A Mathematical Appraisal of Meridional Referactometry

It sometimes happens that a patient who has difficulty responding adequately to the usual tests may be refracted using a stenopaic slit. Conventional methods refract the two principle meridians of the eye and obtain the final prescription by utilizing the crossed cylinder formula of Thomson. It is shown that this approach fails in the case of bi‐oblique astigmatism and that in fact the method providers insufficient data to arrive at a unique prescription in this case.