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ARCH SOC ESP OFTALMOL 2007; 82: 675-680
ORIGINAL ARTICLE
DIURNAL VARIABILITY OF INTRAOCULAR PRESSURE
VARIABILIDAD DIURNA DE LA PRESIÓN INTRAOCULAR
JAÉN-DÍAZ JI1, CORDERO-GARCÍA B1, LÓPEZ-DE-CASTRO F1, DE-CASTRO-MESA C1,
CASTILLA-LÓPEZ-MADRIDEJOS F1, BERCIANO-MARTÍNEZ F1
ABSTRACT
RESUMEN
Objective: To assess whether there are variations in
the intraocular pressure (IOP) between the morning
and afternoon in healthy subjects.
Methods: This study was carried out in a Primary
Care Health Center among usual patients of general
practitioners. Two measurements of the intraocular
pressure were assessed on the same day (between 8
and 9 a.m. and between 5 and 6 p.m.) using a Perkins applanation tonometer. The subjects (119
females and 101 males) had a mean age of 46.3
years, with ages ranging between 14 and 83 years.
They were proportionally distributed among 4 age
groups (14-24, 25-44, 45-64 and >65 years).
Results: The IOP mean values were: right eye,
morning time and afternoon, 13.29 and 11.81 mm
Hg, respectively (p<0.001); left eye, morning time
and afternoon, 13.48 and 12.04 mm Hg (p<0.001).
The IOP was significantly higher in males than in
females, and showed a weak association with age.
Conclusions: We found a diurnal variation of IOP
of approximately 1.5 mm Hg. The time of day when
the IOP is measured needs to be considered as a
variable in research in ocular hypertension and
glaucoma (Arch Soc Esp Oftalmol 2007; 82: 675680).
Objetivo: Comprobar y cuantificar la posible variación de los valores de presión intraocular (PIO) en
sujetos sanos, entre la mañana y la tarde.
Métodos: Estudio descriptivo y transversal realizado en un Centro de Salud entre los consultantes
habituales de una consulta de medicina general. Se
realizaron dos tomas de presión intraocular el mismo día (la primera entre las 8 y las 9 horas y la
segunda entre las 17 y las 18 horas) utilizando un
tonómetro de aplanación tipo Perkins. Los sujetos
(119 mujeres y 101 hombres, edad media de 46,3
años con un rango entre 14 y 83) estaban distribuidos proporcionalmente en cuatro grupos de edad
(14-24, 25-44, 45-64 y >65 años).
Resultados: Los valores medios de PIO fueron:
Ojo derecho en la mañana y en la tarde 13,29 y
11,81 (p<0,001) respectivamente y Ojo izquierdo
en la mañana y en la tarde 13,48 y 12,04 (p<0,001).
La PIO fue significativamente mayor en hombres
que en mujeres, teniendo una correlación muy débil
con la edad.
Conclusiones: Constatamos una diferencia en los
valores de PIO entre la mañana y la tarde, de aproximadamente 1,5 mmHg. El momento del día en
que se determina la PIO debería contemplarse como
una variable más en los estudios de hipertensión
ocular y glaucoma que la determinan.
Key words: Intraocular pressure, glaucoma, variability, tonometry, Primary Care.
Palabras clave: Presión intraocular, glaucoma,
variabilidad, tonometría, Atención Primaria.
Received: 26/6/06. Accepted: 20/9/07.
Santa M.ª de Benquerencia Academic Health Centre. Toledo. Spain.
1 Graduate in Medicine. Specialist in Family and Community Medicine.
Correspondence:
José Ignacio Jaén Díaz
Centro de Salud Santa María de Benquerencia
C/. Guadarrama, s/n
45007 Toledo
Spain
E-mail: [email protected]
JAÉN-DÍAZ JI, et al.
INTRODUCTION
Intraocular pressure (IOP) may be defined as the
resulting balance between aqueous humor production and removal (1). By means of mechanisms that
are not yet well known, its increase is considered to
be one of the main risk factors leading to the development of glaucoma (2). Although 21 mmHg is
commonly accepted as the maximum arbitrary
value for normalcy (3), one should bear in mind, as
with many other biological parameters, that this is a
variable value determined by multiple factors: age
(4), gender (5), race (6), tobacco consumption (7),
local ocular problems (8), obesity (9), hormonal
changes (10), physical exercise (11), etc.
Furthermore, it seems to follow a circadian
rhythm, although this has not clearly been established among humans, with a maximum peak in the
morning and the lowest point by late evening; the
even more confusing changes occurring during the
night have not been taken into account (12-15).
Understanding this cyclical changes in IOP, as
well as their scope and potential factors inducing
change, is very significant not only from a research
viewpoint but also from a clinical perspective in
terms of diagnosis and management of patients suffering from ocular hypertension and glaucoma. For
instance, in a study on the prevalence of ocular
hypertension and glaucoma performed by our team
five years ago during the evening schedule, the existence of IOP average values considerably lower
than those described in similar papers came to our
attention (16).
The purpose of the present study was to check
whether there were differences in the intraocular
pressure values of a certain population during those
times in the day when measurements were taken
and to quantify the resulting differences.
SUBJECTS, MATERIAL AND
METHODS
This is a descriptive and cross-sectional study
performed at a healthcare center in the city of Toledo. Residents in this area were included and distributed proportionately in four age groups (14-24
years, 25-44, 45-64 and = 65), not previously diagnosed with glaucoma or ocular hypertension and
belonging to the population assigned to the healthcare center. Patients chosen among those visiting
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the doctor’s office for any reason between 8 and 9
am were informed of the study and once their consent was obtained, they were subjected to an IOP
measurement and given an appointment for the next
measurement that same day between 5 and 6 pm.
