The endothelium is a thin monolayer of cells at the posterior side of the cornea that dehydrates the cornea. If the cells
deteriorate and lose function, the cornea retains too much fluid. As a result, corneal transparency is lost and vision
Two very common endothelial corneal diseases are the following:
- Pseudophakic bullous keratopathy. A decrease in the function of the endothelium as a result of damage to the
cell layer during or after cataract extraction; and
- Fuchs endothelial dystrophy. This disorder develops without a known cause and may be hereditary.
Both endothelial disorders may be managed with surgery with good visual outcomes. At NIIOS, we developed surgical treatments that are less invasive and enable faster and more complete visual rehabilitation.
Endothelium in a normal cornea (Left) and a diseased endothelial cell layer with dispersed cell loss (Right).
Conventional Penetrating Keratoplasty (PK)
Disorders of the corneal endothelium can be managed with a penetrating keratoplasty (PK). In PK the full-thickness
central portion of a patient’s diseased cornea is removed with a circular cutting device and replaced with a fullthickness donor cornea. For about half a century this has been the standard therapy with varying clinical results.
This surgical technique has different disadvantages. The relevant complications are mentioned below:
A distorted or irregular contour of the donor corneal surface is frequently seen after PK. It seems virtually impossible to
sew a donor corneal button in place with all sutures at equal length, depth and tension even with the most experienced
hands. As a result the optical quality of the cornea is compromised, resulting in reduced visual acuity. Astigmatism can generally be corrected with a contact lens but not with eye glasses.
In PK a full-thickness graft is fixed onto the recipient cornea with sutures. These sutures are removed after sufficient
wound healing, most often at one year after surgery. During this period suture loosening may occur due to various
reasons. A loose suture may cause a cascade of problems, varying from a persistent epithelial defect and sterile
inflammation to an infected corneal ulcer or endophthalmitis. Because sutures are required for a long period, sutures
often cause complications in PK.
Incomplete wound healing
A surgical wound may never reach a tensile strength that equals that of a virgin cornea. As a result, wound dehiscence after minor trauma is relatively common after PK. Because the whole thickness of the cornea is replaced in PK, a break in the corneal wound increases the risk for eye infection.
Penetrating keratoplasty wherein the full-thickness central portion of the diseased cornea is replaced by a matching donor cornea.
Posterior Lamellar Keratoplasty – DMEK and DSEK/DSAEK
We developed a surgical technique for selective transplantation of the corneal endothelium between 1994
and 1996. This was termed posterior lamellar keratoplasty (PLK) or endothelial keratoplasty (EK), which was later popularized in the United States as deep lamellar keratoplasty (DLEK).
In 2001, NIIOS modified the technique to Descemet stripping endothelial keratoplasty (DSEK). When a
microkeratome is used to harvest the donor tissue the term used is Descemet stripping automated endothelial keratoplasty (DSAEK). With these techniques, most of the earlier mentioned complications of PK can be avoided.
In 2005, NIIOS further refined DSEK to Descemet membrane endothelial keratoplasty (DMEK), a technique
wherein only the innermost membrane of the cornea and its monolayer of endothelial cells are replaced.
DMEK (top) and DSEK/DSAEK (bottom). In DMEK only the inner layers of the diseased cornea are replaced by donor tissue. The transplanted tissue in DMEK is thinner than in DSEK/DSAEK.
Slit-lamp image of a cornea following DMEK (left) and DSEK (right). The recipient cornea with attached donor tissue completely clears following DMEK.
With DSEK/DSAEK and DMEK, only the innermost cell layer of the diseased cornea is replaced. A sufficiently
large graft can be inserted through a small incision in the sclera and positioned against the recipient cornea. As
such, the outer recipient cornea – and the entire globe – remains intact. The small scleral wound usually heals up
without any problems. This eliminates the need for sutures and the occurrence of suture-related complications.
Induced astigmatism is also minimized since the outer corneal contour is not compromised. Preservation of the
integrity of the globe is an important advantage of DSEK/ DSAEK and DMEK over PK. In the event that a transplant
does not become functional, a second transplantation can be performed.
In contrast to a PK wherein the whole thickness of the cornea is replaced, DSEK/DSAEK and DMEK only replace the innermost layer of the cornea. As such, these techniques have the following advantages:
- Faster and more complete visual rehabilitation;
- Fewer short and long term complications;
- Less aftercare needed.
Keratoconus is a corneal disease on the front of the cornea. This disorder is characterized by a weakening of the connective tissue layer which creates a progressive bulging of the cornea (ectasia). Increase of this deformation will eventually lead to a reduced visibility. Initially (scleral) contact lenses can improve your vision. With progression of the disease a corneal surgery may be necessary. There are various treatments depending on the severity of your condition.
Penetrating keratoplasty (PKP) / full –thickness corneal transplantation or deep anterior lamellar keratoplasty (DALK)
In presence of an advanced keratoconus you may be considered for a full –thickness corneal transplantation (PKP) or a deep anterior lamellar keratoplasty (DALK). With PKP all layers of your central cornea are replaced by donor tissue. This treatment has several drawbacks including complications caused by sutures, inadequate wound healing and presence of an irregular cornea which may be associated with reduced visibility. In the late nineties, the technique deep anterior lamellar keratoplasty (DALK) was developed by NIIOS. The thought behind this technique is to only replace the diseased part, that is, the connective tissue layer of the cornea, and to fasten it with sutures. The healthy part of your cornea is ‘left in place’, avoiding many of the disadvantages of a full-thickness corneal transplantation.
The purpose of UV-crosslinking is to avoid further deformation of the cornea, thereby delaying or preventing the need of a cornea transplant (PKP or DALK). Because during the treatment Riboflavin (Vitamin B2) eye drops together with ultraviolet-A light are administered, new connections between the connective tissue layers are created making your cornea firmer. This process is called cross-linking. In order to be eligible for UV-crosslinking a certain minimum corneal thickness is necessary.
Bowman layer transplantation
Recently NIIOS developed a new surgical technique: Bowman layer transplantation, Just as with UV-crosslinking, the purpose of Bowman layer transplantation is to delay or prevent further deformation of the cornea and to slow down the need of a corneal transplant (PKP or DALK). This technique may be indicated when your cornea is too thin for UV-crosslinking. With a Bowman layer transplantation, we implant a thin layer of a donor cornea (Bowman layer) between the connective tissue layers of your cornea, making your own cornea to become firmer. Compared to a PKP or DALK a Bowman layer transplantion is less traumatic.
In our clinic we perform all the above described surgical techniques.