Download 5._Laser

LASER IN OPHTHALMOLOGY
& REFRACTIVE SURGERY
Dr.Ali.A.Taqi
5th year students
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LASER
• Is an acronym for the
instrument's mode of
action: (Light
Amplification by the
Stimulated Emission
of Radiation).
• Laser light is
coherent: all photons,
have same
wavelength and are in
phase.
• A laser beam is
collimated, i.e. the
waves of light are
parallel.
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Basic LASER
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Types of Lasers used in Ophthalmology
1-Argon Laser
2-Diode Laser
3-YAG Laser
4-Excimer Laser
What do Lasers do?
• Laser rays have energy. When they hit the target, they
transmit that energy to the target. Heat is also given out. The
effects in the eye are a combination of the Laser and heat
energy.
• Some Lasers are used to create holes, e.g. YAG Laser
Iridotomy in Glaucoma.
• The Excimer Laser has cutting power, used in LASIK.
• The Argon and Diode Lasers are used to create burns that
treat Retinal tears and Diabetic Retinopathy (DMR).
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Use of Laser in Ophthalmology
Lasers have been used widely in treatment of eye
diseases. Such as,
1.Eyelid growths, including lid cancers
2.Trichiasis (Misdirected eye lashes)
3.Open up or block Lacrimal Puncta.
4.Pterygium (Conjunctival degeneration)
5.To alter corneal curvature and correct refractive
errors as in PRK, LASIK etc.
6.Glaucoma (Increased eye pressure)
7.To open opacified posterior capsule, about 6
months after cataract surgery
8.In closing Retinal tears in treatment and
prevention of RD.
9.In Diabetic Retinopathy (DMR)
10.For treatment of tumors like Retinoblastoma.
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Effects of the Laser energy on ocular
tissues
• Radiation wavelengths from 400 to 1400 nm can enter the
eye and reach the retina.
• effects of laser energy on ocular tissues depend on:1----the wavelength and pulse duration of the laser light
2----the absorption characteristics of the tissue (largely
determined by the pigments contained within it).
3----the duration of exposure .
• When the laser energy exceeds the threshold , causes
tissue damage.
• The effects can be ionizing, thermal or photochemical.
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Laser light can be delivered:
1-along a fiber-optic cable to a slit lamp,
2-an indirect ophthalmoscope,
3-an intraocular endolaser probe.
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LASER USED IN OPHTHALMOLOGY
1. Argon blue-green gas laser
It is a mixture of 70% blue (488 nm) and
30% green(514 nm) light.
They are most commonly employed for
retinal photocoagulation for
trabeculoplasty
Photocoagulations aims to treat the outer
retina and spare the inner retina to avoid
damaging the nerve fiber layer.
Argon green (blue screened out)
photocoagulation of the macula does not
cause direct retinal damage. It is well
absorbed by melanin and hemoglobin,
but Xanthophyll (in the inner layer of the
macula) absorbs blue light (but not
green) and thus the use of blue light at
the macula is contraindicated in order to
avoid, direct damage to the retina.
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RETINAL PHOTOCOAGULATION
Factors in retinal photocoagulation
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Retinal photocoagulation
pan photocoagulation for diabetic
retinopathy the aim is the elimination
of abnormal retinal blood vessels
through direct treatment to the blood
vessels or destruction of the ischemic
areas of the retina. This kind of laser
treatment entails marked destruction
of retinal tissue.
• Conversely, application of laser energy
in the macular area has to be modified
owing to factors present in that area,
such as the presence of xanthophyll
pigment, the reduced thickness of the
retina, the increased density of
melanin in retinal pigment epithelium
and the inner choroid, and the need to
minimize retinal damage to avoid
disabling scotomas in the central field
of vision.
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A. NVD and a small vitreous hemorrhage. Panretinal
photocoagulation was given. B. Two months later, the NVD
has completely regressed.
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Laser trabeculoplasty-SLT
• Laser trabeculoplasty is probably the most widely employed laser
technique for the treatment of glaucoma.
• It to be effective in approximately two thirds to three fourths of
patients with primary open-angle glaucoma.
