Pedro you seem to be getting confused between circling minima and flying a visual approach? What do you mean by minima for visual circuit and CTL? to commence the circling manoeuvre in the first instance you would need XX VIS/ XX Cloud base. Circle to land is a visual manoeuvre..usually commenced due tailwind limits. You cannot descend below circling minima for the approach unless you have the required visual reference. Both Boeing and Airbus FCTM have information on these manoeuvres and the exact limitations per individual operator are included in their Part A procedures.