 |
|
|
|
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.
|
 |
|
|
|
|
|
 |
