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INVESTIGATIVE OPHTHALMOLOGY b VISUAL SCIENCE / August 1984
VI, Duke-Elder S, editor. St. Louis, CV Mosby Co., 1973, p.
176.
3. Kaufman PL and Davis GE: "Minified" Goldmann applanating
prism for tonometry in monkeys and humans. Arch Ophthalmol
98:542, 1980.
4. Moses RA: Repeated applanation tonometry. Ophthalmologica
142:663, 1961.
5. Moses RA, Lurie P, and Grodzi WJ Jr: Antero-posterior forces
Vol. 25
on the human eyeball. In Basic Aspects of Glaucoma Research,
Liitjen-Drecoll E, editor. International Symposium, Department
of Anatomy, University Erlangen-Niirnberg, September 17-18,
1981. Stuttgart-NY, FK Schattauer, Verlag, 1982, pp. 199-208.
6. Kraukau CET and Wilke K: On repeated tonometry. Acta
Ophthalmologica 49:611, 1971.
7. Kraukau CET: A vibration tonometer. Ophthalmic Res 1:129,
1970.
Decrease of Anterior Ciliary Arterial Pressure
with Increased Ocular Pressure
Go Sakimoro ond Bernard Schwartz
The relationship of the ocular pressure to the anterior ciliary
arterial pressure was studied by measuring the pressure of
the anterior ciliary artery using a modified pressure chamber.
Of the 40 subjects, 9 were normal, 16 were ocular hypertensive
patients, and 15 were primary, open-angle, glaucoma patients.
A significant negative correlation was found between the anterior ciliary arterial pressure and the ocular pressure such
that the former decreases as the latter increases. These results
support the concept that the blood flow in the anterior ciliary
artery is from the inside of the eye to the outside. Invest
Ophthalmol Vis Sci 25:992-995, 1984
In order to further investigate our previous finding
that blood flowed from the inside of the eye to the
outside in the anterior ciliary arteries,1 we examined
the circulatory dynamics by measuring the pressure of
the anterior ciliary artery in normal, ocular hypertensive, and glaucomatous subjects and determined the
correlations between pressures in this vessel and ocular
pressures.
Materials and Methods. Subjects: As defined previously,2 the study was comprised of normal subjects,
ocular hypertensive and open-angle glaucoma patients
attending the Outpatient Ophthalmology Service of
the Tufts-New England Medical Center (Boston, Massachusetts). Informed consent was obtained from all
subjects. None of the normal subjects or ocular hypertensive patients were taking ocular medications. All
of the glaucoma patients were receiving antiglaucoma
medication.
The pressure chamber method was used for the
measurement of the anterior ciliary arterial pressure.2
A transparent plastic film (Saran Wrap) was used on
the tip of the pressure chamber for measurement of
the anterior ciliary arterial pressure, and a transparent
latex membrane (Tonofilm) was used for the measurement of the episcleral venous pressure.
First, ocular pressure and brachial blood pressure
were measured with the patient seated. The Goldmann
applanation tonometer was used for ocular pressure,
and brachial blood pressure was measured in the standard fashion by sphygmomanometer. For the subsequent measurement of episcleral vein and anterior ciliary arterial pressures, the subject's eye was anesthetized
topically with 0.5% proparacaine and the subject was
seated before the slit lamp. The anterior ciliary arteries
were distinguished from the episcleral veins by wider
caliber, more tortuous course, and slightly brighter
color.2
The episcleral venous pressure was measured before
the anterior ciliary arterial pressure, using the total
collapse of the veins as the end point. The measurement
was made on an episcleral vein at a point approximately
5 mM from the limbus in the temporal quadrant; the
right eyes of 35 patients and the left eyes of four patients
were measured. The diastolic arterial pressure was recorded as the first point at which some portion of the
anterior ciliary artery showed pulsation. The pressure
then was increased and the systolic arterial pressure
was recorded as the point at which the artery collapsed
totally. Pressure measurements were made on the anterior ciliary artery in the temporal and nasal quadrants
approximately 5 mM from the limbus, in the right eye
of 36 subjects and in the left eyes of four subjects.
Only one eye was measured in each subject.
