The topic of corneal transplant surgery can quickly evolve to alphabet soup with all of the acronyms involved.
Our next few blog entries will address corneal transplants, so this is a brief outline of the relevant terminology.
Penetrating keratoplasty (PK) has historically been the only option but is now used primarily for full-thickness keratopathies. Indications would include corneal trauma, ectasias (such as keratoconus with hydrops or deep scarring) and other deep or full-thickness scarring.
Thankfully, with the advent of corneal cross-linking and deep anterior lamellar keratoplasty (DALK), we will be seeing less PK treatment of keratoconus (KCN) in the future. After several failed PK attempts, keratoprosthesis may become the only option.
DALK is a partial thickness surgery that replaces the stroma, leaving Descemet’s and the endothelium intact. Opacification at the interface layers may occur, and subsequent visual acuity may be lower than a fully healed and corrected PK.
DALK is a possible treatment for KCN that is advanced but without hydrops, corneal scars that are more anterior but still too deep for phototherapeutic keratectomy and stromal dystrophies.
If accidental perforation occurs during surgery, a full PK transplant may become necessary.
Descemet’s stripping automated endothelial keratoplasty (DSAEK) is a graft of at least 50 microns thick that includes the endothelium, Descemet’s and some stroma so it holds its shape and is less susceptible to scrolling up. It is easier to manipulate than Descemet’s membrane endothelial keratoplasty (DMEK) and can be a better choice for eyes with more difficult anatomy. It can be used to treat endothelial failure (such as Fuchs and posterior polymorphous corneal dystrophy.
DMEK is a very thin graft that only replaces Descemet’s and the endothelium. It is thought to have a superior visual outcome to DSAEK (about one line better due to lack of host-donor stroma-stroma interface). DMEK treats the same conditions as DSAEK.
Both endothelial keratoplasties (DMEK and DSAEK) are less invasive, have shorter surgery time, shorter healing time and leave the eye less susceptible to injury than PK. These transplants enjoy greater structural integrity because the anterior cornea is left largely intact, making these eyes more resistant to perforation or rupture, ultimately inducing less astigmatism and with a lower risk of infection than PK. Additionally, this is usually a sutureless procedure, reducing or eliminating suture-related complications such as broken suture, neovascularization, infection and subsequent rejection. (Because it is not a full-thickness procedure, in DALK the resultant wound is also stronger than that of a PK).