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CORNEAL TRANSPLANT SURGERY | |
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Fig.1 Corneal transplant with sutures in place The Normal Eye The eye is constructed like a camera and functions in much the same manner. The main functioning parts of the camera are the protective front lens, the focusing lens, the shutter, and the film. The eye has corresponding parts that function in a similar manner. The CORNEA is the forward-most portion of the eye. It is the main window of the eye. It is like the protective lens of a camera. The cornea is what you usually poke when you stick a finger in your eye! The cornea and the lens of the eye are the main focusing apparatus of the eye. Damage to the cornea can cause a normally crystal clear cornea to turn white or gray. If this happens, you can no longer see through it and vision may be lost (unless surgery is performed to restore it). The cornea is made of THREE LAYERS - the epithelium, stroma, and endothelial cell layer The IRIS is behind the cornea. The hole in the iris is the PUPIL. The iris and the pupil become larger and smaller in different lighting conditions to let different amounts of light into the eye like a shutter on a camera. The LENS of the eye is like the lens of the camera in that it focuses light coming through the cornea and through the iris onto the back portion of the eye. The VITREOUS is a thick jelly-like fluid behind the lens that keeps the eye round and semi-soft. The RETINA is a thin membrane at the back of the eye that acts like the film of the camera. It takes pictures that have been focused by the cornea and the lens and sends them to the brain on the NERVE of the eye, the OPTIC NERVE. Why You May Need a Corneal Transplant There are many conditions for which a person might need a corneal transplant. These conditions include, but are not limited to: 1.Lacerations/abrasions of the corneal Epithelium/Stroma 2.Infections of the corneal (bacterial/viral) Epithelium/Stroma 3.Keratoconus (progressive thinning and cone-shaping of the corneal Stroma 4.Chemical injury to the corneal (i.e., household ammonia) Epithelium/Stroma 5.Surgical Trauma (i.e., after cataract surgery or any intraocular eye surgery or after failed refractive surgery) to the Endothelial Cell Layer 6.Fuchs Dystrophy - damage to the Endothelial Cell Layer from the aging process (causing clouding of the cornea and painful blisters) Basically any condition that alters the normally smooth contour of the cornea, the curvature of the cornea, or any condition that leads to clouding of the normally crystal clear cornea, will lead to vision loss and the need for a corneal transplant. CORNEAL TRANSPLANT SURGERY THERE ARE TWO TYPES OF CORNEAL TRANSPLANT: TYPE 1: STANDARD FULL THICKNESS PENETRATING KERATOPLASTY When the Cornea becomes opaque or gray/white from disease or injury (#1-4) or painful from swelling or blisters(#5-6), it no longer functions as the clear window of the eye. It then acts more like a soapy window that you cannot clearly see through. Even if the rest of the eye is healthy, a cloudy cornea will obstruct clear vision. Corneal transplants are the most successful transplant in the body with success rates from 85-95% The STANDARD FULL THICKNESS CORNEAL TRANSPLANT procedure is technically difficult. It is performed under an operating microscope that magnifies the eye 30 to 60 times. The diseased cornea or host cornea ( ALL THREE LAYERS) is cut with a round blade with a hole in its center. This is like a round cookie cutter punching a round disc of cookie dough. The diseased tissue or disc (ALL THREE LAYERS) is removed just as you would pick up the cut out cookie, leaving a rim of cookie dough on the platter. Now you have a hole in the center of the cornea just like the hole in the center of the cookie dough. The surgeon then uses the same or a slightly larger blade to cut a similar piece of tissue from a HEALTHY CORNEA from a person who has recently died. This healthy donor cornea is then placed into the hole where the diseased tissue was removed. The healthy, new piece of corneal tissue is then sewn to the remaining rim of the patient's tissue as shown in the drawing. ( Fig.1 ) The eye then has a healthy, clear new window or corneal transplant. The stitches remain in place for 12 months and vision usually begins to return in 1 to 8 weeks after surgery. It must be remembered; however, that diseases of other portions of the eye, such as disease of the lens or of the retina, can limit the final vision even if the surgery was successful and the cornea is perfectly clear. Other procedures, such as cataract extraction and lens implant, intraocular lens implant removal of vitrectomy, may be and often are performed at the same time as the corneal