A Deeper Look At The Cornea And Corneal Transplants

(Posted on Tuesday, February 6, 2024)

This story is part of a series on the current progression in Regenerative Medicine. This piece is part of a series dedicated to the eye and improvements in restoring vision. 

In 1999, I defined regenerative medicine as the collection of interventions that restore tissues and organs damaged by disease, injured by trauma, or worn by time to normal function. I include a full spectrum of chemical, gene, and protein-based medicines, cell-based therapies, and biomechanical interventions that achieve that goal.

Corneal transplant surgery has come a long way since its inception in 1905. This surgical procedure involves the replacement of a damaged or diseased cornea with a healthy one. It is one of the most frequently transplanted tissues worldwide, with the US alone performing an astonishing 48,000 procedures annually. 

The advances in this field over the past century have significantly increased the rate of success and visual recovery. From the first crude techniques to modern-day precision surgeries, the evolution of corneal transplants has paved the way for innovative breakthroughs.

What is the Cornea?

The cornea is a transparent, dome-shaped layer that covers the front of the eye, contributing up to two-thirds of the eye’s focusing power. It consists of five layers, each with its specific function. 

The cornea, the eye’s transparent outer layer, has four main layers. The epithelium is the outermost layer that acts as a barrier to protect the cornea from any damage or infection. 

Bowman’s thin connective tissue layer is the next layer, which provides structural support to the cornea. The stroma is the thickest layer, making up 90% of the cornea’s thickness, and is responsible for most of the cornea’s refractive power. Descemet’s membrane is a thin layer between the stroma and the endothelium, the innermost layer that regulates the transport of fluids in and out of the cornea.

Explanation of Cornea Transplant

There are different types of corneal transplant procedures available, including penetrating keratoplasty (PK), which replaces all corneal layers; deep anterior lamellar keratoplasty (DALK), which involves the replacement of all layers except for the endothelium; and Descemet’s stripping automated endothelial keratoplasty (DSAEK), which replaces only the endothelium.

Diagram showing corneal tissue transplants (red) used in modern keratoplasty techniques: 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).

Corneal transplant is a standard treatment for several conditions, including keratoconus, a condition where the cornea becomes thin and cone-shaped; Fuchs’ dystrophy, a condition that causes the endothelium to deteriorate; and corneal scarring due to injury or infection. The success rate of corneal transplants is high, and the procedure has helped restore vision in millions of people worldwide.

Effectiveness of Cornea Transplant

Corneal transplant surgeries are performed to help restore vision in individuals who have damaged or diseased corneas. The success rate of these surgeries varies depending on several factors, including the reason for the surgery and the surgical technique used. For instance, transplants performed for keratoconus, where the cornea becomes thin and bulges outwards, typically improve visual acuity after healing.

However, the prognosis for long-term corneal clarity and vision can be poor. For example, transplants that are performed urgently for uncontrolled corneal infection or perforation following severe eye injury or for corneal scarring due to inflammatory diseases can have a poor outcome.

Current Clinical Trials and Outcomes of Cornea Transplant

Ongoing clinical trials investigate new therapies to treat corneal diseases affecting the endothelium. Two such treatments being researched are Descemet’s stripping only (DSO) and the implantation of cultured corneal cells. Recent studies have demonstrated promising outcomes with these therapies, resulting in better patient outcomes and reduced surgical risks. 

DSO is a surgical technique that selectively removes the diseased endothelium while preserving the healthy cornea. This procedure promotes the regeneration of healthy corneal endothelial cells, eliminating the need for a full transplant.

Cultured corneal cells, another promising therapy, involve the removal of a small sample of healthy corneal endothelium cells from the patient. These cells are then grown in a laboratory and implanted back into the patient’s eye. This technique has shown better results than traditional corneal transplants, including faster healing times and improved visual outcomes. 

Moreover, researchers are exploring new methods to improve the quality and availability of donor tissue. Tissue engineering is one such method that involves the creation of artificial corneal tissue in a laboratory. This tissue can replace damaged corneal tissue and is an attractive alternative to traditional donor tissue. 

In conclusion, a cornea transplant is a safe and effective surgical procedure for treating corneal diseases and injuries. While some risks are still associated with the procedure, ongoing research and clinical trials continuously improve outcomes and reduce risks. The future outlook for corneal transplant is positive with the emergence of novel therapies and advances in tissue engineering and stem cell research. However, ensuring an adequate supply of high-quality donor tissue remains a challenge, and ethical considerations must be addressed to maintain donor confidence and promote the continued success of corneal transplants.

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