Nearly all spectacle lenses are made from various types of plastic resin. Basic plastic is fine for small prescriptions but if the first ‘number’ on your prescription is more than +/- 3 then you will benefit from what are called ‘High Index’ plastics. These are thinner and lighter than standard lenses. The higher the index number (eg 1.6, 1.67, 1.74) the thinner the lens, but the more it costs. The dispensing optician will advise you on the best option for your lens power.
*Image shows a -4.00 lens in 1.74 material on the left and standard 1.39 on the right.
Image shows anti-glare coating.