Corneal transplantation

Corneal transplantation is a procedure where an abnormal shape (such as keratoconus) or poorly functioning scarred or opaque cornea is replaced with a donor cornea. Traditionally, all three layers of the cornea are replaced with a corneal transplant. Newer techniques allow selective replacement of the affected layers. This allows the patient to keep their own functioning layers. The three types of cornea transplant are penetrating (where all layers of the cornea are replaced), anterior (where only the front layers are replaced) and posterior (where only the back layer is replaced).

  • Penetrating keratoplasty: This is where all layers of the cornea are replaced. The vast majority of corneal transplants performed until the mid-2000s were of this type.

 

  • Anterior lamellar keratoplasty: In this procedure the front layers of the cornea are replaced. This is most commonly done for keratoconus or any condition affecting only the front layers. The aim is to leave behind a very thin layer of the back cornea, a thin slither of posterior corneal stromal, Descemet’s membrane and endothelium. Typically 50-100µm (one ten to one twentieth of a millimetre) of the patient’s cornea is left and the donor cornea positioned over this.

 

  • Endothelial keratoplasty: In this procedure, only the back part of the cornea, the endothelium and Descemet’s membrane are removed and replaced with the back layers of a donated cornea. 

There are multiple variations of (and terminology for) this technique. I perform the DSAEK or Descemet’s membrane automated endothelial keratoplasty. In DSAEK, an air bubble holds the donated cornea in place.


Where does the donated cornea come from?

The cornea has been provided by a volunteer donor who has passed away and given permission for its use. Both the donated cornea and patient donating the cornea undergo  intensive assessments. The donated cornea itself is examined to ensure that it is clear, examined under high magnification to ensure that the endothelial cell count is of adequate density and further tested to ensure that it is free of infection. An assessment is also made of the donor patient to ensure they have no evidence of significant infection or other pertinent illness. Modern techniques allow the cornea to be kept healthy for up to four weeks before transplantation.

The most common type of corneal transplant is where the central corneal is replaced and this can be further divided into one of three types, depending on which layers are replaced. Only the corneal transplantation where the central cornea is replaced is addressed here.