Why only two silicon hydrogel lenses approved for thirty day wear?

The first two silicon hydrogel lenses on the market, Night & Day (Ciba) and
Purevision (B&L) were approved for thirty day wear.

Since then there are several more silicon hydrogel lenses out, including
others by Ciba, but none AFAIK, other than those two, are approved for
thirty day wear. Most for not more than six or seven days, even with a
thirty day replacement schedule. (Please correct me if I'm wrong.

N&D is still the lens with the highest DK/T. (Surprising too, that that
record has not been matched or beaten yet.) However, Purevision is probably
the lowest DK/T Si-Hy lens. So, it cannot be explained solely by DK/T, why
others have not been approved for thirty days. There are several lenses with
higher DK/T than Purevision, but are not approved for thirty day wear, at
least here in the USA. (It would be interesting to hear though, if some of
them have been approved for that length of wear in other countries. Anyone
know?)

What explains this? Is it just that the companies don't want to go the
expense of the testing that might be required, to get thirty day approval?

I would think it would be advantageous for a company, to get thirty day
approval for a lens, even though most eye doctors do not recommend actually
wearing them for thirty days non-stop. (I'm sure some people do though.) For
instance, I take mine out and clean and disinfect them, leave them off
overnight, etc. about once a week, just to be on the safe side. (Although
sometimes I have gone longer than that, even two weeks.) Yet, even if not
too large a percentage of wearers actually wear lenses for thirty days
straight, one might think that, if a lens has been approved for thirty days
wear, four times longer than one week wear lenses, that they (30 day lenses)
might be safer for any EW, to have been approved for such a long time. Is
there any logic to such an assumption?

But then again, why would Purevision have been approved for thirty days
wear, when other newer materials, with higher dk/t, for example Biofinity,
only for six or seven days?

Are there other factors besides dk/t, that could account for it? Is
Purevision better at resisting deposits than Biofinity and others (besides
N&D)?

Or is it just that the companies did not want to bother with the time and
expense involved of the testing required to get 30 day approval in the USA?
Have some of them been approved for 30 day wear elsewhere (perhaps with a
less expensive and time-consuming testing requirement), but not in the USA?

Just curious. Your input would be appreciated.

On or about Mon, 21 Sep 2009 02:22:22 GMT did "MS" <(E-Mail Removed)> dribble
thusly:

>The first two silicon hydrogel lenses on the market, Night & Day (Ciba) and
>Purevision (B&L) were approved for thirty day wear.
>
[snip]
>Are there other factors besides dk/t, that could account for it? Is
>Purevision better at resisting deposits than Biofinity and others (besides
>N&D)?
>
>Or is it just that the companies did not want to bother with the time and
>expense involved of the testing required to get 30 day approval in the USA?
>Have some of them been approved for 30 day wear elsewhere (perhaps with a
>less expensive and time-consuming testing requirement), but not in the USA?
>
>Just curious. Your input would be appreciated.

I have no idea what goes into the approval process, but I can make some
guesses assuming the process is actually rational.

I've tried both N&D and PureVision. Both are very stiff and feel rather like
smooth plastic. It's hardly a scientific conclusion, but they seem less
likely to hold onto deposits because of that. They also have rough edges,
making them very uncomfortable, but that's another matter.

I now wear primarily Biofinity, with Oasys for switching off. Both are
considerably more flexible and feel less like smooth plastic. They both also
pick up deposits too much to consider wearing for 30 days. I know Biofinity
is approved for 30 day wear in some countries, but I don't see how anyone
could leave them in that long. I typically have them in for less than a week,
and often will pop them out for a quick rub and rinse to improve comfort and
clarity.

Again, that's only my experience and conjecture.

--
- Mike

Ignore the Python in me to send e-mail.

Thanks, Mike

Anyone else? Any of the eye docs here?

By the way, I haven't found either Purevision or the old N&Ds to be
uncomfortable.

I tried one of the new N&Ds--same material as the old, but they have been
supposedly treated some way to make them more comfortable. That lens was
actually quite uncomfortable. My eye doc said that a lot of people have had
trouble with the new N&Ds. I think they messed something up, with their
"improvements".

"Mike Ruskai" <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...
> On or about Mon, 21 Sep 2009 02:22:22 GMT did "MS" <(E-Mail Removed)> dribble
> thusly:
>
>>The first two silicon hydrogel lenses on the market, Night & Day (Ciba)
>>and
>>Purevision (B&L) were approved for thirty day wear.
>>
> [snip]
>>Are there other factors besides dk/t, that could account for it? Is
>>Purevision better at resisting deposits than Biofinity and others (besides
>>N&D)?
>>
>>Or is it just that the companies did not want to bother with the time and
>>expense involved of the testing required to get 30 day approval in the
>>USA?
>>Have some of them been approved for 30 day wear elsewhere (perhaps with a
>>less expensive and time-consuming testing requirement), but not in the
>>USA?
>>
>>Just curious. Your input would be appreciated.
>
> I have no idea what goes into the approval process, but I can make some
> guesses assuming the process is actually rational.
>
> I've tried both N&D and PureVision. Both are very stiff and feel rather
> like
> smooth plastic. It's hardly a scientific conclusion, but they seem less
> likely to hold onto deposits because of that. They also have rough edges,
> making them very uncomfortable, but that's another matter.
>
> I now wear primarily Biofinity, with Oasys for switching off. Both are
> considerably more flexible and feel less like smooth plastic. They both
> also
> pick up deposits too much to consider wearing for 30 days. I know
> Biofinity
> is approved for 30 day wear in some countries, but I don't see how anyone
> could leave them in that long. I typically have them in for less than a
> week,
> and often will pop them out for a quick rub and rinse to improve comfort
> and
> clarity.
>
> Again, that's only my experience and conjecture.
>
> --
> - Mike
>
> Ignore the Python in me to send e-mail.

Any other input on this question?


Thanks in advance.

On Sep 23, 8:09*am, "Mike Tyner" <mty...@mindspring.com> wrote:
> "MS" <m...@nospam.com> wrote
>
> > Any other input on this question?
>
> FDA approval is no guarantee against future legal action.
>
> Every time a company launches a product, they're betting the profits will
> outweigh the lawsuits.
>
> Presumably, 7-day continuous wear will always be statistically safer than
> 30-day wear.
>
> Considering the risks, it isn't easy to justify 30-day wear just for
> convenience.
>
> -MT

In other words, you think that there is not necessarily something
different about ND and PV which make them safer for EW than the other
silicon hydrogel lenses, but it is just that the companies have made a
decision not to market and seek approval for the other lens brands,
for 30 day wear?