Purpose: The aim of this study was to assess the influence of the
position (upright vs. supine) in the intraocular pressure (IOP)
measured with a non-contact portable tonometer.
Methods: Fifty university students with a mean age of 22.3±4.2
years (mean±SD) were recruited to participate in this study. IOP
was measured with the non-contact tonometer Keeler, Pulsair
EasyEye. Measurements in upright and supine positions were
randomly obtained. In the upright position, 2 series of 3 measures
(UP1 and UP2) and a series of 3 measures in the supine position
were performed.
Results: The values obtained in the positions UP1 and UP2 were
compared, as well as the values of the upright and supine positions.
No statistically significant differences were found when comparing
the values obtained in the upright position (P>0.05). Instead,
when the subjects were in the supine position, IOP increased
2.47±2.12mm Hg (mean±SD), as opposed to the value obtained
in the upright position (P<0.001).
Conclusions: Results from this study showed that IOP increased
when measured in the supine position and that the Pulsair EasyEye
tonometer can determine those variations in a healthy young
population

González-Méijome, José Manuel

Jorge, Jorge

Lourenço, Adelaide

Marques, Rui Ramoa

Nascimento, Sérgio M. C.

Queirós, A.

Silva, Sandra

Journal of Glaucoma

Universidade do Minho: RepositoriUM

IOP Variations in the Sitting and Supine PositionsJorge Jorge, PhD, Rui Ramoa-Marques, OD, Adelaide Lourenc¸o, OD, Sandra Silva, OD,Se´rgio Nascimento, PhD, Anto´nio Queiro´s, OD, and Jose´ M. Gonzalez-Me´ijome, PhDPurpose: The aim of this study was to assess the inﬂuence of theposition (upright vs. supine) in the intraocular pressure (IOP)measured with a non-contact portable tonometer.Methods: Fifty university students with a mean age of 22.3±4.2years (mean±SD) were recruited to participate in this study. IOPwas measured with the non-contact tonometer Keeler, PulsairEasyEye. Measurements in upright and supine positions wererandomly obtained. In the upright position, 2 series of 3 measures(UP1 and UP2) and a series of 3 measures in the supine positionwere performed.Results: The values obtained in the positions UP1 and UP2 werecompared, as well as the values of the upright and supine positions.No statistically signiﬁcant diﬀerences were found when comparingthe values obtained in the upright position (P>0.05). Instead,when the subjects were in the supine position, IOP increased2.47±2.12mmHg (mean±SD), as opposed to the value obtainedin the upright position (P<0.001).Conclusions: Results from this study showed that IOP increasedwhen measured in the supine position and that the Pulsair EasyEyetonometer can determine those variations in a healthy youngpopulation.Key Words: intraocular pressure, Pulsair EasyEye, supine position,upright position, non-contact tonometry(J Glaucoma 2010;19:609–612)Intraocular pressure (IOP) is essential to maintain the eyestructure and physiology. In several conditions, IOP mayrapidly change. Numerous studies in the last decades haveshown that IOP in humans undergoes circadian variations,with higher peaks in the morning and lower ones in theafternoon and evening.1–3It is also well known that IOP varies with the bodyposition. IOPs have been reported to be higher when thepatient’s body is in the supine position (SUP) than in theupright position (UP).4,5 In the UP, the eye is approxi-mately 30 cm higher than the heart; however, when thepatient is in the SUP, the eye and the heart are at the samelevel. This diﬀerence in height is thought to aﬀect theepiscleral venous pressure.6–9 The increase of resistance inthe aqueous out-ﬂow is probably the cause for the IOPincrease in the SUP.10The IOP measurement in the SUP is importantin several situations, such as the establishment of a realcircadian curve. Patients with glaucoma, who during theSUP (one-third of their life) experience a considerableincrease of IOP, may notice a worsening of their