• It also is useful in some secondary open-angle glaucomas such as
exfoliation syndrome glaucoma and pigmentary glaucoma; in eyes
that have had previous filtering surgery; and in eyes that have had
surgical or laser iridectomies because of acute angle-closure
glaucoma attacks.
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2. Nd-YAG laser
• The neodynium-yttrium-aluminumgarnet: laser emits infrared (1064
nm) radiation, it is Continuous wave
(C'W)
• It is commonly used to:– the posterior capsule of the lens
following cataract surgery
– the iris (Peripheral Iridotomy) in
narrow angle glaucoma.
• It is emitted from neodynium
molecules which are suspended in a
clear" YAG crystal to achieve higher
concentration ions than is possible in
a gas laser medium, wavelength is
invisible and requires a He-Ne
aiming beam. Before use on a
patient's eye, must ensure that the
laser beam and the aim focused at
the same point.
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Laser iridectomy
• Laser iridectomy is now the
standard surgical treatment
of angle-closure glaucoma.
• Over the past decade, the
high-energy, short-duration
pulsed lasers, such as the
neodymium: yttriumaluminum-garnet (Nd:YAG)
lasers, have achieved
preferred status for
performing laser
iridectomies.
• There are still some
situations, for example, in
eyes with uveitis or
rubeosis iridis, where the
older argon laser
techniques still may be
preferred.
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Laser iridectomy
Indications for Laser Iridectomy
1-Nonperforate surgical iridectomy
2-Acute angle-closure glaucoma
3-Fellow eye of a patient with acute
angle-closure glaucoma
4-Chronic angle-closure glaucoma
5-Positive provocative test result
6-Aphakic or pseudophakic pupillary
block
7-Uveitis with 360° posterior
Synechiae
8-Before a trabeculoplasty to open
the angle approach and facilitate
treatment
9-Differentiating a pupillary block in
aphakia or pseudophakia from
ciliovitreal block
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3-The excimer laser .
• Its name derived from ‘excited dimer' two
atoms forming a molecule in the excited
state.
• In clinical use employ an argon-fluorine
(Ar-F) dimer laser medium to emit 193 nm
ultraviolet (UV) radiation.
• High absorption of UV by the cornea limits
its penetration. Each photon has 6.4 eV,
sufficient to break intramolecular bonds.
• The delivery of a relatively high level of
energy to a small volume of tissue causes
tissue removal (i.e. ablation)
• The ablation depth may be precisely
determined.
• temperature in a tiny volume of treated
tissue becomes very high, but the amount
of heat produced is very small and there is
no significant rise in temperature of
adjacent tissue.
• It is therefore ideally suited to (PRK) and
(LASIK) to reshape the corneal surface &
phototherapeutic keratectomy (PTK) to
remove abnormal corneal surface tissue.
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Refractive eye surgery
•
Is any eye surgery used to improve the refractive state of
the eye and decrease or eliminate dependency
on glasses or contact lenses. This can include various
methods of surgical remodeling of the cornea or cataract
surgery. The most common methods today use excimer
lasers to reshape the curvature of the cornea. Successful
refractive eye surgery can reduce or cure common vision
disorders such as myopia, hyperopia and astigmatism, as
well as degenerative disorders like keratoconus.
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The correction of myopia :•
•
•
•
•
Photorefractive keratectomy (PRK) ,
Laser in situ keratomileusis (LASIK),
Intrastromal corneal ring implants ,
Phakic intraocular lens implants…
Clear lens extraction for very high myopia have been
gaining acceptance among surgeons and patients as the
risks for these procedures decrease.
• With a good surgical outcome and the improvements in
medical technology allowing for high-quality optical devices,
these methods of optical correction of myopia are superior
to spectacle correction by their reduction or elimination of
lens aberrations and by their increase in image size relative
to spectacle correction.
• Obviously, the benefits of these methods of optical
correction must be weighed against the risks, the downside
of which can be considerable.
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Laser refractive surgery
• Although refractive errors are most commonly corrected by
spectacles or contact lenses, laser surgical correction is
gaining popularity.
