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Related Experiment Videos

The "L" in Dk/L.

B A Weissman1, C Pham

  • 1Jules Stein Eye Institute, University of California School of Medicine, Los Angeles.

Optometry and Vision Science : Official Publication of the American Academy of Optometry
|August 1, 1992
PubMed
Summary
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This study measured oxygen permeability (Dk) and oxygen transmissibility (Dk/L) for phemfilcon A hydrogel contact lenses. Results show Dk/L predictions align with central thickness for plus-powered lenses, unlike minus-powered ones.

Area of Science:

  • Ophthalmic optics
  • Biomaterials science
  • Contact lens technology

Background:

  • Accurate measurement of oxygen permeability (Dk) and transmissibility (Dk/L) is crucial for contact lens safety and performance.
  • Phemfilcon A is an ionic hydrogel material with 38% water content used in contact lenses.

Purpose of the Study:

  • To measure the Dk of phemfilcon A hydrogel material.
  • To determine the Dk/L of phemfilcon A contact lenses with varying powers using a polarographic technique.
  • To evaluate existing models for predicting Dk/L based on material properties and lens design.

Main Methods:

  • Oxygen permeability (Dk) was measured using the conventional single-chamber polarographic technique at 35°C.
  • Oxygen transmissibility (Dk/L) was measured for seven powered contact lenses (-5 D to +15 D) using the polarographic cathode as a model cornea.

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  • Boundary and edge effects were corrected for Dk measurements.

    • Main Results:

    • The Dk of phemfilcon A material was determined to be 13 x 10⁻¹¹ cm² ml O₂/s ml mm Hg after correction.
    • Measured Dk/L values for the contact lenses ranged from 5 to 15 x 10⁻⁹ cm ml O₂/s ml mm Hg.
    • Models for L adequately predicted Dk/L for minus-powered lenses, but plus-powered lenses showed Dk/L values closer to predictions based on central thickness.

    Conclusions:

    • The study provides precise Dk and Dk/L values for phemfilcon A hydrogel contact lenses.
    • Lens power significantly influences the measured Dk/L, with plus-powered lenses exhibiting different predictive relationships compared to minus-powered lenses.
    • Current models for oxygen transmissibility may require refinement, particularly for plus-powered contact lenses, to accurately reflect real-world performance based on central thickness.