2. Ophthalmic optics and progressive lenses, definitions and presentation of results

Some basic features of progressive lenses are defined. The backbone of this lens type is the principal meridian and the power progression along the meridian provides clear vision into all distances. A definition of the progression length is given. In the reference points the optical powers are controlled with the focimeter and by means of the fitting cross the lens is centered correctly in front of the wearer's eye.

Another part of this chapter is dedicated to the presentation of the computation results. Isopower plots depict the power increase over the total suface. The inevitable aberrations are described by isoastigmatism lines as regards the surface astigmatism and by the deformation of a rectangular grid as regards the optical distortion.