Ocular pressure was measured by one observer and
anterior ciliary arterial and episcleral venous pressure
by a second; each was masked to the measurements
made by the other. Pressures for the episcleral veins
and the anterior ciliary arteries were recorded as the
average of three consecutive measurements. The median coefficients of variation (SD/mean X percent)
and, in parentheses, the 30th and 70th percentiles for
the reproducibility of each of the sets of pressure measurements were: nasal systolic 5.4 (3.6, 6.6); nasal diastolic 7.5 (5.8, 11.7); temporal systolic 6.6 (5.6, 8.4);
temporal diastolic 7.9 (5.1, 11.3); and episcleral venous
pressure 7.6 (6.0, 11.1).
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993
Reports
No. 8
Table 1. Systemic and ocular characteristics
Percentiles Median (30th, 70th)
Age
Ocular pressure
(mmHg)
Episcleral venous
pressure
(mmHg)
Brachial blood pressure
(mmHg)
Systolic
Diastolic
66
(58, 73)
17.8 (15.9,23.8)
9 .5* (8.3,* 10.6*)
(126, 145)
(67, 77)
133
72
Ocular hypertensives
(n = 16)
Normals
(n = 9)
All subjects
(n = 40)
75
(70, 79)
61
15.8:
(14.5, 17.0)
23.8(18.2, 25.4)
17.0(16.2, 24.5)
9.4 (8.0, 10.3)
9.0(8.2, 10.4)
10.5,f(9.3,t 11.2f)
140
73
129
71
(127, 150)
(67, 78)
* Based on 39 eyes.
(55,68)
Open-angle glaucomas
(n = 15)
(122, 140)
(70,76)
65
140
76
(60, 75)
(128, 151)
(70, 83)
t Based on 8 eyes.
Nonparametric statistical tests were used for analysis.
A stepwise regression analysis3 was used to determine
whether multivariable relationships exist between the
episcleral arterial pressures and various systemic and
ocular characteristics. The levels of significance were
0.05 for the two-tailed t-tests and 0.01 for the correlation and regression analyses.
Results. The systemic and ocular characteristics of
all subjects are described in Table 1. The percentiles
of the anterior ciliary arterial pressure in all subjects
and for each diagnostic group are shown in Table 2.
Within the total population, no significant correlation coefficients were found between the anterior ciliary arterial pressures, episcleral venous pressures, and
systolic and diastolic blood pressures and age. Also,
no significant correlations were observed between systolic and diastolic blood pressures and systolic and
diastolic anterior ciliary arterial pressures. No significant differences were found between men and women
for temporal or nasal diastolic and systolic pressures.
Comparison of the nasal with the temporal arteries in
the same eye using the Wilcoxin Signed Rank test
revealed that the pressures in the nasal vessels were
significantly higher than in the temporal vessels for
both systolic (P = 0.001) and diastolic (P = 0.034)
pressures. Thus, for further analyses the nasal and
temporal arteries were considered separately.
Using the Mann-Whitney U-test, significant differences between the diagnostic groups were discovered
for the frequency distributions of the anterior ciliary
arterial pressures between the normal and the ocular
hypertensive groups (nasal systolic P = 0.016; temporal
systolic P = 0.009; nasal diastolic P = 0.025; temporal
diastolic P = 0.041). However, no significant differences
were found between normals and glaucomas nor between glaucomas and ocular hypertensives.
Statistically significant negative Spearman correlations (rs) were found between the anterior ciliary arterial
pressures and the ocular pressures (nasal systolic rs
= -0.6102, P< 0.0001; temporal systolic r s = -0.6595,
P < 0.0001; nasal diastolic rs = -0.5454, P = 0.0003;
temporal diastolic rs = 0.45 \l,P = 0.0035), indicating
that the higher the ocular pressure, the lower the anterior ciliary arterial pressure (Figs. 1, 2). Both linear
and nonlinear regression models were generated to
describe the relationship between the anterior ciliary
arterial pressures and ocular pressure. The nonlinear
models were found to provide a better fit of the data
(Figs. 1, 2).
Significant positive Spearman correlations (rs) were
found for the anterior ciliary arterial pressures with
the episcleral venous pressures, indicating the higher
the anterior ciliary arterial pressure, the higher the
episcleral venous pressure (nasal systolic rs = 0.4568,
Table 2. Anterior ciliary arterial pressures (mmHg)
Percentiles Median (30th, 70th)
All subjects
(n = 40)
Nasal systolic
Temporal systolic
Nasal diastolic
Temporal diastolic
* Based on 39 eyes.
