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Medical Forum / General / Vision / July 2008AirOptix for Astigmatism?
I am currently wearing Focus Night&Day in the Left Eye, and Purevision Toric in the Right Eye. I am myopic and presbyopic (56 years old), the right eye is fitted for distance, the left for near work. I sleep with the lenses on, however usually take them out to clean them once a week, and leave them off overnight before reinserting. About once per month I change to new lenses. Both lenses are comfortable, but I find the N&D a little more comfortable than the PV. (Or, that may have to do with toric vs. non-toric.) Sometimes the right eye gets a little red. So, I was looking at the Cibavision site, and it looks like they now have a silicon hydrogel toric lens. Surprisingly, it is not called Night&Day Toric, but AirOptix for Astigmatism. Is that the same material as N&D? As breathable as N&D? How do they compare to Purevision Toric? I haven't read up on contact lenses for awhile. Is there anything new in the way of soft multifocals? I tried the Purevision Multifocals once, they did not work so well, so I went back to monovision. Are there any other silicon hydrogel multifocals out now? I see that Ciba now has what appears to be a multifocal toric, called "Progressive Toric". Is that a silicon hydrogel? (I am surprised that all soft lenses are not si-hy by now, due to the much better breathability.) What else is new in the world of silicon hydrogels? Is there anything out now, that beats N&D as far as breathability, and perhaps comfort? Thank you for your input. (I hope there are still some knowledgeable eye docs and laymen reading this forum, where helpful people used to willingly share their knowledge.. I see so much spam here, it is hard to find the real posts. It is sad, what has happened to Usenet, overtaken by spam, trolls, etc.) > I am currently wearing Focus Night&Day in the Left Eye, and Purevision > Toric in the Right Eye. I am myopic and presbyopic (56 years old), the right [quoted text clipped - 32 lines] > so much spam here, it is hard to find the real posts. It is sad, what has > happened to Usenet, overtaken by spam, trolls, etc.) The Air Optix for astigmatism is in the oxygen permeability range of the O2Optix, i.e. slightly more than the Purevision and slightly less than the N&D. I have been fitting the lens for about 2 months, now, and am quite happy with the results. Rotational stability is very good, which is very critical to toric lens success. In addition, the new Ciba family of lenses incorporates wetting polymers. Comfort- wise, I like the new Air Optix Aqua as much or more than anything else I have tried on my own eyes. IMHO, the edge design of the lens is far more significant in determining lens comfort than the DK of the material. The water content is important for dry eye symptoms, i.e. low water better than high water, which is why the silicone hydrogel lenses perform so well with dry eyes. I don't want to forget the new Acuvue Oasys for Astigmatism, which is the same design as the Acuvue Advance for Astigmatism, but with the lower water, higher silicone content Oasys material. IMHO, this lens is the benchmark for rotational stability in a soft lens toric. Nice to see so many new offerings in the universe of soft lenses. How about RGP lenses? Thank you for all the information (below), Dr. Leukoma. I didn't know if any of the eye docs who used to write here, freely sharing info with all who asked, still wrote here any more, with the NG having been so overtaken by spam and Batesers. (Are there no spam filters for Usenet, as there are for e-mail?) Unfortunately, it seems the direction that all unmoderated NGs has gone in recent years, is down. A few questions about what you wrote--- Interesting that since the first si-hy lens came out, N&D, several years ago now, no other lens has overtaken, or even matched it, in dk/t. (Correct me if I'm wrong about that.) I know you wrote that as far as comfort is concerned, higher dk/t is not necessarily more comfortable. But how about for eye health? Wouldn't the more oxygen permeability=better for the eyes? I'm surprised that the manufacturers (including Ciba) have not tried to create lenses with higher dk/t than N&D. (Or perhaps they did try, but so far have failed?) Also, since N&D and Purevision came out, several years ago, have there been no other lenses approved for 30 day wear? I'm surprised at that as well. Since you write that AirOptix has higher dk/t than Purevision, and PV has been approved for 30 day wear, wouldn't it make sense