Polycarbonate lenses is a lens material that has an index of refraction of 1.58.
The higher the index of refraction the less lens material you need to bend light. Polycarbonate has a higher index of refraction than CR-39 plastic and will result in a thinner lens than plastic.
Polycarbonate material is extremely strong and impact resistant. Because of its unique qualities it is the obvious choice for children's eyeglasses and strongly recommended for active people and sports eyeglasses. Polycarbonate material has a built in UV blocker. These lenses will protect your eyes against harmful UVA and UVB light waves. An excellent choice for prescription powers between 3.00 diopters and 4.50 diopters.
If you are concerned about the lenses thickness and want a overall thinner lens appearance, it is recommend that you consider a high index lens.