51*
51
36*
33
(45,* 63*)
(44,57)
(29,* 41*)
(29, 40)
Normals
(n = 9)
62
57
41
37
(59, 67)
(56, 59)
(39, 47)
(31,43)
Ocular hypertensives
(n = 16)
48
45
30
30
(43,
(38,
(27,
(26,
58)
49)
37)
35)
t Based on 14 eyes.
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Open-angle glaucomas
(n = 15)
51f(44,t 66f)
50 (43, 56)
34f (28,t 42f)
32 (28, 40)
994
INVESTIGATIVE OPHTHALMOLOGY 6 VISUAL SCIENCE / Augusr 1984
I00
<
ACAP=84.8le- a 0 2 6 I 0 P
<
rs = -0.6595
p = < 0.0001
n =40
so
0) "</>
60
II
j
40h
10
20
30
40
Ocular Pressure (IOP, mm Hg)
Fig. 1. Relationship between ocular pressure and temporal systolic
anterior ciliary arterial pressure with nonlinear model. ACAP (anterior
ciliary arterial pressure) = 84.81e" 0026IOP (intraocular pressure).
P = 0.0039; temporal systolic rs = 0.5798, P < 0.0001;
nasal diastolic rs = 0.3806, P = 0.0184; temporal diastolic rs = 0.4718, P = 0.0024). The ocular pressure
was also significantly negatively correlated with the
episcleral venous pressure (rs = -0.5573, P = 0.0002).
A stepwise regression analysis was done with the
temporal systolic, temporal diastolic, nasal systolic,
and nasal diastolic pressures of the episcleral arteries
considered separately as dependent variables and the
potential independent variables of age, ocular pressure,
80
ACAP=53.82e-°- 023l0P
a.
o
si
rs =-0.4511
p = 0.0035
n = 40
60
a> t
.2 o
40
o f—
10
20
30
40
Ocular Pressure (IOP, mm Hg)
Fig. 2. Relationship between ocular pressure and temporal diastolic
anterior ciliary arterial pressure with nonlinear model. ACAP (anterior
ciliary arterial pressure) = 53.82e"002:ilOP (intraocular pressure).
Vol. 25
episcleral venous pressure, and systolic and diastolic
blood pressures. The logarithms of the temporal systolic
and diastolic pressures were used for this analysis since
the distributions of these variables showed marked
skewness and kurtosis. The only independent variable that showed a significant relationship with each
of the dependent variables was ocular pressure
(P< 0.001).
Discussion. A highly significant negative correlation
was found between the anterior ciliary arterial pressures
and the ocular pressures, indicating the higher the ocular pressure, the lower the anterior ciliary arterial pressure. To our knowledge, this negative correlation has
not been described previously; however, Weigelin and
Lohlein4 reported no correlation between both pressures. In their study, the range of ocular pressure was
probably not large enough to determine a relationship
(7-24 mmHg). Using model equations (Figs. 1, 2) the
degree of change of anterior ciliary arterial pressures
with ocular pressure can be calculated. An increase in
ocular pressure from 10 mmHg to 40 mmHg results
in about a 50% decrease in diastolic and systolic arterial
pressures.
There were significant differences in anterior ciliary
arterial pressures between normals and ocular hypertensives but not between normals and open-angle
glaucomas. Since the glaucomas were being treated,
this finding probably resulted from the closer similarity
of the ocular pressures of normal and glaucomatous
individuals (Table 1).
We found no significant relationship between anterior ciliary arterial pressures and brachial blood pressures with either Spearman correlation or multiple
regression analysis. However, Weigelin and Lohlein4
and Sayegh et al5 observed what they considered to be
a significant correlation between episcleral arterial
pressure and brachial blood pressure. The differences
between our results and theirs may be explained by
the larger range of ocular pressures among our subjects.
Since we have shown a highly significant decrease in
anterior ciliary arterial pressures with increasing ocular
pressures, this factor would tend to lower anterior ciliary arterial pressures and, therefore, negate any correlation with brachial blood pressures.
The lack of correlation of anterior ciliary arterial
pressures with brachial blood pressure may be the result
of the dominant influence of the ocular pressure, not
blood pressure, in controlling the correlation. Within
limits, the eye can be viewed as a closed system with
local pressure determinants overriding systemic ones.
