ORIGINAL PAPER

Relationship of central corneal thickness to posturalIOP changes in patients with and without glaucomain southern India

Stephen J. Moster • Ghasem Fakhraie •

Rengaraj Venketesh • Mark L. Moster •

Yuanjun Zhao • Marlene R. Moster

Received: 14 January 2009 / Accepted: 16 January 2012 / Published online: 11 May 2012

� Springer Science+Business Media B.V. 2012

Abstract To evaluate the relationship of central

corneal thickness to the changes in intraocular pressure

(IOP) in the sitting and supine position. Observational

case–control study. The study group included Primary

open-angle and chronic angle closure glaucoma

patients. The control group consisted of patients without

glaucoma seen for their routine eye examination.

Central corneal thickness was measured by ultrasound

pachymetry. Patients were then randomized to IOP

measurement by Tonopen either sitting or supine after

maintaining that position for 5 min. The position was

then reversed and IOP measurements taken again after

5 min. Main outcome measure was change in IOP.

One hundred and eighty-two eyes (90 in cases and 92

in controls) were examined. The mean CCT was

538.11 ± 37.17 lm in the study group and 545.34 ±

36.01 lm in the control group (P = 0.185). The mean

IOP in the sitting position was 19.54 ± 5.39 mmHg in

cases and 14.82 ± 4.01 in controls (P \ 0.001). The

mean IOP in the supine position was 20.51 ±

5.48 mmHg in cases and 16.02 ± 3.24 in controls

(P \ 0.001). Mean IOP change from sitting to supine

was statistically significant in both groups (P \ 0.001

for both). Postural change was greater in cases than

controls (P = 0.020). There was no correlation

between postural IOP change and CCT in cases (r =

0.143, P = 0.180) and controls (r = 0.096, P =

0.362). Postural IOP change is greater in glaucoma

patients than non-glaucomatous patients. There was no

correlation between postural IOP change and CCT.

Keywords Intra-ocular pressure � Central corneal

thickness � Postural change

Introduction

Central corneal thickness (CCT) is now known to play

an increasing role in the management of patients with

glaucoma [1]. A direct correlation has been found

between CCT and intra-ocular pressure (IOP), with

thicker corneas associated with higher IOP readings

[2]. This finding has been substantiated with multiple

IOP measuring devices including the Tono-Pen

(Mentor O&O, Norwell, MA), which has easy and

flexibile use [3, 4].

In patients with known glaucoma, thinner corneas

are associated with more severe glaucomatous visual

S. J. Moster � R. Venketesh � M. R. Moster

Aravind Eye Hospital, Pondicherry, Tamil Nadu, India

e-mail: moster@willsglaucoma.org

G. Fakhraie (&)

Eye Research Center, Farabi Eye Hospital, Tehran

University of Medical Sciences, Tehran, Iran

e-mail: drfakhraee@yahoo.com

G. Fakhraie � M. L. Moster � Y. Zhao � M. R. Moster

William and Anna Goldberg Glaucoma Service, Wills

Eye Hospital, Jefferson Medical College, 840 Walnut

Street, Philadelphia, PA 19107, USA

123

Int Ophthalmol (2012) 32:307–311

DOI 10.1007/s10792-012-9522-8

field progression [5]. Additionally, patients with

ocular hypertension and thinner corneas are at higher

risk for developing glaucoma and therefore a thinner

cornea is now viewed as an independent risk factor for

glaucoma [6].

Prior studies have shown that IOP is greater in the

supine than in the sitting position [7, 8]. In addition to

the normal diurnal variation, this postural change

accounts for part of the increased IOP while asleep [7].

There is a positive correlation of increasing visual field

damage with increased postural IOP change when

supine [8]. A recent report found that the 24 h diurnal

variation of IOP in normal cases and glaucoma

patients did not correlate with CCT [9]. However

postural change in relation to CCT was not specifically

addressed.

Although thin CCT and increased postural change

are both associated with glaucomatous damage, it is not

known whether the level of postural IOP change is

affected by CCT. The main objective of this study was to

determine whether there is a correlation between CCT

and IOP changes in sitting and supine positions in

patients with and without glaucoma. This study was

done in southern India where the vast majority of people

sleep on mats on the floor without elevation of the head.

Materials and methods

This was a prospective observational case–control

study. Patients were recruited from the Glaucoma

Service and General Ophthalmology Service at Arav-

ind Eye Hospital, Pondicherry, Tamil Nadu, India.

