August was Organ Donor Awareness Month. Organ donation holds tremendous value in the field of Ophthalmology, as it offers hope and improved quality of life to many individuals suffering from vision impairment or blindness. The transplantation of corneas, the clear front surface of the eye, is the primary focus of organ donation in Ophthalmology. Corneal transplantation is a sight-saving procedure that can restore vision to those with severe corneal diseases or damage, that would otherwise result in irreversible severe visual deterioration or blindness. Corneal tissue, obtained through organ donation, replaces damaged or diseased corneas, enabling recipients to regain their sight and lead more fulfilling lives after their postoperative recovery. In the Western Cape, organ transplants are undertaken in both government and private hospitals e (e.g. heart, kidney, liver, corneal transplants).
You can hear Amanda, the founder of Eyes2Eyes, speak about her lifechanging experience of receiving a corneal transplant here as part of Cape Talk’s Gift of Life podcast series last month. Becoming an Organ Donor is very quick and you can potentially save 7 lives simultaneously. You can sign-up here in 1 minute to register as an Organ Donor.
The rest of the blog will give a little bit more detail on the types of corneal transplants. For clarity, the structure of the cornea is shown in Figure 1. Much has evolved since Eduard Konrad Zirm performed the first successful full thickness corneal transplant (penetrating keratoplasty) in a human in 1905. Various other corneal transplantation techniques now exist, collectively termed “lamellar surgery” and are also summarised below in writing and in Figure 2.
Figure 1: Structure of the Cornea
- Penetrating Keratoplasty (PK)
- Replacement of entire cornea thickness (epithelium, stroma, endothelium)
- Useful when there significant scarring, corneal shape changes (e.g. keratoconus with a history of hydrops), significant involvement of the back of the cornea, and ulcerations or perforations through the cornea
- Details: Compared to other techniques, it requires a longer recovery time after the operation is finished, higher risk of the body mounting an immune reaction against the transplant, higher risk of the transplant losing integrity over the course of the patient’s lifetime, higher risk of needing rigid gas permeable lenses to correct astigmatism from the transplant.
- Deep Anterior Lamellar Keratoplasty (DALK)
- Selective replacement of the corneal stroma. The native Descemet membrane and endothelium remain in place.
- Useful when needing to replace corneal stroma in the presence of healthy endothelium, certain types of corneal stromal dystrophies, and corneal ulcers that are not full thickness.
- Details: The surgery is more complex to perform than PK, but there is less risk of endothelial rejection of the transplant, and the transplant has greater integrity because the wound size is smaller.
- Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK)
- Selective removal of the patient’s Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium and Descemet’s membrane in addition to a thin layer of posterior donor stroma to facilitate handling of the tissue.
- Useful to treat corneal oedema (in the presence of corneal dystrophies), iridocorneal endothelial syndrome, endothelial failure with prior intraocular surgery
- Details: relatively rapid healing time and visual rehabilitation (minimal change to corneal curvature); less risk of graft rejection and suture-related complications compared to PK and DALK; there is risk of postoperative graft dislocation (it is a very thin layer of tissue being transplanted … 100 – 200μm thick!).
- Descemet’s Membrane Endothelial Keratoplasty (DMEK)
- Selective removal of the patient’s Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium and Descemet’s membrane without adding stroma. This tissue graft is 10-15μm thick!!! (± x10 thinner than in DSAEK!!!).
- Useful for similar conditions to DSAEK.
- Details: offers the most rapid visual rehabilitation of any keratoplasty technique; transplants minimal tissue meaning that there is lower risk of allograft rejection and less long-term reliance on topical steroids.
- Full-thickness removal of the cornea and replacement by an artificial cornea
- Useful in patients with history of multiple failed PKs, severe keratitis and ocular surface disease resulting from limbal stem cell failure (e.g. Steven Johnson’s Syndrome) and chemical injury.
The future of corneal transplantation looks promising with advancements in surgical techniques and regenerative medicine. Laser-assisted procedures and 3D bioprinting are enhancing precision and efficiency, leading to shorter recovery times and better outcomes for patients. Laboratory grown corneas may also reduce donor tissue reliance and customization, reducing risks of rejection.
Figure 2: Schematic portraying the region of corneal tissue transplanted (red) for various modern keratoplasty techniques, including penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK), Descemet stripping automated endothelial keratoplasty (DSAEK), Descemet membrane endothelial keratoplasty (DMEK), and Boston Type I Keratoprosthesis (KPRO). Reproduced from University of Iowa from this link.