differences between goldmann applanation tonometry and dynamic contour tonometry in...

Original Article

Differences between Goldmann ApplanationTonometry and Dynamic Contour Tonometry inpseudoexfoliation syndrome_ 444..448

Emilia Grammenandi MD, Efstathios T Detorakis MD PhD, Ioannis G Pallikaris MD PhD andMiltiadis K Tsilimbaris MD PhDDepartment of Ophthalmology, University Hospital of Heraklion, Crete, Greece

ABSTRACT

Purpose: To evaluate differences between GoldmannApplanation Tonometry (GAT) and Dynamic Con-trour Tonometry (DCT) in eyes with pseudoexfolia-tion syndrome (PEX).

Methods: Thirty-eight patients (38 eyes) with PEX inboth eyes (pseudoexfoliative group, PG) as well as 19patients (19 eyes) without PEX in either eye (controlgroup, CG), were included. All eyes were phakic.GAT, DCT, the central corneal thickness (CCT) andthe axial length of the eyeball (AL) were measuredand the difference between GAT and DCT (dIOP) wascalculated. Differences in dIOP between CG and PGand correlations of dIOP with CCT and AL wereexamined.

Results: dIOP was significantly (P = 0.02) higher inPG (mean value 3.69 mmHg), compared with CG(mean value 2.15 mmHg). In PG (but not in CG),dIOP was also significantly correlated with AL butnot with CCT.

Conclusion: The fact that dIOP was significantlyhigher in PG than in CG implies that PEX may affectocular biomechanical properties. The significantassociation of dIOP with AL but not with CCT is inagreement with previous reports and complies withthe fact that pseudoexfoliative material is not depos-ited in corneal stroma.

Key words: diagnostic techniques, pachymetry, pseu-doexfoliation syndrome, sclera.

INTRODUCTION

Pseudoexfoliation syndrome (PEX) is characterizedby the presence of whitish flecks at the anteriorstructures of the eye such as the anterior lens capsule,Zinn zonules and iris.1,2 PEX has been correlatedwith several ophthalmic pathological conditions,including glaucoma.1,2 Furthermore, material of thesame structure has been detected in many extraocu-lar sites, such as the conjunctiva,3 orbit,3 skin,4 liver,5

lungs,5 brain5 and vascular walls;6 and it has beensuggested that PEX is a systemic condition5,6 possi-bly due to a disturbance of basement membranesynthesis.7,8 The presence of pseudoexfoliative mate-rial in the tissues has been reported to adverselyaffect their function resulting in a variety of patho-logical conditions such as corneal mechanical hypa-esthesia (reduced corneal sensitivity to mechanicalstimuli),9 hearing defects10 or ischaemic ophthalmicdisorders.11 The potential connection of the latterwith PEX has been based on the detection of pseu-doexfoliative material to the wall of the centralretinal artery, short posterior ciliary arteries and longposterior ciliary arteries that supply the choroidaland ciliary blood circulation.12,13 The choroid is animportant component of ocular rigidity and thus ofthe biomechanical properties of the eyeball.14

Dynamic Contour Tonometry (DCT; SMT SwissMicrotechnology AG, Port, Switzerland) uses acontoured 10.5-mm-diameter ‘tip’, with a 1.7-mm-diameter sensor, which conforms to the anteriorcorneal surface to measure IOP directly.15 IOP mea-surements by DCT are theoretically less dependenton ocular biomechanical properties, comparedwith Goldmann Applanation Tonometry (GAT).15

� Correspondence: Dr Efstathios T Detorakis, Department of Ophthalmology, University Hospital of Heraklion, 71110, Heraklion, Crete, Greece. Email:

[email protected]

Received 6 August 2009; accepted 18 January 2010.

Clinical and Experimental Ophthalmology 2010; 38: 444–448 doi: 10.1111/j.1442-9071.2010.02275.x

© 2010 The AuthorsJournal compilation © 2010 Royal Australian and New Zealand College of Ophthalmologists

Accordingly, the differences in the measurements ofthe intraocular pressure (IOP) by different tonometrymethods, such as GAT and DCT, have been previ-ously used as indicators of the biomechanical behav-iour of the eye.15 This study aims at evaluatingdifferences between GAT and DCT in eyes with PEXand correlate results with clinical information.Results could help in assessing the potential effectsof PEX on ocular rigidity and its role in the develop-ment of ocular pathological conditions, such asglaucoma.