Ethics approval was obtained from the Aravind

Institutional Review Board. All patients consented to

this study and underwent an enrollment interview.

Medical histories as well as ocular medications were

tabulated.

Inclusion criteria for case (study) group were

patients with primary open-angle glaucoma (POAG)

and patients with primary angle-closure glaucoma

(PACG) based on medical records. Exclusion criteria

were age younger than 30, any prior ocular surgery or

laser trabeculoplasty, any corneal abnormality that

could affect pachymetry or tonometry (like corneal

scar and corneal edema). However, patients with prior

Nd:Yag iridectomies were included. The control

group consisted of patients without glaucoma seen at

Aravind for their routine eye examinations.

Using a patient questionnaire and the medical

record, the following were recorded: age, gender, type

of glaucoma, and eye medications. Patients’ CCT was

measured in the morning while seated, using ultra-

sound pachymetry in both eyes (DHG -500 Pachette;

DHG Technologies, Exton, PA). Based on a random-

ization table, consecutive patients either sat or lied

supine for 5 min. A transition period of 5 min was

considered in order to obtain accurate IOP measure-

ments based on a previous study which found consis-

tent IOP readings after 5 min in both sitting and supine

positions [10]. IOP was measured using a Tonopen

(Mentor O&O, Norwell, MA). Once measured, the

patient changed postural positions (from sitting to

supine or vice versa) for an additional 5 min. IOP was

then measured in the alternate position.

The primary outcome measure for the study was the

relationship between CCT and the change in IOP

between the sitting and supine positions in patients

with and without glaucoma.

Statistical methods

Statistical analysis was performed using SPSS for

Windows version 10.1 (SPSS Inc., Chicago, IL). Intra-

group and inter-group changes for continuous para-

metric variables were evaluated by the paired Student’s

t test and unpaired Student’s t test, respectively. Intra-

group and inter-group changes for continuous non-

parametric variables were evaluated by the Wilcoxon

Signed Rank test and Mann–Whitney U test, respec-

tively. Categorical data were compared by v2 test (or

Fisher exact test when a cell value\5 was expected).

The Pearson Product Moment Correlation Coefficient

was used to evaluate the correlation between the two

continuous variables. For all measurements, a two-

tailed test was used and a P value of \0.05 was

considered significant for measured variables.

Results

Ninety eyes from 45 glaucoma patients (study group

or cases) and 92 eyes from 46 non-glaucoma patients

(control group or controls) were enrolled. The mean

age was 54.78 ± 8.00–52.83 ± 8.78 years in cases

and controls, respectively (P = 0.271). Twenty-one

(47 %) of the cases and seventeen (37 %) of the

controls were female. In the study group, 68 (76 %)

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eyes had POAG and 22 (24 %) eyes had PACG

(Table 1). The mean CCT was 538.11 ± 37.17 lm in

the study group and 545.34 ± 36.01 lm in the control

group. (P = 0.185).

In the sitting position, the mean IOP was 19.54 ±

5.39 mmHg in the study group and 14.82 ±

4.01 mmHg in the control group (P \ 0.001). In the

supine position, the mean IOP was 20.51 ± 5.48

mmHg in the study group and 16.02 ± 3.24 mmHg in

the control group (P \ 0.001). The mean postural IOP

change was 2.3 ± 3.46 mmHg in cases and 1.20 ±

2.85 mmHg in controls (P = 0.020) (Table 2).

In the sitting position, the mean IOP was 17.68 ±

4.04 mmHg in eyes with POAG and 19.86 ± 5.91

mmHg in patients with PACG (P = 0.053). In the

supine position, the mean IOP was 19.87 ± 4.69

mmHg in eyes with POAG and 22.5 ± 7.18 mmHg in

eyes with PACG (P = 0.050). The mean postural IOP

change was 2.19 ± 3.01 mmHg in eyes with POAG

and 2.64 ± 4.65 mmHg in eyes with PACG (P =

0.602).

Overall, there was no association between the

postural IOP change and CCT (r = 0.102, P = 0.171)

(Fig. 1). Also, there was no correlation between the

postural IOP change and CCT in cases (r = 0.143,

P = 0.180) (Fig. 2) and in controls (r = 0.096,

P = 0.362) (Fig. 3).

