I}RIG IIIAL ARTICLE

Comparing Dynamic Contour Tonometry to Goldmann and Hand-Held Tonometry in Normal, Ocular Hypertension, and Glaucoma Populations

KENNETH D. EICHENBALiM, MSE, MIHALY MEZEJ, PhD, JOSEPH W, EICHENBAUM, MD, MPH

ABSTRACT

We prospectively compared dynamic contour tonometry (DCT) to Goldmann (GA[) and hand-held tonometry (HHT) m norlnal, ocular hypertenbion, and glaucoma populations. Both measurements were rnade on each patient within a 5-mi mite period during routine office exams over 4 rnonths.

While DCT is in good overall agreement with GAT and HHT, there is borne sy4ematic deviation at different pres- sure ranges in normal, ocular hypertension, and gJaucoma popuJatJons.

REPRINTS joseph Eichenbaunr, MD, MPH, 1050 Park Avenue, New York., NY, 10028. E mail: joseph. Eichenbaum@mssm.edu.

Kenneth D. Ekhenbaum, MSE, is from the Department ot Structural and Chemical Bioiozy, Mount Sinai School of Medidne. NewYork, NY. DI. Me,_-ei is an Associ- ate Professor in the Depaitment of Structural and Chemical Biology, Mount SinM School of Medic_Joe, New York. NY. Dr. joseph W. Ekhenbaum is o.n Associate Clinical Professor, Department of Ophthalmology, Mount Sinai School of Medi cine, New York, NY, and an Adjunct Assistant Professor of Pharmacology, New York University School or Medicine, NewYork, NY.

DiSCLosurE The authors have stated that they do not have a significant financial interest or other relationship with any product rnanuiacturei or provider of sere'ices discussed in this article. The authors also do not discuss the use of off [abe-[ products, which includes unlabeled, unapproved, or mve4i~ative product.- ol device~.

SubmH~ed for publica~on: I 1/1 ~..'o6. Accepted: ~q ,'os/u/.

Annals of Ophthalmology, voL 39, no. 1, Spring ~'oo/ O CopyriRht 2007 by ASC~ All rights of aI V nature whatsoever r eser,,'ed. 1 530-40~6/07/39:41 -{9/$3o.00, ISSN 1 558-9951 (Online)

INTRODUCTION Measurement of intraocular pressure (IOP) is one of the

basic diagnostic tools in glaucoma diagnosis. In prior studies ( t -4 ) , dynamic contour tonometry !DCT/ has been well co r r e l a t ed with G o l d m a n n app lana t ion tonometry (GAT/. However, l~ge clinical settings often employ hand-held tonometry (HHTI. Because of the prevalent HHT usage, we investigated whether there is a significant difference in HHT vs GAT vs DCT mea- surements in a larger office population. Tonometr ic readings were taken in general popula t ion , ocular hypertension (OHT/, and patients with glaucoma in the same sitting.

Factors related to contact tonometry may be altered by corneal thickness~ mire thickness, observer variability, and repeat tonometry x~ariability (G9). DCT, however, did differ slighdy f'rom GAT (mean difference of 1.7 and 1.8 mmHg, respecti~'elyi in two recent studies, which took corneal thickness into consideration (i~). DCT, which measures the diastolic pressure, would not

be affected by mire thickness, but still required trans- ducer contour to tear meniscus to initiate measurement. To date, there ha~e been no studies comparing normal, OHT, and glaucoma populations using HE[T, GAT, and DCT. To quan t i t a t ive ly assess how much con tac t tonometry measurements vary from contour tonometry in normal , OHT, and g l a u c o m a p o p u l a t i o n s , we

ANN O P H T H A I M O [ . 2u07:3o I l l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

prospectively measured both eyes of each patient using HI-IT, GAT, and DCT in the same sitting in 267 oph-

thalmic office patients o~,er a 4-month interval.

MATERIAILS A N D M E T H O D S After obtaining informed consent from each patient, a

cohort of 79/267 patients with OHT, 42/2.67 patients

with open-angle glaucoma, and 146/267 patients from a general ophthahnic urban population, underwent oph-

thalmic exam (medical history, visual acuity, refraction,

keratometry, motility, biomicroscopy, direct and indirect

ophthalmoscopy, and when necessary, visual fieldsi. No

patients in the coho~c had undergone tel?active surgery, had ocular surgery within the last 6 months, had corneal

edema or scars, or active uveitis.