METHODS

This is a prospective non-randomized case series. Allpatients included were cataract surgery candidates,recruited from the Department of Ophthalmologyof the University Hospital of Heraklion, in Crete,Greece. The pseudoexfoliation group (PG) includedpatients with pseudoexfoliative features in botheyes. The diagnosis of PEX had been based on slit-lamp gonioscopy and biomicroscopy (both beforeand after pupil dilation), as described elsewhere.16

The Control Group (CG) included patients withoutpseudoexfoliative features in either eye. Again, theexclusion of PEX was based on slit-lamp gonioscopyand biomicroscopy (both before and after pupildilation). Gonioscopic assessment aimed at detectingspecific PEX-related features, such as trabecularhyperpigmentation with patchy distribution (espe-cially inferiorly) or a scalloped band of pigmentrunning onto or anterior to Schwalbe’s line (Sampa-olesi’s line). The presence or absence of PEX wasseparately examined by two independent experi-enced examiners (ETD and MKT); and only patientswith consent from both examiners on their PEXstatus were included. Patients with a history ofocular surgery (including cataract or refractivesurgery), trauma or inflammation in either eye wereexcluded to rule out potential effects of woundhealing responses or phakic status (pseudophakia,aphakia) on measurements. Furthermore, to rule outpotential effects of any antiglaucomatous medica-tions on the difference between GAT and DCT read-ings, glaucomatous patients were also excluded.Only one eye (the right eye) was included in theanalyses for both groups. All patients signed awritten informed consent form in accordance withthe tenets of the Declaration of Helsinki.

GAT-IOP (mmHg), DCT-IOP (mmHg), centralcorneal thickness (CCT; mm) and axial length (AL;mm) were examined in all patients by an experi-enced examiner (AG) who was masked againstgroup classification. DCT (SMT Swiss Microtechnol-ogy AG, Port, Switzerland) was performed beforeGAT, to avoid potential massaging effects on thecornea due to the applanation. The quality of each

DCT reading, ranging from Q1 (best quality) to Q5(worst quality) is provided by the instrument (aquality of Q1, Q2 or Q3 is considered acceptable, asrecommended by the manufacturer). In the presentstudy, three readings of good quality (Q1–Q3) weretaken for every patient and the mean value recorded.GAT was performed next (at least 10 min after DCT).The difference between DCT and GAT values (dIOP)was also recorded. The examination of CCT and ALwas performed last with the Alcon OcuScan RxPOphthalmic Ultrasound System, using a 20-Mhzprobe for pachymetry, with a resolution of �1 mmand an accuracy of �5 mm and a 10-Mhz probe forbiometry, with a resolution of �0.1 mm and a theo-retical accuracy of �0.05 mm, according to the manu-facturer (Alcon laboratories, Alcon, Irvine, CA,USA). For both CCT and AL, 10 successive measure-ments were taken and the mean was recorded. Allclinical ophthalmic examinations were performed bythe same experienced examiner (AG) who wasmasked against the classification of participants intopseudoexfoliative glaucoma (PEXG) and CG.

The PG included 38 eyes of 38 patients (17males, 44.73%), aged 70.329 � 6.66 (51–86) years(mean � standard deviation, range). The CGincluded 19 eyes of 19 patients (eight males,42.10%), aged 68.70 � 7.51 (49–80). Statisticalanalysis of findings was performed using SPSS 8.0(SPSS, Chicago, IL, USA). Statistical significancewas set at 0.05. Differences in GAT, DCT and dIOP aswell as in age distribution CCT and AL between PGand CG were examined using independent samplest-test. Differences in gender distribution between PGand CG were examined with Pearson’s chi-squaredtest. The correlations between GAT, DCT or dIOPand CCT, AL or patients’ age were examined inall groups using Pearson’s bivariate correlationcoefficient.

RESULTS

Differences in the age and AL distribution betweenPG and CG were statistically not significant (inde-pendent samples t-test). Furthermore, differences ingender distribution between PG and CG were alsostatistically not significant (Pearson’s chi-squaredtest). GAT-IOP and DCT-IOP did not differ signifi-cantly between PG and CG (independent samplest-test). On the contrary, dIOP was significantlyhigher in PG, compared with CG. GAT-IOP, DCT-IOP and dIOP as well as AL and CCT scores in thegroups examined and statistical significance ofrespective differences are presented in Table 1.

Correlations between patients’ age or CCT andGAT-IOP, DCT-IOP or dIOP and were statisticallynot significant in both groups examined (Pear-son’s bivariate correlation coefficient). Correlations

Tonometric disparities in Pseudoexfoliation 445


between AL and GAT-IOP or DCT-IOP were alsostatistically not significant in both groups (Pearson’sbivariate correlation coefficient). On the contrary, thecorrelation between AL and dIOP was statisticallysignificant in the PG (Pearson’s bivariate correlationcoefficient 0.34, P = 0.04) but not in the CG. Scatter-grams of the correlations between dIOP readings andAL in both PG and CG with associated trend linesand respective bivariate correlation coefficients aswell as levels of statistical significance are presentedin Figure 1a and b, respectively.

