The American Optical SR-IV Programmed Subjective Refractor: principles of design and operation.

The SR-IV refractor has a spherocylindrical optometer system which provides smoothly variable dioptric power of +/- 20.00 D sphere and +/- 8.00 D cylinder. A split-field monitoring system and joy stick permit three-dimensional alignment. A simultaneous-view cross cylinder system provides distortion-free side-by-side comparison of cross cylinder choices for cylinder refinement incorporates automatic sphere compensation during cylinder power refinement and automatic selection of axis steps during axis refinement. A special astigmatic dial and +/- 0.50 D cross cylinders are provided for low vision refractions. Visual acuities are printed as well as the refined refractive findings at either spectacle or contact lens vertex distance.