Patients were considered to have OHT if they had

three or more prior visits with ocular pressures above 21

mmHg, cup:disc ratios of 0.3~).5 without any signs of

central cup pallor, thinning of the optic nerve rim, disc

hemorrhage, nerve fiber layer defects or peripapillary

atrophy, and normal Humphrey 30-2 visual fields on

two occasions or more. Patients were considered to have glaucoma if they had

three or more visits with ocular pressures above 21

mmHg, cup:disc ratios above 0.5 with signs of glauco-

matous optic nerve damage, tincreased number of bare

lamina cribrosa, vessel down sloping, central pallor or

disc rim reduction, or disc hemorrhage I, and three or

more Humphrey 3(I 2 visual fields with arcuate scotoma

or encroaching on central visual field loss.

Patients were considered in the general ophthalmic population if they had no history of OHT, glaucoma,

uvei t is , ret inal vascular lesions, ocular infec t ions ,

corneal disease, recent ocular surgery, or cervical ,

thoracic, or sacral limitations precluding chair measure-

ments of IOR These general ophthalmic populat ion

pat ients were usual ly coming for ref rac t ion update

needs. All measurements were taken by the same examiner

in the following order: HHT, GNK and DCT. The exam-

iner had prac t iced DCT on several co-workers not

included in the study until quality 1 and 2 tracings were

readily obtained on DCT primouts. In cases where HI-IT

or GAT outcomes were in doubt because of mires, tear

ievel, or dye distribution, borderline elevated astigma- tism (>2.5 diopters ?, or strabismus with vertical or hori-

zontal deviation, another drop of tetracaine 0.5% and

floroscein strip were re-applied and the measurement

was repeated. If the repeat reading was d e a r it was

A N N O P H T H A I M O L 2 0 0 7 ; 3 9 ( l ) ...................................................... 4 2

utilized in the data. If it was still unclear as to the end point, then the patient was excluded from the study.

HHT measurements were performed using the Kowa HA-2 hand held applanaLion tonometer (Kowa, Japan I, calibrated previously according Lo the manufacturer 's guidelines. For GAT, a slit lamp (Carl Zeiss, Germanyi with a G o l d m a n n t o n o m e t e r was used, ca l ib ra ted according to the manufacturer 's guidelines. Dynamic

contour tonography was performed using a slit lamp mounted Pascal Dynamic Contour Tonometer (Swiss Microtechnology AG, Port Switzerland l self calibrating; DCT-Pascal is a new method of IOP measuremet~t using contour matching of the cornea t10), digital tracings from the liquid crystal display of the diastolic impulse amplitude were made on each patient. The quality of the DCT data, scaled from 1 to 5, is recorded on a digital display along with a digital pressure measurement. Only

data with quality 1 3 tracings were used; all quality 3 readings were repeated; an a~'erage was taken of Lwo quality 3 tracing patients if they were different. DCT recording time was at least 10 seconds.

During the course of the exam each patient underwent HHT, G~KI", and DCT, in sequeuce within 3 to 5 minutes~ after one to two drops of 0.5% tetracaine. DCT was always performed subsequent to HI,IT and GAT, reduc- ing measurement bias of the electronic data presentation

on the HHT and GAT. Because the focus of this study was to compare HHT,

GAT, and DCT--and as was mentioned abo~,e, two prior studies (1,2) and a more recent study ( t l ) showed no cor re la t ion be tween D CT and corneal th ickness-- - pachymetry was not included in this study.

Statistical Analysis Statistical analysis was performed using SPSS (Statis- tical Software, Chicago, ILl and Microsoft Excel/Wash- ington, USAI. in the 267-patient population (Fig. 1/, the Kolmogorov-Srrlirnov test demonstrated a normal distri-

bution for HHT (p < (I.0011 and GAT (p < 0.001 I, but was not normal for the DCT meas~.~'ements (p < 0.221. Therefore, in this study, comparisons of standard devia- tions and associated normally distributed confidence intervals among the glaucoma, OHT, and general oph- thalmic population subgroups cannot be applied in DCT comparisons. Our alternate statistical methodology to deal with the non-normal DCT distributiou tin compar- ing DCT with H H T and GlgF, respec t ive ly t was to

randomly partition out" patient population (~ = 2671 into five subgroups. Each subgroup (that compared DCT with HHT and GA~I", respectively i was regressed against the 45 ~ line (line of random difference; see Fig. 21. The slope

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of all five subgroup regressions was less than the 45 ~ line. Thus, there is a greater than 96.8% probability (P =

1-(1/2i 5 > 96.8%1 that this did not occur randomly. Pearson correlation coefficients and Bland-Airman

analyses !12) were computed. To represent the amount of disagreement between two different measurement techniques, which are not apparent from r-~,alue coeffi- cient, Bland-Airman plots were generated for both HHT vs DCT and GAT vs DCT. ~lhe difference in pressure of e~'ery pair of measurements was plotted as a function of their mean. This represents ~he closest approximation to the real IOP (t2).

