The "Cornea transplant" or keratoplasty surgery is intended for all corneal diseases that reduce visual acuity. The surgery consists of replacing the damaged tissue with a donor cornea from an Bank of the Eye, and is performed under general or local anesthesia.
This may occur due to the opacity of the tissue (cyclerics, dystrophy or corneal degeneration) or its distortion (keratoconus, trauma). The new corneal flap, restoring the transparency of the cornea, can allow the patient to recover sight. The surgical technique may vary depending on whether the disease affects the corneal tissue in whole or in part.
Currently, more than 100,000 cornea transplants are performed annually worldwide. This is a safe procedure, combined with a low morbidity rate. The international and national guidelines guarantee a reference point for working with high levels of quality. The possibilities of transplantation are linked to the activity of the Bank of the Eye in many regions in our country.
Perforating Keratoplasty (PKP) is the earliest corneal transplantation technique, and has been performed since the 1950s. It remains the most widespread technique worldwide and consists of replacing the entire thickness of a central portion (about 8 mm in diameter) of the damaged cornea with a healthy and transparent corneal graft from a donor. Visual recovery after PKP can be more or less rapid and the results, in terms of visual acuity, can be excellent and with complete recovery. Post-operative astigmatism can often occur, which can be corrected by means of a laser (femtoseconds and/or excimer lasers) after removal of the suture.
Lamellar keratoplasty techniques
Lamellar keratoplasty aims to replace only the portion of the cornea that has been damaged, in order to preserve as much as possible the original corneal tissue and the integrity of the eye.
There are two main lamellar keratoplasty techniques: anterior lamellar keratoplasty, and posterior or endothelial lamellar keratoplasty, depending on whether the anterior or posterior portion of the corneal tissue is removed.
Anterior lamellar keratoplasty
This technique makes it possible to replace the anterior layers of the cornea, from the epithelium to the deep stoma, and is performed depending on the location of the opaqueness in the damaged tissue. This is a new frontier of corneal surgery that minimizes the trauma on the receiver by operating with "closed bulb". Deep Anterior Lamellar Keratoplasty (DALK) consists of replacing almost all corneal tissue. This is a technique introduced by the Saudi doctor Dr. Anwar in 2002 and then well-developed especially in Italy. The main surgical indications are keratoconus, family dystrophy and deep superficial corneal scars following trauma or infection. There are various techniques of DALK, depending on how the anterior portion of the cornea is removed, i. e. by injection of an intrastromal (big bubble technique) or by manual dissection. Removal of the stroma can also be carried out by laser (excimer or femtoseconds laser), but it has been shown, that this assisted laser techniques lead to lower visual recovery. All techniques aim to remove diseased tissue up to the endothelium in order to create an interface, on which he transplanted flap must be sutured, as homogeneous as possible to ensure a better post-operative visual quality. The main advantage of DALK lamellar transplantation is that it avoids the most important causes of perforating surgery failure such as immunological rejection and late decompensation of the transplanted cornea, thus increasing the duration of the transplant itself.
Posterior or endotheliar lamellar keratoplasty
For several years now, thanks to the technical applications of Prof. GerritMelles of Rotterdam and Prof. Mark Terry of Portland, a series of techniques known as endothelial keratoplasty (EK) have been introduced into clinical practice.
Today, the main EK technique is DSAEK (Descemet Stripping Endothelial Automated Keratoplasty), which consists of the removal of a part of the stroma and the endothelium of the patient’s cornea, and its replacement with a lenticule of a diameter or 8-8.5 mm with thickness varying between 50 and 120 microns, consisting of corneal stroma and healthy donor endothelium.
In recent years, another surgical technique called DMEK has been spreading: this consists in the removal of the patient's endothelium and descemet membrane alone and its replacement with a lenticule of about 20 microns thick.
DSAEK is indicated for Fuchs’ dystrophy and bullous keratopathy. These pathologies affect the endothelium in their early stages, and in late stages they lead to the loss of corneal transparency. Today, thanks to DSAEK, it is possible to intervene during the early stages of the disease, thus guaranteeing a high degree of therapeutic success in terms of the quality and stability of vision, and a significant reduction in risks from surgery.
The advantages of posterior lamellar keratoplasty compared to perforativekeratoplasty are manifold: visual recovery is very rapid, generally within 1-3 months of surgery; additionally, the procedure does not require sutures, thus eliminating all related complications, such as high astigmatism and erosion or infections of the corneal surface; and most importantly it respects the integrity of the bulb and maintains its tolerance to trauma almost intact. The risk of rejecting the graft, while present, seems to be lower, but in cases in which the transplanted cornea is at risk of decompensation, the replacement of the endothelial flap is faster and easier that the replacement of a full-thickness cornea.
What are the symptoms of corneal rejection?
Rejection initially manifests itself with very light symptoms, such as blurred vision, a slight sensitivity to light, and minor reddening of the eye. If these symptoms appear suddenly and persist or worsen over the following few days, it is important to immediately seek the attention of one’s ophthalmologist, because the timeliness with which treatment is initiated is of fundamental importance in avoiding irreversible damage to the transplant.
Stem cell transplant
The surface of the cornea is covered by a multi-layer epithelium made of transparent cells, which is maintained and constantly renewed by the stem cells present at its margins, in an area called the corneal limbus.
When the cornea’s stem cells are damaged by chemical substances, mechanical trauma, infections, or contact lens abuse, serious eye damage may arise, including the opacification of the cornea. In these cases, a corneal transplantation alone is not sufficient, since if the stem cells of the limbus have been damage, the cornea will soon begin to lose transparency once again in the absence of an epithelium that can replenish itself. Before the transplant, it is thus necessary to reconstruct the corneal surface, through a graft of stem cells from the patient’s healthy eye; the cells are then multiplied in the lab in order to obtain a sufficient quantity for covering the cornea’s surface. A lamella of 1mm of tissue in which the stem cells reside is taken from a small area between the cornea and the bulbar conjunctiva called the sclerocorneallimbus. This takes 10-15 minutes under topical anesthesia. The collected cells are sent to a laboratory specialized in cell culture. At the end of the amplification and culture phase (about 2-3 weeks) and after all necessary controls, the cultivated cells are grafted onto the cornea. The procedure generally takes place under local anesthesia. Confirmation of the complete success of the operation, namely the recovery of the ocular surface, can be had after a few months.