A full presentation of one hour of all types of lasers in ophthalmology for under graduates and post graduates after going through all the uploaded slides till today. This includes laser photocoagulation, laser iridotomy, and laser capsulotomy in detail
2. Objectives
• 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.
• 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. Light physics
• Laser light differs from “ordinary” light in
several important ways.
• These differences are a direct result of
the manner in which laser light is
generated
Fig. 1. “White” light is composed of all
wavelengths, traveling in all directions.
Fig. 2. Ordinary monochromatic light
consists of light of approximately the
same wavelength. However, the light is
not traveling in one direction.
9. PROPERTIES OF LASER LIGHT
• Monochromatic-emit only one wave length)
• Coherence-all in step with one another-improves focusing
• Polarized-in one plane-easy to pass through media
• Collimated-in one direction & non spreading
• High energy-Intensity measured by Watt J/s
• Laser light can deposit a lot of energy within a small
area hence it is more hazardous than ordinary light
10. LASER Vs. LIGHT
LASER LIGHT
Simulated emission
Monochromatic.
Highly energized
Parallelism
Coherence
Can be sharply focussed.
Spontaneous emission.
Polychromatic.
Poorly energized.
Highly divergence
Not coherent
Can not be sharply
focussed.
11. How LASER is produced ?
Light is a form of energy at which the human eye is sensitive
12. LASER PHYSICS
• Light consists of 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.
• When light is passed through certain kinds of materials, these
photons excite electrons around atoms into the next higher
energy level
• Two basic ways for photons and atoms to interact:
Absorption Spontaneous Emission
Stimulated Emission
14. Absorption
Energized electron in higher
orbit
Electron in orbit
photon
A photon of the “right” energy gets
absorbed and “bumps” an electron into a
higher energy level.
15. Spontaneous Emission
photon
An excited electron falls back to its lower
energy level, releasing a photon in a random
direction
Energized electron in higher orbit
Electron in orbit
16. Stimulated Emission
photon
photon
photon
A photon strikes an excited electron. The electron falls to its
lower energy level, releasing a photon that is going in the same
direction and in exact phase with, the original photon. Note
that only one photon strikes the atom but two photons leave
it—the original photon plus the emitted photon
Energized electron in higher orbit
Electron in orbit
17. • Now consider this ‘stimulated emission’
• 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.
• Thus Stimulated emission is the basis of the laser
action.
18. Laser Construction
1
2
3
A pump source or exciting medium
A gain medium or laser medium.
An optical resonator or laser tube.
19. Pump Source
• Provides energy to the laser system
• Examples: electrical discharges, flash lamps,
and chemical reactions.
• Ex. Excimer lasers use an electrical
discharges.
20. Gain Medium
• It is a major determining factor of the
wavelength of the laser.
• It is Excited by the pump source.
• Here spontaneous and stimulated
emission of photons takes place.
• Gain medium can be solid, liquid, and
gas.
21. • The energy of the emitted laser beam from gain medium
is increased(amplified) still further by causing the light
beam to traverse through the same material multiple
times.
• One requirement is that most “elevatable” electrons
must be at their higher energy level before the light
enters the medium. Such a situation is called a population
inversion.
• This is accomplished by placing a mirror over each end of
the crystal or gas tube so that the distance between
them is an even multiple of the laser light’s wavelength.
• The coherent light beam is reflected back and forth
becoming more and more intense.
• If the exciting energy is supplied in brief pulses, laser
output of higher energy can be obtained in pulses.
LASER tube or Optical Resonator
23. MODES OF LASER OUTPUT
• Continuous Wave (CW) Laser: Delivery of energy in a
continuous stream of photons.
• Pulsed Lasers: Produce energy pulses of a few tens of micro
to millisecond.
• Q Switches Lasers: Delivery of energy pulses is of
extremely short duration (nanosecond).
• A Mode-locked Lasers: Emits a train of short duration
pulses (picoseconds).
