Partial Thickness Corneal Transplant Surgery Options
In some cases, it may not be necessary to perform full thickness corneal transplant surgery to treat corneal disease or damage. Some patients can benefit from a partial thickness corneal transplant (endothelial keratoplasty), in which only the affected layers of corneal tissue are replaced with donor tissue and the patient’s own healthy, properly functioning corneal layers are left in place.
Layers of the Cornea
- Epithelium – This outermost, clear, membrane-like layer helps to keep foreign material, such as dust and bacteria, from entering the eye. It absorbs oxygen and nutrients from the tear film so they are available to the rest of the cornea. The epithelium also contains nerve endings that make the cornea sensitive to injury or pain.
- Bowman’s layer – Directly behind the epithelium, Bowman’s layer is a relatively strong structure that helps to protect the cornea from injury.
- Stroma – From the perspective of looking directly at an eye, the stroma is located behind Bowman’s layer. It is the cornea’s thickest layer. Like Bowman’s layer, it contains collagen fibers that give the cornea both strength and elasticity.
- Descemet’s membrane – This layer also helps to protect the inner structures of the eye. It is very thin and consists of collagen, but a different type of collagen than the stroma. Descemet’s membrane is produced by the cells of the cornea layer that lies behind it, the endothelium.
- Endothelium – This single layer of cells is the cornea’s innermost layer. It performs a pumping function that maintains the proper balance of fluid in the cornea to keep it transparent. If the endothelium is not working properly due to injury or disease, the cornea can swell and become hazy or opaque, preventing clear vision.
Full Thickness Corneal Transplant
A full thickness corneal transplant can be used to treat a wide variety of corneal conditions. In the standard method of performing this procedure, a hand-held surgical blade called a trephine is used to remove a button-shaped section of the central cornea that consists of all the corneal tissue layers. The button is replaced with healthy donated corneal tissue (a graft) from an eye bank. The transplanted tissue is typically sutured into position. The full thickness corneal transplant is an excellent tool for restoring vision, but recovery of best vision can take 6 or as long as 12 to 18 months.
A recent development in full thickness corneal transplants is the use of a femtosecond laser to assist with the procedure (femtosecond laser-assisted keratoplasty). The surgeon programs the laser to create precisely shaped incisions, much more intricate than can be accomplished with a trephine, around the edges of the patient’s central cornea and the donor tissue. The incisions interlock like puzzle pieces, allowing the donated tissue to fit snugly on the eye. This has several advantages compared with a full thickness corneal transplant performed with a trephine. Fewer sutures can be used, and they usually can be removed sooner. The graft is more stable and tends to heal more quickly. The eye tends to heal more evenly as well, which results in a less irregular corneal shape, less astigmatism and therefore better vision.
Femtosecond laser-assisted keratoplasty is not for every patient. The peripheral cornea must be clear enough for the laser to properly create the incisions. A detailed analysis of the cornea with specialized imaging devices can determine whether a patient is a good candidate for the procedure. For those who are not good candidates for femtosecond laser-assisted keratoplasty, standard corneal transplant surgery can still be performed.
Endothelial Keratoplasty
DSAEK
Descemet’s-stripping automated endothelial keratoplasty (DSAEK) is used when Descemet’s membrane and the endothelium are the corneal layers responsible for vision problems. Common causes of endothelial disease or dysfunction include previous eye surgery, various infectious, inflammatory or traumatic conditions, and a hereditary condition such as Fuch’s corneal dystrophy.
How DSAEK is Performed
DSAEK is an outpatient procedure. It is usually performed using local anesthetic, supplemented with intravenous sedation of needed. Descemet’s membrane and the endothelium are replaced with a corneal graft (including a small amount of stroma), but the rest of the cornea is left in place. The graft is obtained from a recently deceased donor and rigorously screened and tested by a qualified eye bank to ensure it is suitable for transplanting.
After your eye is anesthesized, a small incision is made near the edge of your cornea. Through the incision, Descemet’s membrane and the endothelium are removed and replaced with the graft. An air or gas bubble is placed under the graft to hold it in position. No sutures are used to hold the graft in place, but the small incision is sutured closed. If the graft does not adhere sufficiently, a “re-bubble” procedure to re-inject the gas or air bubble may be necessary within the first few weeks after the initial procedure.
The “automated” in the name of DSAEK refers to how the donor tissue is prepared. It is shaved from the donor eye with a microkeratome, a precision oscillating blade.
Advantages of DSAEK vs. Full Thickness Corneal Transplant
Corneal transplant recovery is faster after DSAEK than after full thickness transplant, provided the eye has no other problems that would limit best potential vision. Although quite cloudy immediately after DSAEK, vision typically begins improving within 1 to 2 months after surgery. Patients can usually be fitted for glasses within 4 to 6 months (compared to 12 to 18 months after a full thickness transplant). In addition, because only the thin innermost layers of the patient’s cornea are replaced, corneal integrity is less affected than it is with a full thickness transplant.
DMEK
Descemet’s membrane endothelial keratoplasty (DMEK) is the least invasive of the partial thickness corneal transplants because the least amount of tissue — Descemet’s membrane and the endothelium and no stroma — is removed and replaced with a donor tissue graft. As with DSAEK, DMEK may be used when Descemet’s membrane and the endothelium are the corneal layers responsible for vision problems.
How DMEK is Performed
DMEK is an outpatient procedure. It is usually performed using local anesthetic, supplemented with intravenous sedation of needed. As with the other types of corneal transplant, the corneal tissue graft used in DMEK is obtained from an eye bank following rigorous testing to ensure it is suitable for transplanting.
After your eye is anesthesized, a small incision is made near the edge of your cornea. Through the incision, Descemet’s membrane and the endothelium are removed and replaced with the graft. An air or gas bubble is placed under the graft to hold it in position. No sutures are used to hold the graft in place, but the small incision is sutured closed. If the graft does not adhere sufficiently, a “re-bubble” procedure to re-inject the gas or air bubble may be necessary within the first few weeks after the initial procedure.
Advantages of DMEK vs. DSAEK and Full Thickness Corneal Transplant
Corneal transplant recovery is faster after DMEK than after DSAEK or full thickness transplant, provided the eye has no other problems that would limit best potential vision. Although quite cloudy immediately after DMEK, vision typically begins improving within 1 to 2 weeks after surgery. Patients can usually be fitted for glasses within 1 to 2 months (compared to 4 to 6 months after DSAEK and 12 to 18 months after a full thickness transplant). In addition, because only a very thin tissue graft is used for DMEK, the possibility of graft rejection may be lower than in DSAEK and full thickness transplant, and there is a higher chance that final postoperative vision can reach 20/20 with glasses.
Risks Associated with Corneal Transplants
As with any type of surgical procedure, corneal transplants carry with them some potential risks and complications, which our doctors will discuss with you. The body’s rejection of the graft tissue is among these risks. If graft rejection or another problem occurs, but the eye maintains the potential for vision improvement, a re-graft procedure can be done. The procedure may be the same option as the initial surgery, a different partial thickness corneal transplant option, or a full thickness transplant.
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If symptoms of corneal diseases are making you uncomfortable and interfering with your daily life, call us. Our doctors have the expertise and tools to give you the relief you need.