IOP measurement was performed resorting to
two IOP serial samples for both eyes (first the right
eye and then the left one) after instilling one anesthetic drop and fluorescein (0.25% sodium fluorescein solution and 0.4% oxibuprocaine hydrochloride); patients sat upright, using a Perkins applanation tonometer (MK2 model, Clement Clarke Ltd.,
England) and choosing for each eye the highest
value resulting from both measurements. All measurements were performed using one single examiner with ample experience in this technique.
The data obtained were added to the SPSS 9.0
database for Windows (SPSS for Windows, SPSS
Inc, Chicago, USA) for statistical purposes. The
results were described using the standard parameters (average, standard deviation, percentage) and
95% confidence intervals. The statistical analysis,
once IOP non-normalcy was checked by means of
the Kolmogorov-Smirnov test, resorted to the
Mann-Whitney (U), Kruskall-·Wallis (χ2) and Wilcoxon (Z) tests, the former aimed at comparing
matched data. The Spearman Rho (ρ) correlation
was also estimated.
RESULTS
The final sample consisted of 220 individuals,
119 females (54.1 percent) and 101 males (45.9
percent). The average age was 46.3 years, ranging
from 14 to 83. Age among males was higher than
among females (49.3 versus 43.7; p<.05).
Figure 1 illustrates IOP values obtained for each
eye in the morning and evening. IOP values are
slightly higher in the left eye when compared to the
right, and are also higher in the morning than in the
evening (p<.001). The difference between IOP in
the morning and in the evening was +1.48 mmHg
(95% CI 1.24-1.72) for the right eye and +1.44
mmHg (95% CI 1.21-1.67) for the left eye.
The correlation between age and IOP is very
weak (rho= +0.15 and +0.13 for the right and left
eye, respectively). Table I shows IOP based on the
defined age brackets, usually observing slight increases in IOP when augmenting the age range, although differences were not significant.
ARCH SOC ESP OFTALMOL 2007; 82: 675-680
Daytime variability of intraocular pressure
DISCUSSION
Fig. 1: Intraocular pressure values based on the time of
measurements.
As illustrated in Figure 2, IOP was higher among
males than females. This observation was confirmed in three out of four age groups.
Fig. 2: IOP values based on gender.
Our paper confirmed the differences between
IOP figures recorded in the early hours of the morning and afternoon in the same population group
and measurements taken on the very same day.
The mean IOPs found are similar to those recorded in a previous study on prevalence covering the
same health area (16) and using similar methods,
although the age group was over 40 years of age. In
the latter, no IOP differences were found based on
age nor gender, whereas the present study does
reveal gender-based differences. The impact of age
and gender on IOP values is usually positive, although not all studies assessing such impact confirm
this statement. Thus, focusing on the Spanish population, there are two recent papers that point at such
an impact in one case (17) while the other does not
(18). Likely, the reasons for these discrepancies are
the different methods used and the different populations targeted by the study.
IOP differences between both eyes have already
been described in the past (19,20) and may be due
to the fact that IOP is measured first in one eye and
then in the other; moving or massaging one eye is
known to cause changes in the IOP of the other eye
(21). In any case, this difference is scarcely relevant
in clinical terms, since it stands at approximately .2
mmHg.
Although it still remains unclear, IOP values, just
as other biological parameters and variables, are
known to follow a circadian rhythm, values chan-
Table I. Intraocular pressure (IOP) values based on age ranges, eye and time of measurement
Eye and time
Right
Morning
Left
Morning
Right
Evening
Left
Evening
Age group
N
Mean IOP
Typical deviation
14-24
25-44
45-64
>65
14-24
25-44
45-64
>65
14-24
25-44
45-64
>65
14-24
25-44
45-64
>65
41
59
63
57
41
59
63
57
41
59
63
57
41
59
63
57
12.54
13.17
13.25
14.00
12.63
13.20
13.90
13.89
11.54
11.76
11.81
12.05
11.54
11.92
12.30
12.23
2.684
2.919
2.967
3.454
2.817
2.815
3.031
3.534
2.550
2.445
2.923
3.061
2.675
2.548
3.019
3.301
Statistic significance*
5.355
p=0.148
4.894
p=0.180
0.860
p=0.835
1.154
p=0.764
* Kruskall-Wallis' test.
ARCH SOC ESP OFTALMOL 2007; 82: 675-680
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JAÉN-DÍAZ JI, et al.
ging throughout the day. Usually, although not continuously, healthy subjects yield the highest IOP
values at the beginning of the day, upon waking up,
slowly decreasing during the day until bedtime and
gradually increasing again during the night. Differences between maximum and minimum values
may amount to 8 mmHg (22). This cycle may be
altered or be different in glaucoma patients (20).
As far as we know, the study of daytime IOP
variation has been scarcely addressed in Spanish
population, finding only one paper published in this
respect (23) targeting the population attending an
ophthalmology unit.
Our study shows that in the target population
(general population attending one healthcare center) IOP is lower (approximately 1.5 mmHg) in the
early afternoon than in the morning, both in men
and women. Saccá et al (14) find in non-glaucomatous subjects similar differences between measurements taken at 8 am and 4 pm.
The first consequence, as reported by other authors, is that those patients exhibiting limit IOPs in
the early afternoon should be reassessed in the morning schedule. Confirming this variable also requires caution when interpreting intraocular pressure
values detected in both healthy and glaucomatous
populations and in terms of both diagnostics and
treatment control and related to the time of day
when measurements are performed, backing up the
well-known fact that isolated IOP measurements
provide little information on maximum values,
variation range and variability (20). In fact, this element (the time of IOP measurement) should be
taken into consideration as an additional variable in
epidemiological studies related to ocular hypertension and glaucoma.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
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