• Fundamental System: Optical condition in which only one
type of wave is oscillating in the laser cavity.
• Multimode system: Large number of waves, each in a slight
different direction ,oscillate in laser cavity.
24.
25. CLASSIFICATION OF LASER
• Solid State
Ruby
Nd.Yag
Erbium.YAG
• Gas
Ion
Argon
Krypton
He-Neon
CO2
• Metal Vapour
Cu
Gold
Dye
Rhodamine
Excimer
Argon Fluoride
Krypton Fluoride
Krypton Chloride
Diode
Gallium-Aluminum
Arsenide (GaAlAs)
26. lasers Wavelength
Diode 810 nm
Krypton red 647 nm
Krypton yellow 568 nm
Frequency doubled
Nd YAG
532 nm
Argon green 514 nm
Argon blue 485 nm
TYPES OF OPHTHALMIC LASERS
29. Excimer laser
• Its name derived from ‘excited dimer‘ of two
atoms forming a molecule in the excited state
but which dissociate in the ground state.
• 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. Photoablation)
• Used Photorefractve Keratatomy (PRK) and
Laser in situ Keratomileusis (LASIK)
30. It is a mixture of 70% blue (488 nm) and 30% green
(514 nm) light.
Most commonly employed for retinal
photocoagulation & for trabeculoplasty
Photocoagulation aims to treat the outer retina and
spare the inner retina to avoid damaging the nerve
fiber layer
Absorbed selectively at the RPE, Hemoglobin
pigments, choriocapillaries, layer of rods & cones and
outer & inner nuclear layers.
Readily absorbed by the melanin granules.
Coagulates from RPE to nerve fiber layer
Not used much now days due to more damage to nerve
fiber layer as compared to db.freq.YAG green laser
Argon blue- green laser
31. • Produces a pea green beam.
• Most commonly used laser
• Often termed as “green laser”
• Highly absorbed by Hb & the melanin
pigment.
• It coagulates from RPE to ONL.
• It causes coagulation with least energy
transmission & shows considerable safety
in macular treatment also.
Freq-doubled Nd:YAG laser
32. Pattern Scan Laser(PASCAL)
• The PASCAL Photocoagulator is an
integrated semi-automatic pattern
scan laser photocoagulation system
designed to treat ocular diseases
using a single shot or multiple shots
at a single click to predetermined
pattern array.
• Laser source :Nd:YAG laser (green
or yellow)
• Delivery device: slit lamp or laser
indirect ophthalmoscope (LIO)
• It has Control system for selecting
power , duration and spot size
• It also has micropulse technology
to deliver sub threshold burns by
reducing the duty cycle and thus
less damage to tissue & less heat
production in macular area
• Used for PRP and macular lasers
33. • Melanin absorbs it readily.
• It is not absorbed by xanthophylls & Hb
and hence it is particularly suitable for
macular photocoagulation.
• Frequency 647 nm
• It coagulates deeper into the RPE &
choroids. It has insignificant effect on the
vascular system of retina.
• Disadvantage is that it is painful due to
deeper penetration into choroid
Krypton red laser
34. Diode lasers
It emits an infrared wavelength of 810nm
It is absorbed only by melanin hence
used for macular photocoagulation
It also penetrates the sclera. Thus if
retina is obscured from view through the
pupil, coagulation may still be performed
by placing the probe on the sclera.
Used for grid laser, PRP, Transpupillary
Thermo Therapy and Diode
cyclophotocoagulation
35. 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 range
• It is a continuous wave laser.
Applications
• Correct posterior capsular opacification
• Peripheral iridotomy in patients with acute angle-
closure glaucoma
• femto cataract surgery and femto LASIK surgery.
36. FEMTOSECOND LASER
• Mode-locking -pulses of light of extremely short
duration, in the order of picoseconds (10−12s) or
femtoseconds (10−15s) are produced.
