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Lens Thickness Explained (Index)When you put your prescription information in, the website will calculate how thick the lens will be and then offer a suggestion for the lens that would most likely be best for you. Its not like we are trying to sell you a more expensive lens (although the thought is appealing). The idea is that most people would not want to have really thick lenses (coke bottle glasses?).
When you fill in your prescription info you will notice the first number is a SPH (Spherical) reading. If your prescription has a “plus (+) SPH then the lens will be thicker in the middle and thinner on the edges and will make your eyes look “bugged out” if the lens is too thick.
A “minus” (-) SPH will be thinner in the middle and thicker at the outside edges, making them look distorted on the edges. In a plastic frame, you can hide the thickness sometimes in a “minus” SPH lens.
Still, its not all cosmetic and the quality of your vision can be affected by the thickness. The higher index lens means that it is a more refined lens that can give just as much correction with less material. Better “refractive” properties. Kind of like how some diamonds are clearer than others – better material.
You also reduce the weight of your glasses by choosing a thinner lens. The higher the index, the more expensive lens. Still, I have a pair of 1.67, progressive, sun-darkening lenses (I have a -4.75 SPH) and the whole pair of glasses cost about $150 with a rimless titanium frame. My old pair I got from my brother, who is an optometrist, and his cost on the lenses alone was $400!! And that was a few years ago.