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The Dk/t or Dk/L?

This is a discussion on The Dk/t or Dk/L? within the Frequency 55 Multifocal forums; What is the oxygen transmission ability of Frequency 55 Multifocal contact lenses ? I've always ...


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Old 05-07-2010, 11:30 AM
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Default The Dk/t or Dk/L?

What is the oxygen transmission ability of Frequency 55 Multifocal contact lenses? I've always heard the oxygen permeability of contact lenses expressed as Dk/t. Now I come across a website that calls this value Dk/L. I've never heard of Dk/L before? Is it something new, or something that was phased out some time ago?
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Old 05-07-2010, 02:46 PM
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Quote:
Originally Posted by Zana View Post
What is the oxygen transmission ability of Frequency 55 Multifocal contact lenses? I've always heard the oxygen permeability of contact lenses expressed as Dk/t. Now I come across a website that calls this value Dk/L. I've never heard of Dk/L before? Is it something new, or something that was phased out some time ago?
Hello Zana

Dk is the oxygen permeability of the lens material.

Dk/t is the oxygen transmissibility of the lens. It depends on the thickness of the lens at it's centre and the industry standard measurement is on a -3.00D lens. A lens of 0.10mm centre thickness will have a Dk = Dk/t (expressed as a number).

I think Dk/L is the same as Dk/t.

Note there are at least three different standards for measuring Dk, so if comparing oxygen permeability, check that all use the same method in order to be consistent.

knotlob
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Old 05-07-2010, 03:26 PM
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Quote:
Originally Posted by Knotlob View Post
Hello Zana

Dk is the oxygen permeability of the lens material.

Dk/t is the oxygen transmissibility of the lens. It depends on the thickness of the lens at it's centre and the industry standard measurement is on a -3.00D lens. A lens of 0.10mm centre thickness will have a Dk = Dk/t (expressed as a number).

I think Dk/L is the same as Dk/t.

Note there are at least three different standards for measuring Dk, so if comparing oxygen permeability, check that all use the same method in order to be consistent.

knotlob
You sound a little stumped by this Dk/L thing, too. If I remember correctly, someone asked what the letters d,k, and t stood for, and no one really gave a satisfactory answer. If nobody knows what those letters stand for, I suppose we could use any letters we want, couldn't we?

Here we see a picture of a space shuttle payload provided by MBB or Messerschmitt-Boelkow-Blohm.

Perhaps "Dk/t" is German . . .
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Old 05-07-2010, 04:04 PM
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Originally Posted by Goliath2001 View Post
You sound a little stumped by this Dk/L thing, too. If I remember correctly, someone asked what the letters d,k, and t stood for, and no one really gave a satisfactory answer. If nobody knows what those letters stand for, I suppose we could use any letters we want, couldn't we?

Here we see a picture of a space shuttle payload provided by MBB or Messerschmitt-Boelkow-Blohm.

Perhaps "Dk/t" is German . . .
OK, so you asked for it!!

http://medical-dictionary.thefreedictionary.com/oxygen+permeability

Dk/t

t is the thickness.

L was probably used before. In Dimensional Analysis, where you want to check a formula is correct in terms of units, L would be used for Length (and Length would include any dimension such as thickness, etc), M represents Mass, S represents time, etc. Works well in the System International (SI) that is used in Europe.

D is derived from Diffusivity

k is derived from Solubility (I don't know why they picked k unless it is for a (k) as in (c)onstant.

It is not German as far as I know.

knotlob
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Old 05-07-2010, 04:15 PM
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Default Keep Your Head Down

Quote:
Originally Posted by Knotlob View Post
OK, so you asked for it!!

http://medical-dictionary.thefreedictionary.com/oxygen+permeability

Dk/t

t is the thickness.

L was probably used before. In Dimensional Analysis, where you want to check a formula is correct in terms of units, L would be used for Length (and Length would include any dimension such as thickness, etc), M represents Mass, S represents time, etc. Works well in the System International (SI) that is used in Europe.

