Cornea Transplantation

Excerpt

Corneal disease is the fifth leading cause of global blindness, necessitating interventions such as keratoplasty, the most prevalent and successful human transplantation. The first successful transplant was completed in 1905. Various dystrophic, infectious, degenerative, and inflammatory corneal disorders, often secondary to ocular surface diseases, contribute to corneal blindness. The widespread and intricate epidemiology involves infectious and nutritional disorders like trachoma, xerophthalmia, river blindness, and microbial keratitis, ranking second to cataracts in ocular conditions causing blindness globally. Developing countries, particularly in Africa and Asia, experience higher incidences, and corneal scarring remains a leading cause of reversible blindness in children. Despite corneal transplantation being the primary visual rehabilitation method, its efficacy is constrained by limited expertise and donor corneal tissue availability, particularly in these developing nations.

In the Western world, inherited, degenerative, and iatrogenic conditions like Fuchs corneal endothelial dystrophy, keratoconus, and pseudophakic bullous keratopathy (PBK) are more prevalent, with a favorable prognosis. Corneal transplantation, a globally widespread procedure, addresses diverse indications such as keratoconus, PBK, corneal scars, dystrophies, and microbial keratitis. However, in developing nations, the demand for treatment often outstrips the available supply. A previous article reported that in 2010, the number of corneal transplants in the United States was 42,642; in 2008, there were 12,623 solid organ transplants. In countries like India, where the incidence of microbial keratitis is high, there were 27,075 corneal transplants performed between April 2019 and March 2020. However, due to the COVID-19 pandemic, the number of transplants fell to 12,998 performed between April 2020 and March 2021, as per data from the Eye Bank Association of India. The demand for corneal grafts often exceeds the supply in most eye banks, especially in developing countries, resulting in long waiting periods. This activity provides a comprehensive understanding of corneal transplantation, covering anatomy, history, indications, contraindications, personnel, equipment, techniques, and complications, offering valuable insights for students and clinicians.

History of Corneal Transplantation

The history of corneal transplant traces its roots to 1800, but significant strides occurred in the past 2 decades with the introduction of lamellar transplantation techniques. The evolution of modern corneal transplantation results from centuries of ideas, experimentation with xenografts and allografts, and resilience. As early as 1789, French surgeon Pellier de Quengsy proposed using a transparent material to replace an opaque cornea. The first documented report of anterior lamellar corneal transplantation dates back to 1800. Karl Himley, in 1813, envisioned and experimented with xenografts, with his student Franz Reisinger attempting the first experimental xenograft transplantation in 1824, albeit without success.

In 1838, Richard Kissam achieved a milestone by performing the first therapeutic corneal xenograft using a porcine cornea. The first successful human allograft and penetrating keratoplasty (PKP), following anesthetics and antiseptic surgery developments, was performed by Eduard Zirm in December 1905 on a farm laborer with lime burns. Lamellar corneal transplants emerged as a pivotal advancement, mitigating the risk of endothelial graft failure. The introduction of topical steroids and refined surgical techniques in PKP in 1950 set the gold standard for corneal transplantation. The era of lamellar transplantation began in 2005, revolutionizing keratoplasty techniques. Successful outcomes hinge on meticulous ocular environment preparation, addressing inflammatory factors, and comprehensive systemic control, especially in cases involving rheumatoid arthritis and systemic lupus erythematosus. Preoperative control of diabetes, hypertension, cardiac, respiratory, and renal disease is also mandatory in each case.

Recent Developments

Advancements in immunology, surgical techniques, and tissue banking have greatly influenced the field of corneal transplantation. Over the last 2 decades, significant developments in selective endothelial replacement techniques have led to notable changes in the field. Gerrit Melles introduced a posterior lamellar keratoplasty (PLK) that involved transplanting only a portion of the cornea. The procedure involved making an incision at the limbus and dissecting and replacing the endothelium, the Descemet membrane (DM), and the posterior stroma with a donor button consisting of the same corneal layers. The donor button was held in place by an air bubble.

Mark Terry made modifications to the PLK procedure in 2001. He used viscoelastic material instead of an air bubble and renamed deep lamellar endothelial keratoplasty (DLEK). In 2004, Gerrit Melles modified the technique by removing only the host endothelium and DM, thus eliminating the need for stromal dissection. He replaced it with a donor button of the endothelium, DM, and stroma, creating Descemet stripping endothelial keratoplasty (DSEK). This technique was later automated using a microtome, resulting in Descemet stripping automated endothelial keratoplasty (DSAEK). In 2006, the technique was further developed by transplanting only a donor button of endothelium and DM without the posterior stroma, creating DM endothelial keratoplasty (DMEK). Minor modifications include automated posterior lamella dissection similar to DSEK or DM automated endothelial keratoplasty (DMAEK).

A selective keratoplasty technique related to the anterior cornea is the deep anterior lamellar keratoplasty (DALK), whereby a donor button replaces the epithelium, Bowman layer, and stroma. This selective lamellar transplant involves replacing only the diseased layer of the cornea while retaining the healthy layers, resulting in better visual outcomes and reducing the complication rate. The cornea has 5 layers, and only the Bowman layer, stroma, DM, and endothelium can be replaced. The corneal endothelial cells have poor regenerating capacity, and any loss of these cells due to trauma or disease can lead to corneal edema. In contrast, PKP transplants all 5 layers of the cornea. In the United States, endothelial transplant rates increased significantly from 5% in 2005 to 44.9% in 2010. In 2022, the number of PKPs, DSAEK, and DMEK was almost equal, around 15,000 each. Lamellar transplant is now preferred over PKP for various indications, such as keratoconus, Fuchs endothelial dystrophy, and PBK.