Not all corneal transplants are done with the purpose of restoring vision.
Optical corneal transplants/ Optical Keratoplasties are those done when the cornea is opaque due to any reason, and the sole purpose of the surgery is visual rehabilitation.
A therapeutic keratoplasty is a surgery in which the infected cornea is replaced with a healthy one when the infection is very severe and not responding to treatment with drops. Often it is done to reduce the load of infective pathogens in the eye when the infection has involved a large area of the cornea.
Once the infection completely resolves, they may later require an optical graft(transplant) as a second stage procedure.
A patch graft/ tectonic keratoplasty is done to restore the integrity of the globe, i.e. in cases of tissue loss due to trauma or melting of the cornea due to immune-mediated conditions.
Anatomically, there are 2 broad categories of keratoplasties:
PENETRATING- i.e. the full thickness of the diseased cornea (host) is replaced by full thickness donor cornea (donor graft)
LAMELLAR (DALK/DSEK) KERATOPLASTY- only the diseased layers of the cornea are correspondingly replaced by donor tissue. This is especially done when the pathology does not involve the entire cornea. E.g. if the pathology lies only in the front(anterior) or back (posterior)of the cornea, then only that portion needs to be replaced. This ensures that a certain amount of the host tissue is untouched, and thus reduces the chances of rejection, as well as quickens recovery.
This is a highly specialized surgery and has greater benefits than a full thickness surgery.
Dr Kareeshma spent 18 months during her long term fellowship at Narayana Nethralaya, Bengaluru to get trained in these highly advanced techniques.