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Laser EYE SURGERY

LASIK and Excimer Lasers

Michael Hutchins

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The PROBLEM

pia - near sightedness

sed by either an elongated

or steep cornera.

focal point is in front of thea instead of on it.

cally corrected with concaveative o tical ower lenses.

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THE PROBLEM

eropia - far sightedness

ed by a flat cornea orrt eye.

l point is behind thea.

ected with concave

s (positive optical

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THE PROBLEM

matism arises from different focal points in differentes of the eye.

sed by non-uniform curvature of the cornea or scarrilens.

ular astigmatism cannot be fixed by glasses, just cont

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NTERNAL CORRECTION

IK - Laser Assisted in SItu Keratomileusis

tomileusis is the procedure of opening the eye and

ing the cornea.

IK uses an excimer laser to perform the alterations ar a knife or a femtosecond laser to create the openi

IK is an alternative to wearing glasses or contacts as iects m o ia h ero ia and asti matism.

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LASIK

IK began in 1950 in Bogot, Columbia with the

lopment of keratomileusis.

eakthrough was the 1973 announcement of the exci

.

holam Peyman filed the first LASIK patent in 1989

thod for modifying corneal curvature. It includes the

edure of revealing the cornea, using an excimer lase

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LASIK

SIK is performed while awake

h an occasional mild sedative.

hinged flap is cut with either a

tal blade or a femtosecond

er.

Excimer laser remodels the

rnea by ablating tissue.

e flap is repositioned and left

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LASIK

ing the flap is either done with a microkeratome or

osecond laser.

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Excimer Lasers

mer lasers are UV lasers that utilize

le gas halides.

often use a combination of an inert

uch as argon, krypton or xenon

a highly reactive gas like chlorine orrine.

ort lived molecule called an excimer

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Excimer Lasers

mers are formedn the inert gas

into an excited

, in this state theyd with the halide

rm a molecule.

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Excimer Lasers

n the noble gas

rns to its ground

it repels the halideh gives rise to the

violet light.

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EXCIMER LASERS

cal wavelengths for

us excimers.

bond energy of an H-O

of H2O is about 4.76

nd to break a C-H bond

hane it is 4.38 eV

le light is 2-3 eV while

Excimer Wavelength (nm) Energy (e

Ar2* 126 9.85

Kr2* 146 8.50

F2 157

7.90

Xe2* 172 & 175 7.21 & 7.

ArF 193 6.43

KrF 248 5.00

XeBr

282

4.40

XeCl 308 4.03

XeF 351 3.54

CaF2 193 6.43

KrCl

222

5.59

Cl2

259 4.79

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Excimer Lasers

ultraviolet light is absorbed by tissue and organic matt

dded energy breaks the bonds of molecules at the su

e molecules ablate into the air without adding heat to

. This is called Ablative Photodecomposition.

ent excimer lasers typically pulse for 10 ns at 100 Hz.

se used in eye surgery reposition to follow the eye 40s er second.

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Excimer Lasers

low absorption depth: 0.1

.5m.

gy highly absorbed by

rials.

orm power density over

ively large area.

Discharge circuit - expenand require frequent

maintenanceLaser gas mi

is toxic and corrosive.

The laser must be refille

fresh gas regularly.

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LASIK Side Effects

Surgery induced dry eyes

Over or under correction

Visual acuity fluctuation

Halos or starbursts arounsources at night

Light sensitivity

Ghost images

Wrinkles in flap

Decentered ablation

Debris or growth under fl

Induced astigmatism

Corneal Ectasia

Floaters

Epitheliun erosion

me higher order abberations can

cur as they cannot be diagnosedh normal eye exams.

e is halos and starbursts: visionne during the day but at night

pupil can expand and pass the

ge of the LASIK flap, this givese to halos and other abberations.

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LASIK Alternatives

IK is limited by the excimer laser and can cause somage to the eyes nerves so new methods are being

loped.

ther popular method is PRK it is similar to LASIK wit

ssitating a flap to be cut (necessary for pilots).

pared to LASIK it has a longer recovery period and

mfort.

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References

ipedia entries on: LASIK, Excimer Laser, Excimer, Myeropia, Astigmatism (eye), Keratomileusis, Photorefra

tectomy

-Wikipedia images from:

://eyeclinicpc.com/lasik/lasik.htmand http://

.nseyespecialists.com/images_content/technolasphot