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Automated
Lamellar Keratoplasty (ALK)
In ALK, the surgeon uses the microkeratome
to separate a 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.
Used to treat hyperopia, CK steepens the central cornea by
using radio frequency energy to shrink the collagen in peripheral
cornea. With CK, the surgeon uses a radio frequency probe
rather than a laser to apply the heat. One published multi-center
study reports 12-month data on 203 eyes and notes that 51%
had uncorrected visual acuity of 20/20 or better at that point.1
The device used in the technique received FDA approval in
April 2002. According to the Reuters 2,
the procedure takes approximately 3 minutes and can be performed
in the surgeon's office. Patients may experience visual fluctuations
for the first couple of weeks following the surgery. The report
states that studies have demonstrated the effects last for
at least two years. One percent of patients developed induced
astigmatism as a complication of the procedure. Patients interested
in this option should discuss it with their ophthalmologist.
Micro-thin
Prescription Inserts
Micro-thin Prescription Inserts INTACS™
are two small arcs of medical plastic that a surgeon places
into the mid-periphery of the corneal stroma. Once in place,
the inserts cause a slight stretching of the cornea and a
subtle flattening of the corneal curvature. The change in
curvature varies with the thickness of the inserts. To place
the inserts, the surgeon must first create a small incision
in the periphery of the cornea. The inserts are then placed.
Finally, the surgeon closes the incision (a suture may sometimes
be required). Once placed, the inserts can be removed or replaced
by the surgeon if the patient's vision needs change. Under
U.S. clinical study since 1991, KeraVision INTACS™ received
FDA approval for the correction of -1.00 to -3.00 D of myopia
with no more than 1.00 D of astigmatism in April 1999.
Multiple
Procedures
Doctors will sometimes use two or more
procedures to treat patients suffering from high to severe
myopia. For instance, ophthalmologists have inserted phakic
IOLs and then performed LASIK to achieve the desired refraction
in eyes with more than -15D of myopia pre-operatively. Surgeons
have also performed initial LASIK procedures then inserted
ICRS to correct residual errors.
However, patients should understand that the use of multiple
procedures is a relatively new option in many countries, including
the United States. Very little study data has been accumulated
on the long-term effects of multiple procedures, and patients
may need to look harder to find a surgeon currently performing
such procedures in combination with one another.
RK
Radial keratotomy, or RK, was refined by a Russian ophthalmologist
in 1963 and involves using a diamond scalpel blade to make
usually four to eight tiny spoke-like incisions in the periphery
of cornea. The incisions slightly weaken the peripheral cornea,
causing it to bulge. This flattens the center of the cornea,
thus reducing myopia.
RK has its drawbacks. The resulting change in refractive error
is felt to be less predictable because no one can control
the way the incisions heal. As a result, RK may only reduce
myopia, not completely eliminate it. RK patients may still
need to wear glasses for distance. In addition, with time,
RK can result in overcorrection.
Because of advances in laser technology, surgeons perform
RK only on a select group of patients.
1. Asbell PA, Maloney
RK, Davidorf J, Hersh P, McDonald M, Manche E, Conductive
Keratoplasty Study Group. Conductive keratoplasty for the
correction of hyperopia. Trans Am Ophthalmol Soc 2001;99:79-84
2. FDA Approves Farsightedness Treatment" Reuters Tues
April 16, 2002 5:19 ET accessed from here
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