Clinical and Experimental Vision and Eye Research

Show Contents

Analysis of ocular pulse amplitude values in differentpregnancy stages as measured by dynamic contour tonometry
  CLEVER
ORIGINAL ARTICLE
Analysis of ocular pulse amplitude values in different
pregnancy stages as measured by dynamic contour tonometry
Luciana Arias Fernandez1, Aline Katia Siqueira Sousa1, Larissa Marimoto Doi1, Syril Dorairaj2,
Carlos Alexandre Garcia Filho1, Augusto Paranhos1, Tiago Santos Prata1,2,3

1Glaucoma Unit, Department of Ophthalmology, Federal University of Sao Paulo, Sao Paulo, Brazil
2Glaucoma Unit, Department of Ophthalmology, Mayo Clinic, Jacksonville, FL, USA
3Glaucoma Unit, Department of Ophthalmology, Hospital Oftalmologico de Sorocaba| BOS, Sorocaba, Brazil
Address for correspondence: Syril Dorairaj, Mayo Clinic, 4500 San PabloRoad, Jacksonville, Florida, 32224.
Tel.: 904-953-2377. Fax.: 904-953-7040.
E-mail: dorairaj.syril@mayo.edu
Received: 03-03-2018;
Accepted: 19-03-2018
doi: 10.15713/ins.clever.4
 
ABSTRACT
Background: Orbital circulation is influenced by systemic hormonal status. Ocular pulseamplitude (OPA) is a surrogate measurement of choroidal blood flow. We investigatedthe OPA profile during different stages of pregnancy.
Design: Cross-sectional study.
Participants: We enrolled 24 pregnant and 25 non-pregnant women (age-matchedcontrols).
Methods: Data collected included age, pregnancy period, intraocular pressure (IOP),and central corneal thickness (CCT). Pascal dynamic contour tonometry was used tomeasure OPA values. The mean of three good quality measurements was used for theanalysis. Whenever both eyes were eligible, the right eye was arbitrarily selected.
Main Outcome Measures: Differences in OPA values between pregnant women (ateach trimester) and non-pregnant controls.
Results: Mean age and CCT were similar between pregnant women (27.8 ± 6 years, 547± 25 µm) and controls (28.9 ± 3.4 years, 546 ± 28 µm; P > 0.25). Pregnant women (meangestation period, 20.4 ± 9 weeks) had a lower mean IOP than controls (11.4 ± 2.4 vs. 13 ±2.1 mmHg; P = 0.02). Analysis of covariance (adjusting for IOP difference) revealed thatOPA values in women in the 1st (3 ± 0.6 mmHg) and 2nd trimesters (2.5 ± 0.7 mmHg)of pregnancy were increased compared to those in the last trimester (1.8 ± 0.6 mmHg)and controls (2.1 ± 0.7; P < 0.05). Multivariate analysis showed that gestation period wasthe only variable associated with OPA values during pregnancy (r2 = 0.30, P < 0.01). Age,CCT, and IOP were not statistically significant in this model (P > 0.5).
Conclusions: Our results suggest that OPA values are increased in the first twotrimesters of pregnancy, returning to normal in the last 3 months. These changes in OPAvalues seem not be influenced by age, CCT, or IOP.
Keywords: Dynamic contour tonometry, ocular pulse amplitude, pregnancy
How to cite this article: Fernandez LA, Sousa AKS, Doi LM,Dorairaj S, Filho CAG, Paranhos A, Prata TS. Analysis ofocular pulse amplitude values in different pregnancy stages asmeasured by dynamic contour tonometry. Cli Exp Vis Eye ResJ 2018;1(1):14-17.
 
 

Introduction

Pascal dynamic contour tonometry (DCT) is a relatively newtechnology that claims to measure intraocular pressure (IOP)independently of corneal properties.[1] The DCT uses a contacttonometer tip with a convex contour radius of 10.5 mm, whichis theoretically similar in contour to the cornea, to take up theshape of the cornea and not to deform it. Thus, the resultingIOP measurement is less affected by the thickness of the cornea.

