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Medical Forum / General / Vision / May 2006CooperVision-Hydron Biofinity
Do any of the international (i.e. not Australian!) optometrists in this group use this new silicone hydrogel? - it may be known by a different name in other markets. It has a low modulus so might be a problem solver for the biggest problem with first generation SiH's - CLPC. Would be interested to hear of any feedback from other optoms, good or otherwise. It's only being launched in Australia this month so I don't know a lot about it. Dom Is CLPC due to the modulus or the quality, i.e. slickness of the surface? If you think back, the CSI had a relatively high modulus for a hydrogel lens, and yet was legendary as a CLPC fighter. DrG > Is CLPC due to the modulus or the quality, i.e. slickness of the > surface? [quoted text clipped - 3 lines] > > DrG Don't know about 'slickness' but certainly surface chemistry probably plays a role too: From http://www.siliconehydrogels.org/featured_review/featured_review_jul_05.asp: "Antigenic challenge and mechanical irritation of the conjunctival surface are clearly involved in the development of CLPC. Although accumulation of lens coatings during wear appears to be a key contributing factor, other factors including lens chemistry and modulus of elasticity, edge design, surface properties, fitting characteristics and replacement cycle also play a role." Even if SiH's have issues with allergenic surface properties I'm optimistic that a significant lowering of the modulus has to be a good thing when it comes to CLPC. Dom I have seen that quote, which basically is another way of saying "we don't know what causes CLPC." Surface chemistry? Sure, as it relates to lens/conjunctiva interaction. Personally, I don't think modulus has much to do with it. What is the incidence of CLPC among RGP lens wearers? DrG > I have seen that quote, which basically is another way of saying "we > don't know what causes CLPC." Surface chemistry? Sure, as it relates [quoted text clipped - 3 lines] > > DrG I don't think anyone claims to know THE reason for CLPC... it would appear to be multifactorial and certainly the subject of ongoing research. But to discount modulus as at least a significant contributor is a little premature. As for the reason that CLPC is not an issue with RGP wearers, I'd speculate that the much smaller lens diameter would mitigate against it. The performance of 2nd generation SiHs like the Biofinity will help us to answer these questions, hence my original post. Dom >What is the incidence of CLPC among RGP lens wearers? Good question. The biofilm on SCLs is a chemical stew, and CLPC is a hypersensitivity reaction. Everything in the soup is subject to oxidation. Proteins hydrolyze and change conformation, MPSs oxidize and the whole mess is painted repeatedly over the lens surface to dehydrate and concentrate. Whatever the allergen(s) triggering the reaction, it's reasonable to assume a range of affinities for different materials. Doesn't CLPC virtually disappear with 1-day lenses? -MT In my experience, 1 day lenses do seem to help, but not universally. Other predisposing factors include dry eye + contact lens wear. Also, doesn't CLPC require an underlying allergy? Most patients seem to have peaks. DrG |
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