Contact Lens & Anterior Eye 34 (2011) 121–127
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Contact Lens & Anterior Eye
journal homepage: www.elsevier.com/locate/clae
A novel, dynamic, in vivo, non-contact method of measuring oxygen depletion
rate of the anterior eye
Martin Cardall
a,b
, Shehzad A. Naroo
a,∗
, James S. Wolffsohn
a
a
Ophthalmic Research Group, School of Life Sciences, Aston University, Birmingham B4 7ET, UK
b
Birmingham and Midland Eye Centre, City Hospital, Birmingham, UK
article info
Keywords:
Oxygen
Contact lens
abstract
Purpose: Despite the importance of oxygen measurements, techniques have been limited by their invasive
nature and small corneal area of assessment. The aim of this study was to assess a non-contact way of
measuring oxygen uptake of the whole anterior eye.
Method: The device consisted of a goggle with an oxygen sensitive material on the inner surface. As
the output is affected by temperature, a second probe was inserted into the goggle to compensate. The
goggle was positioned over the eye on 10 subjects (mean age 30.5 ± 5.0 years, 3:2 male:female) to assess
the oxygen depletion of the unrestricted, blinking eye. Measurements were taken over a 3 min period.
The volume contained within the goggle and bone structure of individual eyes was measured by water
volume displacement and the output corrected to O
2
% reduction/cm
3
over a 30 s period. To check the
discriminatory ability of the device, measurements were taken in open-eye and closed-eye conditions,
along with on the subjects’ skin (cheek) for comparisons.
Results: The oxygen depletion measure over 30 s was on average 3.10 ± 1.51 O
2
% cm
3
during open eye
condition, significantly more than during closed eye conditions (1.26 ± 1.52 O
2
% cm
3
). The skin (control)
showed a negligible oxygen uptake (0.19 ± 0.33 O
2
% cm
3
). The results demonstrated good repeatability
with a mean standard deviation of around 0.4 O
2
% cm
3
(equating to 11%).
Conclusions: The technique demonstrated a non-invasive, non-contact method of measuring consumption
of oxygen within the goggle (oxygen depletion rate) and showed good within-visit repeatability.
© 2010 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
1. Introduction
The cornea requires oxygen to maintain normal function and
integrity [1]. Oxygen can be replenished by diffusion from either
the atmosphere or the aqueous, with a minimum oxygen tension
in the stroma [2]. The corneal epithelium receives most of its oxy-
gen supply in the open eye condition from the atmosphere [1]. The
atmospheric oxygen, being composed of 20.9% O
2
or 155 mm Hg
partial pressure (ranges from 151 to 159 mm Hg at sea level), dif-
fuses across the tear film to supply the epithelium [3]. The flow
of oxygen into the cornea is a result of corneal cell consumption
reducing the oxygen within the cornea, causing diffusion to restore
the equilibrium. As the oxygen tension in the aqueous cannot cur-
rently be measured non-invasively, the flow of oxygen into the
anterior cornea is the best in vivo method of assessing corneal oxy-
gen consumption as an indicator of corneal physiology. The amount
∗
Corresponding author at: Ophthalmic Research Group, School of Life and Health
Sciences, Aston University, Birmingham B4 7ET, UK. Tel.: +44 0 121 204 4142;
fax: +44 0 121 204 4048.
E-mail address: s.a.naroo@aston.ac.uk (S.A. Naroo).
of oxygen that passes through a unit area has been termed as oxy-
gen flux [4]. Oxygen flux into human cornea has been recorded
as between 3 and 9 l/cm
2
/h [5–7]. The physiological variation
between studies is probably due to difference in measurement
technique. In the closed eye condition, the majority of the oxy-
gen supply to the epithelium of cornea comes from the palpebral
conjunctival blood vessels [8]. This provides about one-third of the
oxygen concentration compared to the open eye condition. Ben-
jamin and Hill [3] demonstrated that 1 min after lid closure, the
oxygen flow into the cornea doubled. Holden and Sweeney [9]
measured the oxygen tension of the upper palpebral conjunctiva
of 16 humans to be 61.4 ± 6.9 mm Hg (8.2% atmospheric oxygen),
whereas Efron and Carney [10] found oxygen at the anterior corneal
surface beneath the closed eyelid in 12 young adults to be 7.7 ± 3.8%
atmospheric oxygen (56.7 mm Hg), which is similar to measure-
ments by Fatt and Bieber [11], in a single subject (55.5 ± 5.5 mm Hg).
Contact lenses can disrupt the diffusion of oxygen to the cornea.
To determine the effect of contact lenses on the oxygen supply to
the cornea, many studies have been carried out measuring the oxy-
gen ‘uptake rate’ of the cornea with and without contact lenses
[12–14], with the most common method being the polarographic
technique. This method involves a sensor being placed directly
1367-0484/$ – see front matter © 2010 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.clae.2010.11.008