DISCUSSION

This study examined differences in dIOP betweennon-glaucomatous eyes with and without PEX andevaluated correlations of dIOP with CCT and AL inboth groups. Results imply that PEX may affect dif-ferences in IOP readings between GAT and DCT,

which could be related with alterations in the bio-mechanical properties of the ocular walls.

The difference between GAT-IOP and DCT-IOPhas previously been correlated with ocular rigiditychanges in eyes under treatment with latanoprost.15

DCT tip is contoured with concave surface conform-ing to the anterior corneal surface, thus causingminimal corneal distortion.17,18 The fact that IOPmeasurements are performed by an electronicsensortip (thus without errors attributed to force-to-pressure translations) theoretically render DCTmeasurements less dependent on corneal biome-chanical factors, such as CCT, than GAT.19 The latteris further associated with a massaging effect onthe aqueous associated with applanation.15 In thepresent study, DCT and GAT measurements wereseparated by a time interval of at least 10 min toallow for resolution of any induced changes by themeasurement process, as previously described.15 Thefact that DCT readings were higher than GAT read-ings in the CG in the present study is in accordancewith previous findings form population studies,such as the Los Angeles Latino Eye Study (in whichDCT readings were on the average 1.6 mmHg higherthan GAT readings).20

Taking into account the fact that PG and CG didnot differ in age and gender distributions, the sig-nificantly higher dIOP score in the former groupimplies that PEX may be associated with changes inocular rigidity. This possibility is further supportedby the exclusion in the present study of other factorspotentially affecting rigidity, such as glaucoma orprevious ocular surgery or trauma. The exact mecha-nism by which PEX may affect ocular biomechanicalbehaviour cannot be determined based on the find-ings of this study. The possible presence of pseu-doexfoliative material at the vascular walls of

Table 1. CCT, AL, GAT-IOP, DCT-IOP and dIOP in the groupsexamined and statistical significance of differences (independentsamples t-test)

Parameter Group P

PG CG

CCT (mm) 520.51 539.10 0.06AL (mm) 23.10 22.85 0.34GAT-IOP (mmHg) 15.02 15.15 0.89DCT-IOP (mmHg) 18.71 17.30 0.27dIOP (mmHg) 3.69 2.15 0.02

AL, axial length; CCT, central corneal thickness; DCT, DynamicControur Tonometry; dIOP, difference between Goldmann Appla-nation Tonometry and Dynamic Controur Tonometry; GAT, Gold-mann Applanation Tonometry; IOP, intraocular pressure.

12

10

8

6

4

2

21 22 23 24 25 26 27

0

–2

dlO

P (

mm

Hg)

AL (mm)

r = 0.34, P = 0.04

(a)

12

10

8

6

4

2

21 22 23 24 25 26 27

0

–2

dlO

P (

mm

Hg)

AL (mm)

r = 0.29, P = 0.20

(b)

Figure 1. Scattergrams of the correlation between dIOP and axial length (AL) in pseudoexfoliation group (a) and control group (b) withassociated trend lines and respective bivariate correlation coefficients as well as levels of statistical significance.

446 Grammenandi et al.


ophthalmic vessels supplying uveal circulation aspreviously reported9,11 could affect their elasticityand thus the choroidal contribution to ocularrigidity.14,15 Alternatively, potential changes in thesclera, such as the previously described elastoticdegeneration at the lamina cribrosa associated withPEX,21 might also offer an explanation for thedifferences in dIOP recorded between PG and CG.Pseudoexfoliative material has also been detected inorbital tissues, such as extraocular muscles, orbitalconnective tissue and vortex veins,3,6 implying thatvascular compliance or the elastic modulus of thesetissues could be altered in association with PEX.Such periocular changes might also potentially affectthe biomechanical behaviour of the eyeball.

Irrespective of the exact pathophysiologicalmechanism, ocular rigidity changes associated withPEX may have profound clinical implications forpathological conditions in which PEX is involved,such as PEXG. Glaucomatous patients were notincluded in this study, as glaucoma per se as well asvarious antiglaucomatous medications such as pros-taglandin analogues also affect ocular rigidityindependently.22,23 It is well known that PEXGbehaves very aggressively, often in a non-linearfashion frequently necessitating surgical inter-vention.1,2 These clinical features have been prima-rily attributed to the presence of pseusoexfoliativematerial into the trabecular meshwork.1,2 However,the possibility of ocular rigidity changes related withPEX implies such changes may also be involved inPEXG. This possibility could be explored by futurestudies evaluating rigidity in glaucomatous eyeswith and without PEX.

