Editing Corneal transplantation (section)

==Procedure==
[[File:A human eye 1 day after a cornea transplant.jpg|thumb|Cornea transplant one day after surgery.]]
[[File:Cornea Transplant.jpg|thumb|Cornea transplant after one year of healing, two stitches are visible]]
On the day of the [[surgery]], the patient arrives to either a [[hospital]] or an outpatient surgery center, where the procedure will be performed. The patient is given a brief physical examination by the surgical team and is taken to the [[Operating theatre|operating room]]. In the operating room, the patient lies down on an operating table and is either given [[general anesthesia]], or [[local anesthesia]] and a [[sedative]].

With anesthesia induced, the surgical team prepares the eye to be operated on and drapes the face around the eye. An eyelid [[speculum (medical)|speculum]] is placed to keep the lids open, and some lubrication is placed on the eye to prevent drying. In children, a metal ring is stitched to the sclera which will provide support of the sclera during the procedure.

===Pre-operative examination===
In most instances, the person will meet with their ophthalmologist for an examination in the weeks or months preceding the surgery. During the exam, the ophthalmologist will examine the eye and diagnose the condition. The doctor will then discuss the condition with the patient, including the different treatment options available. The doctor will also discuss the risks and benefits of the various options. If the patient elects to proceed with the surgery, the doctor will have the patient sign an [[informed consent]] form. The doctor might also perform a physical examination and order lab tests, such as blood work, [[X-rays]], or an [[EKG]].

The surgery date and time will also be set, and the patient will be told where the surgery will take place. Within the United States, the supply of corneas is sufficient to meet the demand for surgery and research purposes. Therefore, unlike other tissues for transplantation, delays and shortages are not usually an issue.<ref>{{cite web|title=Eye Banking FAQs|url=http://www.restoresight.org/about-us/frequently-asked-questions/|publisher=Eye Bank Association of America|access-date=29 December 2011}}</ref>

===Penetrating keratoplasty===
[[File:Penetrating keratoplasty.JPG|thumb|Replacement of the entire cornea]]
A trephine (a circular cutting device), which removes a circular disc of cornea, is used by the surgeon to cut the donor cornea. A second trephine is then used to remove a similar-sized portion of the patient's cornea.  The donor tissue is then sewn in place with sutures.

[[Antibiotic]] [[eyedrops]] are placed, the eye is patched, and the patient is taken to a recovery area while the effects of the anesthesia wear off. The patient typically goes home following this and sees the doctor the following day for the first postoperative appointment.

===Lamellar keratoplasty===

Lamellar keratoplasty encompasses several techniques which selectively replace diseased layers of the cornea while leaving healthy layers in place.  The chief advantage is improved tectonic integrity of the eye.  Disadvantages include the technically challenging nature of these procedures, which replace portions of a structure only 500&nbsp;[[μm]] thick, and reduced optical performance of the donor/recipient interface compared to full-thickness keratoplasty.

====Deep anterior lamellar keratoplasty====

In this procedure, the anterior layers of the central cornea are removed and replaced with donor tissue. [[Endothelial]] cells and the Descemets membrane are left in place.  This technique is used in cases of anterior corneal opacifications, scars, and ectatic diseases such as keratoconus.

====Endothelial keratoplasty====

Endothelial keratoplasty replaces the patient's endothelium with a transplanted disc of posterior stroma/Descemets/endothelium (DSEK) or Descemets/endothelium (DMEK).<ref>{{Cite journal|last1=Ang|first1=Marcus|last2=Wilkins|first2=Mark R.|last3=Mehta|first3=Jodhbir S.|last4=Tan|first4=Donald|date=1 January 2016|title=Descemet membrane endothelial keratoplasty|url=https://bjo.bmj.com/content/100/1/15|journal=British Journal of Ophthalmology|language=en|volume=100|issue=1|pages=15–21|doi=10.1136/bjophthalmol-2015-306837|issn=0007-1161|pmid=25990654|doi-access=free}}</ref>

This relatively new procedure has revolutionized treatment of disorders of the innermost layer of the cornea (endothelium). Unlike a full-thickness corneal transplant, the surgery can be performed with one or no sutures.  Patients may recover functional vision in days to weeks, as opposed to up to a year with full thickness transplants. However, an Australian study has shown that despite its benefits, the loss of endothelial cells that maintain transparency is much higher in DSEK compared to a full-thickness corneal transplant. The reason may be greater tissue manipulation during surgery, the study concluded.<ref>{{cite journal | pmc = 2959124 | pmid=20031230 | doi=10.1016/j.ophtha.2009.07.036 | volume=117 | issue=3 | title=Descemet's stripping automated endothelial keratoplasty outcomes compared with penetrating keratoplasty from the Cornea Donor Study |vauthors=Price MO, Gorovoy M, Benetz BA, Price FW, Menegay HJ, Debanne SM, Lass JH| journal=Ophthalmology | pages=438–44| year=2010 }}</ref>

During surgery the patient's corneal endothelium is removed and replaced with donor tissue.  With DSEK, the donor includes a thin layer of stroma, as well as endothelium, and is commonly 100–150&nbsp;μm thick. With DMEK, only the endothelium is transplanted. In the immediate postoperative period the donor tissue is held in position with an air bubble placed inside the eye (the anterior chamber).  The tissue self-adheres in a short period and the air is adsorbed into the surrounding tissues.

Complications include displacement of the donor tissue requiring repositioning ("refloating").  This is more common with DMEK than DSEK.  Folds in the donor tissue may reduce the quality of vision, requiring repair.  Rejection of the donor tissue may require repeating the procedure.  Gradual reduction in endothelial cell density over time can lead to loss of clarity and require repeating the procedure.

Patients with endothelial transplants frequently achieve best corrected vision in the 20/30 to 20/40 range, although some reach 20/20.  Optical irregularity at the graft/host interface may limit vision below 20/20.