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Camus Kar Man Choy, Pauline Cho, Wai-Yuen Chung, Iris F. F. Benzie; Water-Soluble Antioxidants in Human Tears: Effect of the Collection Method. Invest. Ophthalmol. Vis. Sci. 2001;42(13):3130-3134.
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purpose. To resolve differences in published data on tear antioxidant levels by
comparing the concentration of water-soluble antioxidants in human
reflex tears collected by capillary tube and by the Schirmer strip
collection method and in basal and reflex tears collected using the
Schirmer strip method.
methods. Yawn-induced reflex tears (collected simultaneously by capillary tubes
and by Schirmer strips) and basal tears (by Schirmer strips and using
local anesthetic) were collected from 12 healthy subjects. Tear
cysteine, ascorbate, glutathione, urate, and tyrosine were measured by
high-performance liquid chromatography within a few minutes of
results. Cysteine, ascorbate, glutathione, and tyrosine were 5 to 10 times
higher (P < 0.01) in both reflex and basal tears
collected by Schirmer strip compared with reflex tears collected by
capillary tube from the same subject. Urate levels were slightly but
nonsignificantly higher in Schirmer strip samples
(P > 0.05).
conclusions. The conflict in published data on tear antioxidants is caused by
differences in collection methods. With the exception of urate,
antioxidants accumulate to very high levels in corneal cells.
Spuriously high antioxidant levels in tears collected using Schirmer
strips, therefore, are most probably caused by contamination with
intracellular constituents. The capillary tube collection method is
proposed as the method of choice for reflex tear collection for
biochemical studies. This less-invasive method facilitates the
evaluation of tear antioxidant levels as a biomonitoring tool for
corneal health. Although moderately increased antioxidant levels may be
beneficial, the authors hypothesize that marked increases may indicate
damage to the ocular surface.
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