• Femtosecond laser technology systems use
neodymium:glass 1053 nm (near-infrared) wavelength
lightto cause photoablation
Indications
• In femto-LASIK to creat Clear Corneal Incisions
• It replaces a mechanical device (microkeratome) to
create a precise corneal flap
• Femto-cataract surgery to create
Corneal incision
Capsulotomy
Phacofragmentation
39. 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. Frequency-doubled Nd:YAG lasers (wavelength 532 nm) are
used for pan-retinal photocoagulation in patients with diabetic
retinopathy. Argon and krypton lasers were used previously,
40. Thermal Effects
(2) Photodisruption:
• Mechanical Effect: Laser Light
Acoustic Shockwaves
Plasma formation
Tissue Damage
Contd. …
Neodymium-doped Yttrium Aluminum Garnet is a crystal that is used as
a lasing medium for solid-state lasers and photodisruption.
Nd:YAG lasers typically emit light with a wavelength of 1064nm, in
the infrared range. Used for posterior capsulotomy in capcular
opacification and Peripheral iridotomy in patients with acute angle-
closure glaucoma
41. Thermal Effects
(3) Photovaporization
Vaporization of tissue to CO2 and water
occurs when its temperature rise is 60
to 100 0C or greater.
Commonly used gas CO2 and ND:glass
Absorbed by water of cells
Visible vapor (vaporization)
Heat Cell disintegration
Cauterization Incision
Refractive surgery like Femtosecond laser, ReLEX SMILE and
Femtocataract surgery use photovaporization effect.
42. Photochemical effects
Photoablation:
• Causes Breaks the chemical
bonds that hold tissue
together essentially
vaporizing the tissue.
Excimer lasers(ArFl)
produces photochemical
effect . It is a form
of ultraviolet laser (193nm)
• Used in refractive surgeries
of the eye like LASIK and
PRK.
Contd. …
43. PHOTOCHEMICAL EFFECT
Photoradiation OR Photodynamic therapy(PDT)
• 42°C and 52°C rise in temperature
• Photoradiation by red (630 nm) Laser light
produces cytotoxic free radicals in a tumor
previously sensitized by a hematoporphyrin-
derived uptake.
• The treatment is called photodynamic therapy-
PDT.
• This new treatment modality combines low-power
diode lasers (689 nm) with an infusion of
verteporfin to ablate subretinal neovascular
membranes and treatment of various tumors in
retina.
• The advantage over conventional
photocoagulation is, lower energy levels results in
much less damage to adjacent normal tissue
44. LASER INSTRUMENTATION
LASER Components are –
• Console: It contain laser medium and tube, power
supply and laser control system.
• Control Panel: It contain dials or push buttons or
touch screen for controlling various parameters.
• Aiming Beam
• Laser Switch
• Safety Filter
• Delivery System:
Slit Lamp Microscope
Indirect Ophthalmoscopes
Endolaser probes
Trans scleral : - Contact
- Non contact
45. ACCESSORY COMPONENT
Corneal Contact Lenses for Laser use
Single mirror goniolens for
goniotomy
Abraham lens and wise lens for
capsulotomy and iriditomy
Goldman style 3-mirror lens for
photcoagulation (PRP) lenses
Volk-Superquad and pan 165 for PRP
Mainster and Area centralis for
focal and grid laser
Indirect Fundus Lenses (20 D) for
Indirect laser delivery
46.
47. 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
48. Slit lamp biomicroscopic laser delivery
• Most commonly employed
mode for anterior and
posterior segment.
• ADVANTAGES:
• Binocular and stereoscopic
view.
• Fixed distance.
• Standardization of spot
size is more accurate.
• Aiming accuracy is good.
49. Laser indirect ophthalmoscope
• Advantages :
• Wider field(ability to reach
periphery).
• Better visualization
• laser application in hazy medium.
• Ability to treat in supine position.
• Disadvantage :
• Difficulty in focusing.
• Difficulty to standardize spot size.
• Expensive.
