Corneal button

Greek physician Galen is said to have first consider the possibility of corneal transplantation^[4] however, there is no evidence that he actually attempted the procedure.^[5] It was only until the 18th century that early surgical proposals for keratoplasty would arise and the 19th century for experimentation in the field to begin.^[6]

In 1813, Karl Himley suggested that opaque animal corneas can be replaced by transplanting corneas from other animals; with his student Franz Reisenger commencing experimentation in 1818.^[5]

In 1844, Edward Kissam undertook the first ever recorded attempt of a xenograft on a human; the donor was a pig and was ultimately unsuccessful.^[6] Henry Power made a suggestion in 1867 that using human tissue rather than animal tissue for transplantation would be more effective however, it would not be until 1905 for the first successful human corneal transplant by MD, Eduard Zirm.^[6]

Since 1905, various techniques and procedures have been developed to increase the effect of the transplantation and success rate. Traditionally, the most common procedure for corneal transplantation was penetrating keratoplasty whereby an entire corneal button is replaced.^[6] Recently however, procedures such as anterior and posterior lamellar techniques where only diseased or damaged layers of the cornea are selectively replaced have become increasingly popular.^[6]

After the death of the donor, the cornea must be retrieved within a few hours and will be screened for diseases and assessed for its viability to be used for a corneal transplantation by assessing its health. If passed, the cornea will be stored in a nutrient solution at an eye bank until needed for an operation.^[1] In most cases, the corneal button is removed from the donor cornea prior to storage as this extends its possible storage time.^[3]

For the operation procedure, the patient is anaesthetised and the damaged or diseased corneal button will be removed using a bladed instrument called a trephine (approximately 8.0–8.5 mm in diameter).^[7] A corneal button of matching size is then put in place of the removed tissue and stitched in place. Usually, twelve clock-hour nylon stitches are used with a continuous band nylon stitch.^[1]

The procedure takes approximately 60–90 minutes however, a few months will be required for vision to return to what it was like preceding the operation; and continue to improve from then on. Approximately 12–18 months after the operation, all stitches will be removed. During this time, anti-rejection drops will be needed to minimise inflammation; the dosage of which is carefully monitored by a corneal surgeon.^[1]

Due to the swelling, it is impossible to predict the quality of vision without removing the stitches. A few months after the stitches are removed, measurements are made of the shape of the cornea and refractive error. If the shape of the cornea is fairly regular and refractive error is similar to that of the other eye, it is usually possible to fix any error with glasses; if not, a hard lens may be necessary to correct vision.^[1]

One of the largest causes for issue in penetrating keratoplasty is the natural immune rejection of a transplanted corneal button which can cause reversible or irreversible damage to the grafted cornea. The types corneal rejection include epithelial rejection, chronic rejection, hyperacute rejection and endothelial rejection and these can occur individually, or in some cases in conjunction.^[8]

There are however, two main preventative methods to reduce the possibility of immune rejection; prevention and management. Prevention involves increasing compatibility of the donor tissue with that of the patient and suppressing host immune response. These analyses of donor corneas are done during a screening phase soon after receiving the donation. The management aspect mainly involves early detection and therapy with corticosteroids along with Immunosuppressive therapy.^[8]