The Lens Type and Lens Material Guide.
Most spectacle lenses are made of plastic materials. Glass lenses as also available but much less common nowadays. More often they are reserve for very high prescription such a thinner finish can be achieve since they are available in higher refractive indices.
Now, it follows that the higher the prescription of your glasses, the thicker and more power the lens is.So, if you want your prescription glasses to be thinner and lighter you can choose to have a higher refractive index lens. This makes the glasses more comfortable to measure and make you feel less self-conscious about how thick the lenses look to other people.
One important factor relating to the lens is the material. This is important when considering the lens prescription also referred to as the power of the lens.
As the lens becomes more powerful e.g., high prescriptions the lens become heavier and thicker. Lenses that correct longsighted at thicker at their centre. Lenses that correct Short-sightedness are thicker at the edges.
Some patients are very self-aware of this appearance and prefer to have their prescription lenses made thinner. This refers to the materials refractive index. The higher the refractive index the thinner the lens is and the lighter it is too. And so, your prescription designer glasses will be more comfortable to wear.