basic laser in ophthalmology for residents

1. Fundamental laser ophthalmology
5 November 2012
Mallawee Charatcharungkiat, MD
Instructor Nawat Watanachai, MD

2. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

3. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

4. Laser physics
• “Light amplification by stimulated emission of
radiation”

5. Laser physics
• “Light amplification by stimulated emission of
radiation”
• 1917
• Atomic transposition process
– Absorption
– Spontaneous emission
– Stimulated emission
Albert Einstein

6. Laser Physics
• Absorption
Unexcited atom
(E0 : Ground state)
Photon
Excited atom
(E1 : Excited state)

7. Laser Physics
• Spontaneous emission
Unexcited atom
(E0 : Ground state)
Photon
Excited atom
(E1 : Excited state)

8. Laser Physics
• Stimulated emission
Unexcited atom
(E0 : Ground state)
2 Photon
Excited atom
(E1 : Excited state)

9. Laser Physics

10. Laser Physics
• After absorption
– Spontaneous emission
• Majority
• Incoherent
– Stimulated emission
• Few
• Coherent Laser
Laser

11. Laser Physics
• Element of laser
1. Active medium
2. Energy input
3. Optical feedback

12. Laser Physics
• Element of laser
1. Active medium
• Allowed stimulated emission
• Particular atomic energy transition
Wavelength of the emission
E = hv = hc /λ

13. Laser Physics
• Element of laser
1. Active medium
• Gas : Argon, Krypton, Carbon dioxide,
Argon-fluoride excimer, Helium with neon
• Liquid : Dye
• Solid : Supported by crystal
Nd:YAG, Er-YLF, Ruby
Infrared holmium-YLF (IntraLase)
holmium-YAG(Laser thermal
keratoplasty)
Semiconductor (diode)

14. Laser Physics
• Element of laser
2. Energy input
• Make majority of atom are in higher energy state than
ground state
• “Population inversion”
• “Pumping”
• “Light amplification”

15. Laser Physics
• Element of laser
2. Energy input
• “Pumping”
– Gas laser : Electrical discharge between
electrode in gas
– Dye laser : Other laser
– Solid crystal : Incoherent light
(Xenon arc flash light)

16. Laser Physics
• Element of laser
3. Optical feedback
• Promote stimulated emission, suppress spontaneous
emission
• Spontaneous emission  not amplify
• Stimulated emission  Coherent laser

17. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

18. Properties of laser
1. Monochromaticity
– Laser emit light only 1 wavelength /
combination several wavelength
– Gas laser  0.01 nm
– Color of light enhance target tissue absorption
or transmission
– Not effected by chromatic aberration
in lens system
– Focus in smaller spot > white light

19. Properties of laser
Chromatic aberration
– Distortion, a failure of lens to focus all colors to the
same convergence point
– Lens have different refractive index for different
wavelength (↓ refractive index - ↑ wavelength)

20. Properties of laser
1. Monochromaticity
– Laser emit light only 1 wavelength /
combination several wavelength
– Gas laser  0.01 nm
– Color of light enhance target tissue absorption
or transmission
– Not effected by chromatic aberration
in lens system
– Focus in smaller spot > white light

21. Properties of laser
2. Directionality
– Laser emit a narrow beam
– Laser amplify only photon that travel along
narrow path between 2 mirrors
– Cause collimating light
– ↑ 1 mm in diameter of beam for every meter
travel
– Focus light to small spot

22. Properties of laser
3. Coherence
– Ability of 2 light beams, or different parts of the
same beam, to produce interference
– Interference

23. Properties of laser
3. Coherence
– “Laser speckle” -- rough surface
– Laser interferometer
Laser beam split to 2 beams
Diffuse by cataract
Overlap in retina
“Interference fringes”
• Non contact biometry (IOL master)
– Partial coherence interferometry

24. Properties of laser
3. Coherence
• Optical coherence tomography (OCT)
– Michelson interferometer
– Interference property of temporally coherent light
– Light source (superluminescent diode), light detector, beam
splitter, movable mirror
– Highest reflection : RPE, ONL, INL, ILM

25. Properties of laser
3. Coherence
• OCT
½ light
½ light

26. Properties of laser
3. Coherence
• OCT

27. Properties of laser
4. Polarization
– Certain direction of light wave
– Linearly polarized
• Electric fields of light wave in the same plane
• Allow maximum transmission through laser medium
without loss caused by reflection

28. Properties of laser
5. Intensity
– Power in a beam of given angular size
– Most important property
– “Brightness”
• Intensity / unit area

29. Properties of laser
5. Intensity
– Radiometric terminology
Term Unit
Energy joule
(1 J = 1 watt x 1 sec.)
Power watt
Energy density J/cm²
Irradiance watt / cm²
Intensity watt / sr
(sr = Steradian, unit of solid
angle)
brightness Watt / sr cm²

30. Properties of laser
5. Intensity
– Radiometric terminology
Term Unit
Energy joule
(1 J = 1 watt x 1 sec.)
Power watt
Energy density J/cm²
Irradiance watt / cm²
Intensity watt / sr
(sr = Steradian, unit of solid
angle)
brightness Watt / sr cm²
Laser output

31. Properties of laser
5. Intensity
– Tissue effect
• Determined by focal point spot size
• Energy density , irradiance
– Spot size
• 50 µm spot size = ¶ (25 x 10 -4) ² cm²
= 2 x 10 -5 cm²