D is derived from Diffusivity

k is derived from Solubility (I don't know why they picked k unless it is for a (k) as in (c)onstant.

It is not German as far as I know.

knotlob
I knew they didn't just pull those letters--

Look out!



Are you all right?

I said "pull" didn't I?

It's okay, they're reloading.

If you're confused, see this link:

http://www.lens101.com/h-s-products-sunglasses/43229-replacement-defective-pair-h-s-products-1010-sunglasses.html
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Old 05-07-2010, 04:25 PM
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Originally Posted by Goliath2001 View Post
I knew they didn't just pull those letters--

Look out!



Are you all right?

I said "pull" didn't I?

It's okay, they're reloading.

If you're confused, see this link:

http://www.lens101.com/h-s-products-sunglasses/43229-replacement-defective-pair-h-s-products-1010-sunglasses.html
'OK, I see', said the blind man

knotlob
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Old 05-10-2010, 02:04 PM
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Quote:
Originally Posted by Knotlob View Post
OK, so you asked for it!!

http://medical-dictionary.thefreedictionary.com/oxygen+permeability

Dk/t

t is the thickness.

L was probably used before. In Dimensional Analysis, where you want to check a formula is correct in terms of units, L would be used for Length (and Length would include any dimension such as thickness, etc), M represents Mass, S represents time, etc. Works well in the System International (SI) that is used in Europe.

D is derived from Diffusivity

k is derived from Solubility (I don't know why they picked k unless it is for a (k) as in (c)onstant.

It is not German as far as I know.

knotlob
I've been lurking around this site for years, and this is the first time anyone has given me a word for the letter "D" in Dk/t that actually begins with the letter "d." I even get a "thickness' for "t." Now all I need is a word that begins with "k" and I'll be all set.
Diffusivity-solubility K(onstant)/Thickness.

That letter "k" makes me think it might be German, (as in "kindergarten" and "kaffee") but it's probably not.
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File Type: jpg kaffe.jpg (27.8 KB, 52 views)

Last edited by Orionebula; 05-21-2010 at 03:55 PM..
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Old 05-13-2010, 12:09 PM
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Default Funny Flag

Quote:
Originally Posted by Knotlob View Post
'OK, I see', said the blind man

knotlob
Look at that picture of the tank above. It's firing a shell and lifting off the ground, but the flag pole is bending back as though the tank were moving forward. Should the flag be bending toward the front of the tank as it's being thrown backward by the force of the blast?
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Old 05-13-2010, 01:27 PM
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Originally Posted by Goliath2001 View Post
Look at that picture of the tank above. It's firing a shell and lifting off the ground, but the flag pole is bending back as though the tank were moving forward. Should the flag be bending toward the front of the tank as it's being thrown backward by the force of the blast?
I'm no expert in Russian T80U Main Battle tanks, but I would say that it is moving at speed over a rough course and is airborne because of that, not because of the projectile firing recoil. The tank's flag attitude is consistent with that.

Modern tank firing systems are designed to automatically compensate for the main tank body not being level or indeed airborne. I would guess the picture was taken to demonstrate that the T80U tank is capable of accurate fire, even when traversing rough ground at speed.

knotlob
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  #10 (permalink)  
Old 05-13-2010, 02:38 PM
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Quote:
Originally Posted by Knotlob View Post
I'm no expert in Russian T80U Main Battle tanks, but I would say that it is moving at speed over a rough course and is airborne because of that, not because of the projectile firing recoil. The tank's flag attitude is consistent with that.

