aplanation de Goldmann et tonomètre dynamique de contour : une étude comparative A. Achiron a,∗,b, O. Blumenfeld a,b, H. Avizemer a,b, L. Karmona a,b, G. Leybowich a,b, V. Man c, E. Bartov a,b, Z. Burgansky-Eliash a,b a
Department of Ophthalmology, The Edith Wolfson Medical Center, Holon, Israel Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel c Department of Ophthalmology, Soroka University Medical Center, Ben-Gurion University, Beer-Sheva, Israel b
Received 1st August 2016; accepted 19 September 2016 Available online 19 November 2016
KEYWORDS DSAEK; Intraocular pressure; iCare; Goldmann applanation; Dynamic contour tonometry
∗
Summary Purpose. — Corneal thickness inevitably increases following Descemet’s stripping automated endothelial keratoplasty (DSAEK), owing to the addition of a donor graft. The current study compares different devices in assessing post-DSAEK intraocular pressure (IOP). Methods. — We compared IOP values measured by the Goldmann tonometry (GAT), iCare rebound tonometry (iCare) and Pascal dynamic contour tonometry (PDCT) in eyes following DSAEK. Agreement between measurements was calculated with correlation analysis and BlandAltman plots. Effects of keratometry, central, thickness (CCT), endothelial cell density (ECD) and axial length on IOP measurements were assessed with Pearson’s correlation. Results. — Twenty eyes of 20 patients (mean age 74.3 ± 14.4, 14 females) post-DSAEK were included in this study. There was a high concordance between the IOP readings obtained by the three devices: a strong and significant correlation was found between GAT and PDCT (r = 0.94, P < 0.001) GAT and iCare (r = 0.86, P < 0.001) and iCare with PDCT (r = 0.81, P < 0.001).
Corresponding author. E-mail address: [email protected] (A. Achiron).
http://dx.doi.org/10.1016/j.jfo.2016.09.009 0181-5512/© 2016 Elsevier Masson SAS. All rights reserved.
IOP after DSAEK
823 However, the iCare measurements were significantly and consistently lower than that obtained with GAT (IOP = 1.68 ± 2.0, P = 0.002, 95% CI: 0.7—2.6) and with PDCT (IOP = 1.61 ± 2.5, P = 0.01, 95% CI: 0.4—2.8). CCT, ECD, CCT, AXL, corneal curvature or astigmatism did not influence IOP measurement by any instrument. Conclusions. — IOP measurement with three different techniques (applanation, rebound and dynamic contour) showed good correlations, despite an increased corneal thickness following DSAEK. However, the iCare, which is based on a rebound tonometry showed significant lower IOP then the two other methods. This should be taken into account when evaluating patients post DSAEK. © 2016 Elsevier Masson SAS. All rights reserved.
MOTS CLÉS DSAEK ; Pression intraoculaire ; iCare ; Aplanation de Goldmann ; Tonomètre dynamique de contour
Résumé Objectif. — Suite à une kératoplastie endothéliale automatisée par le stripping de Descemet (DSAEK), l’épaisseur cornéenne augmente inévitablement en raison de l’ajout du greffon du donneur. Le tissu cornéen qui a été ajouté peut avoir un effet différent sur les mesures de pression intraoculaire (PIO) selon les techniques de mesure utilisées. Cette étude compare différents appareils de mesure dans l’évaluation de la PIO post-DSAEK. Méthodes. — Nous avons comparé les données de PIO post-DSAEK mesurées par le tonomètre à aplanation de Goldmann (GAT), le tonomètre par rebond d’iCare (iCare) et le tonomètre dynamique de contour Pascal (PDCT). L’agrément des mesures a été calculé par analyse de corrélation et graphiques de Bland-Altman. Les données de l’effet de la kératométrie, de l’épaisseur de la cornée centrale, (CCT), de la densité des cellules endothéliales (ECD) et de la longueur axiale sur la PIO ont été évaluées avec la corrélation de Pearson. Résultats. — L’étude a évalué 22 yeux de 21 patients (moyenne d’âge 74,3 ± 14,4, 14 femmes) post-DSAEK. Une concordance importante a été trouvée entre les lectures des PIO obtenues par les 3 dispositifs : une corrélation forte et significative a été obtenue entre GAT et PDCT (r = 0,90, p < 0,001) GAT et iCare (r = 0,94, p < 0,001) et iCare et PDCT (r = 0,80, p < 0,001). Cependant, les mesures obtenues par iCare ont été inférieures de fac ¸on significative et consistante par rapport à celles de GAT (IOP = 1,62 ± 2,0, p = 0,003, 95 % CI : 0,7—2,5) et à celles de PDCT (IOP = 1,56 ± 2,6, p = 0,012, 95 % CI : 0,4—2,7). Aucune relation n’a été trouvée entre ECD, CCT, AXL, la courbure de la cornée ou l’astigmatisme et les données de PIO. Conclusions. — La mesure de PIO par les 3 techniques différentes (aplanation, rebond et contour dynamique) ont révélé de bonnes corrélations, malgré une augmentation de l’épaisseur cornéenne suite a une DSAEK. Cependant, iCare qui se base sur la tonométrie à rebond à mesuré ¸on significative par rapport aux deux autres méthodes. Ces différences des PIO inférieures de fac doivent être prises en compte lors de l’évaluation de patients post-DSAEK. © 2016 Elsevier Masson SAS. Tous droits r´ eserv´ es.
