Re: Deteriorating night vision

Chris Malcolm wrote:
Tiger Lily <me@xxxxxxxxxxx> wrote:
Dennis R wrote:
In article <6qr1duFe99p8U2@xxxxxxxxxxxxxxxxxx>, me@xxxxxxxxxxx says...

polycarbonate, Nicky

it's thinner than regular material
it's very strong (recommended for kids here, especially if they are into sports)
somewhat scratch resistant (the eyeglass place says you don't need the scratch coat)
and i HATE all of the anti-glare lenses i have had, due to the colour that it gives to the lenses, not to mention the finger print problem

the Crizal mentions that finger prints can be a problem with it


Kate: What is your your prescription adjustment for myopia? -3.0,-4.0, greater? I hung out a lot in sci.med.vision. After you wade past their equivalent of Chung and the aspartame nutters, they have several opticians and optometrists who help out. Polycarb is used a lot because it is cheap. At an index of 1.59, it also has about the worst light distortion (expressed as an abbe value) of all lenses materials. In a moderate myopic prescription, it would probably would not be noticed. For a more shatterproof version of a polycarbonate, in North America you could ask for a brand called Trivex.

Hi-Index plastics (1.60,1.64,1.65,1.66,1.67,1.70) are thinner at higher myopic prescriptions like mine (-6.75, -7.25 in each eye respectively). They also have a much better abbe value than polycarb, therefore less distortion. Hi-Index are preferred for progressives for above moderate prescriptions as well.

The new modern anti-reflective coatings are worlds apart from the old "applied" coatings. They are very durable, easier to clean, have little distortion, and built into the lenses before they are ground. Crizal was the first big brand name, but there are other brands. Teflon just got into the act as well. All of these coatings can be ordered with any of the better brand names lenses.

Two interesting threads in sci.med.vision are:

http://tinyurl.com/55lq5y

http://tinyurl.com/65ukgz

Dennis (Type 2)
dang

really interesting, Dennis, thank you

my correction is -5.25 and -5.75
kidlets correction is +3.50 and +4.50

i've been buying him the polycarbonate lenses :(
looks like i should have been getting the high index plastic lenses for him (the optomitrist indicated 'asphyrical' lenses for his glasses and the glasses co told me polycarb is asphyrical........ there weren't exactly giving 'full disclosure')

Aspherical, i.e. lenses not shaped like sections of a spherical
surface. That gives better control of off-axis distortions. But it's
purely to do with the *shape* of the lens, nothing to do with the
*substance* the lens is made from, except that forming an aspherical
lens will be much cheaper in some materials than others.

one place i went to and asked for the asphyrical lens told me that it's a specific lens they use

and yes, the idea is to give teenlet better periferal vision and less distortion in the lens correction

--
kate
type 1 since 1987
www.diabetic-chat.org
www.diabetic-talk.org
http://www.diabetes-support.org.uk/newly%20diagnosed.html
.

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