Modern tank firing systems are designed to automatically compensate for the main tank body not being level or indeed airborne. I would guess the picture was taken to demonstrate that the T80U tank is capable of accurate fire, even when traversing rough ground at speed.

knotlob
Way cool knotlob. You know everything!
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Old 05-13-2010, 03:23 PM
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Originally Posted by Eyeofthetiger View Post
Way cool knotlob. You know everything!
Nah! Google is a great friend

knotlob
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Old 05-13-2010, 04:51 PM
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Originally Posted by Knotlob View Post
Nah! Google is a great friend

knotlob
Whew! That's a relief. You were beginning to spook me. (Cue the Twighlight Zone theme.)
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Old 05-18-2010, 04:29 PM
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Quote:
Originally Posted by Knotlob View Post
I'm no expert in Russian T80U Main Battle tanks, but I would say that it is moving at speed over a rough course and is airborne because of that, not because of the projectile firing recoil. The tank's flag attitude is consistent with that.

knotlob
Nothing like a flag with attitude.
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Old 05-21-2010, 03:57 PM
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Quote:
Originally Posted by Knotlob View Post
I'm no expert in Russian T80U Main Battle tanks, but I would say that it is moving at speed over a rough course and is airborne because of that, not because of the projectile firing recoil. The tank's flag attitude is consistent with that.

Modern tank firing systems are designed to automatically compensate for the main tank body not being level or indeed airborne. I would guess the picture was taken to demonstrate that the T80U tank is capable of accurate fire, even when traversing rough ground at speed.

knotlob
How do you compensate for recoil like that? Remember what Newton said: "For every action there is an equal and opposite reaction."
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Old 05-24-2010, 04:59 PM
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Originally Posted by Orionebula View Post
How do you compensate for recoil like that? Remember what Newton said: "For every action there is an equal and opposite reaction."
Okay, I'm still a little fuzzy on the Dk/t versus the Dk/l thing. Do those letters actually sand for something, or is it like the "c" in the famous E=MC2 equation? E = "energy" and M = "mass", and, for some reason unknown to me, c = the speed of light. Why Einstein picked "c," I don't know.
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Old 05-24-2010, 06:05 PM
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Originally Posted by Hottchick View Post
Okay, I'm still a little fuzzy on the Dk/t versus the Dk/l thing. Do those letters actually sand for something, or is it like the "c" in the famous E=MC2 equation? E = "energy" and M = "mass", and, for some reason unknown to me, c = the speed of light. Why Einstein picked "c," I don't know.
Yes, please read my post #4. It's there. k may be the standard letter for solubility in science and engineering, but I have forgotten since it is a while since I did any of that.

knotlob
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Old 05-25-2010, 08:51 AM
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Default That's Better

Quote:
Originally Posted by Knotlob View Post
Yes, please read my post #4. It's there. k may be the standard letter for solubility in science and engineering, but I have forgotten since it is a while since I did any of that.

knotlob
Thanks, Knotlob. I appreciate you taking the time to explain that formula. I hope we all understand it now.

Sometimes you have to teach things over and over, you know? I have to admire Hottchick for having the courage to say "Um . . . I still don't get it."
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Old 07-03-2010, 09:41 PM
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Thanks, Knotlob. I appreciate you taking the time to explain that formula. I hope we all understand it now.

Sometimes you have to teach things over and over, you know? I have to admire Hottchick for having the courage to say "Um . . . I still don't get it."
I get it, there are three different numbers, so what are they?
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Old 07-04-2010, 03:38 AM
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I get it, there are three different numbers, so what are they?
Sorry, I don't understand the question. What three numbers don't your understand?

knotlob
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Old 07-04-2010, 03:29 PM
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Sorry, I don't understand the question. What three numbers don't your understand?

knotlob
You inidcated that there were three Dk measurements. What are these?
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Old 07-04-2010, 04:33 PM
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Originally Posted by mgash View Post
You inidcated that there were three Dk measurements. What are these?
Dk value for oxygen permeability can be measured as:

Dk iso

Dk fatt.

ISO is International Standards Organisation.

