In human corneal transplantation, the donor tissue is
B i.e. Donated human cadaver eyes Donor corneas are harvested from cadaveric donors within 6 hours after death Q (upto 12 hours after death in cold countries.) Corneal Transplantation (Grafting) /Keratoplasty General Indications To provide a clear visual axis and restore good vision (Optical Keratoplasty) To restore the integrity of the globe in corneal diseases (Tectonic Graft) To remove infective tissue unresponsive to conservative treatment (Therapeutic Graft) To improve the appearance of the eye (Cosmetic Graft) Contraindications Death of unknown cause CNS disease such as Creutzfeldt-Jacob disease, subacute sclerosing panencephalitis, rubella, Reye's syndrome, rabies & infectious encephalitis. Infections such as HIV, Hepatitis, septicemia, syphilis, & endocarditis. Eye disease as retinoblastoma, malignant tumor of anterior segment & active ocular inflammation (uveitis, scleritis, retinitis & choroiditis) Prior ocular surgery (although pseudophakic eyes may be used with good cell density) Congenital or acquired anterior segment abnormalities such as Keratoconus & Fuch's endothelial dystrophy. * Corneas from infants (53 year) are used only very occasionally, even for pediatiric transplants as they are a/w surgical, refractive and rejection problems Graft-Harvesting Donor corneas are harvested from cadaveric donors within 6 hours after death Q (upto 12 hours after death in cold countries.) Graft-Preservation Sho term (upto 96 hours) - Moist chamber (at +40C) method for 24 hours. - M-K (Mc Carey-Kaufman) medium upto 96 hours. Intermediate-term (upto 2 weeks) - K-SOL / DEXOL / OPTISOL-medium Long term (months - years) - Viable: Organ culture & cryopreservation - Nonble: Glycerine Types Full Thickness or Penetrating keratoplasty Paial Thickness or Lamellar Keratoplasty - Superficial LK (replacement of corneal epithelium & superficial stroma) Deep anterior LK (DALK). all opaque tissue almost upto the level of Descemet membrane is removed Descemet stripping endothelial Keratoplasty (DSEK)/DS automated EK (DSAEK; when a microkeratome is used to perform donor lamellar dissection)/ Posterior LK (PLK) Small Patch grafts which can again be full or paial thickness Full Thickness/ Penetrating Keratoplasty (PKP) It is full thickness replacement of diseased corneal tissue with a healthy donor. It can be done in disease involving all or few layers of cornea eg keratoconus, pseudophakic bullous keratopathy, Fuchs endothelial & other dystrophies. An ideal graft size is 7.5 mm; grafts smaller than this may 1/t high astigmatism. Grafts 8.5 mm are prone to postoperative anterior synechiae formation, vascularization and increased intraocular pressure. - PKP has long been the gold standard for treatment of endothelial dysfunction. The limitations of PK include However, because of recent advances & lack of these limitations, endothelial keratoplasty is rapidly gaining popularity. It takes 6 months to many years for the refraction to stabilize 10-15% of patients typically require a hard contact lens for best vision and final mean refractive cylinder of 45D is common PKP incision cuts all corneal nerves, so the inclination to blink and produce tears is reduced postoperatively. This, together with prolonged presence of corneal sutures, increases the risk that ocular surface complications will interfere with recovery. PKP wound never heals back to the full strength of a virgin cornea, so a PKP eye is forever at increased risk of loss from a traumatic injury. Paial Thickness /Lamellar Keratoplasty (LKP) - It is a procedure in which a paial thickess graft of donor tissue is used to provide tectonic stability and /or optical improvement. - It may be of 2 types: anterior LKP and posterior LKP. - In anterior LKP, the transplanted tissue does not include corneal endothelium. This procedure avoids endothelial rejection and thus donor tissue may be obtained from older eyes. Indications for anterior LKP mainly include anterior corneal pathology in which the posterior cornea is unaffected - In deep LKP and posterior LKP, the diseased corneal endothelium is replaced while keeping the anterior corneal surface intact. - Because the donor endothelium is not used, the criteria for anterior LKP are less stringent than those used in PKP; the tissue does not need to be as fresh as that used in PKP. Corneal stroma may be used upto 7 days postmoem (whereas, Posterior LKP has same criteria as PKP) . Endothelial Keratoplasty (EK) i.e. posterior lamellar keratoplasty/ Descemet's Stripping endothelial Keratoplasty involves selective removal of dysfunctional recipient corneal endothelium and replacement with donor tissue consisting of posterior stroma and healthy endothelium. EK is performed through a small incision and spares the majority of host cornea so corneal strength and surface topography are minimally altered & technique is essentially refractive neutral. Fuhermore, corneal innervaton is retained and corneal sutures are not required. So corneal surface complications are minimal. The small incison allows rapid healing and rapid visual recovery after surgery. While fewer patients may achieve 20/20 vision after EK compared with PKP, overall the visual results are more predectible. - DSEK increases corneal thickness because posterior donor stroma is implanted without removal of any recipient stoma. In general, younger patients are likely to achieve better visual acuity after DSEK than older patients (even when have no retinal problems). Whereas PKP was often post phoned until after retirement or at least until visual problems were quite disturbing, EK is now being performed earlier, when visual problems begin to interfere with daily activities, such as reading or driving Infact, it is preferable to perform EK before long standing corneal edema 1/ anterior stromal scarring, because the anterior stroma is not replaced in EK.
Synthetic polymer
Donated human cadaver eyes
Donated eyes from live human beings
Monkey eyes