Variation in disposable corneal trephine sharpness

During a recent corneal transplantation procedure, it was discovered that the disposable corneal trephine being used was dull; it would not even penetrate Bowman's layer of the recipient cornea. In contrast, the replacement trephine was sharp. The appreciable variation of trephine sharpness was confirmed by scanning electron microscopy. The consequences of poor quality in an ophthalmic surgical instrument are discussed.