In the global population distribution comparing HHT, GKF, and DCT in the 267-patient group, ju~[ the right eye of each patient was randomly selected and tallied in all statistical computations. To iden[ify the mean differ- ence be[ween HHT and DCT, GAT and DCT, and HHT and GAT in OHT/glaucoma, and general populat ion groups, Bland-Airman plots were used to qualtitatively assess the arnount of disagreement between two groups.

RESULTS

Patientb with OH'I, glaucoma, refi'actix, e errors of a New

York City ophthalmic practice In = 2671 were measured were measured with hand-held, Goldmann, and Pascal tonometry . The range of pressures is shown in the histogram in Fig. 1A. Fig. 1B-D i11ustrates the distribu- tion of HHT, GAT, and DCT pressures obtained in the general population, OHT, and glaucoma population.

Measurements showed a close correlation between both HHT and DCT, and GAT and DCT IOP readings (Fig. 2A,B/. Mean IOP readings were comparable for DCT rela[ive to HHT and GAT. Mean HHT and GAT were 17.4 rnrnHg and mean DCT was 17.3 rnrnHg.

Because the Kolrnogorov Smirnox, test was normal for the distribution of the HHT !standard deviation = 3.2/ and GAT Istanda'd deviation = 3.1i measurernent~, but was not normal for DCT (mean = 17.3 I, standard devia- t ions are not p r e sen t ed for DCT. The d i f ference~ between the rneasurernents on individual patient tono- metric pressures were analyzed according to Bland-

Airman plots. The B1and-Altman plots, shown in Figs. 3 and 4, illustrated a meat1 difference between DCT and HHT of (i. 1 mmftg in the general population (Fig. 3A,B, n = 1461 and a 0.06-mmHg difference in the glaucoma/ OHT population/Fig. 4A,B, ~ = 121 I. 'Fhe mean differ- ence b e t w e e n GAT and D C T was 0.1)7 m m H g in the general population (Fig. 4Al and 0.13 in the glau- coma/OHT population (Fig. 4B I.

The mean of these deviations turned out to be close to 0, indicating that in the overall population no bias was

found in either of the techniques compared. However, a compar i son of the regress ion l ines f rom the three rneasurernent~ H H T vs D C T and GAT w D C T

(Figs. 2A,B/----with the 45 '~ line (the line that would result in totally randomized differences between the two techniques comparedl indicated a clinically significant difference. Specifically, the regression line in each com- parative plot !Fig. 2A,Bi shows that DCT tends to be slightly higher than both HHT and GAT for readings less than 18 mmHg. However, for readings above 18 mmHg, DCT tends to be slight lower than both HHT and GAT. As discussed in "Methods" section, the deviation of the

regression lines from the 45 ~ line is statistically signifi- cant. Also, the underestimates and overestirnates indb cated by the r eg re s s ion l ines r e su l t ed in the near cancellaLion of the bias when the complete range of pres- sures was considered.

The Pearson cmrelation coefficient for HHT and DCT in the global population was r = I).59~ (Treatment of the DCT distribution is discussed in "Methods" section.) Similarly, the Pearson correlat ion coeff icient in the

global population for GAT and DCT had an r = 0.63. Despite the diverse general patient population, only five patients were exc luded f rom the study. Three had exotropia, which resulted in poor fixation and two had more than 3.(I diopters of astigmatism. The poor fixation prec luded high quali ty DCT readings and the high astigmatism resulted in uncertainty of mires for HI tT and GAT, but quality DCT.

In c o m p a r i n g H H T to GAT (Fig. 5/ , the mean difference between measurements was close co zero and the 95% confidence interval of the diffrrence between rneasurement~ was approx 2.5 rnmHg in the general population and slightly higher than 3.0 in the OHT/glau- coma population.

