2. Objectives
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What is Laser ?
LASER history..
LASER Properties.
How LASER is produced ?
Effects of laser.
Application of LASERs in Ophthalmology.
LASER Safety.
3. What is Laser?
LASER is an acronym for:
L : Light
A: Amplification (by)
S : Stimulated
E : Emission (of)
R : Radiation
Term coined by Gordon Gould.
Lase means to absorb energy in one form and to emit a new
form of light energy which is more useful.
4. LASER history
•
1917 -Sir Albert Einstein created the foundations for
the laser.
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1958 - C.H. Townes, A.L. Schawlow: Theoretical basis for
lasers.
5. 1960 - Theodore Maiman : Built first laser by
using a ruby crystal medium .
6. • 1963 - C. Zweng: First medical
laser trial (retinal coagulation).
• 1965 - W.Z. Yarn: First clinical
laser surgery.
• 1970- The excimer laser was
invented in by Nikolai Basov
•
1971 -Neodymium yttrium
aluminum garnet
(Nd.YAG) and Krypton
laser developed.
7. Lasers have many important applications.
• They are used in common consumer devices such as DVD
players, laser printers, and barcode scanners.
• They are used in medicine for laser surgery and various skin
treatments,
• And in industry for cutting and welding materials.
• They are used in military
and law enforcement devices
for marking targets and
measuring range and speed.
• Laser lighting displays use
laser light as an entertainment
medium (in DJ).
8. PROPERTIES OF LASER LIGHT
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Monochromatic (emit only one wave length)
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Coherence (all in same phase-improve focusing )
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Polarized (in one plane-easy to pass through media)
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Collimated (in one direction & non spreading )
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High energy (Intensity measured by Watt J/s)
9. LASER Vs. LIGHT
LASER
Simulated emission
Monochromatic.
Highly energized
Parallelism
Coherence
Can be sharply focussed.
LIGHT
Spontaneous emission.
Polychromatic.
Poorly energized.
Highly divergence
Not coherent
Can not be sharply
focussed.
10. How LASER is produced ?
Light is a form of energy at which the human eye is sensitive
11. LASER PHYSICS
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Light as electromagnetic waves, emitting radiant
energy in tiny package called ‘quanta’/photon. Each
photon has a characteristic frequency and its energy is
proportional to its frequency.
Three basic ways for photons and atoms to interact:
Absorption
Spontaneous Emission
Stimulated Emission
12. 3 Mechanisms of Light Emission
Atomic systems in thermal equilibrium with their
surrounding, the emission of light is the result of:
Absorption
And subsequently, spontaneous emission of energy
There is another process whereby the atom in an upper
energy level can be triggered or stimulated in phase with
the an incoming photon. This process is:
Stimulated emission
Is an important process for laser action
Therefore 3 process
of light emission:
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
17. Background Physics
• Consider the ‘stimulated emission’ as shown
previously.
• Stimulated emission is the basis of the laser action.
• The two photons that have been produced can then
generate more photons, and the 4 generated can
generate 16 etc… etc… which could result in a
cascade of intense monochromatic radiation.
24. Nd:YAG laser
• (neodymium-doped yttrium aluminum garnet) is a crystal that is used
as a lasing medium for solid-state lasers.
• Nd:YAG lasers typically emit light with a wavelength of 1064nm, in
the infrared.
Applications
• Correct posterior capsular opacification
• Peripheral iridotomy in patients with acute angle-closure glaucoma.
• Frequency-doubled Nd:YAG lasers (wavelength 532 nm) are used for
pan-retinal photocoagulation in patients with diabetic retinopathy.
25. Excimer laser
• Is a form
of ultraviolet laser
• Used
indelicate surgeries
such as eye
surgery eg ;LASIK.
27. THREE TYPE OF OCULAR PIGMENT
Effective retinal photocoagulation depends on how well light penetrates
the ocular media and how well the light is absorbed by pigment in the
target tissue
Haemoglobin:
absorbs blue, green and yellow with minimal red wavelength
absorption, useful to coagulate the blood vessels.
Xanthophyll:
Macular area, Lens
Maximum absorption is blue. minimally absorbs yellow or red
wavelengths
Melanin:
RPE, Choroid
absorbs green, yellow, red and infrared wavelengths
Pan Retinal Photocoagulation, and Destruction of RPE
29. Thermal Effects
(1) Photocoagulation:
Laser Light
Target Tissue
Generate Heat
Denatures Proteins
(Coagulation)
Rise in temperature of about 10 to 20
0C will cause coagulation of tissue.
31. Thermal Effects
(3)photovaporization
Vaporization of tissue to CO2 and water occurs when
its temperature rise 60—100 0C or greater.
Commonly used CO2
Absorbed by water of cells
Visible vapor (vaporization)
Heat
Cell disintegration
Cauterization
Incision
eg..Femtosecond laser
33. PHOTOCHEMICAL EFFECT
Photoradiation (PDT):
•
Also called photodynamic therapy.
E.G. Treatment of
Ocular tumours
and CNV
Photon + Photo sensitizer in ground state (S)
Molecular Oxygen
S + O2 (singlet oxygen)
Free Radical
Cytotoxic Intermediate
Cell Damage, Vascular Damage , Immunologic
Damage
34. LASER INSTRUMENTATION
Three Main Components –
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•
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Console: It contain laser medium and tube,
power supply and laser control system.
