The lenses are of identical quality. Both are outsourced to off-site machine cut lens factories and shipped to store.
I don't know where you got this odd idea about lens quality but it isn't factually supported. You can buy thinner and thicker lenses for additional cost, but both will be as accurate as the prescription is.
They are not necessarily the same if the discount store doesn’t offer the same options. A few cheap places don’t offer ultra high refractive index lenses. With the standard high index lens my lenses are very thick at the edges. Also, not all discount stores offer the same anti-scratch, anti-glare, or photochromic options.
The lenses that you get from a discounter will match your prescription, but expensive shops can have differentiating features.
As places move to outsourcing their lens production they can offer more products, since they aren't physically doing it in-store. The handful of discount "while you wait" places, do indeed, have more limited options but it is fast.
Agreed. I get high index 1.74 by Seiko Optics. They're incredible with the most durable coating I've ever found.
People who've only gotten cheap glasses/lenses don't even know how important it is. I get my frames from DITA (www.dita.com) and they've lasted me 5+ years, never bend, warp, etc. Lenses get replaced every 2 years.
In practice different materials of the same index can have significantly different abberation. When I very recently got work-optimized glasses from a local optician, I could sit down and compare the materials they could get. One of the 1.60 index materials (Hoya, I think) was as good as thicker lenses while another (Essilor?) would have given me noticeable fringing on a monitor.
Now try to get a place like Zenni to so much as tell you what they're selling.
The general trend is that higher-index materials tend to have lower Abbe numbers, but there are exceptions. Polycarbonate is a cheap and popular mid-index material that's widely recommended on the basis of its mechanical strength. Its index of refraction is 1.59 and its Abbe number is 30, but there are numerous materials with a similar index of refraction around 1.6 and substantially better Abbe numbers of 41-42, or materials with a significantly higher index of refraction (1.67) and Abbe numbers that are slightly better than polycarbonate.
Zenni and EyeBuyDirect don't want to promote awareness of chromatic abberation, but they do make it easy to know whether you're ordering polycarbonate, and they both have 1/6/1.61 index materials with better Abbe numbers than polycarbonate. Zenni uses one of the Mitsui MR materials for their 1.6 lenses.
Yes, but aberration is different than the distortion and is caused by different refractive indexes at different wavelengths. I'm just talking about how it distorts your vision overall.
I support your spending as much as you want on frames. I will tell you that I get amazing frames and lenses from Zenni. Their mid-range bifocal glasses (so I can see music on the stand) were better in every way for $90 than I got from my local optician (whom I like very much) for $1,000.
Most of the glasses I get from Zenni cost about $30.
So is mine, and so are mine. The frame has nothing whatsoever to do with the quality of the lenses it contains, though, except inasmuch as it constrains their dimensions. And there's nothing in particular to say that you have to buy both in the same place, either.
I have a difficult prescription and my eyes are very important to me. I can't trust them to discounters.