Automated lamellar keratoplasty
Encyclopedia
Automated Lamellar Keratoplasty, commonly abbreviated to ALK uses a device called a microkeratome
to separate a thin layer of the cornea and create a flap. The flap is then folded back, and the microkeratome removes a thin disc of corneal stroma below. The thickness and diameter of this disc determines the change in refractive error. The surgeon then places the flap back into position. This procedure can correct large amounts of myopia and hyperopia. However, the resultant change is not as predictable as with other procedures.
At this point, the microkeratome is precisely readjusted to match the calculated cut depth for the patient's vision correction. The calculation is based on the patient's glasses and contact lens prescriptions. The surgeon then passes the microkeratome completely over the eye making the power cut. After the power cut, the corneal flap is laid back over the eye where it reattaches.
ALK is an effective technique for very high levels of myopia and is generally used from -5.00 to -30.00 diopters of nearsightedness.
Healing time from ALK is very rapid, usually in about 24 hours or so. Results are immediately realized, though it may take several months for the vision correction to finally stabilize. On the down side, the results of ALK are not as highly predictable as with the laser procedures of LASIK
or PRK
.
Microkeratome
A microkeratome is a precision surgical instrument with an oscillating blade designed for creating the corneal flap in LASIK or ALK surgery. The normal human cornea varies from around 500 to 600 micrometres in thickness; and in the LASIK procedure, the microkeratome creates a 83 to 200 micrometre...
to separate a thin layer of the cornea and create a flap. The flap is then folded back, and the microkeratome removes a thin disc of corneal stroma below. The thickness and diameter of this disc determines the change in refractive error. The surgeon then places the flap back into position. This procedure can correct large amounts of myopia and hyperopia. However, the resultant change is not as predictable as with other procedures.
Procedure
The eye is anesthetized and a ring is fixed to it in order to keep it properly positioned and flat. The microkeratome then makes a small incomplete flap across the cornea by cutting across it. While still attached at one side, the corneal flap is folded back to reveal a sub layer of cornea.At this point, the microkeratome is precisely readjusted to match the calculated cut depth for the patient's vision correction. The calculation is based on the patient's glasses and contact lens prescriptions. The surgeon then passes the microkeratome completely over the eye making the power cut. After the power cut, the corneal flap is laid back over the eye where it reattaches.
ALK is an effective technique for very high levels of myopia and is generally used from -5.00 to -30.00 diopters of nearsightedness.
Healing time from ALK is very rapid, usually in about 24 hours or so. Results are immediately realized, though it may take several months for the vision correction to finally stabilize. On the down side, the results of ALK are not as highly predictable as with the laser procedures of LASIK
LASIK
LASIK or Lasik , commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism...
or PRK
Photorefractive keratectomy
Photorefractive keratectomy and Laser-Assisted Sub-Epithelial Keratectomy are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. The first PRK procedure was performed in 1987 by Dr. Theo Seiler, then at the Free University...
.