Corneal grafts could be divided into the following procedures:
The removal of part of the cornea (the anterior layer) keeping the posterior part of the cornea, which contain the pumping machine of the cornea that keep the cornea relatively dehydrated and clear. This type of surgery have the advantage of being a closed eye surgery with less chance of causing infection, Also there is a lot less chance of causing a corneal rejection, as only the anterior corneal lamella is replaced. The visual outcome is the same as the full thickness corneal graft.
We could still replace the full thickness of the diseased cornea, as a result of a severe infection affecting the whole layers of the corneas, or as a result of scaring or clouding of the full thickness of the cornea.
Full thickness corneal graft has more chance of rejection than partial thickness graft, whoever the visual outcomes are the same.
In many cases the cornea become cloudy and the vision deteriorate as a result of a deficit of the corneal pumping machine, which is situated on the back of the cornea. In such a case, replacing the back part of cornea would mostly clear the cornea, without the need to replace the whole cornea, which mean, a lot less risky procedure and less chance of corneal graft rejection, and finally there is no need for an extensive suturing, which need to be taking out during the following years. Also we need to remember that replacing only the posterior part of the cornea would keep the tensile strength of the cornea, which is diminished in the full thickness corneal graft.