In 25 eyes, age range 60-80 years, in purpose of preoperative treatment prior to cataract surgery, measurements of the radius of curvature as well as main meridians of the anterior and posterior corneal surfaces were performed. Average value of the curvature of the anterior corneal surface (R1) was R1 = 7.84 mm, while posterior radius (R2) was 6.4 mm. Main meridian of the anterior corneal surface was in 70% in plus value (+), while postrerior main meridian was always in minus value. It is very important to highlight that main corneal meridians R1 and R2 always cross outside the 90 degrees angle. That is why the combination of the calculation based on the two main meridians superposition (overrefraction) as a form of crossed cylinders has to be calculated (Astigmatismus directus seu obliquus decusatus) using special formula. One of that kind of formulas is Thompson's. Authors want to emphasise the importance of the optical calculation of the posterior corneal surface in the refractive surgery.