Vasopressin regulates the tonicity of body fluids. These are sometimes known as "tonality", "tonicity" and "tone" (and collectively as "the three T's"). It has the same tonicity as blood. Osmolarity and tonicity are related but distinct concepts. Tonicity of the mylohyoid ridge itself can cause problems with denture retention. Tonicity aberrations are associated with many diseases of the eye (e.g. Adie syndrome).