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Shadi Awwad, MD I. Definitions Keratoplasty is referred to as corneal tranplantation or grafting. Lamellar Keratoplasty is a partial thickness corneal grafting. Penetrating Keratoplasty is a full-thickness corneal grafting. II. Indications 1. Optical -Improving visual acuity by replacing the opaque host tissue by clear healthy donor tissue -The most common indication in this category is Pseudophakic Bullous Keratopathy, followed by keratoconus, corneal degeneration and dystrophy, as well as scarring due keratitis and trauma. 2. Tectonic -In patients with stromal thinning and descemetoceles, to preserve corneal anatomy and integrity 3. Therapeutic -Removal of inflamed corneal tissue refractive to treatment by antibiotics or anti-virals. 4. Cosmetic -In patients with corneal scars giving a whitish opaque hue to the cornea III. Recruitment of donor tissue a. Donor tissue should be removed within six hours after death. b. Viable storage period of the removed corneo-scleral button is two weeks. c. Grafts from donors <12 months or > 70 years are preferably not to be used. d. Contra-indications for donors selection: -Death of unknown cause -Certain infectious diseases of the CNS (Jacob-Creutzfeld, SSPE, Progressive Multifocal Leuko-encephalopathy) -Certain systemic infections ( AIDS, septicemia, syphilis, viral hepatitis) -Leukemia and disseminated lymphoma -Intrinsic eye diseases (tumors, active inflammations, previous intra-ocular surgery) IV. Recipient cornea a. Poor prognostic factors -Absence of corneal sensations -Stromal vascularization -Corneal thinning at the expected recipient-donor margin -Active inflammation V. Surgical Procedure 1. Decide about graft size -Usually graft size is no bigger than 8.5 mm in diameter to avoid post-op increase in intra-ocular pressure, anterior synechiae, and vascularzation. -An ideal size is 7.5 mm. Smaller sizes would give rise to astigmatism due to subsequent tissue tissue tension. 2. Excision of donor tissue -Consists of "trephining" the corneo-scleral button previously excised from the cadaver. -Trephination (cutting) is performed with the donor graft endothelial side up in a concave Teflon block. -The donor button is to be 0.5 mm larger than the planned recipient opening. 3. Excision of recipient tissue -Pupils are usually miosed pre-op to avoid injuring the lens and causing cataract -Trephination is done with either the manual, motorized, or vacuum trephine -Rapid decompression of the eye is to be avoided. Partial thickness cut is hence performed first, than full-thickness trephination is performed. -Four cardinal interrupted sutures are applied at 12, 3, 6, and 9 o'clock respectively. Interrupted or running sutures are then performed. -The anterior chamber volume is reformed by injecting Balanced Salt Solution (BSS) VI. Post-Op Care 1. Topical steroids QID and Mydiatic BID are instilled in the operated eye for the next four weeks. Topical steroids should be continued QD for 6 months, the QOD for another 6 months. 2. Early complications include flat anterior chamber, persistent epithelial defects, and infection. 3. Late complications include glaucoma, astigmatism, late wound seperation, cystoid macular edema, and recurrence of the initial disease in the donor graft. 4. Graft failure: -Early: Cloudiness of the cornea from the first post-op day. It is usually caused by defective donor endothelium or trauma during surgery. -Late: Usually the result of immune graft rejection. 50 % occur in the first 6 months, and the majority occur in the first year post-op. Treatment is by hourly topical steroids, as well as periocular steroid injection, as well PO steroid depending on the clinical picture. |
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