Patent US 5,285,224

Methods and apparatus for measuring or determining refractive errors are disclosed. In some embodiments the invention includes two bars, each containing multiple lenses positioned longitudinally along the bar, and a collar adapted to constrain relative movement of the bars. Moving, or sliding, the bars and collar positions various lenses in the patient's line of sight, permitting the patient to determine which combination produces the best vision. If asymmetrical lenses are included in either bar, rotating the appropriate lens (either directly or by rotating the bar) provides additional information concerning the optimal refractive correction. The collar or bar may further comprise an indicator for signifying the angular rotation of any asymmetrical lens positioned along the patient's line of sight.