ABSTRACT
The oxygen quantifying techniques of Hill and Rasson and Fatt have been compared by Roscoe and Wilson, who have also derived an "average" equivalent oxygen percentage (EOP) calibration equation. This study provides additional data which support their conclusions. Eight subjects wore three different hydrogel contact lens types of various center thicknesses and oxygen transmissibilities. Open-eyelid oxygen polarographic data were taken for each of these lenses worn by the subjects. The "average" EOP calibration equation was used to calculate the EOP values. The relation between center thickness and the ratio of the oxygen tension values derived by the two methods agrees relatively well with that found previously.
Subject(s)
Contact Lenses, Hydrophilic , Oxygen , Adult , Female , Humans , Male , Optometry/methods , Polarography/methodsABSTRACT
A polarographic oxygen electrode was used to measure the oxygen transmissibility of seven contact lenses of varying water content and center thickness. A similar electrode was used to measure the oxygen uptake following wear of these same contact lenses for both the open- and closed-eyelid conditions on five young healthy subjects. Linear regression revealed a strong correlation between oxygen transmissibility and equivalent oxygen percentage (EOP) values for both the open- and closed-eyelid conditions. This strong correlation between these two oxygen parameters shows both are useful in predicting the oxygen tensions across the tear-epithelial interface during contact lens wear.
Subject(s)
Contact Lenses , Cornea/metabolism , Oxygen Consumption , Polarography/methods , Adult , Biological Transport , Electrodes , Eyelids , Humans , Regression AnalysisABSTRACT
Between different oxygen concentrations (mixed with nitrogen) ranging from 0 to 21% were passed over the corneas of six subjects for 5 min. The resulting corneal oxygen responses were measured by polarography. The averages of these responses were used to calculate a "relative oxygen uptake response" (ROUR) value for each oxygen percentage. Analysis of these ordered pairs revealed a curvilinear relation which was best described by a third order equation; marked linearity was demonstrated in the middle of the oxygen range. The use of this third order equation as a "standard" or "average" equivalent oxygen percentage (EOP) calibration equation is suggested.
Subject(s)
Cornea/metabolism , Oxygen Consumption , Adult , Contact Lenses , Female , Humans , Male , Polarography/methodsABSTRACT
The equivalent oxygen percentage (EOP) technique of Hill and the technique of Rasson and Fatt are two commonly used methods to quantify the oxygen tension underneath a contact lens for the open-eyelid case. This study compares these two techniques. Five subjects and six contact lenses of various center thicknesses and oxygen transmissibilities were used. Each subject wore each lens for which the oxygen tension was measured by these two methods. For lenses of approximately 0.23 mm center thickness, the two methods gave similar oxygen values. For contact lenses significantly thicker or thinner, the two methods gave very different oxygen values. However, these oxygen values were related in a specific manner; a strong linear relation was found for contact lens center thickness vs. the ratio of the two oxygen values found by the two methods.
Subject(s)
Contact Lenses , Oxygen/metabolism , Adult , Contact Lenses, Hydrophilic , Cornea/physiology , Female , Humans , Male , MethodsABSTRACT
Equivalent oxygen percentage (E.O.P.) responses, using a mammalian corneal model, were measured for open-and closed-eye conditions with the presence of a Permalens contact lens. Under open-eye conditions, the E.O.P. responses agreed with those measured or predicted by other investigators. However, under closed-eye conditions, the E.O.P. responses were significantly different from those measured or predicted by other investigators. This discrepancy is discussed in terms of its clinical significance for extended wear contact lens patients.
Subject(s)
Contact Lenses/standards , Cornea/physiology , Oxygen Consumption , Animals , Humans , Rabbits , Time FactorsABSTRACT
Equivalent oxygen (E.O.P.) responses, using a mammalian corneal model, were measured for open- and closed-eye conditions, and with and without the presence of a silicone, a standard thickness HEMA, and an ultrathin HEMA contact lens. Under open-eye conditions, the silicone lens even with a center thickness of 0.25 mm, diminished the E.O.P. response insignificantly compared to the no-lens condition. The ultrathin HEMA lens (0.06-mm center thickness) produced a response approximately three times superior to that of the standard thickness HEMA lens. Under closed-eye conditions, only the silicone lens, however, caused the cornea to respond within the Polse-Mandell zone.
Subject(s)
Contact Lenses, Hydrophilic/adverse effects , Cornea/physiology , Oxygen Consumption , Silicone Elastomers/adverse effects , Animals , Humans , Rabbits , Reaction TimeABSTRACT
Oxygen demands of the mammalian cornea were measured under open eye and closed eye conditions. With the lids gently sealed, oxygen availability to the cornea was found to be about 2/3's that predicted by models in the literature. While the silicone contact lens (0.25 mm thickness) tested under those closed eye conditions still allowed enough oxygen to reach the cornea to just avoid clinically detectable edema, a Hema lens of conventional cosmetic thickness (0.15 mm) would be expected to induce significant edema under those sealed lid circumstances.
