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Medical Forum / General / Vision / April 2005Purevision?
Are they legally available in the USA yet, being prescribed here, etc.? How do people find they compare with N&Ds? The new roll-out date has been pushed back to later this month, with the toric version coming in June. I am on the list for inventory. I always liked the Purevision, and up until a few weeks ago I continued to wear them (expired trial lenses from my old inventory). Optically, I think they are great, but the Focus N&D is very close. The DK is slightly less than the Ciba products. I think the lenses are very comparable to each other. The Purevision is a very comfortable lens with inherently great optics because of its modulus. It is probably the stiffest lens available, which means that the surface deforms less during actual wear. It also has unbelievable surface wettability. DrG > The new roll-out date has been pushed back to later this month, with > the toric version coming in June. I am on the list for inventory. [quoted text clipped - 3 lines] > I think they are great, but the Focus N&D is very close. The DK is > slightly less than the Ciba products. What's DK? >> The new roll-out date has been pushed back to later this month, with >> the toric version coming in June. I am on the list for inventory. [quoted text clipped - 5 lines] > >What's DK? D = Diffusion Coefficient of lens material k = Oxygen Solubility of lens material A measure of their oxygen permeability. A function of water content. Lower water content = lower Dk Dk/T = oxygen permeability per lens thickness Basically: More oxygen to the cornea = better eye health Actually, with conventional hydrogels, the Dk is directly proportional to the water content, up to the diffusion coefficient of oxygen in water. With silicone-hydrogels, the Dk is inversely related to the water content and directly related to the silicone content. The Purevision water content is slightly higher than Focus N&D. With respect to the oxygen needs of the cornea, there is something called a threshold, beyond which additional oxygen is of no greater benefit. DrG > Actually, with conventional hydrogels, the Dk is directly proportional > to the water content, up to the diffusion coefficient of oxygen in [quoted text clipped - 3 lines] > content and directly related to the silicone content. The Purevision > water content is slightly higher than Focus N&D. Doesn't that mean Purevision would tend to be drier than Focus N & Ds? I read somewhere the higher the water content of the lenses, the more they absorb water from without? > With respect to the oxygen needs of the cornea, there is something > called a threshold, beyond which additional oxygen is of no greater > benefit. Is this threshold exceeded by Purevision or Focus N & Ds? > Doesn't that mean Purevision would tend to be drier than Focus N & Ds? I > read somewhere the higher the water content of the lenses, the more they > absorb water from without? Is that so? Why is it that a hydrogel lens called Proclear, which has a 62% water content and no silicone, performs well on many patients with dry eyes? The ostensible reason is that the material attracts and holds water to the surface of the lens. There is indeed more to the science than just water content. > Is this threshold exceeded by Purevision or Focus N & Ds? It depends on whether you accept the Holden criterion or the revised Holden-Mertz criterion, i.e. whether you believe that the overnight amount of swelling in an eye without a contact lens is 4% or less than 4%. If you accept the revised criterion, then the Focus N&D exceeds it and the Purevision doesn't. DrG > The new roll-out date has been pushed back to later this month, with > the toric version coming in June. I am on the list for inventory. [quoted text clipped - 9 lines] > the surface deforms less during actual wear. It also has unbelievable > surface wettability. I looked at some Brit sites, which listed only Purevision minus-power torics. Is that possible?  SignatureCheers, Bev =================================================== Red ship crashes into blue ship - sailors marooned. Not only is it "possible," but probable. O2 Optix was "rolled-out" in the prescription range of -1.00 to -6.00. How tepid is that? Didn't they have enough confidence in their own product? DrG >> The new roll-out date has been pushed back to later this month, with >> the toric version coming in June. I am on the list for inventory. [quoted text clipped - 13 lines] > torics. > Is that possible? I've been using PV toric on patients since Sept 04 here in Canada. I got it on the "pre launch" due to my high volume CL practice, I do not think it is in general release here yet. Dr Judy > Are they legally available in the USA yet, being prescribed here, etc.? > > How do people find they compare with N&Ds? Don't know about the US. I'm in Canada, where Purevision was never off the market. PV has a visibility tint which N&D lacks. I've tried patients with "Coke/Pepsi" test of PV vs N&D: results slightly in favour of PV but, frankly, neither one is consistently preferred by all. The fit is slightly different so one suits some people, the other suits some people. Some people find PV dries/ coats more than N&D, some people find the opposite and some find no difference. Generally, both lenses are preferred over conventional hydrogel materials. Dr Judy |
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