by george » Wed Feb 05, 2014 12:54 am
There are pros and cons to the various metals used in frames. Here's some basic information I was able to find doing some research around the web:
Titanium - strong, lightweight, corrosion resistant and hypoallergenic (if pure - the alloys may contain metals that are not hypoallergenic).
Memory titanium - this is a titanium alloy, meaning they mix in other metals with the titanium typically nickel or copper. It is generally cheaper than pure titanium, but also strong, lightweight, corrosion resistant and flexible. It generally will return to its original shape unless you really crimp it. If it has nickel in it, it is generally not considered hypoallergenic as some people may have a reaction to nickel.
Stainless Steel - strong, lightweight, corrosion resistant and hypoallergenic (if it does not contain nickel). May not be quite as light or flexible as titanium.
There are other metals that can be used, but if the generic term is metal, I wouldn't want to guess what they are. The glasses I've ordered from Zenni are "metal" with plastic sleeves on the temple. They seem light and reasonably durable.
I picked the frames with the style I liked best, with sizes that were similar to frames I already owned, with lens sizes that were on the bigger side. My first pair of glasses from Zenni had a shallow frame height, which I didn't particularly like.
As to your question about the index glasses to order - you do have a very minimal prescription. And then there is the "add" for the progressive part of the lens, which you didn't mention. I have always gotten the 1.57 index from Zenni, which I think was the same price as the 1.50 for me. 1.59 is the standard index for polycarbonate which is light, shatterproof and inherently has UV protection. I don't know how the material in the 1.57 compares to polycarbonate, but I've never had my glasses crack or shatter. I've never really put them to the test to see how much stress they can handle though. 1.50 (which is typically plastic) is a little heavier than polycarbonate and a little thicker. It also needs a UV protection coating added. Based on your low prescription strength, I would think the thickness won't be an issue at all and all Zenni lenses includes anti-scratch coating and UV protection.