Abstract

An ophthalmic refractor is provided which is configured for carrying out the Jackson cross-cylinder test. To improve accuracy, an optical encoder is provided in conjunction with each cylinder axis control knob and in conjunction with the lens mount of the cross-cylinder test lens. The cross-cylinder test lens is driven by a d.c. motor and worm gear assembly and a control circuit is provided for selectively energizing the drive motor in correspondence with the settings of the optical encoders. For power mode operation, the control circuit effects motor drive to align the axes of the cross-cylinder lens and pertinent cylinder axis. Correspondingly, for axis mode operation, the control circuit further adjusts the positioning by the motor of the cross-cylinder lens by 45°. Illuminated digital displays are provided on the refractor for direct digital readout of cylinder axis diagnostic data as well as test mode identification.