Download Oxygen levels beneath the closed eyelid.

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Oxygen levels beneath the closed eyelid.
NATHAN EFRON AND L E O G.
rate was then calculated according to the formula:
CARNEY.
The level of oxygen at the anterior cornea! surface beneath the closed eyelid is shown to be equivalent to an
atmosphere of 7.7% oxygen. This finding is in good
agreement with assumptions which have been based on
the oxygen level at the palpebral conjunctiva. However,
in some instances a significant amount of oxygen is derived not only from the palpebral conjunctiva but also
from the atmosphere as a result of an imperfect palpebral
aperture seal.
The oxygen tension at the anterior corneal surface during prolonged lid closure, such as during
sleep, has been of interest for some time. It is now
of increased significance because of the present
popularity of extended-wear contact lenses.
The oxygen tension at the palpebral conjunctiva
was found by Fatt and Bieber' by direct measurement to be 55 ± 5 mm Hg (equivalent to 7.4%
oxygen). They assumed this to be the level of oxygen available to the cornea when the eyelids are
closed, and they based subsequent oxygen profile
calculations, with and without contact lenses of
varying oxygen transmissibilities, on this closedeye boundary condition. "~:< Grote and Zander,"1 on
the other hand, assumed in their oxygen profile
calculations that the level of oxygen at the cornea
of the closed eye corresponded to that of arterial
blood and was 90 mm Hg (equivalent to 12.1%
oxygen).
In this study, we have sought to determine, by
corneal oxygen uptake measurements in the in
vivo human eye, the level of oxygen available to
the cornea during eyelid closure.
Methods. The technique of determining the
equivalent level of oxygen at the corneal surface
was based on that of Hill. 5 Corneal oxygen uptake
recordings were made on the unanesthetized corneas of 12 young adults. None of these subjects
had any significant past ocular history. A fast response-time Clark-type polarographic oxygen
electrode (with a 12.7 fim Teflon membrane and
2 mm cathode) was used. This electrode had the
advantage over those electrodes used previously6
for human in vivo corneal oxygen uptake measurements of reducing the length of time of the
electrode on the subject's eye.
The depletion of oxygen from the electrode was
recorded on a Hitachi QPD 54 pen recorder
(Hitachi, Ltd., Tokyo, Japan), and the depletion
R =
APo 2
t - t0
where APo2 is the arbitrarily chosen depletion
range of 150 to 40 mm Hg, t is the depletion time
(sec), and t0 the electrode response time over the
above range (usually 0.5 to 1.0 sec). The experiment was essentially a two-stage process.
Stage 1. Calibration of corneal response. Air,
nitrogen, and gases of known oxygen content were
each passed over the eye through an airtight gas
mask for a 5 min interval. Immediately following
exposure of the corneal surface to each gas, the
electrode was removed from an air-equilibrated
saline bath at 37° C and placed upon the cornea,
and the depletion rate was recorded. Thus the effect of the gas of known oxygen content could be
expressed by the response ratio, q, which is
defined as:
where Rk is the depletion rate obtained after passing the gas of known oxygen content over the eye
and RAIR and RN.\ are the depletion rates obtained
after exposure of the cornea to air and nitrogen,
respectively. This procedure was carried out on
each subject with gases of 5%, 10%, and 15% O 2
(all balance nitrogen), each gas being used six
times. A linear relationship could then be derived
which could predict from the electrode response
the equivalent level of oxygen present at the anterior corneal surface.
Stage 2. Test procedure. The cornea was exposed sequentially to air and iiitrogen for 5 min
intervals, and the electrode responses were recorded after exposure to each gas. Two experiments were then conducted. In the first experiment, the subjects closed their eyes for 5 min, and
the oxygen depletion rate was recorded immediately upon opening the eyelid. The response
ratio was then expressed as:
R,v, — Rc
where Rc is the depletion rate obtained following
the test condition. The equivalent oxygen level at
the anterior surface of the cornea was then de-
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93
94
Invest. Ophtlwlmol. Visual Sci.
