Do contacts block out UV light to any extent? If so, how effectively,
and what types of UV?
Thanks!
19
Apr
Contacts and UV
Do contacts block out UV light to any extent? If so, how effectively,
and what types of UV?
Thanks!
Larry Bickford wrote:
> In article <337C94EA.3…@juno.com>, rattle-n-…@juno.com wrote:
> > Do contacts block out UV light to any extent? If so, how effectively,
> > and what types of UV?
> > Thanks!
> Many fluorosilicoacyrlate RGP lenses contain UV blocking agents, orginally
> used to help prevent the plastic from deteriorating from UV exposure. Few
> soft lenses block UV.
ALL plastics block UV.
> Is it effective?? Probably, as far as blocking wavelengths to about
> 380nm, which includes all of the UV-b and most of the UV-a. It is not,
> however, a substitute from UV blocking goggles for industrial uses and I’d
> still wear sunglasses when out in the nasty ‘ole sun (especially you folks
> down-under and in Scandinavia, most impacted by the thinning ozone layer.)
> and on the ski slopes.
There is no scientific evidence to prove that the "so-called" UV
blocking CL’s block any more UV than any CL’s.
Read the fine print at the bottom of the Precision ad.
There is no reason for patients to pay more for something that doesn’t
give them anything in return.
Peg
In <3391E92B.4…@worldnet.att.net> "P.S. Achenbach"
<Drs.psa-and-…@worldnet.att.net> writes:
>There is no scientific evidence to prove that the "so-called" UV
>blocking CL’s block any more UV than any CL’s.
>Read the fine print at the bottom of the Precision ad.
>There is no reason for patients to pay more for something that doesn’t
>give them anything in return.
>Peg
The following applies to soft lenses:
If you place a UV absorbing contact on a photochromic lens and expose
the pair to sunlight, the resultant "light spot" under the lens at
least proves that the lens absorbs the activating wavelengths. Try it
with a non-UV lens and no such effect takes place (although some of the
"soft-colors" have this property to a variable degree).
To my knowledge, there is no difference in price (e.g. between
Precision UV and say NewVues).
Bill
In article <3391E92B.4…@worldnet.att.net>, "P.S. Achenbach" <Drs.psa-
and-…@worldnet.att.net> writes
>Larry Bickford wrote:
>> In article <337C94EA.3…@juno.com>, rattle-n-…@juno.com wrote:
>> > Do contacts block out UV light to any extent? If so, how effectively,
>> > and what types of UV?
>> > Thanks!
>> Many fluorosilicoacyrlate RGP lenses contain UV blocking agents, orginally
>> used to help prevent the plastic from deteriorating from UV exposure. Few
>> soft lenses block UV.
>ALL plastics block UV.
True, but for common plastics used in CL’s (ie HEMA), only light below
ca. 230nm is blocked. Therefore, as far as solar uv is concerned these
plastics will not remove ANY uv (air will absorb below 220nm)
>> Is it effective?? Probably, as far as blocking wavelengths to about
>> 380nm, which includes all of the UV-b and most of the UV-a. It is not,
>> however, a substitute from UV blocking goggles for industrial uses and I’d
>> still wear sunglasses when out in the nasty ‘ole sun (especially you folks
>> down-under and in Scandinavia, most impacted by the thinning ozone layer.)
>> and on the ski slopes.
>There is no scientific evidence to prove that the "so-called" UV
>blocking CL’s block any more UV than any CL’s.
Yes there is. For instance, Actifresh 400 (a Hydron lens) will remove
95-98% of all light with a wavelength below 400nm. The transmittance
traces often reproduced in sales literature are recorded using a
spectrophotometer. See "Fresh on the scene", G. Allsop, The Optician,
pages 30-32, March 7, 1997 (a UK journal for optometrists and dispensing
opticians, published by Reed Business Information)
What will differ between lenses is the type of UV blocker used. Many of
the older ones cut off at about 380nm, but blockers are available that
will cut off at around 400nm. Both Actifresh 400 and Precision UV
contain blockers that cut off at 400.
Similarly, in order to sell these lenses to you eye doc’s, we have to
satisfy regulatory bodies (eg the FDA) that our products are safe and
effective. Do you believe that these bodies would allow manufacturers to
make wild unsubstantiated claims?
Trev Glasbey
Hydron Research and Development
Where is the published, scientifically valid study, Larry. Accept the
challenge, or stop with the disparaging remarks.
Peg
See "Fresh on the scene", G. Allsop, The Optician,
> pages 30-32, March 7, 1997 (a UK journal for optometrists and dispensing
> opticians, published by Reed Business Information)
The above mentioned "publication" is not in a scientifically recognized,
refereed journal.
Peg
In article <339AD94F….@worldnet.att.net>, "P.S. Achenbach" <Drs.psa-
and-…@worldnet.att.net> writes
>See "Fresh on the scene", G. Allsop, The Optician,
>> pages 30-32, March 7, 1997 (a UK journal for optometrists and dispensing
>> opticians, published by Reed Business Information)
>The above mentioned "publication" is not in a scientifically recognized,
>refereed journal.
>Peg
If you really want peer reviewed journals, try searching the scientific
literature via Chemical Abstracts. I am not prepared to do this
searching for you, as I an too busy working on uv blockers at the
moment.
With regard to your original posting. I take it that you believe that
dyes work. All dyes absorb particular wavelengths strongly. For
instance, a dye called Procion Blue absorbs at a wavelength of about 590
nm, (ie yellow light). If white light is shone onto this dye, it will
appear blue, since the yellow has been removed. As you may know, dyes
absorb light of a particular wavelength VERY strongly. Procion blue is
therefore added to contact lens monomers to give a blue handling tint.
Typically, only 0.02% of the lens dry weight will be the dye. Now,
consider a dye that absorbs very strongly, at say 350nm. As only non-
visible light is being absorbed, the "dye" will appear colourless (in
actual fact, a slight yellow tinge will be seen, due to the tail end
absorbtion of blue light). Now, just suppose this latter dye is called a
UV blocker, and is added at between 0.5 and 1% of the lens dry
weight…….
If you want any UV traces to demonstrate this, please contact me by e-
mail.
Trev Glasbey
Hydron Research and Development
P.S. Achenbach wrote:
> Where is the published, scientifically valid study, Larry. Accept the
> challenge, or stop with the disparaging remarks.
> Peg
Are you looking for proof that the lenses block UV? This isn’t
hard to show.
Whether there is any big health benefit in blocking UV – that’s
another issue. The benefits seem minor unless you ask someone
with a financial interest in coatings.
I’m glad Vistakon didn’t try to jack up the price when they
added the UV process.
–
Mike Tyner, OD
drm…@bham.com