Download The Effect of Corticosteroids on Aqueous Humor Formation

The effect of corticosteroids on aqueous
humor formation rate and outflow
facility
W. W. Oppelt,* E. D. White, Jr., and E. S. Halpert
The effect of corticosteroids on aqueous humor (AH) formation rate and outflow facility was
measured in the cat eye. AH formation rate was determined by continuous posteroanterior
chamber perfusion with an AH-like buffer containing inulin-C1*. It was found that the total
quantity of inulin-CJi recovered through the anterior chamber outflow cannula could be used
to estimate changes in outflow facility. Intravenous hydrocortisone in doses from 1 to 100 mg.
per kilogram caused a dose-related decrease in AH formation rate. At the same doses and at
0.1 mg. per kilogram, there was a decrease in outflow facility averaging about 23 per cent.
When various doses of hydrocortisone were perfused through the eye chambers or injected
into the vitreous, there was no change in AH formation rate or outflow facility. When hydrocortisone or dexamethasone was dropped onto the cornea, there was again a slight reduction
in AH formation rate and a significant decrease in outflow facility. Particularly with dexamethasone, the effect on the outflow facility seemed to predominate over the effect on AH
formation rate. Data suggest that the rise in intraocular pressure reported after topical or
systemic corticosteroids is mediated by a direct effect of these hormones on the outflow facility.
The outflow facility appears to be more sensitive to corticosteroids than the mechanism controlling AH secretion.
Key words: aqueous humor formation decrease, aqueous humor outflow facility,
pharmacodynamics, hydrocortisone, dexamethasone, perfusion, intravitreal injection,
intravenous injections, drug administration (topical), cats
the glaucomatous eye. He found that, in
comparable age groups, the dexamethasone-induced increase in intraocular pressure (IOP) was greater in the glaucomatous eye that in the normal eye. Becker
and Mills3 demonstrated significant elevation of IOP after topical application of
corticosteroids in glaucomatous patients
and glaucoma suspects. This was interpreted as being due to a decrease in the
outflow facility. In a later publication4
Becker categorized the IOP response to
topical steroids into three groups, in decreasing order of response: (1) patients
with open-angle glaucoma, (2) relatives of
-here has been considerable interest in
the effect of corticosteroids on aqueous humor (AH) dynamics. Armaly1-2 made a
detailed study of the effect of topically applied dexamethasone on the normal and
From the Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Fla. 32601.
Supported by a Fight-for-Sight Grant-in-Aid of
the National Council to Combat Blindness, Inc.,
New York, N. Y., and National Institute of
Health Grant GM 01764.
"Burroughs Wellcome Scholar in Clinical Pharmacology.
535
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Investigative Ophthalmology
October 1969
536 Oppelt, White, and Halpert
patients with glaucoma and glaucoma suspects, and (3) normal persons. These responses were thought to be genetically determined.40 Francois and colleagues,7 however, could not confirm this theory. There
have also been reports of increased IOP
after systemic corticosteroid therapyS11
and after long-term topical prednisone
treatment.1'
It is thought that the mechanism of corticosteroid-induced ocular hypertension involves reduction of the outflow facility.1-3> 4
Nicholas,13 however, commented that the
increased IOP values obtained in normal
volunteers could not be completely explained by changes in outflow facility and
suggested that there had to be a concomitant increase in AH formation. Armaly,1
however, reports a decrease in AH formation.
Animal studies such as those of Tuovinen and co-workers14 and of Linner and
Wistrand15 are, on the whole, inconclusive.
We have in this study measured the effect of intravenous, intraocular, and topical
corticosteroids on AH formation rates, utilizing the technique of continuous posterior-anterior chamber perfusion with an
AH-like buffer containing inulin.10 Additionally, we present arguments that the
perfusion technique can be used to estimate changes in the outflow facility of the
eye. The effect of corticosteroids on this
parameter could thus be determined.
Methods
Male and female cats of mixed breed, weighing
from 2 to 4 kilograms, were anesthetized with
single intrahepatic injections of 30 mg. per kilogram of pentobarbital. Continuous perfusion from
the posterior to the anterior chamber of the eye
with an AH-like buffer containing inulin-C14 was
then begun, as previously described.10 After an
initial equilibration period, to insure adequate mixing, perfusion was maintained at a steady rate
and samples were collected in 30 minute periods.
Radioactivity due to inulin-C14 was determined in
inflow and outflow samples and AH formation
rates were calculated, with the use of the rate of
inflow and the degree of dilution of the inulinC14.16 The total amount of inulin recovered in
each 30 minute period was also measured and
compared to the total amount of inulin infused.
