Laser Eye Surgery

Laser EYE SURGERY
LASIK and Excimer Lasers
Michael Hutchins
The PROBLEM
opia - near sightedness
used by either an elongated
or steep cornera.
focal point is in front of the
na instead of on it.
ically corrected with concave
THE PROBLEM
eropia - far sightedness
sed by a flat cornea or
ort eye.
al point is behind the
na.
rected with concave
es (positive optical
THE PROBLEM
gmatism arises from different focal points in different
nes of the eye.
used by non-uniform curvature of the cornea or scarrin
lens.
gular astigmatism cannot be fixed by glasses, just conta
INTERNAL CORRECTIONS
SIK - Laser Assisted in SItu Keratomileusis
atomileusis is the procedure of opening the eye and
ring the cornea.
SIK uses an excimer laser to perform the alterations an
er a knife or a femtosecond laser to create the openin
SIK is an alternative to wearing glasses or contacts as it
LASIK
SIK began in 1950 in Bogotá, Columbia with the
elopment of keratomileusis.
reakthrough was the 1973 announcement of the excim
r.
Gholam Peyman filed the first LASIK patent in 1989 a
ethod for modifying corneal curvature”. It includes the
cedure of revealing the cornea, using an excimer laser
LASIK
ASIK is performed while awake
th an occasional mild sedative.
hinged flap is cut with either a
etal blade or a femtosecond
ser.
n Excimer laser remodels the
ornea by ablating tissue.
he flap is repositioned and left
LASIK
ting the flap is either done with a microkeratome or a
tosecond laser.
Excimer Lasers
mer lasers are UV lasers that utilize
le gas halides.
y often use a combination of an inert
such as argon, krypton or xenon
h a highly reactive gas like chlorine or
rine.
hort lived molecule called an excimer
Excimer Lasers
mers are formed
en the inert gas
s into an excited
e, in this state they
d with the halide
orm a molecule.
Excimer Lasers
en the noble gas
urns to its ground
e it repels the halide
ch gives rise to the
aviolet light.
EXCIMER LASERS
cal wavelengths for
ous excimers.
bond energy of an H-O
d of H2O is about 4.76
and to break a C-H bond
thane it is 4.38 eV
ble light is 2-3 eV while
Excimer Wavelength (nm)
Ar2*
126
Kr2*
146
F2
157
Xe2*
172 & 175
ArF
193
KrF
248
XeBr
282
XeCl
308
XeF
351
CaF2
193
KrCl
222
Cl2
259
Energy (e
9.85
8.50
7.90
7.21 & 7.0
6.43
5.00
4.40
4.03
3.54
6.43
5.59
4.79
Excimer Lasers
ultraviolet light is absorbed by tissue and organic matte
added energy breaks the bonds of molecules at the sur
se molecules ablate into the air without adding heat to
a. This is called Ablative Photodecomposition.
rent excimer lasers typically pulse for 10 ns at 100 Hz.
se used in eye surgery reposition to follow the eye 400
es per second.
Excimer Lasers
low absorption depth: 0.1 •  Discharge circuit - expen
0.5µm.
and require frequent
maintenanceLaser gas mix
rgy highly absorbed by
is
toxic
and
corrosive.
erials.
form power density over
tively large area.
•  The
laser must be refilled
fresh gas regularly.
LASIK Side Effects
ome higher order abberations can
ccur as they cannot be diagnosed
th normal eye exams.
ne is halos and starbursts: vision
fine during the day but at night
e pupil can expand and pass the
dge of the LASIK flap, this gives
e to halos and other abberations.
Surgery induced dry eyes
Over or under correction
Visual acuity fluctuation
Halos or starbursts around
sources at night
Light sensitivity
Ghost images
Wrinkles in flap
Decentered ablation
Debris or growth under fl
Induced astigmatism
Corneal Ectasia
Floaters
Epitheliun erosion
LASIK Alternatives
SIK is limited by the excimer laser and can cause some
mage to the eyes nerves so new methods are being
eloped.
other popular method is PRK it is similar to LASIK with
essitating a flap to be cut (necessary for pilots).
mpared to LASIK it has a longer recovery period and m
omfort.
References
kipedia entries on: LASIK, Excimer Laser, Excimer, Myo
peropia, Astigmatism (eye), Keratomileusis, Photorefrac
atectomy
n-Wikipedia images from:
p://eyeclinicpc.com/lasik/lasik.htm and http://
w.nseyespecialists.com/images_content/technolasphot