Dk/t - What's it Mean?

Droopy · #1 (**permalink**) 05-14-2008, 03:31 PM

I was reading about PureVision contacts and saw something about Dk/t. That means "oxygen permeability," but why the letters D, K and T, and why is the "D" the only letter that's capitalized?

flowerhorn · #2 (**permalink**) 06-05-2008, 11:29 AM

Dk stand for oxygen permeability of the contact lenses material while t represents the thickness of the lenses. Dk/t has its unit in (cm/sec)(mlO2/ml x mmHg).

As contact lenses act as a barrier to oxygen in reaching the cornea, oxygen permeability (Dk/t) is an important factor to consider while selecting your contact lenses. It will determine the amount of cornea swellings you might get from it.

CaptainKremen · #3 (**permalink**) 06-05-2008, 11:59 AM

Quote:

Originally Posted by flowerhorn

Dk stand for oxygen permeability of the contact lenses material while t represents the thickness of the lenses. Dk/t has its unit in (cm/sec)(mlO2/ml x mmHg).

As contact lenses act as a barrier to oxygen in reaching the cornea, oxygen permeability (Dk/t) is an important factor to consider while selecting your contact lenses. It will determine the amount of cornea swellings you might get from it.

Interesting, but that still doesn't explain the letters D, K and T.
Also . . . "mmHg." Is that "millimeters of mercury" as in blood pressure?

flowerhorn · #4 (**permalink**) 06-08-2008, 02:46 AM

Actually Dk is the permeability coefficient of a given material.If you don't understand coefficient, it is some constant value defined by the scientists. Do you know α represents sound absorption coefficient. The same goes for Dk. It might be the name or some symbol assigned by the person who discovered it.

t as I mentioned above is the thickness of the lenses.

The whole formula emphasizes on the rate of a chosen gas (in this case oxygen) passes through the material (lenses) of a given thickness for a given gas pressure. That is why you find the mmHg there. It is a measure of pressure.
Anyway, the whole derivation of the unit of measurement is quite complex for layman to understand. What you need to know is a higher value is much better than a lower one as it enables more oxygen to reach your cornea.

Should you interested to know how the formula is derived, pm me.

Droopy · #5 (**permalink**) 06-09-2008, 08:37 AM

Quote:

Originally Posted by flowerhorn

Actually Dk is the permeability coefficient of a given material.If you don't understand coefficient, it is some constant value defined by the scientists. Do you know α represents sound absorption coefficient. The same goes for Dk. It might be the name or some symbol assigned by the person who discovered it.

I think I'm beginning to understand. Kind of like good old fashioned E=mc2. E stand for "energy," m stands for "mass" and, for no apparent reason, c stand for the speed of light.
Something like that?