Introduction Descemet’s stripping automated endothelial keratoplasty (DSAEK) is a lamellar corneal transplantation procedure in which donor posterior lamellar tissue is used to replace diseased corneal recipient endothelium and Descemet membrane [1]. In this technique, only the dysfunctional posterior portion of the cornea is replaced through a scleral pocket incision. Thus, DSAEK eliminates surface corneal incisions and sutures, maintains much of the cornea’s structural integrity and induces minimal refractive changes. Due to these advantages mentioned above, there is a shift from penetrating keratoplasty toward DSAEK as the primary procedure of choice for the management of endothelial dysfunction [2].
Intraocular pressure (IOP) elevation after DSAEK procedure is a common complication occurring in 28.8—54% of cases [3]. This IOP elevation is due to various reasons like corticosteroid treatment, preexisting glaucoma, pupillary block or the development of peripheral anterior synechiae. Such IOP elevations may cause damage to endothelial cells and result in the lamellar corneal graft failure [4—6]. After DSAEK, corneal thickness inevitably increases owing to the addition of the donor graft. Moreover, there is a complex of different corneal tissues and a transitional zone which might affect the net corneal consistency. IOP measurement methods, which depend on the corneal thickness and biomechanical properties, such as Goldmann applanation tonometry (GAT), may not provide accurate readings in these eyes.
824 The GAT is the most widely used device for measuring IOP and it is considered the gold standard tonometer [7]. Its accuracy is, however, influenced by corneal thickness, curvature, and biomechanical properties, such as rigidity, viscosity, elasticity and hydration [8—12]. All of which have shown to have high inter-individual variability and to be affected by corneal pathology and surgery [13—15]. A correction algorithm for the GAT may not be accurate for estimating the IOP in individual subjects. Thus, corneal parameters, especially the central corneal thickness (CCT) affect the accuracy of this measurement [16]. Several alternative tonometers have been developed in an attempt to provide measurements that are not affected by corneal properties. The iCare (Tiolat Oy, Helsinki, Finland) is a handheld tonometer which is based on the impact-induction principle also known as rebound tonometry (RT) [17]. The main advantages of the iCare RT device include its quick and simple use and that local anesthesia and slit lamp are not needed. The iCare tonometer has shown good reproducibility and correlation with GAT and other tonometers in healthy and glaucomatous eyes [18]. There are discrepancies regarding the correlation of iCare measurements with CCT. There are some evidences that, similarly to the IOP measurement with GAT, IOP obtained by iCare increase with increasing CCT in normal and in glaucomatous eyes [19]. However, another study on 125 healthy eyes reported on lack of such correlation with CCT, but reported on a correlation between the iCare measurements and corneal hysteresis and corneal resistance factors [20]. The Pascal dynamic contour tonometer ([PDCT], Ziemer Ophthalmic Systems AG, Port, Switzerland) is based on the Pascal principle, which states that pressure applied to a confined fluid is transmitted undiminished throughout the confining vessel of the system. In contrast to the single flattening produced by GAT, the concave tip of the PDCT, achieves a contour match with minimal corneal distortion, allowing all of the forces to be directed to an embedded microchip-enabled solid-state sensor at the tonometer’s tip. Therefore, the PDCT provides an IOP measurement that is not affected by corneal thickness and rigidity [21]. In non-pathologic eyes, IOP measured with iCare, PDCT and GAT were found to be comparable, with a bias of up to 2.5 mmHg between measurements [22]. There are few comparative reports on IOP measurements following DSAEK [2,7,15,23,26—30]. However, only two out of nine reports had evaluated the IOP using all three described tonometers. Klamann et al. showed IOP overestimation with PDCT compared to GAT or iCare in 30 eyes postDSAEK. Mawatari et al., however, did not demonstrate an IOP measurement difference in a group of 11 subjects [2,26]. Therefore, in order to evaluate and validate the previously published findings, we aim to add additional body of evidence and perform IOP measurement with GAT, iCare and PDCT techniques and to assess the effect of corneal characteristics on IOP measurements.
Subjects and methods We evaluated patients who underwent a successful DSAEK procedure at least 3 months prior to testing. DSAEK was performed by a single surgeon in all patients (HA).
A. Achiron et al. Eyes with clinically detectable corneal edema or other corneal pathology such as epithelial defects, scars or infection were excluded from this study. Each participant underwent the following examinations on the same day: a comprehensive ophthalmologic examination including: best-corrected visual acuity, slit lamp biomicroscopy and IOP measurement with iCare tonometer, PDCT and GAT, in that order. The sequence of measurements was chosen to prevent applanation-induced changes of the IOP influencing the other IOP readings. Five minutes waiting time between measurements was allowed. A 2-person reading method was used for GAT measurements, where one researcher adjusted the dial and the second researcher read and recorded the values. Two consecutive measurements were taken of each eye in all three tonometers. If there was a difference higher than 1 mmHg, a third measurement was taken and IOP was averaged across the three measurements. In order to minimize the potential confounding effect of diurnal variation in IOP, all IOP measurements were taken in the morning between 8:00 to 11:00. Patients receiving anti-glaucoma medication were instructed to instill the treatment only after the IOP measurements. Central corneal thickness (CCT) was measured with ultrasonic pachymetry (PacScan300P, Sonomed), endothelial cell density count (ECC) with specular microscopy (TOPCON SP2000P) corneal keratometric readings (K), and axial length measurements (AXL) (IOLMaster, Carl Zeiss Meditec) were taken after the IOP readings. The study was approved by the local institutional review board and all patients gave informed consent prior to participation.
