The Federal Circuit’s decision in Eye Therapies, LLC v. Slayback Pharma, LLC  provides further insight into the tools available for patent claim construction. The Federal Circuit had previously held that a patent’s specification can evidence that the patentee intended for a term in the patent claims to have a different meaning than what is typical. Now, the Federal Circuit has held that the prosecution history—the exchanges between the U.S. Patent & Trademark Office and the patent applicant during the application process—can do the same.

Eye Therapies owns and licenses a patent that teaches a method to reduce eye redness using a low-concentration dose of brimonidine. Originally, the patent claimed a method “comprising” the administration of low-concentration brimonidine. The patent examiner understood the claim to mean a method including but not limited to brimonidine as the active ingredient, so the claim was rejected as being anticipated by another patent, which discloses the administration of brimonidine and brinzolamide for eye treatment. Eye Therapies amended its claims to assert a method “consisting essentially of” such administration and explained to the patent examiner that its method required no active ingredients other than brimonidine. The examiner allowed the amended claims, and Eye Therapies began licensing the patent for product manufacturing and sale.

Slayback Pharma originally sought to copy and market a generic drug version of the product, but after being sued for infringement by Eye Therapies’s licensee, it later brought a challenge to the Patent Office. The Patent Trial and Appeal Board instituted an inter partes review of the patent and determined that its claims were unpatentable. In its decision, the Board noted that “consisting essentially of” typically means that an invention necessarily includes the listed ingredients but was open to unlisted ingredients that do not materially affect the basic and novel properties of the invention, similar to “comprising.” Here, the patented method necessarily included brimonidine to reduce eye redness but was open to unlisted ingredients that also reduced eye redness, so the patent was anticipated and obvious.

Eye Therapies appealed the Board’s decision to the Federal Circuit, which reversed the Board’s claim construction, vacated its decision, and remanded the matter for a new obviousness analysis. Though the Federal Circuit agreed that the general meaning of “consisting essentially of” allows for the inclusion of unlisted ingredients, it held that a patentee may disclaim an alternative meaning in the prosecution history. Here, Eye Therapies changed its claim language to distinguish from another patent that used additional active ingredients to brimonidine and expressly argued that its amended language precluded the use of other active ingredients. That was the patent’s novelty—a method reducing eye redness using only brimonidine. Thus, the prosecution history informed the meaning of “consisting essentially of” in claim construction and precluded a meaning that overlapped with another patent. 

This decision builds upon the Federal Circuit’s decision in Ecolab, Inc. v. FMBC Corp., which held that a patent’s specification can clearly indicate that certain language departs from its typical meaning for purposes of claim construction. Eye Therapies makes clear that a person of ordinary skill in the art would also look to the prosecution history to understand the meaning of a claim. This approach to claim construction can help patent applicants further refine the meaning of terms used in their claims, especially if the intended meaning is atypical. And it may help patent challengers combat broadly written claims by restricting claim construction to particular meanings.