Partial Thickness


The cornea is the clear dome-shaped “window” in the front of the eye.  Behind this clear window lies the iris, or colored portion of the eye.  The cornea serves two purposes: 

  1. It forms the front part of the eye’s outer wall or shell and focuses images on the retina at the back of the eye.
  2. With its curved shape, the cornea acts like a camera lens to transmit light and focus images on the back of the eye. 

The cornea is about 0.5 mm thick and has three main layers to it; an outer layer (epithelium), a middle layer (stroma), and an inner layer, the endothelium.  Endothelial keratoplasty replaces the inner layer of the cornea when it is damaged or no longer functions properly.  When the endothelial layer of the cornea is not functioning then the cornea absorbs extra water and becomes cloudy.  Endothelial keratoplasty is a surgical procedure which replaces the inner endothelial layer of your cornea with healthy functioning endothelium from a donor cornea.  Endothelial keratoplasty (EK) is a form of corneal transplant in which only the layer of the cornea which has been determined not to be functioning properly is replaced.  This is contrast to penetrating keratoplasty (PK) in which the full thickness of the cornea is transplanted.    

Risks of Endothelial Keratoplasty

Endothelial keratoplasty does have some risks in common with full thickness PK and these include a 1 in 1000 chance of serious infection or bleeding.  Additionally, there is a 20% chance of the body’s immune system producing an inflammation to the donor cornea.  This is called a rejection reaction.  Fortunately most rejection reactions can be treated successfully with topical medications.  The transplant may become cloudy either because of rejection or for other reasons.  If this happens it may be necessary for you to have another transplant.  The risk of transplant failing varies depending on what your current corneal condition is, however is in the range of 5%. 

Risks Specific to EK Surgery

Risks of EK corneal transplant surgery that are unique to split thickness surgery include: 

  1. Movement of the endothelial transplant tissue (“disc”) within the eye.  If the disc is in good position on the day after surgery, then it is rare for the disc to dislodge later.  Should the donor tissue disc be found on the first day after EK surgery to be dislocated or dislodged, then it would require another surgery to either put the tissue back into the proper position.
  2. No surgical procedure is free of risk.  Possible complications also include, but are not limited to astigmatism, retinal detachment, glaucoma, and cataract.  Problems unrelated to corneal transplant surgery such as retinal scarring (macular degeneration) or optic nerve damage from increased eye pressure (glaucoma) may lead to poor vision even if the corneal transplant operation is successful.



Preparing For Surgery


A general medical examination and routine laboratory tests ensure that you are well enough to undergo surgery.  Aspirin is not used for 2 weeks prior to surgery, since it tends to cause bleeding during surgery.


Local or general anesthesia can be used; based on age, general health, length of surgery, and patient preference.  Local anesthesia consists of a small injection in the lower eyelid.  Sufficient sedation is given so that the local anesthetic is hardly felt.  In most cases, the surgery can be done on an outpatient basis.  A small weight is placed on the closed eye to soften the eye.  An IV line and heart monitoring are standard safety precautions. 


The entire procedure is done under a microscope.  During the surgery a single 5 mm long line incision is made in the sclera (the “white” part of the eye), a pocket is formed, and just the diseased endothelial layer of your cornea will be removed by gently “stripping” the diseased tissue off, like peeling wallpaper off a wall.  The donor endothelium and back layer of the donor cornea (the lamellar “split thickness” corneal tissue) is then placed through the incision and pocket and placed into position on the back surface of your cornea to replace the diseased tissue which was removed.  A small air bubble is placed to keep the tissue firmly in place until after a few minutes; it can adhere on its own.  The initial incision is then closed with three small sutures in the sclera and the procedure is completed. 


The surgical procedure will take about one hour to perform.  If you also have a cataract of the lens of the eye, then cataract surgery can be performed at the same time as EK surgery.  If cataract and EK surgery are done, then the surgery takes about one and a half hours.  You will be required to lie flat on your back, facing the ceiling for one hour immediately after the operation to help the air bubble help the tissue to adhere. 


After The Procedure


Surgery is usually done as an outpatient procedure at the hospital and you are sent home with a patch on your eye that same afternoon.  We ask that you try to lie flat facing the ceiling as much as possible after you get home for the first night of surgery.  You should have minimal discomfort after surgery, and standard over-the-counter pain medications can be taken if necessary. 


You will return to see Dr. Johnston the next day.  The patch will be removed and your eye will be examined.  You will be placed on antibiotic and anti-inflammatory drops to prevent infection and to help with healing.  This first visit after surgery will only take about 10 minutes, and is primarily done to be sure that the donor disc is in good position.  You will have a brief visit to the clinic one week after surgery, and then again at six weeks, three months and six months.  


Unlike cataract surgery alone or laser vision correction, where one achieves their best vision between two days and two weeks after surgery, it takes six weeks to six months to achieve your best vision post EK surgery.

Revised 17January2017