Development of Corneal Disease Treatments

Dr. Arthur CHENG

Honorary Consultant in Ophthalmology

Specialist in Ophthalmology

Looking like a piece of contact lens, cornea is a clear and transparent membrane that covers the front part of the eye. As a light-refracting apparatus, it contains many sensory nerves and reacts reflexively even to mild stimulation.

Corneal Transplantation

Pathological changes in cornea, such as cornea degeneration, infection, injuries or congenital corneal diseases, may lead to blurred vision, red eyes and pain and eventually loss of vision and corneal scarring. The cornea will appear white and cannot focus anymore. Cornel transplantation will then be required to restore normal vision. Over the years, eye doctors have invented many new techniques in corneal transplantation. Full or partial thickness transplantation can be done based on the level of involvement, thereby greatly improving the accuracy, recovery time and visual outcomes. But donated healthy corneas will be required in most cases.

As cornea contains no blood vessels, the risk of transplant rejection is relatively low. Over 300 corneal transplantations are performed in Hong Kong each year, using corneas from either local or overseas donors, e.g. the US. The waiting time for corneal transplantation is about 2 weeks with overseas corneas, and about 15 months with local corneas.

Delamination Technology

Traditionally, diseased or damaged cornea was replaced by a full-thickness cornea through Penetrating Keratoplasty (PKP). Thanks to the technological advance, Lamellar Keratoplasty is now carried out to replace the diseased cells and retain normal corneal tissue layers. Examples of Lamellar Keratoplasty are Anterior Lamellar Keratoplasty (ALK) and Descement’s Stripping Automated Endothelial Keratoplasty (DSAEK):  ALK can reduce rejection risk by causing minimal damage to the endothelium, while DSAEK can be performed with no suture and reduce recovery time. Penetrating Keratoplasty (PKP) is now reserved for patients with full thickness involvement.

Artificial Cornea Transplantation

In patients with serious burn injuries in cornea and in Stevens - Johnson syndrome, donated corneal transplantation is not suitable due to possible angiogenesis and high rejection risk. In that case, artificial cornea transplantation can be a viable option.

Using artificial cornea, the Boston Keratoprosthesis for example has two distinctly different and isolated zones. A host-tissue-friendly outer skirt is composed of human cornea with high affinity for recipient rim tissue, thereby encouraging deep host tissue integration. The central clear optical region is made up of a polymer material that has low affinity for host tissue, and it discourages vessels ingrowth and scarring of the prosthesis. This arrangement ensures tight integration with the host while keeping the optical clarity with the central zone.

Keratoconus

Keratoconus is a condition where the cornea protrudes outward like a cone. Early symptoms include increase in astigmatism and blurred vision. It is thought to be due to weak corneal structure and frequent eye rubbing, and mostly affects people aged between 20 and 40. Diagnosis requires a special optical device called corneal topography, which is usually available in specialty ophthalmic practice.

Other than corneal transplantation, Corneal Collagen Crosslinking, Intracorneal Stromal Rings (ICRs) Implantation and Topographically Guided Surface Ablation are the major treatments of Keratoconus. Topographically Guided Surface Ablation targets specific areas on the diseased cornea. It is effective in smoothing out the irregular corneal surface and restoring a more normal corneal contour. In conjunction of crosslinking, it is quite effective in stopping disease progression.

Looking Forward: Corneal Stem Cell Transplantation

The outer protective layer of cornea is composed of epithelial cells, which can be regenerated out of corneal limbal stem cells when injured. However, severe burns caused by fire or chemicals, or immune dysfunction can cause damage to the limbal stem cells and cornea opacity. The damage is not correctable by corneal transplantation alone. 

An additional procedure called Limbal Stem Cell Transplant is required to restore patients’ vision. During the procedure, normal limbal stem cells can now be harvested from the unaffected eye to the diseased one using a preserved amniotic membrane as a carrier. Rich in nutrients, the amniotic membrane can speed up stem cell growth to epithelial cells within 1 or 2 weeks and will dissolve afterwards.

Tips for Cornea Care

• Do not rub eyes.
• Wear sunglasses.
• Do not sleep and swim with contact lens.
• Clean eyelashes and use heat pack to promote sebum secretion and relieve dry eyes.
• Press nose wire against the nose bridge while wearing a mask. It prevents dry eyes caused by the exhaled air.