Protein concentrations were determined in each
outflow sample, as previously described,10 and
experiments in which the protein concentrations exceeded 300 mg. per 100 ml. were discarded. The
basic protocol of each experiment consisted of a
2 hour control period to establish the normal
values of AH formation rates and inulin recovery,
followed by a 4 hour experimental period when
various doses of hydrocortisone sodium succinate
were injected intravenously, added to the perfusate, given topically, or injected into the vitreous.
In our system, where IOP and rate of perfusion are maintained constant, some of the infused
inulin will leave the eye through the normal outflow facility and the remainder will exit through
the outflow cannula. It is reasoned that the total
amount of inulin exiting through the outflow
cannula during each time period is a function of
the resistance of the outflow facility. As long as
the pressure of the system is held constant, it
can be assumed that any change in the total
amount of inulin collected must therefore indicate
some change in the resistance of the outflow fa-
Table I'
AH formation (nl/min.)
No. of
experiments
Drug dose First 2 hr.
Inulin recovery (per cent infused inulin)
Average per
Average per
Last 4 hr. cent change\ First 2 hr. Last 4 hr. cent change\
13.710.5
+11.3 ±4.7
68.9 ±2.3
68.6 ± 1.4
+1.8 ±2.9
No drug 12.7 ±0.6t
30
°No drug was administered in these experiments. AH formation rates and inulin recovery during the initial 2 hours of
the experiment
were compared to the values for the final 4 hours. AH formation was calculated for each 30 minute
period.10 These periods were then averaged to calculate control and post-drug formation rates. Inulin recovery was calculated
for each 30 minute period. These periods were then averaged to calculate control and postdrug inulin recovery. Inulin recovery was calculated as follows:
(Volume of outflow in ml./30 min.) x (outflow inulin-C14 counts/min./ml.)
(Volume of inflow in ml./30 min.) x (inflow inulin-C14 counts/min./ml.) x 100 = per cent infused inulin recovered.
An increase in inulin recovery indicates a decrease of the outflow facility, as explained in the text. It should be noted
that there is no significant change in inulin recovery during the first 2 hours of the experiment, compared to the last 4
hours.
| The average per cent change values are the mean of the individual experiments.
1 Standard error of the mean.
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Effect of corticosteroids on aqueous humor 537
Voiitme 8
Number 5
cility of the eye. Thus, we would expect to recover a greater proportion of infused inulin when
there is a decrease in outflow facility and a
smaller proportion when there is an increase in
outflow facility. As we know the rate of perfusion,
inulin concentration in perfusate, and rate of outflow, and can calculate rate of AH formation, it
would be possible to estimate the actual volume
of fluid passing through the outflow facility of
the eye. However, a more simple and direct estimation of a change in outflow facility can be
made by simply noting the change in the total
amount of inulin recovered through the outflow
cannula.
Results
Control experiments. A series of control
experiments (30 eyes) was performed to
obtain normal values of inulin recovery
(Table I). AH formation rates and the
percentage of infused inulin recovered
were calculated for the first 2 hour period
and for the following 4 hour period of each
experiment. The mean rate of AH formation was 12.7 /.il per minute during the initial 2 hour period and 13.7 /.J per minute
during the subsequent 4 hour period.
These are similar to previously reported
control values.10 During the first 2 hours of
the experiment, 68.9 per cent of the infused inulin was recovered in the outflow,
whereas 68.6 per cent was recovered in the
subsequent 4 hour period. Thus, the percentage of inulin recovered is remarkably
stable over a 6 hour experimental period,
suggesting no change in outflow facility
under control conditions.
Intravenous hydro cortisone. A significant reduction in AH formation rate was
noted after intravenous hydrocortisone
when given in doses of 1 to 100 mg. per
Table
No. of
experiments
10
Drug dose
AH formation (nl/min.)
Average
per cent
Control
Drue,
change}
Inulin recovery (per cent infused, inulin)
Average
per cent
Drug
Control
100
21.0 ± 2.0|
12.7 ±1.0
13.3 ± 1.7
9.8 + 0.9
-38 ± 2.7
10
-22 ± 5.9
62 ±1.4
75 ±2.3
75 ±2.4
88 ±2.8
+23 ±4.3
+18 + 4.4
-24 ± 3.4
62 ± 3.5
75+1.9
+22 ±4.5
-15 + 3.5
56 ±2.5
72 ±3.5
+28 ± 4.5
+4 ±4.5
60 ± 3.3
62 ±4.0
+4 ±2.1
1
14.7 ±1.1
11.1 ±0.9
0.1
13.7 ± 0.7
11.6 ±0.7
0.01
13.1 + 0.5
13.7 + 0.9
"Hydrocortisone sodium succinate in the indicated quantities was given in a single intravenous injection at the end of a
2 hour control period. AH formation rates and inulin recovery values were calculated as shown in Table I.
fThe average per cent change values are the mean of the individual experiments.
