Optical lens materials
Mmm ...not quite correct Soupy......
Virtually no optical outlet wants to make glass lenses these days as they are too dangerous and heavy . We used to either chemically toughen them or heat anneal them but they were still dangerous,caused polarised phenomena in heat treated screens in older cars and airliners and you only see them these days in "old" sunglasses brands ,usually from the USA.
Virtually all plastic lenses are injection moulded...stock lenses in single vision in the range+ or- 6.00/-2.00 usually come out of a packet at the optical lab. Doesn't matter if they are CR39 , Trivex, polycarbonate, or the latest 1.60 ,1.67, or 1.74 materials....all 'ground' i.e. individually made to your prescription lenses start as an injection moulded thick " blank".
The main difference in the cause of distortions and cloudy vision is the quality of manufacture , the quality of the research in the design of the curvatures and the quality of the coatings applied for scratch and reflection reduction.
With no-name brands coming out of China or other cheap labour countries ,for instance , you are taking pot luck ...and some chain groups repackage them with names that sound like quality.....surprised?
Companies like Zeiss, Rodenstock,Essilor , Shamir, Coburn,and a few others make lenses of roughly equal high quality probably also in China or Thailand but control and supervise their factories to 1st world standards.
I believe Serengeti lenses are made by Coburn.
I get to try all the materials at no charge and don't think Trivex is any better than polycarbonate except for slight colour dispersion at oblique angles....I can see a slight colour fringe on either side of a power line occasionally.
The newer 1.60 refractive index material is thinner, lighter than Trivex for the same power and has a similar Abbé number so less colour fringes than poly....probably better than Trivex....but I don't notice it much.
Lens design has improved rapidly in the last few years as computers have become more powerful so lens curves can be calculated to give clear vision as the eye looks obliquely through the edges of a lens.
We no longer lathe then grind with carborundum then polish with cerium oxide the way I was taught 43 years ago...now digital surfacing produces infinitely variable shapes for multifocals or "aspheric best form " peripheries....
I still need to go and see one of these machines.....$ 4.00 lenses from India are not of this standard...
My advice is find an optometrist who gives value by using good quality lenses ( they don't have to be the dearest)..
and takes the time to accurately take the optical centre measurements....like a broken record...
Cheers,
Flopt