It is generally accepted that there is also another factor necessary besides hypermetropia to cause squint. This is called by Quere "facteur tropigene causale", this being fully right, if the conception "tropie" comprises all tropic factors, including orthotropia. This factor is the mechanism of binocular vision, which informs us reliably also in case some abnormalities would occur in the receptor organs. The rule of early treatment that biretinal function is not to be allowed as long as there is squint present, cannot be approved by the author. According to him, the correct causal early treatment cannot be anything else than immediately given spectacles. He describes his method, by which this can be attained in the first and second years of life. The advantages as well as the drawbacks of some other methods (supercorrection, occlusion, penalisation, early and postponed operation) are discussed from the viewpoint of the causality and instantaneous acting.