 
A more detailed description of the DCT has been previouslypublished elsewhere.[2] Besides measuring IOP, the DCTalso provides a reading of ocular pulse amplitude (OPA). It iscalculated as the difference between the minimum (diastolic) andmaximum (systolic) values of pulsatile IOP within the eye. OPAhas been suggested as an indicator of choroidal perfusion.[3,4]

Several changes in both systemic and ocular parameters occurduring pregnancy. The most profound physiological changesoccur in the cardiovascular system. There is an increase in heartrate and a decrease in arterial blood pressure, which could beexplained by the reduced systemic vascular resistance observedin these pregnant women. Ocular changes in pregnancy arecommon, including an increase in corneal thickness, alterationin corneal topography, and a decreased IOP.[5,6]

14 Clinical and Experimental Vision and Eye Research, January-June, Vol 1, 2018

Ocular pulse amplitude and pregnancy Fernandez, et al.

To investigate the influence of pregnancy on the ocular bloodflow, we evaluated the OPA profile during different phases ofpregnancy and compared it to non-pregnant women.

Methods

This cross-sectional protocol adhered to the tenets of theDeclaration of Helsinki and was approved by the EthicsCommittee of The Federal University of Sao Paulo. In addition,written informed consent was obtained from all subjects.

Patients

Study patients were recruited from the Obstetrics andGynecology Clinic of the Federal University of Sao Paulo.A total of 24 healthy pregnant patients and 25 healthy, agematched,non-pregnant women were enrolled in the study.All participants underwent a complete ophthalmic evaluation,and those presenting with any significant ocular disease orprevious ocular surgery were excluded from the study. Exclusioncriteria included age < 18 years, Snellen best-corrected visualacuity ≤20/20, spherical equivalent ≥4.00 diopters, systemichypertension, diabetes, and any collagen disease or history ofsteroids use. Demographic data were obtained, including age,self-identified race, and pregnancy period.

Procedures

Initially, all patients underwent OPA measurement using theDCT (Swiss Microtechnology AG, Bern, Switzerland) afterresting for at least 10 min in sitting position. The Pascal DCT is aslit-lamp mounted digital device that uses single-use, disposablecaps. It provides adirect transcorneal measurement of IOPand detects OPA. The DCT measures diastolic IOP usingtheprinciple of contour matching with the built-in miniature SensorTipTM utilizing a solid-state pressure sensor. It displaystheaverage diastolic IOP recorded and the mean OPA through adigital liquid crystal display. Adding the DCT's IOP, readingto the OPA will give the systolic IOP. After a 15-min interval,Goldmann applanation tonometry and ultrasound pachymetrywere performed. The mean of three good quality measurementswas used for all tests. Minimum quality score for OPA readingswas set at ≥3. Whenever both eyes were eligible, the right eyewas arbitrarily selected. All tests were performed by the sameexaminer (AKSS).

 
Statistical analysis

Independent sample t-test and Chi-square test were used toevaluate differences between groups. Analysis of covariance(adjusting for differences in IOP) was performed to compareOPA values between patients in different trimesters of pregnancyand controls. Multiple regression analysis was used to investigatethe effect of age, central corneal thickness (CCT), IOP, andpregnancy period (in weeks) on OPA values. Computerizedanalysis was performed using MedCalc software (MedCalcInc., Mariakerke, Belgium), and statistical significance was set atP < 0.05.

Results

Baseline characteristics of study patients are given in Table 1.Mean age and CCT were similar between pregnant women(27.8 ± 6 years, 547 ± 25 µm) and controls (28.9 ± 3.4 years,546 ± 28 µm; P > 0.25). Pregnant women had a mean gestationperiod of 20.4 ± 9 weeks (range, 9-37 weeks).

As we found a significantly lower mean IOP in pregnantwomen than controls (11.4 ± 2.4 vs. 13 ± 2.1 mmHg; P = 0.02),we used analysis of covariance (adjusting for IOP difference) tocompare OPA values between patients in different trimesters ofpregnancy and controls. These analyses revealed that OPA valuesin women in the 1st (3 ± 0.6 mmHg) and 2nd trimester (2.5 ±0.7 mmHg) of pregnancy were significantly increased comparedto those in the last trimester (1.8 ± 0.6 mmHg) and controls (2.1± 0.7; P < 0.05). Finally, multiple regression analysis showedthat gestation period was the only variable associated with OPAvalues in these patients (r2 = 0.30, P < 0.01). Age, CCT, and IOPwere not significant in this model (P > 0.5).