• Un co-operative patient.
• Learning curve.
51. TYPES OF OCULAR PIGMENT
Effective retinal photocoagulation depends on
• how well light penetrates the ocular media
• how well the light is absorbed by pigment in the target tissue
Ocular pigments
• Hemoglobin:
Blue ,Green and yellow light are absorbed and red light is
passed. RED laser is used to treat blood vessels below
hemorrhage .
• Xanthophyll:
Present in inner and outer plexiform layers of macula.
Maximum absorption is blue. Yellow and red light are passed
Argon blue is not recommended to treat macular lesions.
• Melanin:
Present in RPE and Choroid
Blue ,green and yellow light are absorbed and red light is
passed
Argon Blue, Krypton yellow and ,double frequency YAG lasers
used for Pan Retinal Photocoagulation, and Destruction of
RPE
58. Scanning Laser Ophthalmoscopy
• In the scanning laser ophthalmoscope (SLO), a narrow laser
beam illuminates the retina one spot at a time, and the amount
of reflected light at each point is measured. The amount of light
reflected back to the observer depends on the physical
properties of the tissue, which, in turn, define its reflective,
refractive, and absorptive properties. Media opacities, such as
retinal haemorrhage, vitreous haemorrhage, and cataract, also
affect the amount of light transmitted back to the observer.
Because the SLO uses laser light, which has coherent
properties, the retinal images produced have a much higher
image resolution than conventional fundus photography.
• Used to study
– SLAP test
– retinal and choroidal blood flow
– microperimetry,
59.
60. Tests Performed on the Scanning Laser
Ophthalmoscope
1) Scanning Laser Acuity Potential (SLAP) Test: The letter E
corresponding to different levels of visual acuity (ranging from
20/1000 to 20/60) is projected directly on the patient’s retina. The
examiner directs the test letters to foveal and/or extrafoveal
locations within the macula, and determines a subject’s potential visual
acuity.
This is especially helpful in individuals who have lost central fixation
but still possess significant eccentric vision.
61. 2) Microperimetry / Scotometry
The SLO could visualize a particular area of the retina and test its
sensitivity to visual stimuli, thereby generating a map of the seeing and
non-seeing areas.
62. 3) Hi-Speed FA / ICG
• Fluorescein and Indocyanine Green Angiography (FA/ICG)
performed using the SLO is recorded at 30 images per second,
producing a real-time video sequence of the ocular blood flow
63. Optical Coherence Tomography(OCT)
• Diode laser light in the near-infrared spectrum (810 nm)
• Partially reflective mirror is used to split a single laser beam into two, the
measuring beam and the reference beam
• Measuring beam is directed to the retina , laser beam passes through the
neurosensory retina to the retinal pigment epithelium (RPE) and the choriocapillaris.
At each optical interface, some of the laser light is reflected back to the OCT’s
photodetector
• Reference beam is reflected off a reference mirror at a known distance from the
beam splitter, back to the photodetector. The position of the reference mirror can
be adjusted to make the path traversed by the reference beam equal to the distance
traversed by the measuring beam to the retinal surface. When this occurs, the wave
patterns of the measuring and reference beams are in precise synchronization,
resulting in constructive interference. This appears as a bright area on the resulting
cross-sectional image. However, some of the light from the measuring beam will pass
through the retinal surface and will be reflected off deeper layers in the retina. This
light will have traversed a longer distance than the reference beam, and when the two
beams are brought back together to be measured by the photodetector, some degree
of destructive interference will occur, depending on how much further the measuring
beam has traveled. The amount of destructive interference at each point measured
by the OCT is translated into a measurement of retinal depth and graphically
displayed as the retinal cross-section.
