1. A novel iris image definition estimation system using an astigmatism of the corneal reflection of a non-coaxial light source where virtual images of a light source are measured by a sensor and used for focus adjustment, comprising: a non-coaxial light source which produces an incident light deviating from an optical axis which is transmitted into a cornea at an oblique angle; a meridional virtual image and a sagittal virtual image formed behind the cornea due to astigmatism of corneal reflection; a sensor which captures a composite glint area formed by the meridional and the sagittal virtual images, and subsequently provides information to adjust the a direction of focusing.