**Question:** Which of the following statements regarding corneal transplantation is true?

A. Corneal transplantation is a common surgical procedure for treating corneal diseases and injuries.
B. Corneal transplantation involves replacing the entire cornea.
C. Corneal transplantation is a rare procedure performed only for severe cases.
D. Corneal transplantation requires a long waiting period for the donor tissue.

**Correct Answer: B. Corneal transplantation involves replacing the entire cornea.**

**Core Concept:** Corneal transplantation, also known as keratoplasty, is a surgical procedure used to replace a damaged or diseased cornea with a healthy donor tissue. The primary purpose is to restore vision and protect the patient's eye from further damage.

**Why the Correct Answer is Right:** Corneal transplantation is indeed a common surgical procedure for treating corneal diseases and injuries, such as keratoconus, corneal ulcers, and severe cases of keratitis. The procedure involves replacing the entire cornea (stroma, epithelium, and endothelium) to restore vision and prevent further complications.

**Why Each Wrong Option is Incorrect:**

A. This statement is partially correct as corneal transplantation is indeed a common procedure, but stating that it is performed only for severe cases is misleading. A wide range of corneal diseases and injuries require corneal transplantation.

C. This statement is incorrect as corneal transplantation involves replacing the damaged tissue, not just a part of the cornea. The procedure aims to restore vision and protect the eye, not just treat severe cases.

D. While the waiting period for corneal transplantation can vary, it is not necessarily long. The availability of donor tissue, the expertise of the surgeon, and the specific procedure chosen can influence the duration of the waiting period.

**Clinical Pearl:** Corneal transplantation is a valuable tool for restoring vision and preserving eye health in patients affected by various corneal diseases and injuries. A thorough understanding of the procedure and the available options (penetrating keratoplasty, deep anterior lamellar keratoplasty, and Descemet's Stripping Endothelial Keratoplasty) is crucial for selecting the most suitable approach for each case.