Discussion

The OPA has been described as an indirect measurementof choroidal blood flow, which represents the major part ofthe ocular perfusion.[3] It has been suggested that pulsatileocular blood flow increases in pregnant women in comparisonwith those non-pregnant.[7] Comparing OPA values betweenpregnant patients in different gestation trimesters and controlsusing DCT, we not only found higher values in the former groupbut also a trend for OPA reduction toward the last trimester. Asfar as we know, this is the first study to evaluate the OPA profilealong the gestation period using this technology.

Table 1: Characteristics of pregnant patients and controls
Analysis of ocular pulse amplitude values in differentpregnancy stages as measured by dynamic contour tonometry
C: Caucasian, AD: African descent, M: Mixed, A: Asian, N/A: Non-applicable. Data are given as mean± standard deviation (95% confidence interval)whenever indicated. Independent sample t-test. §Chi-square test. CCT: Central corneal thickness, IOP: Intraocular pressure

Clinical and Experimental Vision and Eye Research, January-June, Vol 1, 2018 15

Fernandez, et al. Ocular pulse amplitude and pregnancy

In the present study, we found OPA values of approximately2 mmHg in healthy women, which is in agreement with previousreports using DCT in healthy controls.[8] When it comes to OPAmeasurements in pregnant participants, there are scant data inthe literature. However, looking at previous reports on ocularblood flow during pregnancy using other technologies, ourfindings seem to corroborate those previously published. Forinstance, Centofanti et al., using a pneumotonometer, found thatpulsatile ocular blood flow, measured in millimeters per minute,increased gradually during pregnancy until the second trimester.On the other hand, lower IOP values were documented in thisperiod. Even though the authors did not provide data on thethird trimester, our results regarding both OPA and IOP seemsimilar to their study.[9] Considering studies that included bloodflow measurements until the last trimester, Horven et al. foundan increase in the corneal indentation pulse amplitude duringthe first half of pregnancy, with values coming to about one-thirdof a non-pregnant woman at term.[10,11]

Some of the previously reported hemodynamic changes thattake place with pregnancy could explain, in part, our findingson OPA and IOP measurements in these patients. Duringgestation, estrogen and progesterone lead to hemodynamicchanges to facilitate venous return.[12] Both hormones elevatethe levels of renin-angiotensin-aldosterone system. Aroundthe 5th week of pregnancy begins a retention of sodium andan increase in blood volume, but not in the same level for allconstituents (blood cells and leukocytes), which results inhemodilution and, consequently, augmented cardiac frequencyand systolic volume.[13] Such changes could be responsible forthe higher OPA values observed in pregnant patients. Regardingthe lower IOP values during pregnancy, there seems to exist aresistance to angiotensin LL effect, added to an increased nitricoxide action,[14-16] causing peripheral vasodilatation. Moreover,prostacyclin promotes generalized vasodilatation,[13] resultingin lower blood pressure values, reaching its nadir in the secondtrimester, and returning to normality after delivery. Thosechanges in venous return have repercussions in the episcleralvenous pressure as well, which could contribute to IOPreduction.[17] Estrogen and progesterone also influence IOP bydecreasing the production of aqueous humor. Another hormone,relaxin, produced during pregnancy, regulates the collagenaseenzymes and promotes relaxation of collagen structures,including the trabecular meshwork, easing the aqueous humoroutflow venous return.[18]

We believe that it is important to stress some specificcharacteristics of the present study. First, it is limited inpart by its small sample size. Even though it was adequatelypowered to reveal significant differences, we believe a largersample would be desirable. Second, blood pressure was notinvestigated. However, a lack of correlation between OPA andblood pressure parameters in healthy controls has been shownin previous studies.[7,19] Finally, one should not extrapolate thesecross-sectional data to an evolving situation such as pregnancy.A prospective study is warranted.

 
In conclusion, our results add information on the ocularhemodynamics profile during pregnancy. It suggests thatOPA values are increased in the first two trimesters, returningto normal values in the last 3 months. These results give basisto a more detailed and longitudinal analysis. In addition, aspregnancy and glaucoma may coexist, it would be interesting toevaluate whether and how these OPA changes could influence aglaucomatous pregnant patient.

