May 3 2006
A Mayo Clinic study
comparing femtosecond (bladeless) and mechanical microkeratome LASIK surgeries
has found equal results from both types six months post-surgery, using a variety
of vision and eye health measurements.
The study's findings will be presented next week in three abstracts at the
Association for Research in Vision and Ophthalmology meeting in Fort Lauderdale,
Fla.
LASIK (Laser-assisted in situ keratomileusis) involves treating
nearsightedness, farsightedness or astigmatism by reshaping the eye's cornea to
alter the way the eye refracts light. LASIK involves creating a flap, removing a
defined amount of corneal tissue by an excimer laser, and replacing the flap. In
standard LASIK with a mechanical microkeratome, the flap is created by a blade;
in bladeless LASIK, the newer type, the flap is created by a femtosecond laser.
"At six months after surgery, there are no differences between the eyes that
had bladeless or microkeratome LASIK with respect to visual acuity (vision as
measured by reading an eye chart), contrast sensitivity (ability to discriminate
bright objects from dark objects), or in perception of stray light or glare,
such as the glare from oncoming headlights," says Sanjay Patel, M.D., Mayo
Clinic ophthalmologist and study investigator.
Given the equivalent findings thus far in eye health and vision between the
two types of LASIK, Dr. Patel slightly prefers bladeless LASIK due to its
potential safety, which was not measured in his study. "I'd say the short-term
outcomes are equal and the risks are, in theory, less with the bladeless
technique, although our study was not designed to compare risks," he says.
"Bladeless LASIK is potentially safer because of its computer-controlled
precision, the ability to visualize the flap being created, and to stop the
procedure whenever necessary. That said, however, the risk of complications with
a traditional, microkeratome blade is very small: some vision loss from surgery
with a microkeratome blade occurs in well under 1 percent of all cases. The
long-term risks of either procedure, however, are unknown, and defining them is
the primary purpose of our study."
The study followed 20 patients who received LASIK for nearsightedness or
astigmatism. Each patient was treated with microkeratome LASIK in one eye and
bladeless LASIK in the other eye. The researchers found no difference in
subbasal nerve density between types of surgery, though the density decreased
after both treatments compared to density before LASIK. Corneal sensitivity did
not differ between microkeratome and bladeless LASIK. Subbasal nerve density and
corneal sensitivity do not impact vision, but rather the potential to heal from
a scratch or other injury to the eye. High-contrast visual acuity, the
capability to see fine details, and contrast sensitivity, the ability to
perceive contrast in objects and their environments, also did not differ between
LASIK types. The researchers found corneal backscatter was greater with
bladeless LASIK for the first three months after surgery, yet the patients
perceived no difference in vision after three months between their eyes treated
with bladeless or microkeratome LASIK. Backscatter is haziness in the cornea
that is usually invisible to the naked eye and is identified through testing in
a physician's office. Cell densities in all layers of the cornea also did not
differ between the LASIK surgeries.
The ultimate goal of the Mayo Clinic study of microkeratome versus bladeless
LASIK is to obtain long-term information about patients' vision and eye health
five years following surgery. The results presented now represent the first six
months of findings.
http://www.mayo.edu