ocularcondition because of the higher risk of neural damage.11Another situation of interest is related to bedridden peopleas they are temporarily or permanently conﬁned to a SUP.In practice, these patients do not have their eyes regularlychecked, and the position-related increase in IOP mightincrease the risk of ocular damage.12 The problem herearises from the diﬃculties in measuring IOP with certaininstruments that require a seated position. Portable non-contact tonometer (NCT) can overcome these diﬃcultieseven in the hand of nonmedical staﬀ, thus increasing theprobability for those patients to be screened regularly.Another aspect, not frequently mentioned by opto-metrists and ophthalmologists, is related to the signiﬁcantvariation of IOP during surgical procedures when thepatient is under anesthetic, whether he is in the SUP or inthe prone position.13,14The purpose of this article is to quantify the IOPvariation between the UP and SUP within a population ofyoung adults using a portable NCT.METHODSFifty eyes from an equal number of university students(11 male and 39 female), with ages ranging from 18 to 34years (22.3±4.2 y; mean±SD), were recruited for thisstudy. All subjects were free of ocular disease, had nocomplaints regarding excessive lachrymation, were nottaking any medication, and had good health. The studyprotocol was reviewed by the Scientiﬁc Committee of theFaculty of Science at the University of Minho (Portugal).After all procedures were explained, the subjects signed aninformed consent form before being enrolled in the study.An experienced optometrist evaluated IOP with theair-puﬀ tonometer Pulsair EasyEye (Keeler Instruments,Inc, Broomall, PA.) In each eye, 2 series of 3 measurementsin the UP were performed (UP1 and UP2) and 1 series of3 measures in the SUP. Three diﬀerent orders of measure-ments were established (UP1-UP2-SUP or UP1-SUP-UP2or SUP-UP1-UP2) and they were carried out in a randomorder. The measurements were performed after the subjectwas in the position to be measured (UP or SUP) for 15minutes. All measurements were taken between 14:00 and16:00 hours to minimize the eﬀect of diurnal variationsin IOP.The values obtained in the position UP1 and UP2were compared, to analyze the repeatability of the PulsairEasyEye tonometer. To obtain the variation betweenthe UP and SUP, the values obtained in the SUP wereCopyright r 2010 by Lippincott Williams & WilkinsDOI:10.1097/IJG.0b013e3181ca7ca5Received for publication April 20, 2009; accepted November 10, 2009.From the Clinical and Experimental Optometry Research Lab,Department of Physics (Optometry), School of Sciences, Universityof Minho, Braga, Portugal.Reprints: Jorge Jorge, PhD, Departamento de Fı´sica, Universidade doMinho, Campus de Gualtar, 4710 Braga, Portugal (e-mail: jorge@ﬁsica.uminho.pt).ORIGINAL STUDYJ Glaucoma  Volume 19, Number 9, December 2010 www.glaucomajournal.com | 609compared with the average of the 2 measurements seriesobtained in the UP [UPm=(UP1+UP2)/2].In this study, data were analyzed using the statisticalpackage SPSS v.17.0. The bias was statistically assessedas the mean of the diﬀerences compared with zero. Thehypothesis of zero bias was examined by the nonparametricWilcoxon signed ranks test. The 95% limits of agreement(mean of the diﬀerence±1.96 SD of the diﬀerences) werealso calculated, as recommended by Bland and Altman.15,16This analysis allows the detection of any trend in thediﬀerence variability as a function of the mean value to bemeasured.RESULTSWe collected data from both eyes and found resultsbetween right and left eyes to be highly correlated.Therefore, we opted to report data from left eyes only inthis report.Table 1 displays the mean and SD of IOP measure-ments in both positions. The mean diﬀerence and the levelof statistical signiﬁcance are also present, as well as thelimits of agreement between each pair of measuredsituations (UP vs. UP2 and UPm vs. SUP) to be comparedat the 95% conﬁdence interval.These values reﬂect a