The Lens Index number (1.50, 1.57, 1.59, 1.61, 1.67, ) are the degree of refraction the lens provide click here
Photochromic lenses are Special lens which on exposure to UV light turns dark. Click here to know more
Sunglasses lenses which also reduces the glare from light are called polarized lenses click here to know more
Polycarbonate lenses are lenses which are impact resistant, stronger and more light weight than standard lens, Click here to know more about all lens index and material.
If you are willing to turn your prescription glasses into sunglasses then tinted glasses are the best option. Know all about tinted glasses and suitable tint for you by clicking here