We have developed an automatic optical system attached to the Slit Lamp in order to provide automatic keratometry at low cost. The system consists of projecting a light ring as a target at the patient's cornea and the further analysis of the deformation of the target in order to obtain the radius of curvature as well as the axis of the associated astigmatism. The reflected image of the target is displayed in a PC's monitor and a dedicated developed software performs the analysis of the image, that provides the corneal keratometry. Also, the projection of two additional targets provide information about two other regions of the cornea. The clinician is able to understand the behavior of the cornea's curvature radius in these regions by the comparison of the graphical analysis of regular astigmatism that is generated by the software. Irregular astigmatism's measurements are possible in the developed system. The system is easy to use and it has a friendly software interface for the user. Measurements in volunteer patients have been made and the results that were obtained in the system, for the standard target ring are in good agreement with commercial automatic and manual systems, presenting a correlation coefficient of 0,99347 and 0,97637, respectively regarding the radius of curvature and 0,96841 and 0,9568, respectively, regarding the axis. The system's precision is 0,005 mm for the curvature radius and 2 degrees for the axis component.