In Cochlear v. Oticon, the former owned a patent for a hearing aid that transmits soundwaves transcranially from a patient's deaf side to the patient's non-deaf ear.
Oticon sought to invalidate the patent by inter partes review in the patent office.
The preamble to the patent claim recited a "hearing aid apparatus for sound transmission from one side of a patient's head to the patient's cochlea on another side of the patient's head for rehabilitation of unilateral hearing loss".
Cochlear argued that its claim preamble limited the patent to profound hearing loss. It evidently sought to distinguish the patent claim from prior art.
The Federal Circuit explained that "'as a general rule preamble language is not treated as limiting.'" However, a patent claim preamble "limits the invention if it recites essential structure or steps, or if it is necessary to give life, meaning, and vitality to the claim." But "'preamble language merely extolling benefits or features of the claimed invention does not limit the claim scope without clear reliance on those benefits or features as patentably significant." Further, a preamble is not limiting "only to state a purpose or intended use for the invention."
In this instance, the preamble of "rehabilitation of unilateral hearing loss"is "merely a statement of intended use of the claimed hearing aid. It identifies no structure for the apparatus claimed." "Moreover, this use itself is not an inventive or patentably distinct aspect of the claimed invention."
Patent applicants often try to use the preamble in the patent claim to describe a specific implementation of the invention, in an attempt to limit what prior art can be used to invalidate the patent. However, it can be more helpful to limiting the scope of relevant prior art by including the preamble language in the body of the claim.