Eyeglass wearers who are very myopic and hyperopic are often identified by the thickness of their lenses. Fortunately, today there are different ways to make glasses glasses thinner and lighter.
Why thin glasses?
The glasses are thinned for aesthetics. It is true that it is prettier when the glasses do not go beyond the frame. More beautiful but also more comfortable, the glasses are indeed lighter to the touch. Tapered glasses also enlarge the eyes behind the glasses in case of positive glasses and shrink less in case of negative glasses. It is therefore more pleasant to watch. In addition, they are flatter, so that the mount changes less shape when mounting glasses.
The refractive index of the material is an important parameter.
For the thinning of the glass, it is the index of refraction of the material which is the most important parameter. This index indicates how the light moves in the glass. The higher the refractive index of the material, the more glasses can be thinned. The disadvantage of a higher refractive index is that the glass shines more. This is why spectacle lenses are provided with a suitable antireflection coating.
Since a power of 2.00dpt, you can take a first thinning, a second thinning we advise from 4.00dtp and a third from 6.00dpt. A glass with a refractive index of 1.5 is not thinned
With 1.6 it is ± 20% thinner
With 1.67 it is ± 30% thinner
With 1.7 it is ± 30% thinner
With 1.74 it is ± 35% thinner
With 1.8 it is ± 50% thinner
With 1.9 it is ± 65% thinner
The way the glass thins also depends a lot on the size of the frame.
The larger the frame, the thicker the glasses, so extra thinning is sometimes necessary.