Fatt is the name of a researcher who developed (or helped develop) a method of determining oxygen permeability. The pressure units are, I think, different so give different results. ISO uses pressure units of hecto Pascals. Multiply the old Fatt permeability units by 0.75 to convert to Dk iso.

So a contact lens material with a Dk fatt value of 100 would be Dk iso value of 75 only. Manufacturers don't always quote the same method (or even specify which method) they have used to determine the Dk value.

The Fatt method is not reliable for Dk values more than 100 units.

A another method based on High Pressure Liquid Chromatography (HLPC) can be used. Technically the method used to determine Dk should be specified.

I cannot at present find the name of the third method (assuming it exists !!), but I am sure I read something about this a few months ago.

knotlob
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Old 07-06-2010, 11:48 AM
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Originally Posted by Hottchick View Post
Okay, I'm still a little fuzzy on the Dk/t versus the Dk/l thing. Do those letters actually sand for something, or is it like the "c" in the famous E=MC2 equation? E = "energy" and M = "mass", and, for some reason unknown to me, c = the speed of light. Why Einstein picked "c," I don't know.
I guess if "c" can mean "the speed of light" then why can't "k" equal "solubility," whatever that is?
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Old 07-06-2010, 03:02 PM
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Originally Posted by Eyeofthetiger View Post
I guess if "c" can mean "the speed of light" then why can't "k" equal "solubility," whatever that is?
I did some further reading on this a couple of days ago and found that k is indeed the normal science/engineering symbol for solubility (in this case oxygen in the lens material).

knotlob
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Old 07-07-2010, 11:15 AM
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Default Stay on Target

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Originally Posted by Goliath2001 View Post
Look at that picture of the tank above. It's firing a shell and lifting off the ground, but the flag pole is bending back as though the tank were moving forward. Should the flag be bending toward the front of the tank as it's being thrown backward by the force of the blast?
An interesting observation, to be sure, Goliath, but what does that have to do with Dk/t?
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Old 07-07-2010, 11:17 AM
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Default Solubility Issues

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Originally Posted by Knotlob View Post
I did some further reading on this a couple of days ago and found that k is indeed the normal science/engineering symbol for solubility (in this case oxygen in the lens material).

knotlob
Okay, Eyeofthetiger was a bit confused about the word "solubility." I take it from your posting that it refers to oxygen being dissolved through the contact lens material and coming in contact with the cornea?
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Old 07-07-2010, 01:58 PM
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Originally Posted by Type40 View Post
Okay, Eyeofthetiger was a bit confused about the word "solubility." I take it from your posting that it refers to oxygen being dissolved through the contact lens material and coming in contact with the cornea?
I think that is the easiest way to look on it, yes, but hopefully the contact lens isn't actually touching the cornea, but floating on a thin layer of tear.

knotlob
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Old 07-07-2010, 03:40 PM
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Originally Posted by Knotlob View Post
I think that is the easiest way to look on it, yes, but hopefully the contact lens isn't actually touching the cornea, but floating on a thin layer of tear.

knotlob
Oh, so the oxygen dissolves though the lens and into the tear layer, which then delivers the dissolved O2 to the corneal epithelium?
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Old 07-07-2010, 03:59 PM
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Oh, so the oxygen dissolves though the lens and into the tear layer, which then delivers the dissolved O2 to the corneal epithelium?
Yes, I believe so.

knotlob
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Old 08-17-2010, 04:24 PM
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Originally Posted by Knotlob View Post
Yes, I believe so.

knotlob
Awesome. Now that we're up to nearly 30 posts and no longer talking tanks, I think we finally have this Dk/t thing hammered out, even if you spell it Dk/L.
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Old 04-05-2011, 11:27 AM
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Default Good WOrk

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Originally Posted by John316 View Post
Oh, so the oxygen dissolves though the lens and into the tear layer, which then delivers the dissolved O2 to the corneal epithelium?
Way to summarize, John316. Well done. You even found an illustration and everything.
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