PubMed · 3183271
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P C Nicolson. 1988. Hydrogen peroxide systems.. https://pubmed.ncbi.nlm.nih.gov/3183271/
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PURPOSE: Although oxygen transmissibility has been a favored index to describe the physiologic performance of contact lenses, it has been maintained by some that the flux through a contact lens would be a more useful guide. Here, a model is described that allows contact lens oxygen flux to be estimated under open and closed eye wearing conditions. METHODS: The equivalent oxygen potential (EOP) was used to approximate the oxygen concentration beneath a contact lens. A logarithmic relation between corneal oxygen consumption and this oxygen level was substituted into Fick's Law to provide a mathematical model. Paired data of EOP and oxygen transmissibility (Dk/t), from a previous empiric derivation, were entered into a nonlinear regression analysis of this model. RESULTS: The modelling procedure produces a good fit to the selected data. The estimated maximum flux during open eye wear is 7.5 microL/cm2 x h, consistent with previous determinations. Error estimates increased from 0 to 0.55 microL/cm2/h at Dk/t values of 0 and 200 x 10(-9) Barrer/cm, respectively, for the open eye. CONCLUSION: This study provides a workable model for estimating the oxygen flux through contact lenses. Varying the underlying relation between the oxygen tension beneath a lens and the oxygen flux produces minimal variation to the result. The model has a number of clinical applications, such as demonstrating the advantages of highly transmissible contact lenses and the limits to which increasing oxygen transmissibility can alter the corneal physiologic environment.
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PURPOSE: The purposes of the study were as follows: (1) to compare the apical fitting relationship of habitual contact lens fluorescein patterns in keratoconus as determined by clinician assessment of on-eye patterns to those determined by photograph readers looking at slides of fluorescein patterns and (2) to determine the validity of the techniques used in assessing the apical fitting relationships of rigid corneal contact lenses on keratoconic corneas. METHODS: Central fluorescein patterns of rigid contact lens-wearing keratoconus patients enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study were graded as "definite touch," "touch," "clearance," or "definite clearance" by certified clinicians. Photographs of these patterns were evaluated independently by certified, masked photograph readers using the same grading scale. RESULTS: Agreement between "re-reads" of the same fluorescein pattern slides by the photograph readers was substantial (weighted kappa = 0.751). Agreement between assessments of habitual fit fluorescein patterns at the baseline vs. the repeat visits was poor for the photograph readers (weighted kappa = 0.254) and moderate for the clinicians (kappa = 0.480). Agreement between clinicians' and photograph readers' assessment of the habitual contact lens fluorescein pattern at the baseline visit was fair (weighted kappa = 0.382). CONCLUSIONS: Repeatability and validity of this technique were fair to excellent. Many factors influence fluorescein pattern interpretation, and improvement of the objective method of fluorescein pattern assessment by photograph readers will require improved methodology that takes these factors into consideration.