Is there a difference between a 1.66 high index bifocal lens and a 1.67 high index bifocal lens?

Question

I've just placed an order for a pair of high-index bifocals. When I discussed the lenses with the optician, I requested a 1.67 high index bifocals. But when I came home, I discovered that the paperwork (itemized bill) says 1.66. Is there a difference and why would they put 1.66 instead of 1.67 on the statement? Thank you!

Answer 1

I agree fully with Pedestal...and will just add that it is just a matter of different brands.

The 1.66 or 1.67 would be identical in thickness, it's just what they decided to call it.

Seiko for instance calls it 1.67, but Essilor calls their Hi Index a 1.66...

Both companies have excellent lenses...1.66 doesn't mean any lesser quality than 1.67

Answer 2

There's unlikely to be any real difference in the thickness of the lenses, but there can be a lot of difference in the performance of one brand of 1.66/7 lenses compared to another, depending on the quality of the coating, Abbe number...  the actual difference between 1.66 or 1.67 index is negligible, compared to the other factors.  

I can't easily speculate what exactly happened: did you mention the exact number first or did they?

If you said "1.67"  they will have heard "high index plastic" and used their favourite lens for your Rx, which might have been a 1.66 or 1.67.

Positively, picked because they know it's a good lens for its other properties or, negatively, because it's the one on which they make the best margins.

But that *is* getting speculative.