D I S C U S S I O N

.in this study involving OHT/glaucoma, and general population groups there was excellent overall agreement between HHT, GAT, and DCT. Unlike other studies !i~2), which did not include glaucoma, OHT, and general ophthalmic patients, this study showed correlation of HHT, GAT, and DCT measurements in three patient pop- ulations. Also, this study showed correlation between HHT, G:gf', and DCT, whereas the prior studies just compared GAT and DCT. Since HHT is a very corn- rnonly used measurement device in glaucoma screening settings, the cornparison of HI-IT to GAT and DCT is currently quite clinically relevant. HHT and GAT (Fig. 5 t were usually within 3 mmHg of each other in the gen- eral population and the OHT/glaucorna population.

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In reviewing the data of the general population and the OHT/glaucoma population, we concur with the prior observation (1,2) that DCT tends to slightly over-read relative to HHT and GAT. However, this overreading

tendency may be limited to a certain pressure range. The slopes of the regression lines in Fig. 2A,B were consis-

tent ly below the 45 ~ line (~lope = 11, which would reflect completely random difference~ between two tech- niques, i[herefore, we indicate in Fig. 2A,B the areas of under-reading and over-reading of DCT relative to HIIT and GAT above and below 18, respectively.

This popu la t ion consis ts of 121 g l a u c o m a / O H T

patients. This probably produced a cohort of slightly higher-pressure readingb. Pressure readings above 18 rnrr~-Ig tbr HHT and GAT, respectively, reflect tendency

to under read the DCT relative to HHT and GAT. From the statisfical standpoint, the question is if the deviation between the random line and the regression line slope is sybtematic or not. To answer this question, we randomly partitioned the patients into five subgroups, each from the general population and the glaucoma/OIlT popula- tions and calculated the regression for each subgroup.

Each subgroup yielded a regression slope of tess than 1.0 (~o be specific, 0.42, 0.42, 0.39, 0.55, and 0.83 for HI-IT vs. DCT; ea~d 0.40, 0.43, I)~48, 0.79, and I)~70 for GAT vs DCTI~ The p r o b a b i l i t y of this o c c u r r i n g

randomly is (1/215=1/32 = 0.0313. ~Ihus, we can con- clude with 96.8% confidence that at higher pressures the DCT vs I-[HT/GAT has a slight tendency to under read.

This stud> similar to Barleon et al. (ItL found that DCT IOP is higher than GAT (and I l i lT! in rower IOPs, but lower than GAT Iand HItTI in higher IOPs~

Although DCT was carried out after HHT and GAT,

thereby reducing the role of electronic measurement bias on I l i lT and G2~K it is possible that IIHT prior to GAT could have ~ome element of bias in GAT measurement in this ~ingle-e• study. However , instrument

calibration of the Kowa hand held tonometer and the Goldmann tonometer was in accord with manufacturer's guidelines. Where keratometry, ectasia, strabismus,

nys tagmus or physica l l imitat ions such as extreme obesity or cervical arthropathy were significant mitigating

elements to HHT or GAT, 10 patients were excluded from the study.

Because all of the patients included in this study were not new to the practice, there was no difficulty with acceptance of HHT, GAT, as well as the introduction of DCT. In fact, following a quality 3 DCT tracing, which

would prompt the examiner to request another DCT measurement, patients would readily comply with repeat DCT measure menu

In the clinical setting, with normal, OHT, and patier, ts with glaucoma, the quality and quantity of the DCT reading was a reliable measurement of IOP compared to hand held and Goldmann tonometric measurements.

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2. Schneider E. Grehn F. lntraocular pressure measurement-compari- son of dynamic contour tonometry and goldmann applanation tonometlTr J Glaucoma 2006.15:2 6.

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8. Sude~h S. Moseley MJ. Thompson JR. Accuracy of goldmann tonometry in cliuical practice. Acta Ophthalrnol tCopenh) 1993'71:185-18g.

9. Stodtm~ister R, If IOP measurement is onl~ am ~stimate. then what? OpNhalmolog5 2001:108:1364 1366.

10. Kanugiesser }II5,~ Kniestedt C. Robert YC, Dynarr, iv contour tonoru etry: Presentation of a new tonometer. J Glaucoma 2005"14: 344 350.

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[2. Bland JM, .&[tman D~J, Statistical rr*eihods for assessing agreement between bx, o mettmds of clinical measur,~ment. Lancet 1986: 1:307 310r

A N N O P I t T H A [ M O [ . 2007:3o (1) ...................................................... 49