The claims must be drafted in terms of the "technical features of the invention". This means that claims must not contain any statements relating, for example, to commercial advantages or other matters not related to "carrying out" the invention, but statements of purpose are allowed if they assist in defining the invention.
It is not necessary that every feature is expressed in terms of a structural limitation. Functional features may be included provided that a skilled person would have no difficulty in providing some means of performing this function without exercising inventive skill (see F‑IV, 6.5). For the specific case of a functional definition of a pathological condition, see F‑IV, 4.22.
Claims to the use of the invention, in the sense of the technical application thereof, are allowable.