Originally Posted by
Pete Hanlin
;)
I think the poll is rather interesting, however. Even after all the discussion, people are voting for option number one. Only three have voted for the correct answer (#2), and one of them was me, so...
Concerning Chip's question on eyes lost to various lens materials, I have always thought that anyone over the age of 18 should be able to choose whatever s/he wants for their lens material and design (including 1.8 index at 1.5mm if they so desire- given a thorough education concerning the material's tendancy to break). Of course, I am a proud card carrying member of the Republican Party's Conservative Branch (R.C.P.B.). Sorry Steve, that was too good of a description to pass up! Plus, its fitting- since I received my new voter's registration card just last week... just in time to vote for the President's younger brother!
Really though, what have we come to in this country? Perhaps we should keep people from buying Corvettes (they are capable of acheiving very unsafe speeds). Maybe we should require auto dealers to adhere to a "Duty to Warn" if their client doesn't purchase a Volvo (which is, after all, the safest car out there).
Perhaps John can look up some figures on just how many lenses are returned for shattering in the UK (since they allow the use of materials and designs the FDA has outlawed here in the states)?
Is ninety nine percent of the whole poly/trivex/whatever push just to protect ourselves from lawyers, or to protect the public?
I sure hope not! Polycarbonate stands as a terrific material even without the fact that it is the most impact resistant material currently used for ophthalmic lenses. Its light weight, high index, UV blocking properties, and ease of manufacture makes it a very attractive product.
Polycarbonate is the only ophthalmic product out there (other than Poly Methyl Methacrylate, which Chip is familiar with from his PMMA contact lens days) that is a thermoplastic resin. This means a manufacturer can take it in solid form, heat it up, press it into a shape, let it cool and BAM- you have a lens (whole process takes about five minutes, and you can chop up the material left over at the end of the process and sell it to other manufacturers who use lower grade polycarbonate for re-use).
All other materials are thermoset:
Allyl Diglycol Carbonate becomes CR-39... it must be activated (which makes the material start to heat up) and "sets" or "cures" into its cast shape. Once it has been locked into its final form, it will never melt again (it will ignite if sufficiently heated, but it will never be molded again), and anything left over at the end of the process is simply wasted. Also, it takes a considerable amount of time to properly cure the material if you want to end up with a quality product.
Methacrylate becomes your mid-index materials and is generally a UV curable product (you cast it and plop it under a UV lamp and it hardens). Once its set, that's it for this material too. The advantage of this material is that UV curing doesn't usually take as long as some other forms of curing.
Styrene and Thiourethane become your higher index materials and producing them involves toxic by-products that are basically unacceptable given the the EPA (Environmental Protection Agency) in this country. That is why most of your higher index materials come from abroad (mostly Japan). This is a cured product as well, and the curing can be very tricky.
Again, sorry for the length... however, the point is (I'm trying to find a way to win Steve over to Polycarbonate, and he is a proud card-carrying member of the Green Party), if you like efficiency and a relatively "green" product, Polycarbonate is for you! Given proper processing, poly is a financial, optical, manufacturing, environmental, and retail dream!!! Cue the poly theme song "Poly's great, poly's good, its used in lenses and in hoods" to the tune of the Barney song...
Thus concludes this installment of "Poly- A better way of life!"
;)
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