signiﬁcant increase of the IOPvalue in the SUP. The diﬀerence obtained in the 2 series ofmeasurements performed with the subjects in the UP was assmall as 0.50mm Hg, not being statistically signiﬁcant(P=0.082). In contrast, the mean diﬀerence of measure-ments obtained in the UP and SUPs was of 2.47mm Hghigher in the SUP, being statistically signiﬁcant (P<0.001).Figure 1 displays the sets of diﬀerences as an averagefunction to graphically illustrate the agreement betweenmeasurements obtained in both positions (UP and SUP). InFigure 1B, the graphic points out that, when IOP increases,the diﬀerence in the values obtained in the SUP alsoincrease.Figure 2 presents the percentage of subjects with meandiﬀerences between the 2 positions of r1mm Hg (r1),between 1 and 2mm Hg (>1 and r2), between 2 and3mm Hg (>2 and r3), and >3mm Hg. In 50% of thesubjects, the diﬀerence between the 2 series of measure-ments in the UP (UP1 vs. UP2) wasr1mm Hg and in 92%of the subjects, the diﬀerence was r3mm Hg.When comparing the results obtained in the UP andSUPs (UPm vs. SUP), it is remarkable that only 20% of thesubjects present a diﬀerence ofr1mm Hg, whereas in 36%of the subjects the diﬀerence is higher than 3mm Hg.DISCUSSIONThere are few tonometers capable of measuring IOP inthe SUP or in the prone position. The Model 30 pneumo-tonometer, the digital tonometer TGDc-01, the PulsairEasyEye, the Perkins, and the hand-held Schiotz tonometersare able to obtain IOP values in other positions besides theupright one.TABLE 1. The Mean Values and the SD, the Maximum and Minimum, the Mean Difference, the Level of Statistical Significance, and theLimits of Agreement Between Each Pair of Measured Situations (UP1 vs. UP2 and UPm vs. SUP)Limits of AgreementN=50 Mean±SD Minimum; Maximum Mean Diﬀerence P Mean 1.96SD Mean+1.96SDUP 1 12.0±2.55 8.0; 20.0 0.5±1.99 0.082  3.40 4.40UP 2 11.5±2.78 7.0; 17.0UPm 11.8±2.47 7.5; 18.0  2.47±2.12 <0.001  6.63 1.69SUP 14.2±3.25 8.0; 24.0Wilcoxon Signed Ranks Test.SUP indicates supine; UP, upright; UPm, upright mean.FIGURE 1. Sets of differences as an average function obtainedin both positions: (A) upright position; (B) upright and supineposition.Jorge et al J Glaucoma  Volume 19, Number 9, December 2010610 | www.glaucomajournal.com r 2010 Lippincott Williams & WilkinsThe Pulsair EasyEye is a portable air-puﬀ tonometerthat determines IOP in multiple positions and has provedto be reliable in the UP.17 Ogbuehi and Almubrad18claimed that Pulsair EasyEye NCT is a useful method formonitoring IOP in the normotensive range, being a suitablealternative to the Goldmann applanation tonometer (GAT)for screening purposes, particularly in patients on whom itwould be diﬃcult or impossible to conduct a GAT. In theirstudy, Babalola et al19 stated that, based on their ﬁndings,there was no signiﬁcant diﬀerence in the mean IOP, asmeasured by GAT and NCT using the Keeler PulsairEasyEye tonometer. However, in this literature, there areno results to conﬁrm the repeatability of the Keeler PulsairEasyEye tonometer when the air-puﬀ is delivered indiﬀerent positions. This results conﬁrm earlier publishedones and the Pulsair EasyEye tonometer presents a goodrepeatability in the UP.Concerning the variations between the UP and theSUPs, there was a statistically signiﬁcant increase in theIOP values of 2.47±2.12mm Hg. Other publications havealso reported this trend for tonometers with a diﬀerentfunctioning principle. In 2006, Wozniak et al20 publishedthe results of a research which used the Perkins contacttonometer in both healthy subjects and with primary open-angle glaucoma patients. They concluded that the IOPmeasurement was higher in the SUP than in the UP andthat there were no statistically signiﬁcant diﬀerences in IOPchanges between groups during diurnal IOP measurementsin an UP. Conversely, in the SUP, IOP was signiﬁcantlyhigher than in the UP, and increased more in the glaucomapatients than in healthy controls. The authors concludedthat such observation