The choice of spectacle lenses material is important for different strengths: it is better to make lenses of greater strengths from thinned material to avoid accumulation of too much weight on the nose. The purpose of the spectacles usage determines the optical strength of the lenses.

Monofocal spectacle lenses have the same strength all over the whole lens, e.g. in the so called 'common glasses' with which you see either far or near. Vision range i.e. how far or near you can see is affected by the lenses strength, adaptability of the user's eyes and eye lenses elasticity – called accomodation.

Spectacles meant for near vision may be monofocal (in this case one sees the closer area determined by their strength and the user's eye adaptability), bi- or multi focal.

Bifocal spectacles have two different strengths – through the upper part of the lenses you see into far distance and the 'slot' in the lower part is for reading where the close add, i.e.suitable strength for reading, is inserted fitting your eyes needs.

The close add for multifocal spectacles is designed with smooth transition, i.e. the lenses have a different strength for reading, but the border between the areas is not visible.