In Vivo Oxygen Uptake into the Human Cornea

PURPOSE. We provide a new procedure to quantify in situ corneal oxygen uptake using the micropolarographic Clark electrode. METHODS. Traditionally, upon placing a membrane-covered Clark microelectrode onto a human cornea, the resulting polarographic signal is interpreted as the oxygen partial pressure at the anterior corneal surface. However, the Clark electrode operates at a limiting current. Hence, oxygen flux is directly detected rather than partial pressure. We corrected this misunderstanding and devised a new analysis to quantify oxygen uptake into the cornea. The proposed analysis is applied to new polarographic data for 10 human subjects during open-eye oxygen uptake. RESULTS. Average open-eye corneal oxygen uptake over 10 subjects is approximately 11 lL/(cm 2 h), approximately five times larger than the average reported by researchers who invoke the original mathematical analysis. Application of the classical interpretation scheme to our experimental data also garners uptake values that are approximately a factor of three to five times smaller than those obtained with our new procedure. CONCLUSIONS. The classical procedure originally developed by Fatt and colleagues misinterprets the behavior of the Clark microelectrode. We corrected the analysis of the in situ polarographic technique to provide a simple yet rigorous procedure for analyzing both previous data in the literature and those newly obtained. Our proposed interpretation scheme thus provides a reliable tool for in vivo assessment of corneal oxygen uptake. (Invest Ophthalmol Vis Sci. 2012;53:6331-6337

In Vivo Corneal Oxygen Uptake During Soft-Contact-Lens Wear

PURPOSE. We develop a new method to compute in situ corneal oxygen uptake during softcontact-lens (SCL) wear using a micro-polarographic Clark electrode. METHODS. After steady SCL wear and subsequent removal, a membrane-covered polarographic microelectrode is immediately placed onto the cornea. The resulting polarographic signal is related to the steady-state corneal oxygen uptake rate during soft-contact-lens wear. We devise a new analysis to quantify oxygen uptake into the cornea during lens wear. The proposed procedure is applied to new polarographic data for 10 human subjects with 12 different commercial lenses during open eye. We compare our results with recent theory. RESULTS. Average corneal oxygen uptake rates at open eye during SCL wear for 10 subjects wearing 12 different commercial lenses vary from 2 to 10 lL(STP)/cm 2 /h. High oxygen permeability lenses have uptake rates of~10 lL(STP)/cm 2 /h, in close agreement with our previously obtained no-lens human uptake rates of 9 to 13 lL(STP)/cm 2 /h at open eye. 40 Application of the classical data-interpretation procedure to our experimental data gives corneal-uptake results that are approximately three to five times smaller than those obtained with our new interpretation scheme. CONCLUSIONS. We provide a simple and reliable tool to quantify corneal-oxygen-uptake rates during in vivo soft-contact-lens wear. Comparison of our newly measured in vivo oxygen uptakes to model prediction for SCLs of varying oxygen transmissibility is in good agreement with available theory. Keywords: corneal-oxygen uptake, soft contact lens, polarographic oxygen sensor, long-time analysis, corneal oxygenation T he human cornea is nourished and supplied anteriorly with oxygen by the environment. Contact lenses with low oxygen where D L k L is the lens oxygen permeability and L L is the lens thickness) impede environmental oxygen supply 1-3 and may cause corneal edema, acidosis, and various adverse events associated with oxygen deficiency. 7-27 Most efforts focus on mathematical modeling, 1-3,7,24,28-32 but-with some exceptions 1-3 -do not incorporate the metabolic processes of the human cornea. Consequently, in vivo experimental methods to ascertain the corneal oxygen uptake have received attention, 33-36 most notably the polarographic oxygen sensor (POS) of Fatt et al. 40 The POS technique employs a Clark oxygen microelectrod

L' arcispedale S. Anna di Ferrara : rivista trimestrale di scienze mediche

Purpose Our aim was to quantitate day-to-day changes in the tear and meibum lipid profile of individual subjects in a pilot study of healthy humans. Methods Matched tear and meibum samples were obtained from four subjects on three consecutive days. Quantitative lipid profiles of human basal tears and meibum were compared using multivariate analysis by principal components. Results Substantial differences in the lipid profile between subjects were observed, while lipid profiles were steady across the three consecutive days of sampling. Multivariate principal component analysis demonstrated that lysophosphatidylcholine was the largest variant lipid class between subjects in tears, while wax esters comprised the most variation between subjects in meibum secretions. Conclusion Interday variability is shown to be much smaller than interpatient variability, suggesting that tears and meibum subjects both have unique profiles in humans

Nervnaja sistema : mezvuzovskij sbornik

Purpose To compare the lipid composition of human meibum across three different meibum expression techniques. Methods Meibum was collected from five healthy non-contact lens wearers (aged 20-35 years) after cleaning the eyelid margin using three meibum expression methods: cotton buds (CB), meibomian gland evaluator (MGE) and meibomian gland forceps (MGF). Meibum was also collected using cotton buds without cleaning the eyelid margin (CBn). Lipids were analyzed by chip-based, nano-electrospray mass spectrometry (ESI-MS). Comparisons were made using linear mixed models. Results Tandem MS enabled identification and quantification of over 200 lipid species across ten lipid classes. There were significant differences between collection techniques in the relative quantities of polar lipids obtained (P<.05). The MGE method returned smaller polar lipid quantities than the CB approaches. No significant differences were found between techniques for nonpolar lipids. No significant differences were found between cleaned and non-cleaned eyelids for polar or nonpolar lipids. Conclusion Meibum expression technique influences the relative amount of phospholipids in the resulting sample. The highest amounts of phospholipids were detected with the CB approaches and the lowest with the MGE technique. Cleaning the eyelid margin prior to expression was not found to affect the lipid composition of the sample. This may be a consequence of the more forceful expression resulting in cell membrane contamination or higher risk of tear lipid contamination as a result of reflex tearing.© 2016 Elsevier Inc