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Sho C. Takatori, Clayton J. Radke; In-Situ Polarographic Assessment of Corneal Oxygenation: A Re-Evaluation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4701.
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© ARVO (1962-2015); The Authors (2016-present)
In 1963, Hill and Fatt introduced the now classic polarographic method to determine corneal oxygen uptake. Since then, the experimental method has been improved and is used extensively with or without SCL wear. Upon careful examination, however, we find that Fatt and coworkers misinterpreted the behavior of the Clark electrode, invalidating the procedure by which corneal oxygen uptake is evaluated. We correct the current analysis of the in-situ polarographic technique and provide an improved procedure to quantify corneal oxygen uptake.
Upon placing a membrane-covered Clark electrode onto the human cornea, the signal of the electrode is traditionally interpreted as the transient oxygen partial pressure at the anterior corneal surface, p(t,0). However, the Clark electrode operates at limiting current, and hence measures oxygen flux rather than partial pressure. To correct this misunderstanding, we revisit the analysis to obtain a flux-based equation describing the anterior corneal oxygen partial pressure (Eq 1). The desired anterior flux into the cornea, J(0), does not appear in Eq 1. Therefore, experimental data are plotted in a semi-log graph of ln[p(t,0)] versus time t. A least-squares fit admits the rate constant, k1, when the membrane and cornea permeabilities and thicknesses are known. Oxygen flux into the cornea, J(0), then follows from Eq 2.
We analyzed published polarographic data of Fatt (1978) for a Bausch & Lomb Plano T lens with transmissibility DLkL/LL = 5.89 hBarrer/cm to obtain J(0) = 1.4 μL/(cm2 h), a lower value than that reported by Fatt (4 μL/(cm2 h)) but in good agreement with Brennan (2005) and Chhabra et al (2009). For a Sauflon 85 lens with DLkL/LL = 22.1 hBarrer/cm, we find J(0) = 2.3 μL/(cm2 h), whereas the classic technique fails.
Use of the Clark electrode to determine in-situ corneal oxygen uptake with and without SCL wear is an important and commonly used tool for assessing corneal oxygenation. Unfortunately, the traditional analysis of measured data dating back over 40 years is incorrect. We have corrected the published analysis to provide a rigorous and simple procedure for analyzing both previous data in the literature and those newly obtained.
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