Cornea refers to the clear structure in the front part of the human eye, which allows the light to the eyes. Cornea, along with the crystalline lens helps focus image on the retina (the light sensitive layer of the eye). Whenever the structure and function of the cornea is disturbed, it has a direct impact on the quality of vision.
Several factors such as infections, deposits, degenerations, dysfunction of inner layer etc. can reduce the clarity of the cornea. This has a direct impact on vision. Other problems such as keratoconus, post injury scars alter the shape of the cornea, which result in visual deterioration.
Initially, some of these conditions can be managed by wearing hard contact lenses. However, in the later stages, it often becomes necessary to replace the dysfunctional cornea with a healthy human donor cornea. This procedure is called corneal transplantation. An eye bank helps collect corneal tissue from an eligible donor within six hours after death, and places it in a storage solution to keep the tissue viable for transplantation. Out of all the transplantation surgeries in the human body, corneal transplantation has the highest success rate due to lack of blood vessels in the cornea. This reduces the risk of rejection, and also there is no need of strong immunosuppressive medications after surgery.
Advances in corneal transplantation
When the whole cornea is replaced during surgery, it is referred to as penetrating keratoplasty. Over the past decade, newer surgical techniques have evolved, which allow selective replacement of the diseased portion of the cornea. These procedures are termed as lamellar keratoplasty. Certain conditions affect the front part of the cornea, wherein the inner layer containing cells which help keep the cornea clear (endothelium) are perfectly healthy. The affected layers can be successfully removed without sacrificing the inner layer by a procedure called as anterior lamellar keratoplasty. This prevents the need for long term postoperative steroid therapy and its side effects such as cataract and glaucoma. As the inner layer is preserved, the body does not recognise that a donor tissue has been added to the cornea and virtually eliminates risk of rejection of the transplanted donor tissue.
This has had a big impact on the management of a condition called keratoconus, wherein the cornea loses its normal shape and becomes conical. Instead of performing a traditional full thickness corneal transplantation surgery wherein the inner healthy layer of the host cornea is sacrificed (with increased risk of rejection of transplanted donor cornea), deep anterior lamellar keratoplasty (DALK) procedure spares this inner layer of the host cornea, without any risk of rejection. Certain conditions wherein the inner layer of cells of the cornea (endothelium) becomes dysfunctional, the corneal tissue swells and loses its clarity, thereby affecting vision. Newer surgical procedures have evolved which selectively replace this dysfunctional layer of the cornea, and are called endothelial keratoplasty.
Unlike traditional full thickness corneal transplantation surgery, these procedures do not require any incisions or stitches on the cornea. This has several advantages, such as rapid recovery of vision, minimal discomfort, and reduced risk of postoperative complications. In certain conditions wherein a normal corneal transplantation procedure would not be successful, artificial corneal prosthesis has been developed at the Massachusetts Eye and Ear Infirmary, Boston, USA to help restore eyesight. This is called the Boston Keratoprosthesis, which is made of polymethyl methacrylate (PMMA), and is fixed onto a donor cornea and then transplanted onto a diseased eye. It is quite successful but requires more frequent follow up visits with the corneal surgeon and long term usage of medications.
Corneal transplantation surgery on an average takes about 30 to 60 minutes. Postoperative care is necessary for the initial four to six weeks, following which most of normal day to day activities can be resumed. However, it is necessary to have your eye examined every two to three months, or as advised by the corneal surgeon.
Any untoward symptoms such as blurring of vision, increased sensitivity to light, pain, redness, etc. calls for an immediate consultation with the corneal surgeon. Ignoring these symptoms and delaying consultation with an eye specialist can lead to problems in the corneal graft.
Always remember to keep at hand medications (eye-drops) as advised by the corneal surgeons. Success of corneal transplant surgery is dependent not only on the initial surgical procedure performed by the surgeon, but also on the postoperative care taken by the patient.
Overall, all corneal transplantation surgery is highly successful and helps restore eyesight in most cases of corneal disorders. It is important that the public understands the importance of eye donation, and remembers to call the local eye bank at the time of death of anyone in their family. Without donor corneal tissue, none of these surgical procedures would be possible to help restore eyesight. Support eye donation, and help restore eyesight to the corneal blind!