Sight Restored with Synthetic Corneas
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Corneal damage is the second biggest cause of blindness world wide, affecting nearly 10 million people annually. There are approximately 5 million people in the world who suffer corneal damage from trachoma, an eye infection caused by the bacterium Chlamydia trachomatis. Another 1.5 million to 2 million are affected by corneal damage from ulceration and trauma. In the U.S. about 42,000 cadaver cornea transplants are performed each year and another 10,000 corneas are exported to various countries of the world. For more than a century doctors have considered transplantation of corneal tissue from deceased donors to be the best treatment. First performed in 1905, a corneal transplant at that time consisted of a procedure that replaces the damaged cornea with donor tissue. The surgeon removes the cornea from the donor eye. The new cornea is then implanted in the patient's eye with tiny dissolving sutures which hold the new cornea in place.
Using this method, nearly 50,000 corneal transplants were performed in the United States. Patient selection is usually based on the following criteria: vision should not be better than 20/400 and blink and tear mechanisms should be reasonably intact. The retina should be in place and there should not be extreme optic nerve cupping. The opposite eye has reduced vision, and nasal light projection is intact. Consider a shunt if the patient is suffering from an advanced stage of glaucoma. The healing process following a transplant is long and may take a year or longer. The time from surgery to the removal of the sutures is commonly 6 to 18 months.
The patient may be on steroids for months. Initially following the surgery the donor button is swollen and even following the healing the button is usually thicker than the corneal bed in which it rests. Graft rejection signs are reported to occur from one month to 5 years following surgery. The rejection rates for bilateral grafts are higher than if only one eye is grafted in surgery. If the second eye is to be grafted, the wait is usually a period of at least a year between grafts. If signs of rejection occur, an aggressive treatment with steroids is begun. Usually the reaction is overcome and the graft remains clear. Over 90% of grafts are successful with some studies reporting 97% to 99% success rates at 5 and 10 years.
Large amounts of astigmatism are common following keratoplasty. One study found an average of 5.56 diopters of cylinder correction required following surgery. Therefore, the patient's spectacle prescription may fluctuate for some months after surgery. Refractive changes and keratometry or corneal topography can be used as indicators to follow the healing process. Though the rate of success with keratoprosthesis is high, in rare cases, certain serious complications could occur, such as glaucoma and extrusion of the implant, sudden iritis or inflammation of the ocular tissues.
Marianne O'Connor Price, executive director of the Cornea Research Foundation states, "The U.S. is very fortunate that everybody who needs a transplant here is able to get one, but there is definitely a shortage around the world. Even people here could benefit if there was a synthetic cornea that eliminated the chance of rejection.” The new study was reported in the Science Translational Medicine. It described the use of biosynthetic collagen that was produced by FibroGen Inc. of San Francisco. A team headed by Dr. May Griffith of the Ottawa Hospital Research Institute in Canada molded the collagen into an artificial cornea. Initial tests on animals were highly successful. She claims that the goals are to regenerate the cornea from within. Dr. Per Fagerholm of Linkoping University in Sweden implanted a cornea in one eye of each of 10 patients who suffered from central corneal scarring.
Soon cells that lined the healthy portion of the cornea started growing in the collagen material. Vision improved from 20/400 to 20/100, meaning that they could see objects four times farther away than before the operation. The reason they all didn't see better immediately was that the sutures used in this study resulted in roughness on the corneal surface. The contact lenses compensated for surface roughness resulting in improved vision. Less disruptive sutures will be used in the next clinical study which should correct the problem. The researcher found that after two years, no complications had developed and with the prudent use of contact lenses, vision was as good as with cadaver transplants. It should be noted that contact lenses were commonly used as an adjunct with cadaver corneas, as well.
This study is the first to show that an artificially made lens can blend into the human eye and provide regeneration of the corneal nerves and tissue. Dr. Griffith revealed that her group was now in the process of building a "clean room" to manufacture more of these remarkable corneas. She also hopes to initiate larger trial sessions after the first of the year starting with 20-25 patients.