There was no correlation between the type of

glaucoma and higher postural IOP change (r = 0.157,

P = 0.101). There was no correlation between the

number of glaucoma medications and postural IOP

change (r = 0.032, P = 0.762). Also, there was no

correlation between age and postural IOP change in all

eyes (r = -0.117, P = 0.118), in eyes with glaucoma

(r = -0.092, P = 0.386), and in eyes without glau-

coma (r = -0.194, P = 0.063).

Table 1 Patients’

demographics and

characteristics

a Standard deviationb Primary open-angle

glaucomac Primary angle-closure

glaucomad Central corneal thickness

Group P value

Study group Control group

N = 45 N = 46

Age (Years)

Mean ± SDa 54.78 ± 8.00 52.83 ± 8.78 0.271

Range 32–67 42–83

Gender

Female 21 (47 %) 17 (37 %)

Male 24 (53 %) 29 (63 %) 0.353

Type of glaucoma

POAGb 34 (76 %)

PACGc 11 (24 %)

Glaucoma medication

Mean ± SD 1.24 ± 0.645

Range 0–3

CCTd (lm) 538.11 ± 37.17 lm 545.34 ± 36.01 lm 0.185

Table 2 Intraocular

pressure and central corneal

thickness in study group

and control group

a Standard deviationb Central corneal thickness

Group P value

Study group

(N = 106)

Mean ± SDa

Control group

(N = 110)

Mean ± SD

Sitting IOP (mmHg) 19.54 ± 5.39 14.82 ± 4.01

Supine IOP (mmHg) 20.51 ± 5.48 16.02 ± 3.24

CCTb (lm) 538.11 ± 37.17 545.34 ± 36.01 0.185

Postural IOP change (mmHg) 2.3 ± 3.46 1.20 ± 2.85 0.020

Int Ophthalmol (2012) 32:307–311 309

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Discussion

Studies have shown that CCT has an important role in

the pathogenesis, diagnosis, and management of

glaucoma and ocular hypertension [1, 2, 11, 12]. The

progressive thinning or the presence of a thin cornea

may have pathogenic or prognostic roles in some types

of glaucoma. Central corneal thickness has an effect

on applanation tonometry, producing falsely low IOP

readings for patients with thinner corneas [1]. The

Ocular Hypertension Treatment Study found that CCT

is the most potent determinant of whether patients

with ocular hypertension will develop glaucoma [12].

It has also been determined that postural changes,

specifically the supine position, increase IOP and

contribute to optic disk damage. Is it possible that

these two factors are related? Could thinner corneas

contribute to a greater increase of IOP, and thus

explain why patients with thinner CCT’s have greater

amounts of visual field loss?

As one would expect, we found that IOP was

significantly greater in glaucoma patients in both

sitting and supine positions. In addition, we found a

greater increase in IOP in assuming the supine position

in glaucoma patients than in control subjects. Accord-

ing to our study, there was no correlation between the

CCT and the magnitude of postural IOP change in

patients with and without glaucoma. Also, there was

no correlation between the higher CCT and the lower

postural IOP change in patients with POAG, Patients

with PACG, and patients without glaucoma.

IOP increases when lying down should be taken

into account for the daily treatment of patients who

have apparently controlled IOP [13]. According to

Kiuchi et al. [8], the significant increase in IOP at the

supine position contributes to the progression of visual

field loss in glaucoma patients. It is recommended that

patients diagnosed with normal-tension glaucoma

have their supine IOP recorded in order to plan a

treatment strategy [14].

We observed a significant difference in IOP

between the sitting and supine positions in both

glaucoma and normal subjects in this population and

confirmed studies which found that postural IOP

changes are greater in POAG patients than in normal

controls [13, 15]. When comparing POAG patients to

Fig. 1 Scatter plot of postural intraocular pressure change

against central corneal thickness in all cases

Fig. 2 Scatter plot of postural intraocular pressure change

against central corneal thickness in study group

Fig. 3 Scatter plot of postural intraocular pressure change

against central corneal thickness in control group

310 Int Ophthalmol (2012) 32:307–311

123

PACG patients, our results showed that there was no

significant difference between the postural IOP

changes of both groups.

In summary, we found that IOP is greater in the

supine position than sitting position in both patients

with and without glaucoma, and that the postural

change is greater in glaucoma patients than in non-

glaucoma patients. This could play a role in glauco-

matous damage in this Southern Indian population,

where patients routinely sleep on mats completely flat.

Acknowledgments Disclosure The authors have no finan-

cial interest in the subject matter of this paper.

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