• The excimer laser precisely removes part of the superficial
stromal tissue from the cornea to modify its shape. Myopia
is corrected by flattening the cornea and hypermetropia by
steepening it.
• In photorefractive keratectomy (PRK),the laser is applied
to the corneal surface. In laser assisted in situ
keratomileusis (LASIK), a hinged partial thickness corneal
stromal flap is first created with a rapidly moving
automated blade, the flap is lifted and the laser applied
onto the stromal bed.
• Unlike PRK, LASIK provides a near instantaneous
improvement in vision with minimal discomfort. Serious
complications during flap creation occur rarely. Intraocular
lenses can also be placed in the eye but this carries all the
risks of intraocular surgery and the possibility of cataract
formation.
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LASIK by excimer laser for myopia
A. Hinged flap made with microkeratome.
B. Laser ablation (shaded area destroyed)
of bed to alter curvature.
C. Flattened cornea after replacement of
flap.
Indications :
corrects high degrees of myopia
” Laser in situ keratomileusis (LASIK),
which combines keratomileusis with the
accuracy of the excimer laser, is used
worldwide to correct a broad range of
refractive abnormalities.
• The safety and efficacy of the
procedure combined with the quick
visual recovery and minimal patient
discomfort have made LASIK the most
popular refractive procedure for the
treatment of all but the highest levels
of myopia and astigmatism, and low to
moderate hyperopia
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(LASIK) technique
1-Thin flap of cornea fashioned 2-Bed treated with excimer laser
3-Flap repositioned
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Photorefractive Keratectomy
• Photoablation occurs
because the cornea has
an extremely high
absorption coefficient at
193 nm, with a single 193
nm photon having
sufficient energy to break
carbon-carbon and
carbon-nitrogen bonds
directly that form the
peptide backbone of the
corneal collagen
molecules.
• Consequently, excimer
laser radiation ruptures
the collagen polymer into
small fragments, and a
discrete volume of
corneal tissue is removed
with each pulse of the
laser
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Complications of LASIK
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 4. Diode lasers
 It emit an infrared (wavelength of
810 nm) in continuous wave mode.
 It is absorbed only by melanin i.e.
why most commonly used for retinal
photocoagulation;
 low scattering of this wavelength
ensures good penetration of the
ocular media and of edematous
retina. It also penetrates the sclera.
 The transparency of sclera to diode
laser also allows photocycloablion of
the ciliary body in 'end stage
glaucoma.
 It has been used endoscopically to
create a dacriocystorhinostomy
(DCR).
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Aiming beam lasers and hand held pointers
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Laser Pointer Safety Tips
• Tip 1: Don’t Use Laser Pointers Without Labels
• Tip 2: Don’t Point Laser Beams at Faces or Eyes
• Tip 3: Don’t Point Laser Pointers at Aircraft
• Tip 4: Don’t Point Laser Pointers at Automobiles
• Tip 5: Don’t Hold a Laser Beam on the Skin
• Tip 6: Don’t Point at Unidentified Objects when Astronomy
Pointing
• Tip 7: Don’t Point Lasers at Animals for Any Reason
• Tip 8: Don’t Give Laser Pointers to Children
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Safety Considerations
• Never look directly into the laser beam.
• Do not aim the laser at reflective surfaces.
• Never view a laser pointer using an optical instrument, such as
binocular or a microscope.
• Do not allow children to use laser pointers unless under the
supervision of an adult.
• Use only laser pointers meeting the following criteria
– Labeled with FDA certification stating "DANGER: Laser
Radiation" for Class 3R lasers or "CAUTION: Laser Radiation"
for Class 2 pointers.
– Classified as Class 2 or 3R according to the label. Do not use
Class 3b or 4 products.
– Operates at a wavelength between 630 nm and 680 nm.
– Has a maximum output less than 5 mW, the lower the better.
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Intrastromal Corneal Ring Segments
(INTACS)
• The
polymethylmethacrylate
ring segments
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References.
• Clinical optics,2ND edition 1997.
• Wright interactive ophthalmology.
By K.Wright ,1997 on CD.
• Duane's ophthalmology ,basic
science, on CD,2003.
• Web search for images.
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