Statistical analyses We included a single eye per patient in the analysis. Descriptive statistics were expressed as mean ± standard deviation (SD). IOP values showed normal distribution by the Shapiro-Wilk test. Significance levels for comparisons were calculated with the paired-samples t-test. Bland-Altman plots were examined to assess agreement between each pair of measurement methods. The mean pressure measurement for each pair of methods was plotted on the x axis, with the difference in measurements between methods plotted on the y axis. If the two measurements were nearly identical, the mean difference would be close to zero. The upper and lower limits for these plots were the mean ± 1.96 times SD of difference between variables. Correlations between CCT, ECC, K, AXL and IOP measurements were assessed using the Pearson correlation coefficient. For all analyses, P values of less than 0.05 were considered statistically significant.
Results Twenty eyes of 20 patients (mean age 74.3 ± 14.4, 14 females) were included in this study. Mean follow up time post-DSAEK was 19.6 ± 17.4 months (range 3.5—49 months). Mean IOP measured by iCare was 13.3 ± 4.1 mmHg, by PDCT 14.9 ± 4.1 mmHg and by GAT 14.9 ± 5.4 mmHg. The average K reading was 42.2 ± 4.0, the CCT was 668.8 ± 85.4 m, the ECD was 1357 ± 500 cells and the AXL was 23.7 ± 2.5 mm.
IOP after DSAEK
825 Bland-Altman plots indicated that pressure measurements by iCare were significantly lower than that obtained with GAT (IOP = 1.68 ± 2.0, P = 0.002, 95% CI: 0.7 to 2.6) or with PDCT (IOP = 1.61 ± 2.5, P = 0.01, 95% CI: 0.4 to 2.8). No difference was found between GAT and PDCT measurement (P = 0.7) (Fig. 1). However, despite the differences observed in the absolute IOP values, correlation analysis showed good agreement between all tonometers’ measurements (GAT-PDCT r = 0.94, P < 0.001; GAT-iCare r = 0.86, P < 0.001 and iCare-DCT r = 0.81, P < 0.001) (Fig. 2).
Figure 1. Difference between IOP measurements in post-DSAEK patients. Bland-Altman plots depicting the averaged IOP, as measured by two methods against the difference in IOP measured by the same two methods. The y-axis shows the IOP measured. The middle line gives the estimated mean difference. The upper and lower lines represent the 95% limits of agreement for the difference. Up: PDCT versus GAT: mean difference = —0.06 ± 2.6 mmHg, P = 0.9, 95% CI: —1.3—1.1. Middle: iCare versus GAT. Mean difference = —1.68 ± 2.0 mmHg, P = 0.002, 95% CI: 0.7—2.6. Down: iCare versus PDCT. Mean difference = —1.61 ± 2.5 mmHg, P = 0.01, 95% CI: 0.4—2.8).
Figure 2.
Correlation analysis between GAT, iCare and PDCT.
826
A. Achiron et al.
Table 1
Comparative studies on IOP measurements following DSAEK.
Author
Year
N
GAT
PDCT
1 2 3 4
Vajaranant et al. [5] Bochmann et al. [23] Salvetat et al. [7] Mawatari et al. [2]
2008 2009 2011 2011
50 33 19 11
15.9 19.1 17.7 14.4
19.8 20.9 13.9
13.6 13.2
5
Klamann et al. [26]
2012
30
12.5
16.1
13.2
6 7 8 9 10
Li et al. [27] Yi et al. [30] Pal et Sengupta [28] Clemmensen et Hjortdal [25] Unterlauft et al. [29]
2013 2013 2013 2014 2015
37 28 46 17 23
16.2 13 19.4 14.2 15.3
16 21.5 14.7 16.7
iCare
16
Figure 3. Frequency histogram of IOP between GAT, iCare and PDCT. This histogram shows the percentage of eyes falling within different intervals of differences in IOP measurement.
Frequency analysis of IOP between the three tonometers showed that when comparing GAT-iCare and PDCT-iCare only in 31% and 22% the differences were within ± 1 mmHg while the GAT-PDCT were within ± 1 mmHg in 54% of eyes (Fig. 3). When a difference of up to ± 3 mmHg was considered, 81% (GAT-iCare), 72% (PDCT-iCare) and 81% (GAT-PDCT) of eyes were within this range. When analyzing corneal biomechanics, no significant associations were found between CCT, AXL, ECD, corneal curvature or astigmatism with IOP measurement by all 3 devices.
Discussion Glaucoma following DSAEK is a common complication. Careful evolution of IOP is vital as medical and surgical interventions to control IOP are often needed postoperatively [6,31]. We found nine comparative studies on IOP measurements following DSAEK (Table 1) [2,7,15,23,26—30]. Six reports demonstrated that IOP by PDCT was higher than IOP by GAT while one study did not find a significant IOP among these devises. Three studies showed that IOP by GAT are similar to IOP obtained by iCare.