References
  1. Kanngiesser HE, Kniestedt C, Robert YC. Dynamic contourtonometry: Presentation of a new tonometer. J Glaucoma2005;14:344-50.
  2. Punjabi OS, Kniestedt C, Stamper RL, Lin SC. Dynamiccontour tonometry: Principle and use. Clin Exp Ophthalmol2006;34:837-40.
  3. Zion IB, Harris A, Siesky B, Shulman S, McCranor L,Garzozi HJ, et al. Pulsatile ocular blood flow: Relationship withflow velocities in vessels supplying the retina and choroid. Br JOphthalmol 2007;91:882-4.
  4. Mollan SP, Wolffsohn JS, Nessim M, Laiquzzaman M,Sivakumar S, Hartley S, et al. Accuracy of goldmann, ocularresponse analyser, pascal and tonoPen XL tonometry inkeratoconic and normal eyes. Br J Ophthalmol 2008;92:1661-5.
  5. Carlin A, Alfirevic Z. Physiological changes of pregnancy andmonitoring. Best Pract Res Clin Obstet Gynaecol 2008;22:801-23.
  6. Sunness JS. The pregnant woman's eye. Surv Ophthalmol1988;32:219-38.
  7. Centofanti M, Zarfati D, Manni GL, Bonini S, Migliardi R,Oddone F, et al. The influence of oestrogen on the pulsatileocular blood flow. Acta Ophthalmol Scand Suppl 2000;78:38-9.
  8. Pourjavan S, Boelle PY, Detry-Morel M, De Potter P.Physiological diurnal variability and characteristics of the ocularpulse amplitude (OPA) with the dynamic contour tonometer(DCT-Pascal). Int Ophthalmol 2007;27:357-60.
  9. Centofanti M, Migliardi R, Bonini S, Manni G, Bucci MG,Pesavento CB, et al. Pulsatile ocular blood flow duringpregnancy. Eur J Ophthalmol 2002;12: 276-80.
  10. Horven I, Gjonnaess H. Corneal indentation pulse and intraocularpressure in pregnancy. Arch Ophthalmol 1974;91:92-8.
  11. Horven I, Gjonnaes H, Kroese A. Blood circulating changes inthe eye and limbs with relation to pregnancy and female sexhormones. Acta Ophthalmol 1976;54:203-14.
  12. Pritchard JA, Adams RH. Erythrocyte production anddestruction during pregnancy. Am J Obstet Gynecol1960;79:750-7.
  13. Gallery ED, Brown MA. Control of sodium excretion in humanpregnancy. Am J Kidney Dis 1987;9:290-5.
  14. Ignarro LJ, Buga GM, Wood KS, Byrns RE, Chaudhuri G.Endothelium-derived relaxing factor produced and releasedfrom artery and vein is nitric oxide. Proc Natl Acad Sci U S A1987;84:9265-9.

16 Clinical and Experimental Vision and Eye Research, January-June, Vol 1, 2018

Ocular pulse amplitude and pregnancy Fernandez, et al.

  1. Takiuti NH, Carvalho MH, Kahhale S, Nigro D, Barbeiro HV,Zugaib M. The effect of chronic nitric oxide inhibition onvascular reactivity and blood pressure in pregnant rats. SaoPaulo Med J 1999;117:197-204.
  2. Palmer RM, Ferrige AG, Moncada S. Nitric oxide releaseaccounts for the biological activity of endothelium-derivedrelaxing factor. Nature 1987;327:524-6.
  3. Wilke K. Episcleral venous pressure and pregnancy[proceedings]. Acta Ophthalmol Suppl 1975:40-1.

 
  1. Phillips CI, Gore SM. Ocular hypotensive effect of late pregnancywith and without high blood pressure. Br J Ophthalmol 1985;69:117-9.
  2. Grieshaber MC, Katamay R, Gugleta K, Kochkorov A,Flammer J, Orgul S. Relationship between ocular pulseamplitude and systemic blood pressure measurements. ActaOphthalmol 2009;87:329-34.

Clinical and Experimental Vision and Eye Research, January-June, Vol 1, 2018 17