A<unk>  is a replacement cornea to be transplanted in the place of a damaged or diseased cornea normally approximately 8.5–9.0mm in diameter. It is used in a corneal transplantation procedure (also corneal grafting) whereby the whole, or part, of a cornea is replaced. The donor tissue can now be held for days to even weeks of the donor's death and is normally a small, rounded shape. The main use of the<unk>  is during procedures where the entirety of the cornea needs to be replaced, also known as penetrating keratoplasty.
Corneal button
Optic cup 
Corneal limbus
Scleral lens
Lacrimal groove
Optic pit
Stenopaeic slit
Intraocular lens