P
Months F/U
IOP-CCT correlations
< 0.01 0.0002 < 0 .001 GAT-iCare (P = 0.11) GAT-PDCT (P = 0.23) iCare-PDCT (P = 0.33) GAT-iCare (P = 0.05) GAT-PDCT (P = 0.001) iCare-PDCT (P = 0.001) 0.4 N/A < 0.05 > 0.05 N/A
3 3 to 6 3 3
N/A No No No
3
No
N/A 3 3 3 12
Yes No No No No
One study showed that IOP by PDCT was higher than IOP by iCare while two studies were not able to repeat this finding. Only two studies used all three described tonometers with one showing IOP over estimation with PDCT and the other contradicted this observation [2,26]. In this study, the IOP measurements conducted by three different techniques (applanation, rebound and dynamic contour) were highly correlated. However, the IOP values with iCare were significantly lower than with PDCT or GAT (0.7—2.5 mmHg). This is consistent with a report by Salvetat et al. which have shown in 19 DSAEK patients, underestimation of IOP measurement with iCare compared with GAT (IOP = 4.0 ± 3.3 mmHg). A report by Rosentreter et al. also demonstrated the underestimation of iCare compared to GAT and PDCT in normal corneas and in pathological corneas such as in previous keratoplasty, keratoconus, corneal scars, corneal dystrophies, and bullous keratopathy [7,22]. Our results demonstrated that IOP was not correlated with CCT. The addition of a 100—200 m graft to the postDEASK corneas, which consist of endothelium-Descemet membrane and posterior stroma, increases cornea thickness but may not affect corneal rigidity, similar to the observation in edematous corneas where IOP is not affected by corneal thickness [25]. As demonstrated in 33 edematous pre-DSAEK corneas, the CCT decreased from 703 to 650 m but no change in IOP or correlation between CCT and preor post-surgery IOP could be found [24]. In contrast to normal corneas where CCT correlate with IOP, increment in CCT post-DSAEK may not exert an effect on ocular rigidity and subsequently on IOP [7]. This was demonstrated by a study that did not find significant IOP differences after grouping 460 post-DSAEK eyes according to donor graft thickness (to < 100 m, 100—150 m or > 150 m groups) [32]. In addition, Unterlauft et al. suggested that the graft does not contribute directly to the corneal biomechanical properties as IOP rise were independent of CCT at 1 year postoperatively [29]. Further evolution of the bio-elasticity changes that occur post-surgery may aid in estimation of IOP. Clemmensen et Hjortdal had used the ocular response analyzer to evaluate the response of post-DSAEK corneas to an air puff, and its
IOP after DSAEK relation to CCT and to IOP measured with GAT and PDCT [25]. The corneal hysteresis (corneal ability to recover from stress deformation) and resistance factor were lower in the DSAEK patients compared to normal control, while no IOP difference exist between the groups. It was suggested that the added graft is not integrated in the host cornea and therefore has no effect on corneal biomechanical rigidity and subsequently on IOP. One limitation of our study is that we did not include control group. However, Jóhannesson et al. showed that the agreement between the three instruments was clinically acceptable in 150 normal volunteers [33]. Another limitation is that we did not measure the IOP in a random sequence in order to prevent GAT induced corneal changes. We did not notice any correlations between corneal curvature or astigmatism and IOP measurement with any methods, similar to report by Salvetat et al. [7]. This was expected as DSAEK avoids surface corneal incisions and sutures, therefore preserves corneal curvature characteristics. In conclusion, our results demonstrated that GAT, iCare and PDCT have good correlation when evaluation IOP posts DSAEK. However, the iCare, which is based on a rebound tonometry, showed significantly lower IOP then both applanation tonometry and dynamic contour tonometry. To conclude, studies performed on this issue, including the current one, have all small numbers of participants, with somewhat contradicting finding. This should be taken into consideration when applying these findings to clinical practice of obtaining reliable IOP measurements following DSAEK.
Acknowledgements We would like to thank Mrs. Carol Chea-Elmaleich for translating the abstract to French.
Disclosure of interest The authors declare that they have no competing interest.
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827 [5] Vajaranant TS, Price MO, Price FW, Gao W, Wilensky JT, Edward DP:. Visual acuity and intraocular pressure after Descemet’s stripping endothelial keratoplasty in eyes with and without preexisting glaucoma. Ophthalmology 2009;116(9):1644—50. [6] Moisseiev E, Varssano D, Rosenfeld E, Rachmiel R. Intraocular pressure after penetrating keratoplasty. Descemet’s stripping automated endothelial keratoplasty. Can J Ophthalmol 2013;48:179—85. [7] Salvetat ML, Zeppieri M, Miani F, Tosoni C, Parisi L, Brusini P. Comparison of iCare tonometer and Goldmann applanation tonometry in normal corneas and in eyes with automated lamellar and penetrating keratoplasty. Eye 2011;25:642—50. [8] Kohlhaas M, Boehm AG, Spoerl E, Pursten A, Grein HJ, Pillunat LE. Effect of central corneal thickness, corneal curvature, and axial length on applanation tonometry. Arch Ophthalmol 2006;124:471—6. [9] Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol 2000;44:367—408. [10] Liu J, Roberts CJ:. Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis. J Cataract Refract Surg 2005;31:146—55. [11] Broman AT, Congdon NG, Bandeen-Roche K, Quigley HA;. Influence of corneal structure, corneal responsiveness, and other ocular parameters on tonometric measurement of intraocular pressure. J Glaucoma 2007;16(7):581—8. [12] Whitacre MM, Stein R:. Sources of error with use of Goldmanntype tonometers. Surv Ophthalmol 1993;38(1):1—30. [13] Ceruti P, Morbio R, Marraffa M, Marchini G:. Comparison of dynamic contour tonometry and Goldmann applanation tonometry in deep lamellar and penetrating keratoplasties. Am J Ophthalmol 2008;145:215—21. [14] Luce DA. Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg 2005;31:156—62. [15] Vajaranant TS, Price MO, Price FW, Wilensky JT, Edward DP. Intraocular pressure measurements following Descemet stripping endothelial keratoplasty. Am J Ophthalmol 2008;145:780—6. [16] Chihara E. Assessment of true intraocular pressure: the gap between theory and practical data. Surv Ophthalmol 2008;53:203—18. [17] Kontiola AI. A new induction-based impact method for measuring intraocular pressure. Acta Ophthalmol Scand 2000;78:142—5. [18] Martinez-de-la-Casa JM, Garcia-Feijoo J, Castillo A, GarciaSanchez J. Reproducibility and clinical evaluation of rebound tonometry. Invest Ophthalmol Vis Sci 2005;46:4578—80. [19] Rao A, Kumar M, Prakash B, Varshney G. Relationship of central corneal thickness and intraocular pressure by iCare rebound tonometer. J Glaucoma 2014;23:380—4. [20] Chui WS, Lam A, Chen D, Chiu R. The influence of corneal properties on rebound tonometry. Ophthalmology 2008;115: 80—4. [21] Kaufmann C, Bachmann LM, Thiel MA. Comparison of dynamic contour tonometry with goldmann applanation tonometry. Invest Ophthalmol Vis Sci 2004;45:3118—21. [22] Rosentreter A, Athanasopoulos A, Schild AM, Lappas A, Cursiefen C, Dietlein TS. Rebound, applanation, and dynamic contour tonometry in pathologic corneas. Cornea 2013;32:313—8. [23] Bochmann F, Kaufmann C, Becht C, Bachmann LM, Thiel MA. Comparison of dynamic contour tonometry with Goldmann applanation tonometry following Descemet’s stripping automated endothelial keratoplasty (DSAEK). Klin Monbl Augenheilkd 2009;226:241—4. [24] Chang DT, Pantcheva MB, Noecker RJ. Corneal thickness and intraocular pressure in edematous corneas before and after
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ORIGINAL ARTICLE
Intraocular pressure measurement after DSAEK by iCare, Goldmann applanation and dynamic contour tonometry: A comparative study Mesure de la pression intraoculaire après DSAEK par iCare, aplanation de Goldmann et tonomètre dynamique de contour : une étude comparative A. Achiron a,∗,b, O. Blumenfeld a,b, H. Avizemer a,b, L. Karmona a,b, G. Leybowich a,b, V. Man c, E. Bartov a,b, Z. Burgansky-Eliash a,b a
Department of Ophthalmology, The Edith Wolfson Medical Center, Holon, Israel Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel c Department of Ophthalmology, Soroka University Medical Center, Ben-Gurion University, Beer-Sheva, Israel b
Received 1st August 2016; accepted 19 September 2016 Available online 19 November 2016
KEYWORDS DSAEK; Intraocular pressure; iCare; Goldmann applanation; Dynamic contour tonometry
∗
Summary Purpose. — Corneal thickness inevitably increases following Descemet’s stripping automated endothelial keratoplasty (DSAEK), owing to the addition of a donor graft. The current study compares different devices in assessing post-DSAEK intraocular pressure (IOP). Methods. — We compared IOP values measured by the Goldmann tonometry (GAT), iCare rebound tonometry (iCare) and Pascal dynamic contour tonometry (PDCT) in eyes following DSAEK. Agreement between measurements was calculated with correlation analysis and BlandAltman plots. Effects of keratometry, central, thickness (CCT), endothelial cell density (ECD) and axial length on IOP measurements were assessed with Pearson’s correlation. Results. — Twenty eyes of 20 patients (mean age 74.3 ± 14.4, 14 females) post-DSAEK were included in this study. There was a high concordance between the IOP readings obtained by the three devices: a strong and significant correlation was found between GAT and PDCT (r = 0.94, P < 0.001) GAT and iCare (r = 0.86, P < 0.001) and iCare with PDCT (r = 0.81, P < 0.001).
Corresponding author. E-mail address: [email protected] (A. Achiron).
http://dx.doi.org/10.1016/j.jfo.2016.09.009 0181-5512/© 2016 Elsevier Masson SAS. All rights reserved.
IOP after DSAEK
823 However, the iCare measurements were significantly and consistently lower than that obtained with GAT (IOP = 1.68 ± 2.0, P = 0.002, 95% CI: 0.7—2.6) and with PDCT (IOP = 1.61 ± 2.5, P = 0.01, 95% CI: 0.4—2.8). CCT, ECD, CCT, AXL, corneal curvature or astigmatism did not influence IOP measurement by any instrument. Conclusions. — IOP measurement with three different techniques (applanation, rebound and dynamic contour) showed good correlations, despite an increased corneal thickness following DSAEK. However, the iCare, which is based on a rebound tonometry showed significant lower IOP then the two other methods. This should be taken into account when evaluating patients post DSAEK. © 2016 Elsevier Masson SAS. All rights reserved.
