ABSTRACT

A. INTRODUCTION Spherical and cylinder corrections with spectacles for the refractive errors of the eyes have been performed since the thirteenth and nineteenth centuries. From the latter time, refractive errors have been measured for sphere and cylinder components in the general ophthalmic practice. Although corneal topographic analysis can be performed to evaluate the corneal irregular astigmatism, and rigid contact lenses can be used to correct corneal irregular astigmatism, it is still difficult to evaluate the irregular astigmatism components in refraction and to correct for irregular astigmatism with any optical device until recently.