About two decades ago, penetrating keratoplasty or full-thickness corneal transplantation was almost exclusively used to eliminate corneal blindness. Thanks to the latest developments in ophthalmic surgery, the possibilities for corneal transplantation have reached the new heights. Nowadays, the exclusive lamellar replacement of affected corneal areas is possible and used in various circumstances.
Endothelial keratoplasty allows the surgeon to restore the patient’s vision without replacing the outer part of the cornea (corneal epithelium, Bowman’s membrane, and stroma).
Modern corneal transplantation is carried out taking into account the morphology of the cornea, which consists of five layers of tissue:
- Epithelium.
- Bowman’s membrane.
- Stroma.
- Descemet’s membrane.
- Endothelium.
The modern approach to corneal transplant surgery is tissue-selective. The surgeon replaces only the damaged area of the cornea with a lamellar donor transplant. In the case of endothelial keratoplasty, the posterior part, containing corneal endothelial cells, is replaced. This is a very important monolayer of cells that maintain the transparent state of the cornea by ensuring the optimal balance of water and nutrients. If the endothelium is damaged, the cornea begins to swell and become cloudy. As a result, the vision is decreased.
Endothelial keratoplasty is carried out in one of two main modalities: Descemet’s membrane endothelial keratoplasty (DMEK) and Descemet’s stripping endothelial keratoplasty (DSEK). In DMEK, the transplant contains exclusively Descemet’s membrane and endothelium (with a thickness of about 30 microns). In DSEK, the transplant is cut out along with a thin strip of corneal stroma, with a thickness varying from 60 to 200 microns.
Endothelial keratoplasty has several advantages:
- The incision is small, not exceeding 5 mm; it requires minimal or even no sutures.
- The «closed chamber» technique significantly reduces intra- and postoperative risks.
- In combined procedures (with cataract extraction and intraocular lens (IOL) implantation), it is possible to calculate the appropriate IOL optical power with a high degree of accuracy.
- The postoperative rehabilitation period is significantly reduced.
- Long-term use of postoperative medications is not required.
This type of corneal transplantation is recommended for replacement of diseased endothelium in the following cases:
- Bullous keratopathy (clouding of the cornea after cataract surgery or trauma).
- Congenital hereditary endothelial dystrophy.
- Fuch’s endothelial corneal dystrophy.
- Endothelial dysfunction of the earlier transplanted penetrating corneal graft.
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Transplantation of the posterior corneal layers is a microinvasive procedure. It requires skill with a number of special microsurgical instruments.
Contraindications to endothelial keratoplasty include:
- Significant decrease in the transparency of the cornea, preventing the surgeon to clearly control manipulations inside the eye.
- Pronounced iris defects.
- Aphakia (absence of the lens).
- Vitreous absence (avitria).
- Chronic hypotension (after antiglaucoma tube-shunt surgery).
The surgical procedure involves either general or local anaesthesia, depending on the age and health condition of the patient.
The surgery involves several steps:
- The patient is prepared for surgery.
- Lamellar corneal transplant containing endothelial layer is cut from the donor cornea.
- A small tunnel incision is created in the eye wall.
- The patient’s endothelium and Descemet’s membrane are separated and removed.
- The endothelial transplant is inserted in the folded state.
- The transplant unfolds and is fixed with an air or gas bubble to the recipient’s posterior corneal layers.
- The wound is closed.
It is worth noting that the preparation of the lamellar corneal transplant can be carried out manually, or by using a microkeratome or femtosecond laser. The surgeon makes this choice based on their preferred technique and status of the eye.
