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B. A. Fink, J. Stehulak, G. Mitchell, R. M. Hill; Corneal Oxygen Uptake Rates: A Low (0.4 mPa) Modulus Contact Lens Example. Invest. Ophthalmol. Vis. Sci. 2009;50(13):905.
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Asked here, under blink conditions, for a silicone hydrogel material (Galyfilcon A) of modulus 0.4 mPa: (1) does lens power (i.e., by manifest center thickness and distribution of lens mass) influence oxygen uptake rate at the epithelial surface; and (2) how do the principal meridian curvatures, and net corneal toricity, relate to that uptake rate?
Mean oxygen uptake rates were determined using a Clark-type polarographic electrode applied at the corneal center. The right eye only of 15 subjects was used. Responses to the air (no contact lens) condition, and to 300 sec of static PMMA lens wear, were taken as uptake rate controls. Three refractive power design series were applied to each eye: -6.00, -1.00, +4.00D. One-way repeated measures ANOVA statistics, together with the Tukey-Kramer adjustment for multiple comparisons were used.
Individuality among subjects was most evident when viewing the data as ratios of dynamic uptake rate (relative to air)/static uptake rate (relative to air), with ranges found for the -6.00D series of 139 to 52, the -1.00D series of 149 to 77, and the +4.00D series of 136 to 80 (where values less than 100 represent reduced hypoxic stress).
Changes in post-lens oxygen uptake rate (hypoxic stress) were observed with blinking, but were highly individualized. This suggests that factors, in addition to lens modulus, may be influencing these responses as well, e.g., tear viscosity, lid tension, lid movement (force vectors and directions) and possibly even the epithelial glycocalyx.
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