Control Panel: It contain dials or push
buttons for controlling various parameters.
Contain a standby switch as a safety
measure.
Delivery System:
Slit Lamp Microscope
Indirect Ophthalmoscopes
35. ACCESSORY COMPONENT
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Aiming Beam
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Laser Switch
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Safety Filter
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Corneal Contact Lenses for Laser use
Single mirror gonio lens
Abraham or wise iriditomy lens
Goldman style 3-mirror lens
Panretinal lenses
e.g. Rodenstock, Mainster, Volk-Quadri spheric
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Indirect Fundus Lenses for Indirect Ophthalmoscopes
36. USING THE OPHTHALMIC LASER
PREPARATION OF THE PATIENT FOR laser:
Local Anaesthetic
Position of the patient at Slit Lamp
THE SURGEON:
Comfortable position at Slit Lamp
Semi-darkened Room
Appropriate Contact Lens
39. Laser Iridotomy, Laser Iredectomy
• always pre-treat with argon prior to doing a Yag.
• a small spot size (~50microns) with a relatively high power
(500 or so). Place about 10-15 spots in a flower petal type
pattern in a iris crypt in the supero-nasal quadrant in the
far peripheral iris.
• This hopefully coagulates any iris stromal vessels and
prevents bleeding when doing the Yag portion.
• Start Yag power at about 3 to 4 mJ, only take about 5 - 10
shots to get that wonderfully rewarding gush of pigment
and fluid.
• Remember to check IOP about 1 hour post op, warn them
about signs/symptoms of IOP spike and keep on pred forte
qid for about a week to prevent inflammation.
45. panretinal photocoagulation
• PRP place laser spots in the peripheral retina for 360
degrees sparing the central 30 degrees of the retina.
POWER, SIZE, NUMBER, AND SESSIONS
Recommendations in the ETDRS for an initial treatment
consisted of 1,200 to 1,600 burns of moderate intensity, 500μm size, one-half to one-spot diameter spacing at 0.1-second
duration, divided over at least two sessions.
typical starting power setting for a 300-μm spot of 0.1second duration might be around 250 mW, but this is highly
dependent on the operator's laser, the status of the ocular
media, and the pigmentation of the retina.
46. Panretinal photocoagulation (PRP) ctd
Indications
1. Proliferative diabetic retinopathy with high risk
characteristics
2. Neovascularisation of iris
3. Severe non proliferative diabetic retinopathy associated
with-poor compliance for follow up-before cataract
surgery-renal failure-one eyed patient and-pregnancy
4. central retinal vein occlusion, branch retinal vein
occlusion,
5. sickle retinopathy,
6. Eales disease and IRVAN (idiopathic retinal vasculitis,
aneurysms, and neuroretinitis )
47. How does panretinal photocoagulation
work?
• Sublethally injured RPE cells that surround areas of
photocoagulation necrosis and produces significant
thinning of the outer retina.
• By decreasing the oxygen consumption at the
photoreceptor–RPE complex, more oxygen is available
to diffuse into the inner retina and vitreous.
• Enhanced oxygen diffusion into the inner retina
and vitreous reduces inner retina ischemia and the
stimulus for neovascularization.
• PRP reduces retinal ischemia and the hypoxia-induced
expression of VEGF.
48.
49. Focal or grid photocoagulation
• Macular edema from diabetes or branch vein occlusion .
• Retinopathy of prematurity(ROP)
• Closure of retinal microvascular abnormalities such as
microaneurysms, telangiectasia and perivascular leakage
• Focal ablation of extrafoveal choroidal neovascular
membrane
• Creation of chorioretinal adhesions surrounding retinal
breaks and detached areas.
• Focal treatment of pigment abnormalities such as leakage
from central serous chorioretinopathy
• Treatment of ocular tumors.
50. Focal or grid laser settings
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50-100 micron spot size, 0.05-0.1 sec( for focal spot size
50micron, for grid 100-200 micron)
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Spots must be atleast one burn width apart
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seal specific leaking blood vessels in a small area of the retina,
usually near the macula.
51. Pathophysiology of focal Laser
several theories
• laser energy removes unhealthy RPE cells which are
then replaced by more viable RPE cells.
• photocoagulation stimulates the existing RPE cells to
absorb more fluid.
• laser treatment may stimulate vascular endothelial
proliferation and improve the integrity of the inner
blood-retinal barrier.
52. FEMTOSECOND LASER
Mode-locking is a technique in optics by which a laser can be made to
produce pulses of light of extremely short duration, on the order of
picoseconds (10−12s) or femtoseconds (10−15s).
Indications
1. Clear Corneal Incisions
in LASIK it replaces a mechanical device
(microkeratome) to create a precise corneal
flap, also in cataract surgery to create the
incision
1. Capsulotomy
2. Phacofragmentation
53.
54.
55. LASER HAZARDS
EYE
• Small lesion to extensive haemorrhage
• Disruption of retina and choroid
• Immediate loss of vision
• Epiretinal membrane formation
• Macular hole,gliosis
SKIN
• Erythema
• Carcinogenesis
57. PREVENTION OF LASER HAZARDS
Engineering Control Measure:
laser housing
filters and shutter for safe
observer viewing
Personal protective devices, like
protective eye wear or goggles
with side shields, protective
clothes may be included.