• OCT images are displayed in false color to enhance differentiation of retinal
structures. Bright colors (red to white) correspond to tissues with high reflectivity,
whereas darker colors (blue to black) correspond to areas of minimal or no
reflectivity. The OCT can differentiate structures with a spatial resolution of only 10
μm
66. Wavefront Analysis and Aberrometery
• Lasers are used in the measurement of complex
optical aberrations of the eye using wavefront
analysis and Hartmann-Shack aberrometer
68. Lids and Adnexa
Skin: (usually CO2 laser)
Lid Tumours : carbon dioxide laser ,benign and
malignant ,bloodless but scarring, lack of a
histologic specimen, and inability to assess
margins.
Blepharoplasty (carbon dioxide or erbium:YAG
laser )
Xanthalesma ( green laser)
Aseptic Phototherapy
Pigmentation lesion
Laser Hair Removal Technique
Tattoo Removal
Resurfacing
Lacrimal Surgery Endoscopic Laser
Dacryocystorhinostomy
69. Anterior Segment
• Conjunctival Growths and Neovascularization
• Corneal Growths and Neovascularization
• Refractive Surgery
• Laser in Glaucoma
• Laser in Lens
71. Photorefractive keratectomy
In photorefractive keratectomy
(PRK),the laser is applied to the
corneal surface
The excimer laser precisely
removes part of the superficial
stromal tissue from the cornea
to modify its shape
INDICATION
low myopia (up to 6D)
low hyperopia (up to 3D)
Astigmatism upto 3D
COMPLICATION
Sub epithelial haze which usually
resolves after 1-6 months
72. LASIK
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.
Lamellar dissection with the microkeratome
Refractive ablation with the excimer laser
In Intra-LASIK or Femto-LASIK or All-Laser LASIK,
corneal flap is made with Femtosecond laser instead of
microkeratome
INDICATION
myopia (up to 8D)
low hyperopia (up to 3D)
Astigmatism upto 3D
COMP;ICATION
Wrinkles in flap
Cellular interface proliferation
77. ND YAG laser Iridotomy
• Laser- Q-switched Nd:YAG
lasers (1064 nm)
• Area- Peripheral third of the
iris but inside the arcus
• Site- Iris crypt or a thinned
area of the iris
• Location - Between 11 o’clock
and 1 o’clock
• Size -200 - 500 μm in size
• Power - 4-8 mJ
• Pulses/burst - 1-3
• Spot size – Fixed
• Gush of pigment and fluid is
noted at the end of t/t
78. Argon or Db.Freq.YAG Laser
Iridotomy
Photocoagulative (lower energy & longer exposure)
Iris color (pigment density) is the most imp factor
Iris color can be divided into three categories:
a) light brown : 600–1000 mW with a spot size of 50 µm
and a shutter speed of 0.02–0.05 second
b) dark brown: 400–1000 mW , spot size of 50 µm and
a shutter speed of 0.01 second
c) blue iris: 200- µm spot, 200–400 mW, 0.1 second to
reach from pigment epithelium to the stroma , Then
the spot size reduced to 50 µm and power increased
to 600–1000 mW at 0.02–0.1 second to perforate
82. Laser trabeculosplasty (LTP)
a) Argon laser trabeculoplasty (ALT) : 50 µm spot size
and 1000-mW power for 0.1 second , 3–4° apart 20–
25 spots per quadrant
b) Selective Laser trabecuLopLasty (SLT) : Q-
switched, frequency-doubled 532-nm Nd:YAG laser,
400-µm spot , 0.8 mJ power , 180° with 50 spots or
360° with 100 spots , 3–10 ns duration
COMPLICATIONS
Iritis
Pressure elevation
Peripheral anterior
synechiae
Hyphema
83. Excimer Laser Trabeculostomy((ELT)
• precise and no thermal damage to surrounding tissues
• ab-interno (used intracamerally) : 308-nm xenon-
chloride (XeCl) excimer laser delivers photoablative
energy
84. Laser sclerostomy
• Nd:YAG laser, the dye
laser, 308-nm XeCl
excimer laser, argon
fluoride excimer laser,
erbium:YAG laser, diode
lasers, the holmium:YAG
laser etc . are used
• Ab-externo : probe
applied to the scleral
surface under a
conjunctival flap.