The absence of a significant correlation between episcleral venous pressure and blood pressure as well as
the negative correlation between ocular pressure and
episcleral venous pressure confirm our finding in an
independent sample of subjects.2
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No. 8
995
Reporrs
The decrease of episcleral arterial pressure with increased ocular pressure may be the result of decreased
flow of blood in the episcleral arteries. On the basis
of our previous fluorescein angiographic studies of the
anterior ciliary arteries,1 we postulated that the blood
flow is from the inside of the eye to the outside. Thus,
with increased ocular pressure there may be a decrease
in the flow in the iris and choroid,6 with a resultant
decrease in flow of blood into the episcleral arterial
system. However, other explanations are possible. With
an increase in ocular pressure, the episcleral arteries
could dilate with a resultant decrease in pressure; or
a shunting of blood away from the episcleral arterial
system could occur with a resulting decrease in episcleral arterial pressure.
Finally, it has been known for some time that the
anterior ciliary arteries provide the blood supply to
the drainage area of the anterior chamber, including
the canal of Schlemm.7"9 As far as we are aware, there
is only one published study of changes in the blood
supply to this area in glaucomatous eyes.10 Our observations suggest that increased ocular pressure decreases anterior ciliary arterial pressure and thus may
decrease blood flow in these arteries, which supply
blood to the drainage area of the anterior chamber,
including Schlemm's canal. Therefore, a decrease in
nutrition of this area may be a pathogenic factor,
impeding aqueous humor drainage in glaucoma.
Key words: anterior ciliary arterial pressure, episcleral venous
pressure, ocular hypertension, open-angle glaucoma
From the Department of Ophthalmology, New England Medical
Center, and Tufts University School of Medicine, Boston, Massachusetts. The work for this study was done while Dr. Sakimoto was
a Glaucoma Fellow at New England Medical Center. He is now at
the Department of Ophthalmology, Kagoshima University Faculty
of Medicine, Usukicho, 1208-1, Kagoshima-shi 890, Japan. Supported
by grants from the Massachusetts Lions Eye Research Fund, Inc.,
and from Research to Prevent Blindness, Inc., New York, New York,
and by grant RO1-EY04905 from the National Institutes of Health,
Bethesda, Maryland. Read in part before the annual meeting of the
Association for Research in Vision and Ophthalmology, Sarasota,
Florida, April 27, 1981. Submitted for publication: March 7, 1983.
Reprint requests: Bernard Schwartz, MD, PhD, Department of Ophthalmology, New England Medical Center, 171 Harrison Avenue,
Boston, Massachusetts 02111.
References
1. Talusan ED and Schwartz B: Fluorescein angiography: Demonstration of the flow pattern of anterior ciliary arteries. Arch
Ophthalmol 99:1074, 1981.
2. Talusan ED and Schwartz B: Episcleral venous pressure: Differences between normals, ocular hypertensives and primary
open angle glaucomas. Arch Ophthalmol 99:824, 1981.
3. KJeinbaum DG and Kupper TT: Applied Regression Analysis
and Other Multivariable Methods. North Scituate, MA, Duxbury
Press, 1978, pp. 37-59; 131; 231-232.
4. Weigelin E and Lohlein H: Blutdruckmessungen an den episkleralen Gefassendes des Auges bei Kreislaufgesunden Personen.
Albrecht von Graefes Arch fur Ophthalmol 153:202, 1952.
5. Sayegh F, Azmoun A, and Weigelin E: Critical comparison of
vasotonometric (Rethy) and ophthalmodynamometric measurements. Ophthalmic Res 5:300, 1973.
6. Bill A: Capillary permeability to and extravascular dynamics of
myoglobin, albumin and gamma globulin in the uvea. Acta
Physiol Scand 73:204, 1968.
7. Ashton N and Smith R: Anatomical study of Schlemm's canal
and aqueous veins by means of neoprene casts. III. Arterial
relations of Schlemm's canal. Br J Ophthalmol 37:577, 1953.
8. Dvorak-Theobald G: Further studies on the canal of Schlemm.
Its anastomoses and anatomic relations. Am J Ophthalmol 39:65,
1955.
9. Jocson VL and Grant WM: Interconnections of blood vessels
and aqueous vessels in human eyes. Arch Ophthalmol 73:707,
1965.
10. Friedenwald JS: Circulation of the aqueous. V. Mechanism of
Schlemm's canal. Arch Ophthalmol 16:65, 1936.
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