J Standard error of the mean.
Table III*
No. of
experiments
Drug dose
(tig/ml.)
100
10
AH formation (irt/min.)
Average
per cent
Control
Drue,
changef
16.4±0.5| 16.2 ±1.2
-0.4 ±7.6
13.3 ±1.4
12.4+1.2
-4
+5.5
Inulin recovery (per cent infused inulin)
Average
per cent
Control
change
Dm a
70 ±3.6
63 ± 2.3
74 ±2.5
70 ± 1.7
+ 5.6 ±4 .0
+1.1
±3 .7
61 + 2.7
+ 9 + 3 .2
69 ± 3.6
1
16.0 ±2.0
15.5 ±2.0
-4 ±3.0
"Buffer, containing hydrocortisone sodium succinate in the indicated concentrations, was substituted for the control buffer
at the end of the control period and was used for the rest of the experiment. AH formation and inulin recovery values were
calculated as shown in Table I.
fThe average per cent change values are the mean of the individual experiments.
(Standard error of the mean.
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Investigative Ophthalmology
October 1969
538 Oppelt, White, and Halpert
kilogram (Table II). However, there was
a significant increase in inulin recovery
after doses of hydrocortisone ranging from
0.1 to 100 mg. per kilogram. This indicates
a hydrocortisone-induced decrease of outflow facility, which is substantially the
same at low or high doses of this agent.
It should also be noted that at 0.1 mg. per
kilogram of hydrocortisone there was still
a maximum effect on outflow facility, while
the reduction in AH formation rate was
insignificant.
Intracameral perfusion with hydrocortisone. Here we note that concentrations of
hydrocortisone in the perfusate, ranging
from 0.001 to 0.1 mg. per milliliter, produce no change in either AH formation
rate or outflow facility (Table III).
Intravitreous injection of hydrocortisone.
At the beginning of each experiment, either
0.1 or 0.01 mg. of hydrocortisone was injected into the vitreous of one eye and the
other eye was injected with an equal volume of AH buffer. There was no difference
in AH formation rate or outflow facility
in the hydrocortisone-injected eye, compared to the buffer-injected eye (Table
IV).
Topical application of hydrocortisone or
dexamethasone (ophthalmic solution). In
these experiments, after the 2 hour control
period, hydrocortisone, either 0.25 or 0.025
mg., was dropped onto the cornea every
30 minutes for 4 hours. At the higher dose
there was a 20 per cent decrease in AH
formation rates with a 23 per cent increase
in inulin recovery, indicating a decrease in
outflow facility. Somewhat greater effects
were noted toward the end of the experiment, suggesting a cumulative drug effect.
Table IV*
AH formation (nl/min.)
No. of
experiments
4
Drug dose
injected
(ne)
100
Control
15.4 ±1.9$
Drug
14.4 ±1.9
Inulin recovery (per cent infused inulin)
Average
per cent
chang.e\
Control
Drug
Average
per cent
changed
-6 ±2.6
66 + 3.9
73 ±4.4
+10 ±2.2
73 + 4.7
70 ± 4.3
4
13.0 ±1.1
-1±5.7
+ 4 ±3.0
10
13.2± 1.1
°At the beginning of each experiment the vitreous of the control eye was injected with 100 /tl of AH buffer and the
vitreous of the contralateral eye was injected with 100 /ttl of AH buffer containing hydrocortisone sodium succinate in
the indicated quantities. Each injection was made with a Hamilton syringe and a 27 gauge needle through the sclera
in the temporal quadrant of the eye, approximately 4 mm. posteriorly to the limbus. AH formation rates and inulin
recovery values were calculated as shown in Table I.
tThe average per cent change values are the mean of the individual experiments.
t Standard error of the mean.
Table V*
AH formation (nl/min.)
