Tear Oxygen Under Hydrogel and Silicone Hydrogel Contact Lenses in Humans

Abstract

Purpose To determine the tear oxygen tension under a variety of conventional and silicone hydrogel contact lenses in human subjects. Methods Three hydrogel and five silicone hydrogel lenses (Dk/t = 17 to 329) were coated on the back surface with an oxygen sensitive, bovine serum albumin-Pd meso-tetra (4-carboxyphenyl) porphine complex (BSA-porphine). Each lens type was placed on the right eye of 15 non-contact lens wearers to obtain a steady-state open eye tear oxygen tension using oxygen sensitive phosphorescence decay of BSA-porphine. A closed-eye oxygen tension estimate was obtained by measuring the change in tear oxygen tension after 5 min of eye closure. In separate experiments, a goggle was placed over the lens wearing eye and a gas mixture (PO2 = 51 torr) flowed over the lens to simulate anterior lens oxygen tension during eye closure. Results Mean open eye oxygen tension ranged from 58 to 133 torr. Closed eye estimates ranged from 11 to 42 torr. Oxygen tension under the goggle ranged from 8 to 48 torr and was higher than the closed eye estimate for six out of the eight lenses, suggesting that the average closed eye anterior lens surface oxygen tension is <51 torr. For Dk/t >30, the measured tear oxygen tension is significantly lower than that predicted from previous studies. Conclusions The phosphorescence decay methodology is capable of directly measuring the in vivo post lens PO2 of high Dk/t lenses without disturbing the contact lens or cornea. Our data indicate that increasing Dk/t up to and beyond 140 continues to yield increased flux into the central cornea.

Racial Differences in Ocular Oxidative Metabolism

“…Further analysis of corneal oxygen consumption by noninvasive methods is planned. 39 If such noninvasive tests correctly predict intraocular PO 2 in patients, they could be useful for larger-scale clinical, epidemiologic, and genetic analyses.…”

Analysis of the application of the generalized monod kinetics model to describe the human corneal oxygen‐consumption rate during soft contact lens wear

“…From a physical point of view, the relationship between oxygen consumption Q c and oxygen partial pressure p c should be continuous, yielding a value of zero consumption when p c is zero, and increasing along with p c until a saturation level is reached. In this respect, Bonanno et al determined the oxygen consumption rate in humans by applying established oxygen diffusion models to estimations of tear oxygen tension p c underneath hydrogel lenses. They used time‐domain phosphorescence measurement techniques to provide tear film oxygen tension values during in vivo contact lens wear on human eyes .…”

“…In this respect, Bonanno et al determined the oxygen consumption rate in humans by applying established oxygen diffusion models to estimations of tear oxygen tension p c underneath hydrogel lenses. They used time‐domain phosphorescence measurement techniques to provide tear film oxygen tension values during in vivo contact lens wear on human eyes . This information is very useful to further study the processes of oxygen difussion and consumption in the cornea.…”

The significance of oxygen during contact lens wear

“…The closer PLOT comes to the open eye, no-lens anterior surface value of 155 mmHg (or whatever level is typical for any given individual), the more normal corneal oxygenation would be expected to be. PLOT has been measured for a range of lenses [25,26] and those in the mid transmissibility region, around 50 barrers/cm, support levels that are about 50% of normal, sea-level, atmospheric values. Increasing this to 75% requires around 140 barrers/cm.…”