• Ab-interno : through a
goniolens
89. • Laser synechialysis : lyse iris adhesions
• Goniophotocoagulation: anterior
segment neovascularization , rubeosis ,
fragile vessels in a surgical wound
• Photomydriasis (pupilloplasty) : enlarge
the pupillary area by contracting the
collagen fibers of the iris
90. Lasers In Lens
•Posterior Capsular Opacification :
•T/t- (Nd:YAG) laser posterior capsulectomy
•laser- source used is the Nd:YAG 1064-nm.
•Use minimum energy: 1 mJ if possible.
•Identify and cut across tension lines.
•Perform a cruciate opening: Begin at 12 o'clock
in the periphery, progress toward 6 o'clock, and
cut across at 3 and 9 o'clock.
•Clean up any residual tags.
•Avoid freely floating fragments.
•capsulotomy should be as large as the pupil in
isotopic conditions
•COMPLICATIONS
•Iop elevation
•Iritis
•Cystoid macular elevation
•Retinal detachment
•Iol pitting
•P Acne endophthalmitis
91. Femto-lasers in cataract surgery
• New level of precision and
reproducibility is achived.
• Femtosecond laser technology
systems use neodymium:glass 1053
nm (near-infrared) wavelength
light.
• This feature allows the light to be
focused at a 3 mm spot size,
accurate within 5 mm in the
anterior segment
• The Laser creates
a) Corneal incisions with precise
dimensions and geometry.
b) anterior capsulotomies with
accurate centration and intended
diameter, with no radial tears.
c) lens fragmentation (customized
fragmentation patterns)
93. Laser in vitreous
• Vitreolysis of anterior vitreous tag in PC rent to avoid traction
and cystoid macular edema
• Vitreous membranes & traction bands
• Vitreous floaters
• Retinoblastoma seeds
95. CLASSIFICATION OF
CHORIORETINAL BURN INTENSITY
• Light : Barely visible retinal blanching
• Mild : Faint white retinal burn
• Moderate: Dirty white retinal burn
• Heavy : Dense white retinal burn
96. Focal and Grid laser
Focal Grid
• Spot size -50 to 100u size 50 to 200u size.
• Duration -0.05 to 0.1sec. 0.05 to 0.1 sec.
• Intensity -Moderate Light to medium
• Power – 70 to 100 mW 70 to 100 mW
Wavelength– argon green, db.fq. YAG green, dye
yellow or diode red
Area of treatment – within 500um of center of
macula avoiding the fovea
Lense used – area centralis, meinster standar or
goldman 3 mirror lens
97. Indication of Focal or grid
photocoagulation
1. Macular edema from diabetes or branch vein occlusion
2. Retinopathy of prematurity(ROP)
3. Closure of retinal microvascular abnormalities such as
microaneurysms, telangiectasia or angiomas
4. Focal ablation of extrafoveal choroidal neovascular
membrane
5. Creation of chorioretinal adhesions surrounding retinal
breaks and detached areas.
6. Focal treatment of pigment abnormalities such as RPE
leakage in central serous chorioretinopathy(CSR}
7. Treatment of ocular tumors
8. Posterior hyloidotomy in large sub hyloid haemorrhage
98. How focal laser works ?
• 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.
Several theories
99. Focal or grid laser treatment
Modified grid laser in dme
Laser to ischemic areas in ROP
Posterior
hyloidotomy
Laser barrage arouind retinal tear. 3
rows of laser burns given .
100. Pan retinal photocoagulation
• Number - 2000-3000 spots distributed in 3 to 4 sittings
• Spot size- 500 mm size with goldmann lense and 200-300
mm size with panfunduscopic lens.
• Duration- 0.05-0.10 sec.
• Intensity- moderate intensity laser burns
• Wavelength– argon green, db.fq. YAG green, dye yellow or
diode red.
