AB fluid is mainly used to remove proteins from hard contact lenses and keratoplasty lenses, etc. If AB fluid has expired, it is not recommended to continue using it. First of all, the efficiency of the AB solution in removing protein deposits from lenses will decrease after the expiration date because the AB solution itself is used to remove the protein through the action of enzymes, but the activity of the enzymes will decrease after the expiration date and thus the expected effect of protein removal cannot be achieved. Finally, the deterioration of the main components of the AB solution may cause contamination of the lens of the keratocontact lens, which may affect the health of the cornea and lead to complications such as keratitis and corneal epithelial damage. Therefore, it is important to observe whether the AB solution is within the expiration date when using it for protein removal.