January 1979
Reports
Table I. Corneal response calibration data
Subject
Sex
Age (yr)
Equation predicting oxygen
levels (8) from response
ratio q
Correlation coefficient*
M
19
iy
8=16q-0.71
M
33
si
8=19q-3.21
M
19
iy
8=19q-1.29
F
19
iy
8 = 12q+3.83
M
23
&j
8 = llq+3.77
0.89
0.91
0.89
0.74
0.77
* Statistically significant in all cases (p < 0.001, except for subject 10 where p < 0.01).
Table II. Level of oxygen at corneal surface beneath closed lid in air and in nitrogen
Subject
Level of oxygen beneath closed lid
in air (%) (Mean ± S.D.)
Level of oxygen beneath closed lid
in nitrogen (%) (Mean ± S.D.)
Significance (p value) of difference
between the two test conditions
(t - test)
7.0 ± 1.9
8. 1 ± 4.2
2. 2 ± 1. 9
7. 0 ± 6.0
8.0 ± 1.9
2.7 ± 1.4
8. 7 ± 3. 7
2. 8 ± 2. 7
3. 8 ± 7.3
8.9 ± 0.8
<0.002
NS
NS
NS
NS
NS = Not significant.
termined from the calibration data. This was repeated six times on each of the 12 subjects. In the
second experiment, nitrogen was passed over the
closed eye for the entire 5 min interval to ensure
that the oxygen reaching the cornea came only
from the palpebral conjunctiva. This second experiment was also carried out six times on each of the
12 subjects.
Results. The calibration data of Table I show
that a linear relationship exists between the response ratio values and known oxygen levels. In
Table II, results are given for the levels of oxygen
beneath the closed lid in air and beneath the
closed lid in a nitrogen (anoxic) environment. The
mean level of oxygen at the corneal surface beneath the closed lid in air was 7.7% ± 3 . 8 (56.7
mm Hg). This was not significantly different from
the level found beneath the closed lid in an anoxic
environment, 5.8% ± 4 . 1 (42.8 mm Hg). For
three of the 12 subjects, however, there was a
significant increase of oxygen available to the cornea for the closed eye in air compared to the
closed eye in an anoxic environment.
Discussion. It was found in this study that the
mean level of oxygen at the corneal surface beneath the closed lid in air is 7.7% oxygen. It would
seem, then, that oxygen profile calculations based
on an assumed closed-lid boundary condition of
7.4% oxygen are well-founded. Corneal oxygen
profile calculations using this boundary condition
assumed that the only supply of oxygen to the cor-
nea with lid closure was from the palpebral conjunctiva. To test this assumption, we replaced the
ambient air during lid closure with an anoxic environment and found that there was no statistically
significant change in the mean level of oxygen at
the cornea. However, in three of the 12 subjects
used in this study, there was significantly less oxygen available to the cornea when nitrogen was
passed over the closed eye, suggesting that in
these subjects there was a reduced effectiveness of
the palpebral aperture as a seal to oxygen from the
atmosphere. Indeed, such a result is not unexpected, since Howitt and Goldstein' have shown
that in 23% of 145 subjects a physiologic lagophthalmos was evident. This would inevitably contribute to the variations in the results under the
two closed-eye conditions used in the present
study.
We thank H. Barry Collin for his valuable suggestions
on the preparation of this paper.
From the Comeal Biophysics Laboratory, Department of Optometry, University of Melbourne, Parkville,
Victoria, Australia. Submitted for publication Dec. 30,
1977. Reprint requests: Dr. L. G. Carney, Department
of Optometry, University of Melbourne, Parkville, Victoria, Australia 3052.