The significant correlation between AL and dIOPdetected in the PG, as well as the lack of a significantcorrelation between dIOP and CCT, are in agreementwith previous reports on latanoprost-treated eyesand imply that dIOP reflects PEX-associated biome-chanical changes of the whole eyeball (includingsclera) rather than purely corneal biomechanicalchanges.15 These findings also comply with the factthat PEX does not affect corneal stroma (PEX-relatedcorneal changes are mostly endothelial) thus cornealelastic properties would not be expected to beaffected in PEX.24,25 The fact that CCT score waslower in PG compared with CG (although the differ-ence did not exceed statistical significance) is inagreement with previous studies reporting lowerCCT in pseudoexfoliative eyes.24,26 However, webelieve that this marginal difference is unlikely toaffect results, as previously reported, as the effect ofCCT on GAT is statistically weak (R2 ranging from0.06 to 0.17), whereas dIOP may be more pro-nounced only in very thick or very thin corneas.27,28

The relatively small number of patients includedand the non-randomized design may be considered

as potential weaknesses of this study. On the otherhand, the prospective recruitment and the fact thatthe examination of CCT, AL, GAT and DCT wereperformed in a masked fashion against the diagnosisof PEX possibly enhance the validity of results. Thefact that dIOP was significantly higher in PG, com-pared with CG, implies that pseudoexfoliative eyesmay display altered biomechanical properties, suchas ocular rigidity. The latter has been implicatedin the pathogenesis of several ophthalmic condi-tions, including age-related macular degeneration29

and glaucoma.30 The possibility of PEX-associatedchanges in ocular rigidity may be further explored bylarger randomized studies, which could also includeglaucomatous patients. Findings could help not onlyin better understanding the pathophysiology of PEXbut also in improving the management of associatedconditions such as PEXG.

REFERENCES

1. Newell F. The glaucomas. In: Newell F, ed.Ophthalmology. Principles and Concepts. St Louis, MO:Mosby, 1992; 380–1.

2. Skuta G. Pseudoexfoliation syndrome, pigment dis-persion syndrome and the associated glaucomas.In: Tasman W, Jaeger EA, eds. Duane’s ClinicalOphthalmology. Philadelphia, PA: JB Lippincot Co,1989; 1–10.

3. Schlotzer-Schrehardt U, Kuchle M, Naumann GO.Electron-microscopic identification of pseudoexfolia-tion material in extrabulbar tissue. Arch Ophthalmol1991; 109: 565–70.

4. Streeten BW, Dark AJ, Wallace RN, Li ZY, Hoepner JA.Pseudoexfoliative fibrillopathy in the skin of patientswith ocular pseudoexfoliation. Am J Ophthalmol 1990;110: 490–99.

5. Streeten BW, Li ZY, Wallace RN, Eagle RC Jr, Keshge-gian AA. Pseudoexfoliative fibrillopathy in visceralorgans of a patient with pseudoexfoliation syndrome.Arch Ophthalmol 110: 1757–62.

6. Schlotzer-Scherardt UM, Koca MR, Naumann GOH,Volkholz H. Pseudoexfoliation syndrome. Ocularmanifestation of a systemic disorder? Arch Ophthalmol1192: 1752–6.

7. Harnish JP, Barrach HJ, Hassel JR, Sinha PK. Identi-fication of a basement membrane proteoglycan inpseudoexfoliative material. Albrecht Von Graefes ArchKlin Exp Ophthalmol 1981; 215: 273–8.

8. Li ZY, Streeten BW, Wallace RN. Association of elastinwith pseudoexfoliation material. An immunoelectronmicroscopic study. Curr Eye Res 1988; 7: 1163–72.

9. Detorakis ET, Koukoula S, Chrisohoou F, Konstas AG,Kozobolis VP. Central corneal mechanical sensitivityin pseudoexfoliation syndrome. Cornea 2005; 24: 688–91.

10. Detorakis ET, Chryoschoou F, Paliobei V et al. Evalu-ation of the acoustic function in pseudoexfoliationsyndrome and exfoliation glaucoma: audiometric and

Tonometric disparities in Pseudoexfoliation 447


tympanometric findings. Eur J Ophthalmol 2008; 18:71–6.

