The Basics:
The cornea is the clear, living tissue on the very front part of the eye. Light passes through the clear cornea on its path toward the retina in the back part of the eye. Sometimes, the cornea is referred to as the "window" to the eye. Occasionally, either through disease or injury, the corneal tissue is damaged to a point where light can no longer effectively pass through it, resulting in reduced vision. When indicated, an ophthalmologist can perform a corneal transplant procedure, to replace the damaged cornea with a clear donor cornea. This is an extremely delicate microsurgical procedure.


What is DSEK?
DSEK is a corneal transplant technique where the unhealthy, diseased, posterior portion of a patient’s cornea is removed and replaced with healthy donor tissue obtained from the eye bank. Unlike traditional corneal transplant surgery known as penetrating keratoplasty (PKP), the DSEK procedure utilizes a much smaller surgical incision and requires no corneal sutures. This usually results in more rapid visual rehabilitation for the DSEK patient.

Who is a Candidate?
DSEK is indicated for those patients who have corneal pathology located on the posterior aspect of their cornea known as the endothelial layer. The endothelial layer of the cornea is a monolayer of cells lining the back (interior) surface of the cornea. The cells are attached to a membrane called Descemet’s membrane. A healthy endothelial layer consists of small, hexagonally shaped cells with a density of 2500 to 3000 cells/mm2.

Figure 1a
Healthy monolayer of endothelial cells attached to Descemet’s membrane. Red line in the leftmost figure represents Descemet’s membrane and endothelium. The middle diagram represents an enlargement of a cross section that from top to bottom includes the epithelial layer (a), stromal layer (b), Descemet’s membrane with attached monolayer of endothelial cells (c) and anterior chamber (d). The rightmost diagram illustrates normal size and shape of healthy endothelial cells.

                      

When endothelial cells are healthy, they pump fluid out of the cornea. You are born with a fixed number of endothelial cells, and cells are gradually lost with aging. They are also lost through injury, acute glaucoma, intraocular surgery (such as cataract surgery) or inflammation. Many patients have an inborn disease of the corneal endothelium known as Fuchs' Endothelial Dystrophy, where they are either born with a relatively low number of cells, or they are lost most rapidly than normal.

If not enough healthy cells are present, the cornea will over-hydrate and become cloudy. Vision eventually deteriorates to a point where these patients feel like they are looking through wax paper. Such patients are good candidates for the DSEK procedure.


Figure 1b
Unhealthy monolayer of endothelial cells attached to Descemet’s membrane. The middle diagram illustrates a cross section of an over-hydrated swollen cornea. The top layer of surface (epithelial) have become so swollen that small blisters (bullae) have formed (a). The stroma is thickened with fluid filled pockets (b). A sparse covering of stressed endothelial cells lies over a thickened Descemet’s membrane (c). The rightmost figure depicts large, low density, irregularly shaped endothelial cells.

                    

Traditional Penetrating Keratoplast
y; Figure 2
The goal of surgery is to provide new, healthy endothelial cells from a donor cornea. In traditional corneal transplant surgery (PKP) the central portion of your cornea is removed and replaced with a similar portion from a donor eye, with healthy cells on the inner surface. The cornea is slow to heal, and sutures must be left in place for 1 year or longer. New glasses cannot be prescribed for 6 to 15 months. The shape of the corneal surface is altered, and that slows recovery of vision. It also usually means that you need strong glasses or a hard contact lens in order to see well.


 
 
 




Traditional Penetrating
Corneal Transplant (PKP)

Description of the DSEK Corneal Transplantation Procedure

The first part of the DSEK procedure involves removal of the unhealthy endothelial cells and attached Descemet’s membrane. The second part of the procedure involves replacing this unhealthy tissue with a thin layer of corneal tissue with healthy endothelial cells from a donor eye.

Before the DSEK procedure the patient is sedated with intravenous medication. The IV sedation renders the patient totally unconscious for about 1 to 2 minutes. During this time a local anesthetic is given to completely numb the eye. When the patient awakes, the sensory nerves of the eye have been blocked so the patient will not feel or see anything during the procedure.

After the local anesthetic has taken effect, the patient is taken to the operating room and the eye is draped in a sterile fashion. DSEK is a microsurgical technique that is performed under a special operating microscope. The first step of the operation involves making a very small (5mm) incision outside the edge of the cornea. Another instrument called an anterior chamber (AC) maintainer is also placed at the temporal aspect of the limbus (3 o’clock). The AC maintainer is an irrigating port that infuses sterile saline into the anterior chamber of the eye and maintains the eye’s shape during the operation. It is within this small space known as the anteriorchamber that the DSEK procedure is performed. The average height of the anterior chamber is only 3.5mm which explains why the magnification of an operating microscope is needed to perform the delicate microsurgical maneuvers of the DSEK procedure.

 
 
Figure 3
Left illustration depicts a keratome making a small incision at the 12 o’clock limbus and an AC maintainer at the 3 o’clock limbus. To the right, the cross sectional figure shows the opening of the AC maintainer within the small blue space which represents the anterior chamber.




                      

Figure 4
Depicts a fine hook scoring Descemet’s membrane around the margin ot the circular portion to be removed.


                    

Figure 5
Depiction of the delicate stripping of diseased Descemet’s membrane. The actual removal of the circle of Descemet’s tissue is done with a device called a Descemet’s stripper. This device looks like a small garden hoe or rake(Figure 4). As Descemet’s membrane is stripped away it is pulled through the small incision site and removed from the eye. This delicate membrane with its attached endothelial cells is only 20 to 30 microns thick!
 


