Corneal transplants 101

There are many types of corneal transplants. The cornea is the clear window of the eye which a contact lens sits on. It is also resonsible for focusing light into the eye through the lens and into the retina. Often times, either due to an inherited disease process such as fuch's dystrophy and/or keratoconus or as a result of a chemical or corneal infection, the cornea can start to swell and scar. Depending of the nature of the disease process, a corneal transplant offers patients a chance to replace either part or all of the cornea. Because the cornea is a clear tissue without blood vessels, the cornea is an immune naïve and immune privileged tissue. Thus we can use essentially any donors cornea and transplant it to any recipient without having to find a genetic match. 

Penetrating keratoplasty (full thickness transplant) – a penetrating keratoplasty is a full thickness corneal transplant in which a complete corneal donor tissue replaces the patients cornea. Typically the donor tissue is sutured onto the recipient tissue in 16 radial sutures. The first six months, the goal is to make sure the cornea clears and does get infected or reject. At approximately 6 months, the surgeon will start removing sutures carefully until either all tight sutures are gone or no sutures remain. Typically it takes 9-12 months for the entire healing process to complete. After 9-12 months, most patients will be fitted for spectacles and or hard contact lens. Patients will be on a steroid drop for the rest of their life as their anti-rejection medication

Endothelial keratoplasty (partial thickness transplant) – endothelial keratoplasty refers to replacing only the inner diseased layer of tissue of the cornea while leaving the healthy outer layers behind. Because only the diseased layer of the receipient cornea is transplanted, recovery is often faster only taking 2-3 months. Additionally, the rate of rejection and risk of surgery is greatly reduced. Endothelial keratoplasty, however require either an air bubble or a gas bubble be injected into the eye at the end of the surgery to allow for the donor cornea to remain in proper position. Thus, positioning face up is crucial after surgery in order to guarantee a good outcome which is typically done for 2-3 days after surgery. If you are unable to position face up for 2-3 days after surgery, a partial corneal transplant may not be the best option for you. Although partial transplants are very successful and have become the more common transplant procedure, a singificant side effect is the inability of the transplant to attach to your cornea in which case, a re-bubble procedure is necessary to inject for air or gas into the eye. This is especially more common if you have had a glaucoma tube shunt or trabeculectomy surgery in the eye. 

  There are 2 types of endothelial keratoplasties

• DSAEK – the older method endothelial keratoplasty where the inner cellular layer and part of the stromal layer is also transplanted into the patient  

•  DMEK – newer method, thinner tissue where only the inner corneal cellular layer is transplanted

Your surgeon will determine which type of partial transplant is appropriate for you. 

Indications for surgery

• Indications for penetrating keratoplasty include corneal scar, corneal ectasia (keratoconus and pellucid marginal degeneration), corneal infections and corneal perforation.
• Indication for endothelial keratoplasty include corneal swelling from viral infections, genetic conditions such fuchs dystrophy/posterior polymorphous dystrophy and acquired corneal swelling from pseudophakic bullous keratopathy 

Risks for surgery

• Infection
• Rejection
• Graft failure
• Hemorrhage
• Graft detachment (for endothelial keratoplasty)
• high intraocular pressure
• permanent pupil damage
• optic nerve damage

All of which may result in partial or complete vision loss