Following a sight test many patients are issued with a prescription for spectacles. The principle components of a spectacle are the lenses and the frame. The prescription dictates the power, but lenses can be supplied in many different materials and forms. Thin lens technology reduces thickness and weight, whilst retaining strength. Varifocal lenses allow those with both distance and near prescriptions to have one lens that fills both functions. Modern spectacle frames are strong and lightweight; available in many colours and designs; being made from metal or plastic or a combination of both.