might be because of a faultyregulation of the ﬂuid shift in glaucoma patients and couldcause the progression of glaucomatous damage.In a article published in 2005, Garcia-Resua et al21also veriﬁed an increase in the IOP values, when themeasurements were obtained in the SUP, by comparisonto the UP using a TGDc-01 tonometer. The obtaineddiﬀerence was of 0.42mm Hg with a larger SD when themeasurements were obtained in the SUP (4.19 and 4.06mmHg in the SUP and UP, respectively). However, earlierreports identify several potential sources of error in thisinstrument and this could justify such results.22–24 Thiscould explain the low diﬀerence obtained between the 2positions, when compared with our results and results fromother studies using more reliable tonometers.Several studies have been developed concerningthe IOP variation during 24 hours in normal popula-tions,4,5,25–27 in glaucomatous patients28 and with diﬀerentages.29 Although presenting a variation of the IOP meanvalues, those studies introduced a trend for IOP to increasein the SUP period during sleep. Nevertheless, the mainconcern is not the time usually spent in the SUP or proneposition during the sleeping period. The causes for the IOPincrease in the prone or SUP are still subject for discussion.Nevertheless, earlier studies have found that the IOPvariation from postural change is because of an obstructionof the aqueous outﬂow provoked by an increase in theepiscleral venous pressure.10This issue might be much more important in peoplepermanently bedridden, as well as those submitted to longsurgical interventions and recovery times. For those people,there might be a higher risk of suﬀering ocular damagerelated to an IOP increase.14,30In summary, results from this study have shown thatIOP increases in the SUP, and that the Pulsar EasyEyetonometer is sensitive to those variations.ACKNOWLEDGMENTSThe authors thank the work of Filomena Louro andAdriana Mesquita from the Scientiﬁc Editing Programme ofUniversidade do Minho for revising this article.REFERENCES1. Hara T, Hara T, Tsuru T. Increase of peak intraocularpressure during sleep in reproduced diurnal changes byposture. Arch Ophthalmol. 2006;124:165–168.2. Syam PP, Mavrikakis I, Liu C. Importance of early morningintraocular pressure recording for measurement of diurnalvariation of intraocular pressure. Br J Ophthalmol. 2005;89:926–927.3. Wilensky JT. Diurnal variations in intraocular pressure. TransAm Ophthalmol Soc. 1991;89:757–790.4. Ozcan MS, Praetel C, Bhatti MT, et al. The eﬀect of bodyinclination during prone positioning on intraocular pressure inawake volunteers: a comparison of two operating tables.Anesth Analg. 2004;99:1152–1158; table.FIGURE 2. Frequency distribution of differences between bothpositions for: (A) upright position and (B) upright and supineposition.J Glaucoma  Volume 19, Number 9, December 2010 IOP Variations in Sitting and Supine Positionsr 2010 Lippincott Williams & Wilkins www.glaucomajournal.com | 6115. Perlman JI, Delany CM, Sothern RB, et al. Relationshipsbetween 24 hours observations in intraocular pressure versusblood pressure, heart rate, nitric oxide and age in the medicalchronobiology aging project. Clin Ter. 2007;158:31–47.6. Blondeau P, Tetrault JP, Papamarkakis C. Diurnal variationof episcleral venous pressure in healthy patients: a pilot study.J Glaucoma. 2001;10:18–24.7. Buchanan RA, Williams TD. Intraocular pressure, ocularpulse pressure, and body position. Am J Optom Physiol Opt.1985;62:59–62.8. Longo A, Geiser MH, Riva CE. Posture changes and subfovealchoroidal blood ﬂow. Invest Ophthalmol Vis Sci. 2004;45:546–551.9. Singleton CD, Robertson D, Byrne DW, et al. Eﬀect of postureon blood and intraocular pressures in multiple system atrophy,pure autonomic failure, and baroreﬂex failure. Circulation.2003;108:2349–2354.10. Lam AK, Douthwaite WA. Does the change of anteriorchamber depth or/and episcleral venous pressure causeintraocular pressure change in postural variation?. Optom VisSci. 