If a rough surface is placed in a path of light then the scattering can be significant. This occurs as the light rays bounce off in different directions at different points along the surface. This is the principle behind frosted glass for bathroom windows. Spectacle lenses are therefore highly polished to minimise the scattering of light. It is also important that the lenses maintain their polished surface. So, in order to maintain lenses that do not significantly scatter the light, a way has to be found of improving the abrasion resistance of lenses.