MOTS CLÉS DSAEK ; Pression intraoculaire ; iCare ; Aplanation de Goldmann ; Tonomètre dynamique de contour
Résumé Objectif. — Suite à une kératoplastie endothéliale automatisée par le stripping de Descemet (DSAEK), l’épaisseur cornéenne augmente inévitablement en raison de l’ajout du greffon du donneur. Le tissu cornéen qui a été ajouté peut avoir un effet différent sur les mesures de pression intraoculaire (PIO) selon les techniques de mesure utilisées. Cette étude compare différents appareils de mesure dans l’évaluation de la PIO post-DSAEK. Méthodes. — Nous avons comparé les données de PIO post-DSAEK mesurées par le tonomètre à aplanation de Goldmann (GAT), le tonomètre par rebond d’iCare (iCare) et le tonomètre dynamique de contour Pascal (PDCT). L’agrément des mesures a été calculé par analyse de corrélation et graphiques de Bland-Altman. Les données de l’effet de la kératométrie, de l’épaisseur de la cornée centrale, (CCT), de la densité des cellules endothéliales (ECD) et de la longueur axiale sur la PIO ont été évaluées avec la corrélation de Pearson. Résultats. — L’étude a évalué 22 yeux de 21 patients (moyenne d’âge 74,3 ± 14,4, 14 femmes) post-DSAEK. Une concordance importante a été trouvée entre les lectures des PIO obtenues par les 3 dispositifs : une corrélation forte et significative a été obtenue entre GAT et PDCT (r = 0,90, p < 0,001) GAT et iCare (r = 0,94, p < 0,001) et iCare et PDCT (r = 0,80, p < 0,001). Cependant, les mesures obtenues par iCare ont été inférieures de fac ¸on significative et consistante par rapport à celles de GAT (IOP = 1,62 ± 2,0, p = 0,003, 95 % CI : 0,7—2,5) et à celles de PDCT (IOP = 1,56 ± 2,6, p = 0,012, 95 % CI : 0,4—2,7). Aucune relation n’a été trouvée entre ECD, CCT, AXL, la courbure de la cornée ou l’astigmatisme et les données de PIO. Conclusions. — La mesure de PIO par les 3 techniques différentes (aplanation, rebond et contour dynamique) ont révélé de bonnes corrélations, malgré une augmentation de l’épaisseur cornéenne suite a une DSAEK. Cependant, iCare qui se base sur la tonométrie à rebond à mesuré ¸on significative par rapport aux deux autres méthodes. Ces différences des PIO inférieures de fac doivent être prises en compte lors de l’évaluation de patients post-DSAEK. © 2016 Elsevier Masson SAS. Tous droits r´ eserv´ es.
Introduction Descemet’s stripping automated endothelial keratoplasty (DSAEK) is a lamellar corneal transplantation procedure in which donor posterior lamellar tissue is used to replace diseased corneal recipient endothelium and Descemet membrane [1]. In this technique, only the dysfunctional posterior portion of the cornea is replaced through a scleral pocket incision. Thus, DSAEK eliminates surface corneal incisions and sutures, maintains much of the cornea’s structural integrity and induces minimal refractive changes. Due to these advantages mentioned above, there is a shift from penetrating keratoplasty toward DSAEK as the primary procedure of choice for the management of endothelial dysfunction [2].
Intraocular pressure (IOP) elevation after DSAEK procedure is a common complication occurring in 28.8—54% of cases [3]. This IOP elevation is due to various reasons like corticosteroid treatment, preexisting glaucoma, pupillary block or the development of peripheral anterior synechiae. Such IOP elevations may cause damage to endothelial cells and result in the lamellar corneal graft failure [4—6]. After DSAEK, corneal thickness inevitably increases owing to the addition of the donor graft. Moreover, there is a complex of different corneal tissues and a transitional zone which might affect the net corneal consistency. IOP measurement methods, which depend on the corneal thickness and biomechanical properties, such as Goldmann applanation tonometry (GAT), may not provide accurate readings in these eyes.
824 The GAT is the most widely used device for measuring IOP and it is considered the gold standard tonometer [7]. Its accuracy is, however, influenced by corneal thickness, curvature, and biomechanical properties, such as rigidity, viscosity, elasticity and hydration [8—12]. All of which have shown to have high inter-individual variability and to be affected by corneal pathology and surgery [13—15]. A correction algorithm for the GAT may not be accurate for estimating the IOP in individual subjects. Thus, corneal parameters, especially the central corneal thickness (CCT) affect the accuracy of this measurement [16]. Several alternative tonometers have been developed in an attempt to provide measurements that are not affected by corneal properties. The iCare (Tiolat Oy, Helsinki, Finland) is a handheld tonometer which is based on the impact-induction principle also known as rebound tonometry (RT) [17]. The main advantages of the iCare RT device include its quick and simple use and that local anesthesia and slit lamp are not needed. The iCare tonometer has shown good reproducibility and correlation with GAT and other tonometers in healthy and glaucomatous eyes [18]. There are discrepancies regarding the correlation of iCare measurements with CCT. There are some evidences that, similarly to the IOP measurement with GAT, IOP obtained by iCare increase with increasing CCT in normal and in glaucomatous eyes [19]. However, another study on 125 healthy eyes reported on lack of such correlation with CCT, but reported on a correlation between the iCare measurements and corneal hysteresis and corneal resistance factors [20]. The Pascal dynamic contour tonometer ([PDCT], Ziemer Ophthalmic Systems AG, Port, Switzerland) is based on the Pascal principle, which states that pressure applied to a confined fluid is transmitted undiminished throughout the confining vessel of the system. In contrast to the single flattening produced by GAT, the concave tip of the PDCT, achieves a contour match with minimal corneal distortion, allowing all of the forces to be directed to an embedded microchip-enabled solid-state sensor at the tonometer’s tip. Therefore, the PDCT provides an IOP measurement that is not affected by corneal thickness and rigidity [21]. In non-pathologic eyes, IOP measured with iCare, PDCT and GAT were found to be comparable, with a bias of up to 2.5 mmHg between measurements [22]. There are few comparative reports on IOP measurements following DSAEK [2,7,15,23,26—30]. However, only two out of nine reports had evaluated the IOP using all three described tonometers. Klamann et al. showed IOP overestimation with PDCT compared to GAT or iCare in 30 eyes postDSAEK. Mawatari et al., however, did not demonstrate an IOP measurement difference in a group of 11 subjects [2,26]. Therefore, in order to evaluate and validate the previously published findings, we aim to add additional body of evidence and perform IOP measurement with GAT, iCare and PDCT techniques and to assess the effect of corneal characteristics on IOP measurements.