for AO also to be a 30 day lens? Or, do the lens manufacturers just now want to deal with the testing process any more, that they have to go through, to get lenses approved for 30 day wear? (As mentioned, although wearing N&D and Purevision, I usually take out my lenses once per week, clean them, leave them out overnight. So, I guess 6 or 7 day lenses should be fine for me. But, if I hear a lens has been approved for 30 day wear, I figure that that lens is probably healthier to sleep in at all, than a lens approved for 7 days. So, I'm surprised if no manufacturers try to get that 30 day approval any more.) So--are you saying that the lenses which are supposed to be better for dry eyes, even with the word "Aqua" in them, which one would think have a higher water content, actually have a lower water content--like Oasys, Air Optix Aqua, etc.? Do those lenses have a lower water content than N&D? What about Biofinity? I remember positive comments about that lens here, when it was first coming out, about a year ago. How does that compare to the others? So, of the si-hy toric lenses, do the Air Optix for Astigmatism lenses have the highest dk/t? How do the Oasys torics compare in that regard? How about multi-focal si-hys? Are the Purevision the only one out there still? That's surprising to me too. With the increased aging of the baby boomers, increased presbyopia, a lot of people wanting to look younger, not wear reading glasses, etc., one would think that there would be a lot of research and development into multi-focal designs. Is that not happening? Once again, thanks a lot for the info. :-) The Air Optix for astigmatism is in the oxygen permeability range of the O2Optix, i.e. slightly more than the Purevision and slightly less than the N&D. I have been fitting the lens for about 2 months, now, and am quite happy with the results. Rotational stability is very good, which is very critical to toric lens success. In addition, the new Ciba family of lenses incorporates wetting polymers. Comfort- wise, I like the new Air Optix Aqua as much or more than anything else I have tried on my own eyes. IMHO, the edge design of the lens is far more significant in determining lens comfort than the DK of the material. The water content is important for dry eye symptoms, i.e. low water better than high water, which is why the silicone hydrogel lenses perform so well with dry eyes. I don't want to forget the new Acuvue Oasys for Astigmatism, which is the same design as the Acuvue Advance for Astigmatism, but with the lower water, higher silicone content Oasys material. IMHO, this lens is the benchmark for rotational stability in a soft lens toric. Nice to see so many new offerings in the universe of soft lenses. How about RGP lenses? > Interesting that since the first si-hy lens came out, N&D, several years ago > now, no other lens has overtaken, or even matched it, in dk/t. (Correct me [quoted text clipped - 4 lines] > create lenses with higher dk/t than N&D. (Or perhaps they did try, but so > far have failed?) Pure silicone is hydrophobic. The dk/t of a silicone-hydrogel lens is inversely related to the water content. Focus N&D is 24% water. Air Optix is 33% water. Oasys is 38% water, etc. There is a body of literature relating to overnight corneal swelling and the dk/t of a lens. With respect to this factor, dk/t definitely matters and the higher the better. It has been suggested that the minimum dk/t for safe overnight wear should be 125. But, the point is that beyond that number what are the tradeoffs with respect to comfort, wettability, etc. of increasing the silicone content? > Also, since N&D and Purevision came out, several years ago, have there been > no other lenses approved for 30 day wear? I'm surprised at that as well. [quoted text clipped - 3 lines] > testing process any more, that they have to go through, to get lenses > approved for 30 day wear? > (As mentioned, although wearing N&D and Purevision, I usually take out my > lenses once per week, clean them, leave them out overnight. So, I guess 6 or > 7 day lenses should be fine for me. But, if I hear a lens has been approved > for 30 day wear, I figure that that lens is probably healthier to sleep in > at all, than a lens approved for 7 days. So, I'm surprised if no > manufacturers try to get that 30 day approval any more.) I believe that the reason might be that for safety reasons the lens manufactures have decided not to go in that direction and also because most eye docs are conservative and adhere to the minimum amount of overnight wear for their patients. > So--are