1997;74:664–667.11. Kiuchi T, Motoyama Y, Oshika T. Postural response ofintraocular pressure and visual ﬁeld damage in patientswith untreated normal-tension glaucoma. J Glaucoma. 2009.Doi:10.1097/IJG.0b013e3181a98f30.12. Spapen HD, D’Haese J, Diltoer M, et al. Bedside evaluationof intraocular pressure in critically ill patients, ventilatedat diﬀerent levels of positive end-expiratory pressure. ActaAnaesthesiol Belg. 1993;44:39–43.13. Cheng MA, Todorov A, Tempelhoﬀ R, et al. The eﬀect ofprone positioning on intraocular pressure in anesthetizedpatients. Anesthesiology. 2001;95:1351–1355.14. Hunt K, Bajekal R, Calder I, et al. Changes in intraocularpressure in anesthetized prone patients. J Neurosurg Anesthe-siol. 2004;16:287–290.15. Bland JM, Altman DG. Statistical methods for assessingagreement between two methods of clinical measurement.Lancet. 1986;1:307–310.16. Bland JM, Altman DG. Comparing methods of measurement:why plotting diﬀerence against standard method is misleading.Lancet. 1995;346:1085–1087.17. Kumar S, Middlemiss C, Bulsara M, et al. Telemedicine-friendly,portable tonometers: an evaluation for intraocular pressurescreening. Clin Experiment Ophthalmol. 2006;34:666–670.18. Ogbuehi KC, Almubrad TM. Accuracy and reliability of theKeeler Pulsair EasyEye non-contact tonometer. Optom Vis Sci.2008;85:61–66.19. Babalola OE, Kehinde AV, Iloegbunam AC, et al. Acomparison of the Goldmann applanation and non-contact(Keeler Pulsair EasyEye) tonometers and the eﬀect of centralcorneal thickness in indigenous African eyes. OphthalmicPhysiol Opt. 2009;29:182–188.20. Wozniak K, Koller AU, Sporl E, et al. Intraocular pressuremeasurement during the day and night for glaucoma patientsand normal controls using Goldmann and Perkins applanationtonometry. Ophthalmologe. 2006;103:1027–1031.21. Garcia RC, Giraldez Fernandez MJ, Cervino EA, et al.Clinical evaluation of the new TGDc-01 ‘‘PRA’’ palpebraltonometer: comparison with contact and non-contact tono-metry. Optom Vis Sci. 2005;82:143–150.22. Losch A, Scheuerle A, Rupp V, et al. Transpalpebralmeasurement of intraocular pressure using the TGDc-01tonometer versus standard Goldmann applanation tonometry.Graefes Arch Clin Exp Ophthalmol. 2005;243:313–316.23. Lam AK, Lam CH, Chan R. The validity of a digital eyelidtonometer (TGDc-01) and its comparison with Goldmannapplanation tonometry-a pilot study. Ophthalmic Physiol Opt.2005;25:205–210.24. Ruokonen PC, Schwenteck T, Draeger J. Evaluation of theimpedance tonometers TGDc-01 and iCare according to theinternational ocular tonometer standards ISO 8612. GraefesArch Clin Exp Ophthalmol. 2007;245:1259–1265.25. Barkana Y, Anis S, Liebmann J, et al. Clinical utilityof intraocular pressure monitoring outside of normal oﬃcehours in patients with glaucoma. Arch Ophthalmol. 2006;124:793–797.26. Liu JH, Kripke DF, Hoﬀman RE, et al. Elevation of humanintraocular pressure at night under moderate illumination.Invest Ophthalmol Vis Sci. 1999;40:2439–2442.27. Liu JH, Bouligny RP, Kripke DF, et al. Nocturnal elevation ofintraocular pressure is detectable in the sitting position. InvestOphthalmol Vis Sci. 2003;44:4439–4442.28. Liu JH, Kripke DF, Weinreb RN. Comparison of thenocturnal eﬀects of once-daily timolol and latanoprost onintraocular pressure. Am J Ophthalmol. 2004;138:389–395.29. Liu JH, Kripke DF, Twa MD, et al. Twenty-four-hour patternof intraocular pressure in the aging population. InvestOphthalmol Vis Sci. 1999;40:2912–2917.30. Walick KS, Kragh JE Jr, Ward JA, et al. Changes inintraocular pressure due to surgical positioning: studyingpotential risk for postoperative vision loss. Spine. 2007;32:2591–2595.Jorge et al J Glaucoma  Volume 19, Number 9, December 2010612 | www.glaucomajournal.com r 2010 Lippincott Williams & Wilkins

IOP variations in the sitting and supine positions

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IOP variations in the sitting and supine positions

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