Traditionally, the doctrine of prosecution history estoppel has been defined as an equitable tool for determining the scope of patent claims. The doctrine bars the patentee from construing its claims in a way that would resurrect subject matter previously surrendered during prosecution of the patent application, and thus prevents a patentee from enforcing its claims against otherwise legally equivalent structures if those structures were excluded by claim limitations added to avoid prior art.
The traditional view that depending upon the nature and purpose of an amendment, the doctrine may have a limiting effect within a spectrum ranging from great to small to zero was recently changed by the Federal Circuit. Accordingly, all amendments made for the purpose of patentability are now deemed to have the effect of depriving the inventor of a claim interpretation that includes equivalent structures.