In human corneal transplantation, the donor tissue is:

Ans. is 'b' ie donated human cadaver eyes (Ref: Parson, 19/e, p229).In corneal transplantation or keratoplasty the diseased cornea is removed and replaced with healthy cornea obtained from a cadavers.The cornea should be removed from cadaveric donors within 6 hours after death, sometimes upto 12 hours after death in countries with cold climates (Kanski, 5/e, p145 writes, it to be within 24 hours of death).The cornea can be transplanted immediately or preserved in an eye bank by various preservation techniques for varying intervals.Short team preservation requires the cornea to be used within 48-72 (maximum 96) hours.Intimidate term preservation by organ culture methods - within 30 days.Long term preservation by cryopreservation - within 1 year.Corneal graft can be of following typesFull thickness or penetrating keratoplasty.Partial thickness or lamellar keratoplasty.The come; s an immunologically privileged organ because of its non-vascular nature and hence corneal graft rejection less common than that of other organs.