Abstract: A refractometer for measuring spherical refractive errors of an eye is shown. The refractometer includes an objective first lens system adapted to be moved along a predetermined path between a first position and a second position. A linear diopter scale measuring means is responsive to the movement of the objective first lens system for providing spherical refractive diopter measurements. A fixed second lens system is positioned at a selected location from the first position and is in alignment with the objective first lens system. A Pechan inverting prism system is located in the focal plane or the fixed second lens system and the first position. An adjustment means is operatively coupled to the objective first lens system for moving the same between said first position and said second position. A method for self-testing for spherical refractive errors of an eye using a refractometer of the present invention is shown.