11. Cursiefen C, Hammer T, Küchle M, Naumann GO,Schlötzer-Schrehardt U. Pseudoexfoliation syndromein eyes with ischemic central retinal vein occlusion. Ahistopathologic and electron microscopic study. ActaOphthalmol Scand 2001; 79: 476–8.

12. Mitchell P, Wang JJ, Smith W. Association of exfolia-tion syndrome with increased vascular risk. Am J Oph-thalmol 1997; 124: 685–7.

13. Detorakis ET, Achtaropoulos AK, Drakonaki EE,Kozobolis VP. Hemodynamic evaluation of the poste-rior ciliary circulation in exfoliation syndrome andexfoliation glaucoma. Graefes Arch Clin Exp Ophthalmol2007; 245: 516–21.

14. Lefrançois A. Pression intraoculaire angle irido-cornéeen, corps ciliaire. In: Mondon H, Metge P, eds.La Myopie Forte. Paris: Masson, 1994; 104–12.

15. Detorakis ET, Arvanitaki V, Pallikaris IG, Kymionis G,Tsilimbaris MK. Applanation tonometry versusdynamic contour tonometry in eyes treated withlatanoprost. J Glaucoma 2009; July 9 [Epub ahead ofprint].

16. Vesti E, Kivela T. Exfoliation syndrome and exfolia-tion glaucoma. Prog Retin Eye Res 2000; 19: 345–68.

17. Punjabi OS, Kniestedt C, Stamper RL, Lin SC.Dynamic contour tonometry: principle and use. ClinExperiment Ophthalmol 2006; 34: 837–40. Review.

18. Kaufmann C, Bachmann LM, Thiel MA. Comparisonof dynamic contour tonometry with goldmann appla-nation tonometry. Invest Ophthalmol Vis Sci 2004; 45:3118–21.

19. Ozbek Z, Cohen EJ, Hammersmith KM, Rapuano CJ.Dynamic contour tonometry: a new way to assessintraocular pressure in ectatic corneas. Cornea 2006; 25:890–4.

20. Francis BA, Hsieh A, Lai MY et al.; Los Angeles LatinoEye Study Group. Effects of corneal thickness, cornealcurvature, and intraocular pressure level on Goldmannapplanation tonometry and dynamic contourtonometry. Ophthalmology 2007; 114: 20–6.

21. Netland PA, Ye H, Streeten BW, Hernandez MR.Elastosis of the lamina cribrosa in pseudoexfoliationsyndrome with glaucoma. Ophthalmology 1995; 102:878–86.

22. Agrawal KK, Sharma DP, Bhargava G, Sanadhya DK.Scleral rigidity in glaucoma, before and during topicalantiglaucoma drug therapy. Indian J Ophthalmol 1991;39: 85–6.

23. Ebneter A, Wagels B, Zinkernagel MS. Non-invasivebiometric assessment of ocular rigidity in glaucomapatients and controls. Eye 2009; 23: 606–11.

24. Detorakis ET, Koukoula S, Chrisohoou F, ?onstas AG,Kozobolis VP. Central corneal mechanical sensitivityin pseudoexfoliation syndrome. Cornea 2005; 24: 688–91.

25. Naumann GO, Schlotzer-Schrehardt U. Keratopathy inpseudoexfoliation syndrome as a cause of cornealendothelial decompensation: a clinicopathologicstudy. Ophthalmology 2000; 107: 1111.

26. Sobottka Ventura AC, Böhnke M, Mojon DS. Centralcorneal thickness measurements in patients withnormal tension glaucoma, primary open angleglaucoma, pseudoexfoliation glaucoma, or ocularhypertension. Br J Ophthalmol 2001; 85: 792.

27. Doughty MJ, Zaman ML. Human corneal thicknessand its impact on intraocular pressure measures: areview and metaanalysis approach. Surv Ophthalmol2000; 44: 367–408.

28. Pepose JS, Feigenbaum SK, Qazi MA, Sanderson JP,Roberts CJ. Changes in corneal biomechanics andintraocular pressure following LASIK using static,dynamic, and noncontact tonometry. Am J Ophthalmol2007; 143: 39–47.

29. Friedman E, Ivry M, Ebert E, Glynn R, Gragoudas E,Seddon J. Increased scleral rigidity and age-relatedmacular degeneration. Ophthalmology 1989; 96: 104–8.

30. Agrawal KK, Sharma DP, Bhargava G, Sanadhya DK.Scleral rigidity in glaucoma, before and during topicalantiglaucoma drug therapy. Indian J Ophthalmol 1991;39: 85–6.

448 Grammenandi et al.


differences between goldmann applanation tonometry and dynamic contour tonometry in...

Documents