Final answer:
During a keratoplasty, a corneal trephine is used to cut a precise, circular area of the cornea to replace damaged tissue with donor tissue.
Step-by-step explanation:
The instrument used during a keratoplasty, which is a surgical procedure to replace part of the cornea with corneal tissue from a donor, is the D. Corneal trephine. This specialized instrument is designed to cut a precise, circular area of the corneal tissue. The other instruments listed, such as the #11 knife blade, Sphenoidal punch, and Westcott scissors, have different specific uses in surgery but are not the primary tools for performing the corneal cut in a keratoplasty.