Drug
Control
Drug
Average
per cent
change}
14.7 ±0.9$
11.8 ±0.6
-20 ± 3.2
59 ± 3.6
73 ±5.0
+23 ± 2.6
13.2 ±1.7
12.1 ±0.5
- 8 ±2.5
56+
1.2
62 ±1.8
+11+ 0.9
15.3 + 3.5
14.9 ±4.0
- 5±4.1
56 ± 12.7
64 + 2.4
+17 ±11.6
No. of
experiments
Control
6
0.25 (H)
6
0.025(H)
0.1 (D)
3
Inulin recovery (per cent infused inulin)
Average
per cent
change}
Drug dose
(mg./half
hour)
76 ±7.9
+13 ± 4.9
58+ 4.4
12.4 + 2.7
-18 + 4.0
4
0.4 (D) 14.0 ±2.5
"After a 2 hour control period, hydrocortisone sodium succinate (H) or dexamethasone ophthalmic solution (D),
in the indicated quantities, was dropped directly onto the cornea of each eye every 30 minutes. AH formation rates
and inulin recovery values were calculated as shown in Table I.
| The average per cent change values are the mean of the individual experiments.
t Standard error of the mean.
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Volume 8
Number 5
Effect of corticosteroids on aqueous humor 539
Smaller, but similar, changes in AH dynamics were noted after the smaller dose
of hydrocortisone (Table V).
In other cats, dexamethasone ophthalmic
solution containing either 0.4 or 0.1 mg. of
dexamethasone was dropped onto the cornea every half hour after the 2 hour control period. Particularly at the higher dose,
a significant increase in inulin recovery
was noted (indicating a decreased outflow
facility) with a small, insignificant reduction in AH formation rate. This indicates
that the outflow facility is more sensitive
to dexamethosone than the AH secreting
system.
Discussion
Continuous posterior-anterior chamber
perfusion of the eye has proven to be a
useful technique for the study of AH dynamics. We have used it to measure AH
formation rates directly.10 Here it is particularly applicable, as drug effects can
easily be determined because it is possible
to use each eye as its own control and the
measurements can be made independently
of change in intraocular pressure. The current report describes the application of the
technique to an estimation of a change in
outflow facility of the eye. We found that
the total amount of inulin recovered from
the outflow facility is quite stable over a
6 hour experimental period (Table I). As
inulin acts as an inert molecule in the
eye,10 any change in the outflow facility
of the eye, as long as the rate of infusion
and the pressure of the system are kept
constant, will be reflected in a change of
the total quantity of inulin recovered
through the outflow cannula. It is thus
possible to determine and separate effects
of pharmacologic manipulations on the AH
formation rate and outflow facility. This,
again, can be done using each eye as its
own control and independently of any effects the agent may have on vascular volume of the eye, which might also affect
IOP.
There is agreement in the literature that
topical corticosteroids frequently cause an
increase in IOP. Becker4 suggests that this
is more likely to happen in glaucomatous
patients or their relatives and that the rise
in IOP in response to corticosteroids can
be used to make the diagnosis of "preglaucoma." Occasionally, increased IOP has
also been observed after systemic corticosteroids are given. Most authors have suggested that the increase in IOP after topical or systemic corticosteroids is due to a
decrease in the outflow facility, although a
direct demonstration of such an effect has
not been available. Our studies indicate
that intravenous hydrocortisone has a moderate effect in reducing the rate of formation of AH. At very high doses (100 mg.
per kilogram) a 38 per cent reduction in
AH formation is noted; surprisingly, there
still is some reduction in AH formation at
1 mg. per kilogram. Thus, the secretory system for AH seems to be quite sensitive to
an acute increase in blood corticosteroid
activity and responds to this by decreasing
the rate of AH secretion.
The increase in inulin recovery, noted
after intravenous doses of hydrocortisone,
indicates that there is a significant decrease in the outflow facility of the eye. It
is interesting to note that the degree of
response of the outflow facility does not
change with different doses of hydrocortisone. For example, the effect noted at 100
mg. per kilogram is quite the same as the
one noted at 0.1 mg. per kilogram. This
suggests that the "receptor" controlling
outflow resistance is extremely sensitive to
systemic corticosteroids and has high affinity for the agent. This may be the explanation for the "all-or-none" type of response noted in the outflow resistance
when using small doses of intravenous hydrocortisone. It is thus quite likely that the
occasional increase in IOP noted after systemic corticosteroids is due to the effect of
these agents on reducing the outflow facility. This system appears to be more sensitive to corticosteroids, at least by a factor of 10, than the one controlling AH secretion. This is seen at the 0.1 mg. per
kilogram dose level when the effect on AH
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Investigative Ophthalmology
October 1969
540 Oppelt, White, and Halpert
secretion is insignificant, while there is still
a full effect on outflow facility.
Perfusion of high and low concentrations
of hydrocortisone through the eye chambers, as well as injection of the agent directly into the vitreous humor, did not
cause any change in AH formation rates or
inulin recovery. This indicates either that
the agent does not reach the sites where
secretion and outflow resistance are controlled or that these sites are sensitive to
corticosteroids only from the blood side.