Key words: corneal oxygen uptake, oxygen electrode,
closed eye, palpebral aperture seal, palpebral conjunctiva
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Volume 18
Number 1
Reports
95
Subject
11
12
F
22
M
20
M
20
M
19
M
28
M
19
8 = 14q + 1.41
8 = 13q + 2.39
8 = 14q + 1.01
8 = 9q + 5.06
8 = 16q - 0.18
8 = 14q + 2.45
0.84
0.67
0.86
0.63
0.89
0.82
M
19
16q + 0.40
10
0.86
Subject
6
7
8
9
10
11
12
8.1 ± 3. 1
11.1 ± 1. 0
9. 5 ± 2.8
6. 4 ± 3.5
5.0 ± 4. 5
8.7 ± 3. 4
10.8 ± 1. 6
5.7 ± 2. 5
6.9 ± 3. 4
8. 1 ± 2.5
4. 2 ± 5.5
5.2 ± 4. 9
5.2 ± 3. 5
7.3 ± 2. 7
NS
<0.05
NS
NS
NS
NS
<0.05
REFERENCES
1. Fatt, I., and Bieber, M. T.: The steady-state distribution of oxygen and carbon dioxide in the in vivo
cornea. I. The open eye in air and the closed eye,
Exp Eye Res. 7:103, 1968.
2. Fatt, I., Freeman, R. D., and Lin, D.: Oxygen tension distributions in the cornea: a re-examination,
Exp. Eye Res. 18:357, 1974.
3. Fatt, I., Bieber, M. T., and Pye, S. D.: Steady-state
distribution of oxygen and carbon dioxide in the in
vivo cornea of an eye covered by a gas permeable
contact lens, Am. J. Optom. 46:3, 1969.
4. Grote, J., and Zander, R.: Corneal oxygen supply
conditions, Adv. Exp. Med. Biol. 75:449, 1976.
5. Hill, R. M.: Oxygen requirements of the cornea with
flexible lenses. In Bitonte, J. L., and Keates, R. H.,
editors: Symposium on the Flexible Lens, St. Louis,
1972, The C. V. Mosby Co., pp. 105-116.
6. Farris R. L., Takahashi, G. H., and Donn, A.: Corneal oxygen flux in contact lens wearers. In Bitonte,
J. L., and Keates, R. H., editors: Symposium on the
Flexible Lens, St. Louis, 1972, The C. V. Mosby
Co., pp. 413-425.
7. Howitt, D. A., and Goldstein, J. H.: Physiologic
lagophthalmos, Am. J. Ophthalmol. 68:355, 1969.
Rhodopsin determinations in C57BL/6Jpallid strain mice. M. G. LEWIS AND D. T.
ORGANISCIAK.
The influence of light environment on rhodopsin concentration per eye was determined in littermate pigmented
and nonpigmented C57BL/6J-pallid gene mice reared
under cyclic light or continuous dark environments. Attempts to exacerbate a congenital manganese deficiency
in pallid strain mice included dietary deprivation and
supplementation with manganese and exposure to intense light followed by the determination of rhodopsin
recovery rates in darkness. Homozygous pallid mice
(pa/pa) reared in cyclic light had rhodopsin levels which
were significantly lower than heterozygous (+/pa) or
homozygous ( + /+) black control mice. Dark-rearing resulted- in a significant increase in rhodopsin per eye in
pallid strain mice and equivalent levels in adult mice, but
young pallid, strain mice did not achieve the same
rhodopsin concentration as young + / + mice. Although
dietary manganese deprivation or supplementation did
not significantly alter rhodopsin levels among pallid
mice, the deficient diet resulted, in lower rhodopsin per
eye in the young +/+ control animals. The recovery of
rhodopsin in darkness following intense light exposure
was equal and complete within 24 hrfor most genotypes.
However, recovery by pallid, mice after 24 hr was significantly lower than by pigmented. or albino genotypes.
In studies of the retina, environmental light is a
variable shown to have effects on rhodopsin content and rod outer segment (ROS) length,'""' ROS
phospholipid/opsin ratios,5 disc shedding,*' and
the rate of phagocytosis." Eye pigmentation is an
additional factor which may mediate the effects of
light environment on rhodopsin concentrations.3
We recently obtained a strain of C57BL/6J mice
which carry the mutant gene pallid and display a
dilution of pigmentation enabling the homozygous
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