Purpose: To compare the efficacy of topical 0.03% tacrolimus with systemic mycophenolate mofetil (MMF) in preventing corneal allograft rejection after repeat keratoplasty.

Design: Prospective, randomized clinical trial Introduction: Repeat keratoplasty continues to be an important indication for corneal transplantation in many centers, and it accounts for up to 41% (varying from 6% to 41%) of all keraptoplasty cases performed.

Methods: This study will enroll all patients who are candidate for repeat keratoplasty after a failed penetrating keratoplasty. Group 1 will receive MMF orally 1 g twice daily for the first 6 months and then 1 g daily for the next 6 months, and group 2 will receive topical 0.03 % tacrolimus 3 times a day for 12 months. All patients are treated with topical and oral corticosteroids postoperatively. The participants are observed closely for signs of graft rejection, and the rates of rejection-free graft survival are calculated and compared between the two groups at postoperative month 12

Inclusion Criteria:

• all patients who are scheduled for repeat corneal transplantation following failed primary penetrating keratoplasty (PK )

Exclusion Criteria:

• uncontrolled increase in intraocular pressure
• active herpetic keratitis and corneal ulcer
• limbal stem cell deficiency
• a history of limbal stem cell transplantation
• age less than 18 years
• pregnancy, a history of malignant disorders
• abnormal liver or kidney function
• the presence of poorly controlled systemic hypertension
• diabetes mellitus
• systemic infections
• active peptic ulcer disease
• any gastrointestinal disorders led to patient exclusion