In addition, researchers are working to improve plastic like artificial corneas and also to create stem cell treatments that could spur corneal growth
(See
Corneal Burns Successfully Treated with Stem Cells from the Aug. 2010 issue of this
publication). Dr. Alan Carlson, cornea transplant chief at Duke University's eye center was not involved in the research; however he expressed strong support for the project. He said, "I characterize this work as a major advance in the direction that we need to go. To make this mimic donor tissue to the extent that your own cells ultimately become incorporated in this tissue, I think that is the most exciting aspect." Dr. Carlson cautioned that these were not full thickness corneal transplants. The lowest layer of the patient's original cornea was not replaced. Patients who had problems with the outer layers of the cornea make up about 10 percent of the transplant cases.
It is thought that the new biosynthetic corneas might be cheaper than donated corneas which average approximately $2,500 per eye with some documentation of fees reported as high as $35,000 in the U.S. Many patients seek reduced costs available in India or Singapore where the fees may be as little as 1/4 the costs in the U.S. or U.K. Prosthetic corneas made of synthetic plastic are used for patients who have experienced unsuccessful donor grafts. They are difficult to implant and are known to cause infections, glaucoma or retinal detachment.
Dr. Walter Stark directs the center for cataract and corneal diseases at Johns Hopkins Hospital, Wilmer Eye Institute in Baltimore and is a professor of ophthalmology at the school of medicine. He also approves of the monumental steps taken toward the use of biotechnical created collagen. However, he agrees with Dr. Carlson as he refers to the complication that seems to exist when treating the lower layers of the cornea which are slower to heal and would require a rather thick application of this new material. Dr. Stark notes, "The outcomes of this study were not nearly as good as those achieved with human donor corneas. This may become an excellent technique, but right now it is not ready for clinical use." Some of the conditions that may cause the need for a corneal transplant are: corneal failure following other eye surgery, such as cataract surgery, keratoconus, hereditary corneal failure such as Fuch's dystrophy, scarring after infections, such as herpes, ejection after a first corneal transplant, scarring after an injury.
An alternative method for corneal transplant procedure is the use of highly precise lasers. They use short but intense laser pulses thereby cutting and shaping corneal tissue to suit each patient's eyes in a precise manner. The procedure is called Femtosecond Laser-Enabled Keratoplasty (FLEK). Dr. William W. Culbertson says, “This will rapidly become the gold standard for corneal transplant surgery." In the past two years Dr. Culbertson has performed nearly 50 FLEK corneal transplant procedures on a wide range of patients. Very good results with a faster rehabilitation period have been reported. However, a common problem is astigmatism. This may occur when a mismatch of the donor and the recipient takes place. Slightly asymmetric suture tension may cause astigmatism as well. These types of conditions can usually be corrected with contact lenses. Corneal transplant patients also run a risk caused by a sudden injury or impact to the head which might dislodge the new tissue. In that event the tissue can be reattached or a second transplant can be performed.
"There had not been a major advancement in corneal transplantation techniques for the past 30 years." said Dr. Sonia Yoo, a corneal specialist and associate professor of clinical ophthalmology at
Bascom- Palmer. "We have been able to store donor tissue for longer periods of time and develop more effective anti-rejection medications. Now the use of lasers is a quantum leap to the next level. "Dr. Yoo and her associates feel that femtosecond laser technology opens the door to many new advanced options for cornea transplantation. The equipment's sophisticated computer controlled software allows physicians to program a nearly infinite variety of three dimensional shapes and highly precise dimensions. This procedure is also used to perform partial transplants. A thin layer of damaged cells is peeled away on the front or back surface of the cornea and replaced with healthy donor tissue. Surgeons feel that this represents a revolution in corneal surgery since the cornea can be split into different layers depending on the patient's needs. It is a more precise, controlled method than manual dissection of the cornea and reduces the risk of transplant rejection. In cases where corneal transplant tissue has failed several times, an artificial cornea may provide a different option for restoring vision.
Today, corneal specialists can intervene earlier in the progression of some corneal diseases. Instead of watching and waiting until a significant amount of scarring occurs, a thinner slice of the anterior surface of the cornea may be removed and replaced with an exact matching, clear piece of tissue. This is an amazing option considering that the patient might have been forced to struggle with uncomfortable contact lenses and a lower level of function for many years in the past.
Future patients in need of a corneal transplant procedure have the comfort of knowing that they will be the recipients of the momentous progress being made via techniques developing to attack the problem from several different points of view.
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