Figure 6
Illustration of removal of an 8mm circular disk of diseased Descemet’s membrane from the anterior chamber through the tiny incision site. The figure on the right is a cross sectional view of the same maneuver.


                     

Only a thin portion of the donor cornea, containing the bottom (posterior) stroma, Descemet’s membrane and endothelial cells, is used in the procedure. This must be prepared by dividing the donor cornea into two portions. This is accomplished with a device called a microkeratome. The microkeratome has been used for decades in refractive surgery and is most commonly used today to cut the flap in LASIK surgery. The microkeratome works like a mini carpenters plane. The microkeratome can be adjusted to cut various thicknesses of cornea. It makes a very smooth cut, so that the cornea heals with minimal scarring, permitting good vision. The donor cornea is placed in a device (artificial anterior chamber) that holds it in position while the microkeratome cut is being made. The donor cornea is then removed from the artificial anterior chamber and a circular disc is cut from the center. The endothelial cells of the donor tissue are coated with a protective gel and then the donor disc is folded like a taco with the endothelial cells on the inside.

Figure 7
A device called an artificial anterior chamber is used to hold the donor cornea while the microkeratome is passed over the surface, slicing off the top portion.
                     
Figure 8
Illustration demonstrating the division of a full thickness cornea into two parts. The top 80% of this divided cornea can be used for other types of corneal transplants. The bottom 20% is used to prepare donor tissue for DSEK. This division of tissue is accomplished with a specialized instrument called a microkeratome. Protective gel is placed on the endothelial side of the DSEK transplant and then it is folded like a taco.


                     

The folded donor tissue is then inserted through the surgical incision site into the anterior chamber of the patient’s eye. Once the folded tissue is inside the eye the anterior chamber maintainer is used to deepen the front of the eye and unfold the tissue through gentle irrigation. Instead of folding the DSEK transplant and pushing it into the eye, it can be placed in a glide and pulled into the anterior chamber. The tissue is then opened so that the donor endothelial cells are oriented to the posterior or backside of the tissue.


Figure 9
The taco shaped DSEK donor tissue is inserted into the anterior chamber through the tiny surgical incision (left). A gentle flow of fluid is used to unfold the taco (right).


                  



Figure 10
Instead of folding the DSEK transplant it can be placed in a glide and pulled into the anterior chamber.


After the tissue has been unfolded it is positioned to cover the area of the previously stripped Descemet’s membrane. Then the anterior chamber is filled with air.
 

Figure 11
Shows a cross sectional view of the injection of air into the anterior chamber from a cross sectional view.

The air filled anterior chamber is needed to hold the transplant tissue in position.

                  

Figure 12
Depicts anterior chamber full of air with a well-positioned DSEK transplant.

The small incision site is closed with sutures and the eye is covered with a patch. The patient is then sent home with instructions to return the following day.

        
                  



Figure 13
The DSEK transplant is in excellent position and the small incision is closed with 3
sutures. Note that there are no corneal sutures present which helps to minimize post operative
astigmatism.

 


Advantages and Disadvantages of the DSEK Procedure

The incision into the eye is smaller in DSEK than in traditional PKP. This incision heals more quickly and is a little safer, since it reduces the risk of sight threatening complications such as intraoperative expulsive hemorrhage or post operative traumatic wound rupture. Typically after PKP you will need strong glasses or a hard contact lens to see well; this is not the case with DSEK.

However, there are some trade-offs: with DSEK vision is often slightly reduced by haze developing between the donor tissue and your cornea. Also there is about a 10% chance that the donor tissue will dislocate during the first night after surgery. If this occurs the donor tissue must be re-floated into position.



Frequently Asked Questions About DSEK

How long does the procedure last?
The total time the patient will be in the surgery center is approximately 2 to 2.5 hours. Once the patient is taken to the operating room the procedure is completed in 30 to 45 minutes.

When will I need to return for a follow-up office visit?
You will return for a follow up 2-3 hours after the procedure and then again the next day after surgery. During this visit the health and position of the new transplant will be checked. If everything is in proper order you will start your post op eye drops as directed and return for a follow up visit in 1-2 weeks.

What type of eye drops will I need after surgery?
You will continue using antibiotic eye drops (Zymar) and antiinflamatory drops (Acular) that you started three days prior to surgery. Use the Zymar and Acular 4x per day for one week after surgery unless otherwise instructed. You will also use a steroid eye drop (Econopred 1% or Pred Forte) 4x per day until otherwise instructed. The steroid drops are required to prevent rejection of your new transplant. If you are also using glaucoma eye drops continue to use them after surgery unless otherwise instructed.

When will I see an improvement in my vision?
Visual recovery varies depending on the severity of your corneal cloudiness prior to surgery. Most patients notice improvement in their vision during the first two weeks after surgery with continued improvement during the next 1 TO 6 months. This recovery represents a dramatic improvement over the time required following conventional corneal transplant surgery (PKP), which usually takes six to twelve months. Some DSEK patients may not notice visual improvement as quickly as they would like, because they have other ocular conditions such as cataract or retinal problems that must be addressed.

Can my DSEK transplant undergo rejection?
Although the rate of rejection with DSEK does not appear to be any higher than rejection rates with PKP, endothelial rejection can occur following DSEK. The signs and symptoms of such rejection episodes are the same as they are for PKP patients. Briefly, if you experience redness, photophobia (light sensitivity) and blurred vision assume that you are having a rejection episode and call my office so that you can be evaluated immediately. Most rejection episodes can be successfully terminated by using steroid eye drops. The sooner a rejection is treated the better the chance for transplant survival.



 
j
j j j j j
j
Copyright © 2009 Robert C. Arffa, M.D., 1370 Washington Pike, Bridgeville, PA 15017