transplant. ADVANTAGES AND DISADVANTAGES OF TRADITIONAL TECHNIQUE Standard full thickness corneal transplant surgery has consisted of removing the entire cloudy cornea and replacing it with a full thickness donor cornea, thereby replacing all three layers of the cornea. This surgery was first developed one hundred years ago and the wonderful 90% success rate reported today is based on numerous refinements to this same basic technique. It has certainly stood the test of time. The traditional corneal transplant operation has a long and successful track record with an exceptional 90% success rate. The rate of rejection is only about 8%-10% It is relatively easy to combine other surgeries with it, such as cataract extraction or glaucoma surgery. The disadvantages of the traditional corneal transplant operation are the time involved in performing the actual operation (45 to 60 minutes), the difficulties in suturing the new cornea in place, and occasional problems with the sutures which can become loose, cause infections, or cause astigmatism (an irregular corneal shape). The astigmatism after traditional corneal transplant surgery can be so significant that eyeglasses alone would not give adequate vision and some patients ultimately require contact lenses or additional surgery to reduce or eliminate the astigmatism. Because the wound is a full 360 degrees and the sutures used are finer than human hair, the corneal transplant wound is always very delicate and at risk to rupture or break open from trauma, even several years after the surgery. The visual recovery can take 6 to 16 months. TYPE 2: DESCEMETS STRIPPING ENDOTHELIAL KERATOPLASTY (DSEK): Ophthalmic researchers and surgeons have long recognized that for many patients needing a corneal transplant, only the diseased or missing endothelial cells ( #5-6) needed to be replaced as the stroma and epithelial layers were normal. The endothelial layer is composed of a single layer of thousands of small fluid pumping cells. These endothelial pump cells are responsible for pumping fluid out of the cornea so it can remain clear and thin and provide good vision for the eye. If a critical number of endothelial cells become dysfunctional, damaged, or destroyed, the cornea fills up with fluid and becomes swollen and cloudy and causes blurry vision. When this occurs, a corneal transplant operation is indicated. Prior to the DSEK procedure, these patients would receive the standard full thickness corneal transplant. Now, however, these patients are treated with the newer DSEK corneal transplant. This new technique appears to be a significant improvement over the standard operation. The surgical skill and expertise required is the same, but the surgery itself takes less time with an experienced surgeon, involves a smaller surgical incision, requires far fewer sutures, heals faster and more reliably, and the vision returns faster than with a standard full thickness corneal transplant. The patients endothelial layer is stripped from the rest of the cornea The donor endothelium is folded like a taco and inserted into the eye through a small corneal incision.An air bubble is injected into the eye to push the donor endothelium up against the posterior surface of the patients cornea.The pumping action of the new donor endothelium creates a suction which bonds the donor tissue to the patients own cornea Complications Despite the most advanced surgical techniques and the most expert surgeons, complications can and do occur. The most serious complications are less common and the lesser complications are usually treatable. Those risks include, but are not limited to: Loss of vision, loss of the eye itself, loss of vitreous, nucleus or capsule, irregular pupil, retinal detachment, retinal tear, macular edema, wound leaks, infection, malposition or later movement of the intraocular lens, inability to place the intraocular lens, infection, hemorrhage in (explusive) or behind (retro-bulbar) the eye, glaucoma, rejection, graft failure, high post-operative astigmatism, the need to wear glasses/contact lenses after surgery, the need for later astigmatism surgery or repeat transplant, unexplained poor vision, double vision, lid droop, and halos or glare, especially at night. Dislocation of the donor graft, in DSEK, may lead to the need for re-positioning or replacement of the graft or in some cases a full standard corneal transplant. Anesthesia related complications include, but are not limited to: perforation of the globe, drooping lid, cardiac irregularities, respiratory depression, hypotension, nerve damage, hemorrhage or drug reactions which can lead to loss of vision, loss of the eye, or loss of life. These complications can occur at surgery or at a later time. | |
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