• Lens used – PRP 165 or goldman 3 mirror lens
• Pattern- Scatter pattern PRP. Place laser spots in the
peripheral retina for 360 degrees sparing the central 30
degrees of the retina.
• Laser spots are given 1 spot apart 1 DD away from the disc
nasally , 2DD away from macula temporally and beyond the
arcades superiorly and inferiorly
101. Indications of Panretinal
photocoagulation (PRP)
1. Proliferative diabetic retinopathy with high risk
characteristics
2. Severe non proliferative diabetic retinopathy associated
with-poor compliance for follow up or before cataract
surgery or renal failure or one eyed patient or pregnancy
3. Central retinal vein occlusion and branch retinal vein
occlusion with nvd or nve or nvi
4. Sickle cell retinopathy,
5. Eales disease and IRVAN (idiopathic retinal vasculitis,
aneurysms, and neuroretinitis )
6. Retinopathy of prematurity (ROP)
7. Coats Disease
8. Radiation retinopathy
9. Neovascularisation of iris in ocular iscemoc syndrome
102. How does panretinal photocoagulation
work?
• Injured RPE cells that surround areas of
photocoagulation undergo necrosis and produces
significant thinning and anoxia 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 hypoxia to anoxia
thus decreases expression of VEGF.
106. CHORIODAL MELANOMA
• Photocoagulation technique.
• Initial destruction of the
surrounding choroidal blood
supply in 1-2rows -200-500
microns ,0.5-1sec-intense
burn.
• Direct tumour
photocoagulation at low energy
long duration(5-30sec) burns.
RETINOBLASTOMA
• Diode (infrared)laser tumor
surface in regions of disease
activity tumor cell death by
raising the temperature of
tumor cells to above 45°C for
~1min(reduces blood supply ,
apoptosis).
107. Transpupillary
thermotherapy(TTT)
• Thermotherapy involves using ultrasound,
microwave, or infrared radiation to deliver heat
to the eye.
• It involves application of diode (infrared) laser to
the tumor surface or in regions of CNVM activity.
• Retinoblastoma It cause tumor cell death by
raising the temperature of tumor cells to above
45°C for ~1 min., thus reducing blood supply and
producing apoptosis.
• Classic subfoveal or extrafoveal choroidal
neovacular membrane
111. PDT Procedure
• For age-related macular
degeneration and pathologic
myopia : i.v Verteporfin at
6mg/m2 BSA over 10 mins.
Five minutes after the
cessation of infusion, light
exposure (laser emitting light
of 692 nm) with an irradiance
of 600 mW/m2 is started,
delivering 50 J/cm2 within
83 s .
• Angiod Streaks and CSR
light dose of 100 J/cm2 over
an interval of 166 s
114. • ANSI (American National Standard Institute)
• Class-I : Causing no biological damage.
• Class-II : Safe on momentary viewing but chronic
exposure may cause damage.
• Class-III: Not safe even in momentary view.
• Class-IV : Cause is more hazardous than Class-III.
LASER HAZARDS
115. • Protective shutters built into the equipment,
• Filters incorporated into the slit-lamp biomicroscope,
• Divergence of the beam at the exit optics
• Accessory lenses should have Anti Reflective Coating
• Reflected laser light should be within nominal hazard
zone
• When a hand lens is used in place of biomicroscopy,
precautions must be taken to minimize the chance of
specular reflection from instruments and lens.
• Personal protective devices, like protective eye wear or
goggles with side shields, protective clothes may be
included
• Warning signs listing the laser’s type and class should
be posted at all entrances to the laser suite.
Laser safety
117. Lasers can….
Save a child’s eye as in
Retinoblastoma.
Change a personality as in LASIK.
Cure a middle aged person with
Glaucoma.
Restore Vn. in a person with After
Cataract.
Preserve & Retain Vn. in pts. with DR
& ARMD
The possibilities are endless…...