Subjects and methods We evaluated patients who underwent a successful DSAEK procedure at least 3 months prior to testing. DSAEK was performed by a single surgeon in all patients (HA).
A. Achiron et al. Eyes with clinically detectable corneal edema or other corneal pathology such as epithelial defects, scars or infection were excluded from this study. Each participant underwent the following examinations on the same day: a comprehensive ophthalmologic examination including: best-corrected visual acuity, slit lamp biomicroscopy and IOP measurement with iCare tonometer, PDCT and GAT, in that order. The sequence of measurements was chosen to prevent applanation-induced changes of the IOP influencing the other IOP readings. Five minutes waiting time between measurements was allowed. A 2-person reading method was used for GAT measurements, where one researcher adjusted the dial and the second researcher read and recorded the values. Two consecutive measurements were taken of each eye in all three tonometers. If there was a difference higher than 1 mmHg, a third measurement was taken and IOP was averaged across the three measurements. In order to minimize the potential confounding effect of diurnal variation in IOP, all IOP measurements were taken in the morning between 8:00 to 11:00. Patients receiving anti-glaucoma medication were instructed to instill the treatment only after the IOP measurements. Central corneal thickness (CCT) was measured with ultrasonic pachymetry (PacScan300P, Sonomed), endothelial cell density count (ECC) with specular microscopy (TOPCON SP2000P) corneal keratometric readings (K), and axial length measurements (AXL) (IOLMaster, Carl Zeiss Meditec) were taken after the IOP readings. The study was approved by the local institutional review board and all patients gave informed consent prior to participation.
Statistical analyses We included a single eye per patient in the analysis. Descriptive statistics were expressed as mean ± standard deviation (SD). IOP values showed normal distribution by the Shapiro-Wilk test. Significance levels for comparisons were calculated with the paired-samples t-test. Bland-Altman plots were examined to assess agreement between each pair of measurement methods. The mean pressure measurement for each pair of methods was plotted on the x axis, with the difference in measurements between methods plotted on the y axis. If the two measurements were nearly identical, the mean difference would be close to zero. The upper and lower limits for these plots were the mean ± 1.96 times SD of difference between variables. Correlations between CCT, ECC, K, AXL and IOP measurements were assessed using the Pearson correlation coefficient. For all analyses, P values of less than 0.05 were considered statistically significant.
Results Twenty eyes of 20 patients (mean age 74.3 ± 14.4, 14 females) were included in this study. Mean follow up time post-DSAEK was 19.6 ± 17.4 months (range 3.5—49 months). Mean IOP measured by iCare was 13.3 ± 4.1 mmHg, by PDCT 14.9 ± 4.1 mmHg and by GAT 14.9 ± 5.4 mmHg. The average K reading was 42.2 ± 4.0, the CCT was 668.8 ± 85.4 m, the ECD was 1357 ± 500 cells and the AXL was 23.7 ± 2.5 mm.
IOP after DSAEK
825 Bland-Altman plots indicated that pressure measurements by iCare were significantly lower than that obtained with GAT (IOP = 1.68 ± 2.0, P = 0.002, 95% CI: 0.7 to 2.6) or with PDCT (IOP = 1.61 ± 2.5, P = 0.01, 95% CI: 0.4 to 2.8). No difference was found between GAT and PDCT measurement (P = 0.7) (Fig. 1). However, despite the differences observed in the absolute IOP values, correlation analysis showed good agreement between all tonometers’ measurements (GAT-PDCT r = 0.94, P < 0.001; GAT-iCare r = 0.86, P < 0.001 and iCare-DCT r = 0.81, P < 0.001) (Fig. 2).
Figure 1. Difference between IOP measurements in post-DSAEK patients. Bland-Altman plots depicting the averaged IOP, as measured by two methods against the difference in IOP measured by the same two methods. The y-axis shows the IOP measured. The middle line gives the estimated mean difference. The upper and lower lines represent the 95% limits of agreement for the difference. Up: PDCT versus GAT: mean difference = —0.06 ± 2.6 mmHg, P = 0.9, 95% CI: —1.3—1.1. Middle: iCare versus GAT. Mean difference = —1.68 ± 2.0 mmHg, P = 0.002, 95% CI: 0.7—2.6. Down: iCare versus PDCT. Mean difference = —1.61 ± 2.5 mmHg, P = 0.01, 95% CI: 0.4—2.8).
Figure 2.
Correlation analysis between GAT, iCare and PDCT.
826
A. Achiron et al.
Table 1
Comparative studies on IOP measurements following DSAEK.
Author
Year
N
GAT
PDCT
1 2 3 4
Vajaranant et al. [5] Bochmann et al. [23] Salvetat et al. [7] Mawatari et al. [2]
2008 2009 2011 2011
50 33 19 11
15.9 19.1 17.7 14.4
19.8 20.9 13.9
13.6 13.2
5
Klamann et al. [26]
2012
30
12.5
16.1
13.2
6 7 8 9 10
Li et al. [27] Yi et al. [30] Pal et Sengupta [28] Clemmensen et Hjortdal [25] Unterlauft et al. [29]
2013 2013 2013 2014 2015
37 28 46 17 23
16.2 13 19.4 14.2 15.3
16 21.5 14.7 16.7
iCare
16
Figure 3. Frequency histogram of IOP between GAT, iCare and PDCT. This histogram shows the percentage of eyes falling within different intervals of differences in IOP measurement.
