Podcast
Questions and Answers
What is the DK/e value provided for a -3.00D lens?
What is the DK/e value provided for a -3.00D lens?
At 35°C
Which method uses a Clark electrode to detect oxygen transmission?
Which method uses a Clark electrode to detect oxygen transmission?
- Coulometric Method
- Chromatographic Method
- Polarographic Method (correct)
- Optical Method
Different manufacturers use the same methods for measuring lens oxygen permeability.
Different manufacturers use the same methods for measuring lens oxygen permeability.
False (B)
At what temperature should the measurements of lens optical density be taken?
At what temperature should the measurements of lens optical density be taken?
The higher the Dk, the higher the permeability to ___
The higher the Dk, the higher the permeability to ___
What is the maximum percentage of oxygen in breathable air?
What is the maximum percentage of oxygen in breathable air?
What is the Dk/e classification range for 'Faible (Low)'?
What is the Dk/e classification range for 'Faible (Low)'?
What two factors contribute to the calculation of Dk/e?
What two factors contribute to the calculation of Dk/e?
Match the following Dk/e values with their equivalent oxygen percentage (EOP):
Match the following Dk/e values with their equivalent oxygen percentage (EOP):
Flashcards
Dk/e value
Dk/e value
A measure of lens oxygen permeability, calculated by dividing Dk (permeability) by the lens thickness (e).
Oxygen Permeability (Dk)
Oxygen Permeability (Dk)
The ability of a material to allow oxygen to pass through.
Dk/e Units
Dk/e Units
The units for Dk/e are 10⁻⁹ (Fatt (cm⋅mL(O2)⋅mL−1⋅mm Hg−1).
Optical Density (Dx)
Optical Density (Dx)
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Polarographic Method
Polarographic Method
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Coulometric Method
Coulometric Method
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Equivalent Oxygen Percentage (EOP)
Equivalent Oxygen Percentage (EOP)
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Wettability
Wettability
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-3.00D Lens
-3.00D Lens
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Lens Thickness
Lens Thickness
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Study Notes
Permeabiliy and Transmissibility of Lenses
- By convention, manufacturers specify DK/e at 35°C
- Lens power increases closer to the centre
- Lens power decreases as you move towards the edge
- Measurements for different len types varies, making direct comparisons difficult
- Comparing data from different methods/specifications in technical documents is sometimes tricky
- Measurements are dependent on experimental conditions like temperature, pressure and concentration, so these factors should be considered when comparing
- Current measurements for materials SI-HI are only slightly reliable
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