Conventional instruments for measuring or correcting refractive errors of the human eye contain large numbers of individual spherical and cylindrical lenses. Refracting instruments having continuously variable power (optometers) are mechanically simpler and allow smooth adjustment of power by the subject (subjective optometers) or smooth adjustment of power by automated photo-electronic sensing mechanisms (objective optometers). Optometers with spherical optical systems have had some clinical success, but those with spherocylindrical optical systems, described since the 1800's, have never been practically useful. Power ranges have been too small, scales have been non-linear, and adjustments have been awkward. Renewed interest in the automation of clinical refraction has led to the development of a spherocylindrical optical system overcoming the disadvantages of previous systems. Cylindrical lenses movable in a prescribed fashion along the optical axis provide continuously variable spherocylindrical power over a wide linear range. This system, in addition to forming the basis of a new refracting instrument, may provide a useful means for manipulation of spherocylindrical power in other optical applications.