Frequency analysis of IOP between the three tonometers showed that when comparing GAT-iCare and PDCT-iCare only in 31% and 22% the differences were within ± 1 mmHg while the GAT-PDCT were within ± 1 mmHg in 54% of eyes (Fig. 3). When a difference of up to ± 3 mmHg was considered, 81% (GAT-iCare), 72% (PDCT-iCare) and 81% (GAT-PDCT) of eyes were within this range. When analyzing corneal biomechanics, no significant associations were found between CCT, AXL, ECD, corneal curvature or astigmatism with IOP measurement by all 3 devices.
Discussion Glaucoma following DSAEK is a common complication. Careful evolution of IOP is vital as medical and surgical interventions to control IOP are often needed postoperatively [6,31]. We found nine comparative studies on IOP measurements following DSAEK (Table 1) [2,7,15,23,26—30]. Six reports demonstrated that IOP by PDCT was higher than IOP by GAT while one study did not find a significant IOP among these devises. Three studies showed that IOP by GAT are similar to IOP obtained by iCare.
P
Months F/U
IOP-CCT correlations
< 0.01 0.0002 < 0 .001 GAT-iCare (P = 0.11) GAT-PDCT (P = 0.23) iCare-PDCT (P = 0.33) GAT-iCare (P = 0.05) GAT-PDCT (P = 0.001) iCare-PDCT (P = 0.001) 0.4 N/A < 0.05 > 0.05 N/A
3 3 to 6 3 3
N/A No No No
3
No
N/A 3 3 3 12
Yes No No No No
One study showed that IOP by PDCT was higher than IOP by iCare while two studies were not able to repeat this finding. Only two studies used all three described tonometers with one showing IOP over estimation with PDCT and the other contradicted this observation [2,26]. In this study, the IOP measurements conducted by three different techniques (applanation, rebound and dynamic contour) were highly correlated. However, the IOP values with iCare were significantly lower than with PDCT or GAT (0.7—2.5 mmHg). This is consistent with a report by Salvetat et al. which have shown in 19 DSAEK patients, underestimation of IOP measurement with iCare compared with GAT (IOP = 4.0 ± 3.3 mmHg). A report by Rosentreter et al. also demonstrated the underestimation of iCare compared to GAT and PDCT in normal corneas and in pathological corneas such as in previous keratoplasty, keratoconus, corneal scars, corneal dystrophies, and bullous keratopathy [7,22]. Our results demonstrated that IOP was not correlated with CCT. The addition of a 100—200 m graft to the postDEASK corneas, which consist of endothelium-Descemet membrane and posterior stroma, increases cornea thickness but may not affect corneal rigidity, similar to the observation in edematous corneas where IOP is not affected by corneal thickness [25]. As demonstrated in 33 edematous pre-DSAEK corneas, the CCT decreased from 703 to 650 m but no change in IOP or correlation between CCT and preor post-surgery IOP could be found [24]. In contrast to normal corneas where CCT correlate with IOP, increment in CCT post-DSAEK may not exert an effect on ocular rigidity and subsequently on IOP [7]. This was demonstrated by a study that did not find significant IOP differences after grouping 460 post-DSAEK eyes according to donor graft thickness (to < 100 m, 100—150 m or > 150 m groups) [32]. In addition, Unterlauft et al. suggested that the graft does not contribute directly to the corneal biomechanical properties as IOP rise were independent of CCT at 1 year postoperatively [29]. Further evolution of the bio-elasticity changes that occur post-surgery may aid in estimation of IOP. Clemmensen et Hjortdal had used the ocular response analyzer to evaluate the response of post-DSAEK corneas to an air puff, and its
IOP after DSAEK relation to CCT and to IOP measured with GAT and PDCT [25]. The corneal hysteresis (corneal ability to recover from stress deformation) and resistance factor were lower in the DSAEK patients compared to normal control, while no IOP difference exist between the groups. It was suggested that the added graft is not integrated in the host cornea and therefore has no effect on corneal biomechanical rigidity and subsequently on IOP. One limitation of our study is that we did not include control group. However, Jóhannesson et al. showed that the agreement between the three instruments was clinically acceptable in 150 normal volunteers [33]. Another limitation is that we did not measure the IOP in a random sequence in order to prevent GAT induced corneal changes. We did not notice any correlations between corneal curvature or astigmatism and IOP measurement with any methods, similar to report by Salvetat et al. [7]. This was expected as DSAEK avoids surface corneal incisions and sutures, therefore preserves corneal curvature characteristics. In conclusion, our results demonstrated that GAT, iCare and PDCT have good correlation when evaluation IOP posts DSAEK. However, the iCare, which is based on a rebound tonometry, showed significantly lower IOP then both applanation tonometry and dynamic contour tonometry. To conclude, studies performed on this issue, including the current one, have all small numbers of participants, with somewhat contradicting finding. This should be taken into consideration when applying these findings to clinical practice of obtaining reliable IOP measurements following DSAEK.
Acknowledgements We would like to thank Mrs. Carol Chea-Elmaleich for translating the abstract to French.
Disclosure of interest The authors declare that they have no competing interest.
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