Which statement about ALK or TK is correct?

• A. They have the same contraindications as PKP in all cases
• B. They permit tissue with local endothelial disease or prior ocular surgery that does not compromise the stroma
• C. They require no prior ocular surgery
• D. They require corneas from Downs syndrome

Answer: (B)

The key idea is that ALK and TK replace only the front layers of the cornea, leaving the back part (especially the endothelium) intact in many cases. Because the transplantation targets the anterior stroma, the donor tissue’s endothelial health isn’t as critical as it is for full-thickness grafts. This means you can use tissue where the endothelial part is diseased or where there has been prior ocular surgery, as long as the anterior stromal tissue is suitable to support a clear graft. In contrast, full-thickness keratoplasty relies on a healthy donor endothelium to keep the graft clear, which is not the situation addressed by ALK or TK. That’s why the statement describing permissive use of tissue with local endothelial disease or prior surgery, provided the stroma is fine, best fits these procedures.