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What is a corneal transplant?
Corneal transplants are one of medicine's most successful transplant operations. The procedure involves removing the cornea from the donor eye with a special instrument resembling a small cookie cutter. The same method is used to remove the damaged cornea from the patient's eye. The surgeon then stitches the new cornea into place.
For many individuals, a corneal transplant may be the only hope for restored vision, and may be necessary when the cornea is cloudy or damaged due to disease, injury, accident, or hereditary conditions. In these situations, the cornea must be removed and replaced with healthy donor tissue. The procedure is successful in 90 percent of cases, restoring sight and, in some cases, even providing sight for the first time.
R: increased Redness
S: increased Sensitivity to light
V: decreased Vision
P: increased Pain
Today, regrafts are one of the most common reasons for corneal transplants. Regrafts occur when a patient needs a second corneal transplant because the first one was unsuccessful. Some additional reasons include:
- Corneal ulcers, a type of infection that often leads to scarring
- Trauma
- Fuch's Dystrophy
- Damage to the epithelial layer of the cornea, through improper cleaning and use of contact lenses.
Sleeping in contact lenses leads to a greater risk of corneal ulcers; the symptoms include:
Keratoconus
Keratoconus is considered a slowly progressive, no inflammatory corneal dystrophy characterized by changes in corneal collagen structures and organization. A reduced number of collagen cross-linking and pepsin digestion higher than normal induce an overall structural weakness of the corneal tissue, resulting in a stiffness that is only 60% that of the normal cornea. Decreased mechanical corneal stability plays an important role in the progressive protrusion of the keratoconic cornea, resulting in mild to marked impairment of visual acuity owing to irregular astigmatism, progressive myopia, corneal thinning and central corneal scarring.
Common methods if vision correction for keratoconus range from spectacles to rigid gas-permeable contact lenses and more recently to wave front-corrected spectacles and soft contact lenses. Intracorneal ring segments implantation improves uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA) in patients with mild to moderate keratoconus and contact lens intolerance.
However, long-term follow-up shows that intracorneal ring segments fail to provide a permanent flattening effect. A significant progression of K-values in treated corneas has been observed, demonstrating that this device can only temporarily correct the keratoconic eye’s refractive errors; keratoconus is a progressive disease that requires corneal grafting in the most advanced cases. Recently, a new technique, corneal collagen cross-linking (CXL), has been introduced by Wollensak et al to stabilize progressive keratoconus, prevent some of the underlying pathphysiologic mechanisms of the disease, and avoid the need for penetrating keratoplasty.
Cross-linking
Collagen cross-linking increases the biomechanical strength of the human cornea by about 300% by the combined action of a photosensitizing substance (riboflavin) and ultraviolet (UV) light from a solid-state UVA source. The treatment creates additional chemical bonds inside the anterior 200-300 microns of the corneal stroma by means of photo polymerization. There is minimal exposure to the surrounding structures of the eye. collagen cross-linking increases the resistance to pepsin digestion by enhancing corneal anticollagenase activity, and induces a thicker collagen fiber diameter.
Confocal microscopy studies have also shown apoptosis of keratocytes in the anterior and intermediate stroma followed by a gradual keratocytes repopulation.
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