you saying that the lenses which are supposed to be better for dry > eyes, even with the word "Aqua" in them, which one would think have a > higher water content, actually have a lower water content--like Oasys, Air > Optix Aqua, etc.? Do those lenses have a lower water content than N&D? These names are conjured up by the marketing and advertising people. What does the term Oasys conjure up? Images of palm trees in the middle of the Sahara? Anyway, see my post above. > What about Biofinity? I remember positive comments about that lens here, > when it was first coming out, about a year ago. How does that compare to the > others? Somebody will have something good or bad to say about any lens. We call those anecdotal reports. I don't use Biofinity in my practice. If I wanted to, I would pursue it, but my "dance card" is currently full with other products. I test drive all the new lenses by wearing them. If my own experience is negative, then I lose interest. > So, of the si-hy toric lenses, do the Air Optix for Astigmatism lenses have > the highest dk/t? How do the Oasys torics compare in that regard? See my post above. HOWEVER, remember that thickness also determines how much oxygen gets to the eye through the lens, and some lenses might be thicker than others, thereby equalizing the playing field somewhat. I do not know specifically how that relates to the Air Optics vs. the Oasys, but I have no doubt that some manufacturer will come along with a study of sorts to tell me theirs is better than the competition. *grin* > How about multi-focal si-hys? Are the Purevision the only one out there > still? That's surprising to me too. With the increased aging of the baby > boomers, increased presbyopia, a lot of people wanting to look younger, not > wear reading glasses, etc., one would think that there would be a lot of > research and development into multi-focal designs. Is that not happening? Multifocals is a huge market, and it won't be long before there is more competition....I expect before the end of 2008. Thanks again for the info, Dr. Leukoma. More questions below.... Pure silicone is hydrophobic. The dk/t of a silicone-hydrogel lens is inversely related to the water content. Focus N&D is 24% water. Air Optix is 33% water. Oasys is 38% water, etc. There is a body of literature relating to overnight corneal swelling and the dk/t of a lens. With respect to this factor, dk/t definitely matters and the higher the better. It has been suggested that the minimum dk/t for safe overnight wear should be 125. But, the point is that beyond that number what are the tradeoffs with respect to comfort, wettability, etc. of increasing the silicone content? ---------------------my response--- In that case, would you consider Focus N&D to be the safest lens to wear overnight? I'm still surprised then, that manufacturers have not tried to surpass it, in terms of dk/t. (Or, have they tried to do so, and failed?) (One could wonder as well, why Cibavision has made a toric version of AirOptix, without making any toric version of the more permeable N&D?) One would think that, even if the minimum dk/t considered safe for overnight wear is 125, that minimum should not be good enough, and that they would try to make the lenses as safe as possible for overnight wear, while of course trying to retain comfort, etc. Perhaps N&D went as far as that can go, but I would think that, with modern science, they could achieve still higher dk/t, while preserving comfort, etc. Also, you wrote that the lesser the water content, the better for dry eye. Yet, Oasys is advertised as being especially good for dry eye, yet it has a higher water content than N&D. Is N&D actually better for dry eye than Oasys? -------------------Dr. Leukoma wrote---------------------- I believe that the reason might be that for safety reasons the lens manufactures have decided not to go in that direction and also because most eye docs are conservative and adhere to the minimum amount of overnight wear for their patients. -----------------my response-------------------- Yes, I can imagine that even with 30 day lenses, many docs recommended that their patients take them out and clean them more often. In fact, that's what my eye doc recommended, and I take them out and clean them (and leave them out overnight), every 7 days. However, as I mentioned, if I hear a lens has been approved for 30 day continuous wear, I would tend to think (even if incorrectly), that that lens is safer for any kind of EW, even one night, than lenses approved for a smaller time period. I would think it advantageous