Relationship Between Water Content and Oxygen Permeability

Ragnarox · #1 (**permalink**) 12-12-2007, 04:05 PM

I read someone say that 1-Day Acuvue contacts have a high oxygen permeability because they also have a high water content. I didn't realize the two were connected. Does it always follow that the more water in the contact lens, the better the oxygen permeability, or is it--like most things in life--more complicated than that?

Ragnarox · #2 (**permalink**) 12-20-2007, 09:23 AM

Okay, I just read something that stated that the more water content in a contact lens, the better the oxygen permeability. Then in went on to say that the opposite is true for silicone hydrogel contacts. I'm so confused!

nicholas · #3 (**permalink**) 12-20-2007, 02:22 PM

Although it's generally true, I don't think higher water content always equals higher Dk with hydrogels. For the most part it's true though. With silicone hydrogels, the silicone is responsible for the oxygen permeability, and silicone is hydrophobic (water-repelling). Silicone hydrogels have lower water contents but can have many times the Dk of traditional hydrogel materials. It's really apples and oranges, that's why it's confusing.

Ragnarox · #4 (**permalink**) 12-20-2007, 04:14 PM

Thanks for answering so quickly. You sound pretty smart. If you don't mind me asking, are you an eye doctor?

nicholas · #5 (**permalink**) 12-24-2007, 12:13 PM

Ha ha, no I'm not. I just know a little about this stuff. Thanks for the question though.

Ragnarox · #6 (**permalink**) 10-21-2009, 04:45 PM

Quote:

Originally Posted by nicholas

Ha ha, no I'm not. I just know a little about this stuff. Thanks for the question though.

Well, I guess you had me fooled. Go ahead and see if you can fool anyone else on Lens 101.

Knotlob · #7 (**permalink**) 11-22-2009, 06:04 AM

Take a look at this link:

http://www.optometric.com/article.aspx?article=101727

It discusses the evolution of silicone hydrogel lenses and includes some graphs showing Water Content versus Lens Stiffness versus Oxygen Permeability (dK value).

Silicone Hydrogel lenses are generally different to conventional lens materials but there are variations amongst the individual silicone hydrogel materials.

knotlob

SandiStix · #8 (**permalink**) 11-23-2009, 09:07 AM

Quote:

Originally Posted by Knotlob

Take a look at this link:

http://www.optometric.com/article.aspx?article=101727

It discusses the evolution of silicone hydrogel lenses and includes some graphs showing Water Content versus Lens Stiffness versus Oxygen Permeability (dK value).

Silicone Hydrogel lenses are generally different to conventional lens materials but there are variations amongst the individual silicone hydrogel materials.

knotlob

Thanks for the link, Knotlob. I checked it out and part of the article says "In a slightly modified molecule, a polar group is added without changing the trimethyl structure." This isn't light reading, folks. There's a lot of scientific gobbledygook here.

Maybe you can help me with just one thing, Knotlob. What is "modulus"? I saw it many times in the article, and it sounds like something important, but it never defines this word. Maybe you can explain it.

Thanks.

Knotlob · #9 (**permalink**) 11-23-2009, 10:08 AM

Quote:

Originally Posted by SandiStix

Thanks for the link, Knotlob. I checked it out and part of the article says "In a slightly modified molecule, a polar group is added without changing the trimethyl structure." This isn't light reading, folks. There's a lot of scientific gobbledygook here.

Maybe you can help me with just one thing, Knotlob. What is "modulus"? I saw it many times in the article, and it sounds like something important, but it never defines this word. Maybe you can explain it.

Thanks.

I think modulus in this case is probably referring to Modulus of Elasticity or some similar property, but I read it as the relative stiffness/flexibility of the lens.

knotlob

Ragnarox · #10 (**permalink**) 11-23-2009, 11:43 AM

Quote:

Originally Posted by Knotlob

I think modulus in this case is probably referring to Modulus of Elasticity or some similar property, but I read it as the relative stiffness/flexibility of the lens.

knotlob

Hi Knotlob. Let me see if I understand this modulus thing. If a contact lens has a "high modulus" that means it's stiff right? Why not just say "low flexibility" or something simpler? I can understand what SandiStix meant my "scientific gobbledygook." Have you ever heard of a "spherical inertial sequential pylon destabilizer?" It's also known as a "bowling ball." Can we just say what we mean, people?

Knotlob · #11 (**permalink**) 11-23-2009, 02:39 PM

Quote:

Originally Posted by Ragnarox

Hi Knotlob. Let me see if I understand this modulus thing. If a contact lens has a "high modulus" that means it's stiff right? Why not just say "low flexibility" or something simpler? I can understand what SandiStix meant my "scientific gobbledygook." Have you ever heard of a "spherical inertial sequential pylon destabilizer?" It's also known as a "bowling ball." Can we just say what we mean, people?

I agree entirely with your sentiments Ragnarox. However, I merely provided a link to the article - I did not write it! Plain words are always best, but some professions (especially the legal ones) seem to like to hide behind their own particular vocabulary/jargon).

knotlob

Ragnarox · #12 (**permalink**) 11-23-2009, 03:10 PM

Quote:

Originally Posted by Knotlob

I agree entirely with your sentiments Ragnarox. However, I merely provided a link to the article - I did not write it! Plain words are always best, but some professions (especially the legal ones) seem to like to hide behind their own particular vocabulary/jargon).

knotlob

I'm sorry about that, Knotlob. When I said "Why not just say 'low flexibility' or something simpler?" I guess I was asking the author of the article you put a link to. I can see how you could have misunderstood me. That's the trouble with text. Without voice inflection and body language, it's so easy to be misunderstood. I hope you won't let my carelessness keep you from contributing any more posts to Lens 101. I've enjoyed reading what you've posted so far.

Knotlob · #13 (**permalink**) 11-23-2009, 03:17 PM

Quote:

Originally Posted by Ragnarox

I'm sorry about that, Knotlob. When I said "Why not just say 'low flexibility' or something simpler?" I guess I was asking the author of the article you put a link to. I can see how you could have misunderstood me. That's the trouble with text. Without voice inflection and body language, it's so easy to be misunderstood. I hope you won't let my carelessness keep you from contributing any more posts to Lens 101. I've enjoyed reading what you've posted so far.

Hi Ragnarox

No offence taken. I agree that Text/email is difficult without facial & voice nuances.

I think I also need to be careful how I write my texts as I see how they can be misinterpreted also (re the Bausch & Lomb Hilafilcon B) which you queried

knotlob

BettyBoop · #14 (**permalink**) 11-23-2009, 04:17 PM

Wow. This thread has taken an interesting turn. This could have turned into a really nasty flame war that would have to be deleted, but the two people involved displayed a lot of maturity.

Me, I will quite often write a post, revise it, read it again, and revise it again. Sometimes I revise my post four or five times until I'm sure it's just right . . . and sometimes I still accidentally offend someone.

Like I said, you two handled this misunderstanding beautifully.