This situation is somewhat similar to the
response of AH formation to ouabain.
Here, intravenous drug also is effective
while intracameral drug is not.17 On the
other hand, intravitreous ouabain has a
profound effect in reducing IOP.18 Another
possibility for the lack of effect produced
by intraocular hydrocortisone is that the
agent is rapidly inactivated in the eye.
The effects of topical steroids, particularly dexamethasone, are quite intriguing.
Here, again, we have a definite decrease
in the outflow facility to the same degree
as that seen with intravenous hydrocortisone. Again, especially with dexamethasone, we have the suggestion that the corticosteroid effect on outflow facility is considerably greater than the effect on AH
formation. This may be the explanation for
the observation that topical corticosteroids
cause an increase in IOP more frequently
than systemic steroids. It is very puzzling
why there is such a striking effect on outflow facility when rather small quantities
of corticosteroids are given topically,
whereas there is no effect when large concentrations are perfused through the eye
chambers or injected directly into the vitreous humor.
It is difficult to pinpoint a molecular
mechanism by which corticosteroids can
reduce AH formation rate and outflow facility. One wonders about direct effect on
ion transport or on blood vessels or blood
flow. Recently, there have been suggestions
that corticosteroids cause the mast cells
in the trabecular network to release mucopolysaccharides.1'12 It is possible that this
increases outflow resistance and may be
the mechanism of the corticosteroid effect
on outflow facility.
REFERENCES
1. Armaly, M. F.: Effect of corticosteroids on
intraocular pressure and fluid dynamics. I.
The effect of dexamethasone in the normal
eye, Arch. Ophth. 70: 482, 1963.
2. Armaly, M. F.: Effect of corticosteroids on
intraocular pressure and fluid dynamics. II.
The effect of dexamethasone in the glaucomatous eye, Arch. Ophth. 70: 492, 1963.
3. Becker, B., and Mills, D. W.: Corticosteroids
and intraocular pressure, Arch. Ophth. 70:
500, 1963.
4. Becker, B.: Intraocular pressure response to
topical corticosteroids, INVEST. OPHTH. 76:
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484, 1966.
Becker, B., and Chevrette, L.: Topical corticosteroids testing in glaucoma siblings, Arch.
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Becker, B., and Hahn, K. A.: Topical corticosteroids and heredity in primary open-angle
glaucoma, Am. J. Ophth. 57:543, 1964.
Francois, J.: Heintz-De Bree, C , and Tripathi, R. C : The cortisone test and the
heredity of primary open-angle glaucoma,
Am. J. Ophth. 62: 844, 1966.
Stern, J. J.: Acute glaucoma during cortisone therapy, Am. J. Ophth. 36: 389, 1953.
Covell, L. L.: Glaucoma induced by systemic
steroids therapy, Am. J. Ophth. 45: 108,
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Bernstein, H. N., and Schwartz, B.: Effects
of long-term systemic steroids on ocular pressure and tonographic values, Arch. Ophth.
68: 742, 1962.
Bernstein, H. N., Mills, D. W., and Becker,
B.: Steroid-induced elevation of intraocular
pressure, Arch. Ophth. 70:15, 1963.
Spiers, F.: Unilateral acute rise in intraocular
pressure following long-term bilateral local
treatment with prednisone (ultracortenol) in
a case of uveitis, Acta ophth. 43:323, 1965.
Nicholas, J. P.: Topical corticosteroids and
aqueous humor dynamics, Arch. Ophth. 72:
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Tuovinen, E., Esila, R., and Liesmaa, M.:
The influence of corticosteroids on intraocular
pressure in rabbits. III. The immediate influence of massive intravenous doses of betamethasone and dexamethasone on the intraocular pressure of the rabbit eye, Acta ophth.
44: 823, 1966.
Linner, E., and Wistrand, P. J.: Adrenal cortex and aqueous humor dynamics, Exper. Eye
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Oppelt, W. W.: Measurements of aqueous
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Volume 8
Number 5
Effect of corticosteroids on aqueous humor 541
humor formation rates by posterior-anterior
chamber perfusion with inulin: Normal values and the eflFect of carbonic anhydrase inhibition, INVEST. OPHTH. 6: 76, 1967.
17. Oppelt, W. W., and White, E. D., Jr.: Effect
of ouabain on aqueous humor formation rate
18. Bonting, S. L., and Becker, B.: Studies on
sodium-potassium activated adenosine triphosand aqueous humor flow in the rabbit eye
after intravitreal injection of ouabain, INVEST.
OPHTH. 3: 523, 1964.
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