for the manufacturers, to get that approval. (Is it true that some lenses are approved for 30 day wear in Europe, but not in the US? Why? Does the US gov have much stricter testing requirements than the EU?) ----------------Dr. Leukoma wrote---------------------------------- See my post above. HOWEVER, remember that thickness also determines how much oxygen gets to the eye through the lens, and some lenses might be thicker than others, thereby equalizing the playing field somewhat. --------------------my response----------------------- Yes, but doesn't the letter "t" in dk/t refer to thinness? The dk is the inherent permeability of the material, and the t is the thinness of the lens, which together make up dk/t, the permeability of the lens. So, isn't thinness already part of the equation, when one looks at dk/t numbers? Thanks again for your responses, Dr. L.! :-) > Thanks again for the info, Dr. Leukoma. More questions below.... > [quoted text clipped - 63 lines] > > Thanks again for your responses, Dr. L.! :-) The dk/t changes with lens thickness. If there were not differences in thickness across the surface of the lens, it would have no refractive power. Anyway, I think you are asking lots of good questions, but in another respect are over-thinking the situation. I think of silicone-hydrogel lenses as a group, with relatively minor differences between them. Those differences are probably not significant in terms of corneal physiology, but may be perceived by the patient in terms of different comfort levels, vision, etc. Naturally, the manufacturers will exploit those differences for economic advantage. As I tried to get across, the silicone part of the lens is inherently hydrophobic. Many years elapsed since the introduction of the first silicone elastomer lens (Dow Corning) which had great oxygen permeability but poor comfort, and the silicone-hydrogel lens (Purevision) which had both properties. >The dk/t changes with lens thickness. If there were not differences >in thickness across the surface of the lens, it would have no >refractive power. I think I see what you mean now. That if a dk/t value is stated for N&D lenses, for example, that is perhaps an average of N&D lenses, but that in actuality it will vary, based on the refractive power of the lenses? (Is it the same as with eyeglasses--higher minus power equals thicker lens?) Is the stated value an average of all the refractive powers the lens comes in, or do they (to make their lens look better) base the stated value on the thinnest lens (I assume plano)? I think I read, in the description of AirOptix lenses, that the regular ones have a dk/t of 138. Yet, in the description of the toric version, I think it listed a dk/t of 108. Are toric lenses thicker, creating necessarily a lower dk/t? In fact, I think you wrote that a dk/t of 125 is considered the minimum permeablity, for safe overnight wear. Are therefore, the AOAs, with that listing of 108, perhaps not so safe for overnight wear? That makes me wonder about the Purevision Toric, that I wear in my right eye. Do you have any idea what the stated dk/t of that lens (specifically the toric) is? (I assume, as with the AirOptix, that the toric version is probably lower dk/t than the regular.) (I looked on the box, and couldn't find that info.) The powers on my particular PVT is BC 8.7, SPH -5.0, CYL -0.75, and AX 180. I have been sleeping in it, as well as the N&D in my left eye, but now wonder if it is safe to do so? (In fact, with this current eye infection, it started in that right eye. In fact, as long as I was wearing the contacts, it was only the right eye that was infected (last Tuesday). In taking out both lenses that evening, I probably contaminated the left eye, due to touching the eyes in the lens removal. The next morning both eyes were infected. (Of course, I have not reinserted contacts in my eyes since, waiting for the infection to heal completely. I've been using the Zymar since Wednesday.) ) So I'm wondering, if wearing that thicker, less permeable PV Toric in my right eye, made it more prone to infection? (I have been wearing that lens (not meaning specific lens, but that brand and power) in my right eye for approaching a year now, and this is the first time I caught an infection in it, so I don't know if there is any relation.) I recall years ago, a URL was posted here of the dk/t of various lens brands. Anyone have a URL like that now? Is the table kept up to date, as new lenses come out? Does it include the dk/t info on torics? |
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