Epikeratoplasty for keratoconus
|Epikeratoplasty for Keratoconus
In a normal eye, rays of light are focused onto the retina by being bent,
not only by the lens of the eye, but also by the cornea - the transparent
window at the front of the eye. Most of the bending of the light rays
is in fact achieved by the cornea, and the lens of the eye only does the
fine tuning to vary the focus for distance and near vision. In keratoconus,
the central part of the cornea becomes thinned, and the surface of the
cornea is irregular, and this causes the vision to be blurred.
Living contact lens
Epikeratophakia has been called 'the living contact lens'. Donor corneal
tissue is formed into a new shape in the same way as a contact lens is
manufactured, and the tissue is then freeze-dried. The freeze-drying process
kills all the cells in the donor cornea so there are no living cells in
the tissue to stimulate any rejection of the graft. Instead of being temporarily
placed on the cornea like a contact lens, the 'epi' graft is stitched
in place. In time, the patient's corneal cells grow into the graft to
make it like a permanent living contact lens. The stitches holding the
graft in place can be removed and no further maintenance is needed.
After the operation, a close check is kept on the eye until the epithelium has healed, since any delay in the healing may allow infection or other problems to develop in the graft. Once the epithelium has healed (usually after 4 - 5 days) the eyelid suture is removed and the eye can be left uncovered. It is necessary to put ointment in the eye for two or three months as the epithelium takes some time to stabilise on the graft. Occasionally if there are problems with instability of the epithelium, a bandage soft contact lens is used to protect the graft as it heals. If any of the fine sutures that are used to fix the graft work loose they may cause irritation and need to be removed after application of local anaesthetic drops.
Epikeratophakia is carried out on the outer surface of the cornea, and
so the risk of damage to the inside of the eye is negligible. The procedure
is potentially reversible. The visual recovery may be slow and the quality
of visual result achieved may not be 100%. The purpose of the epikeratophakia
operation for keratoconus is to restore a normal thickness and contour
to the cornea. The vision will be generally improved, but to obtain the
best vision spectacles or contact lenses may still be necessary. If there
is a large residual optical error after epikeratophakia, further surgery
such as relaxing incisions, or excimer laser photo-refractive keratectomy
(PRK) may be carried out, to improve the unaided vision.