32. Properties of laser
5. Intensity
– Continuous laser
• Argon, Krypton  watts
– Pulsed laser
• Nd:YAG  joules
• Average, peak power

33. Properties of laser
Sun has power 10 26 watts, but emits in all direction
Helium neon laser 1 mW has
100 x radiance of sun

34. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

35. Laser system
• Types of medical laser

36. Laser system
• Types of medical laser
– CO2 (λ = 9.2-10.8 µm)
• Gas laser
• Nonophthalmic surgery : Gynecology, ENT
• Absorbed by water
– Er:YAG (λ = 2.94 µm)
• Solid laser
• Strongest absorption by water  shallow penetration
depth  low vaporization, small collateral damage

37. Laser system
• Types of medical laser
– Nd:YAG (λ = 1064 µm)
• Important ophthalmic laser
• Low absorption and scatting  deep penetration
– Argon/Krypton (λ = 488,515,568,647 nm)
• Gas laser
• Retinal photocoagulation in the past
– Excimer laser (λ = 157,193,248,308,351 nm)
• ArF (193 nm) Strong absorption in protein 
submicrometer penetration in tissue
• Refractive surgery (Corneal ablation)

38. Laser system
• Contact lens
– Aberration
• Focal spot size of laser beam is limited by diffraction
and aberration
• ↑ central aberration  ↑ focal spot size
• Photocoagulation  Flat contact lens to control
aberration
– Magnify spot size on retina
– Increase view of field

39. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

40. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

41. Laser-tissue interaction
1960, Theodore Maiman built the first successful
laser with ruby crystal medium
1927-2007

42. Laser-tissue interaction
1. Photocoagulation
Target tissue absorb light energy
Convert to thermal energy
Tissue Temperature > 65 °C
Tissue protein denaturation and coagulative necrosis

43. Laser-tissue interaction
1. Photocoagulation
– Laser type
• Green, red, yellow, infrared
– Approach
• Transpupillary with slit lamp
• Indirect ophthalmoscope
• Endophotocoagulation with vitrectomy surgery
• Transscleral application with contact probe

44. Laser-tissue interaction
1. Photocoagulation
– Pigment in Ocular tissue  absorption
• Melanin : green, yellow, red, infrared
• Macular xanthophyll : Blue > yellow, red
• Hemoglobin : blue, green, yellow > red

45. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

46. Laser-tissue interaction
1. Photocoagulation
– Choice of laser wavelength
• Green laser
– Well absorb by melanin, hemoglobin, less absorb by
xanthophyll
– Retinal vascular abnormality, CNV
– Argon green laser (514 nm)
» Popular wavelength for retina photocoagulation
– Frequency-doubled Nd:YAG laser (532 nm)
» Continuous , pulsed output
» Its absorption and clinical use similar to Dye yellow but
more reliable due to solid medium

47. Laser-tissue interaction
1. Photocoagulation
– Choice of laser wavelength
• Red laser
– Good penetrate through cataract, VH than other laser
– Less absorb by xanthophyll
– CNV near fovea
– Deep burn  discomfort
– Krypton red laser (647 nm)
» Well absorb only melanin
 deeper outer retinal and choroidal
burn
» Less absorb by hemoglobin
 good for VH, CNV
overlying thin subretinal Hge
 bad for retinal vascular abnormality

48. Laser-tissue interaction
1. Photocoagulation
– Choice of laser wavelength
• Infrared laser
– Similar to red laser
– Deeper penetrate through tissue
– Semiconductor diode laser (805-810 nm)
» Near infrared spectrum
» Well absorb by melanin only
 deeper outer retinal and choroidal burn
» Similar property to krypton red laser but less discomfort
due to near invisible laser (no sensation of flashing)
» Treatment of choice for ROP
» Transscleral contact retinal photocoagulation 
Penetrate sclera and silicone scleral exoplant

49. Laser-tissue interaction
1. Photocoagulation
– Choice of laser wavelength
• Yellow laser
– Penetrate through cataract
– Less absorb by xanthophyll
– Destroy vascular structure with little damage to adjacent
tissue
– Dye yellow laser (560-580 nm)
» Well absorb by Hemoglobin, melanin
» Safe for macular photocoagulation
» Less useful in VH, preretinal hemorrhage, CNV overlying
with subretinal hemorrhage

50. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

51. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Macular edema
– Direct closure of leaking vascular
» Microaneurysm  laser induced endovascular
thrombosis
 heat induce
vessel wall contraction
– Grid
» Multifactorial and unclear
» RPE damage  retinal capillary and venule endothelial
proliferation  restore inner blood-retinal barrier
» Decrease total surface area of leaking retinal vessels

52. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Scatter photocoagulation for NV
– Destruction of oxygen consuming photoreceptor  ↓VEGF
– Wilson et al.  Gene expression
- Angiotensin II type 2 receptor (Inhibit VEGF)
- Calcitonin receptor-like receptor
- Interleukin-1
- Fibroblast growth factor
- Plasminogen activator inhibitor II

53. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Central serous chorioretinopathy
– Unclear
– Laser direct at site fluorescence leak
Destroy sick RPE
Healthy neighboring RPE proliferate, seal defect,
reestablish outer blood-retinal barrier
– Focal obliteration of hyperpermeable choriocapillaris
– Coagulum mechanically plug RPE leakage site

54. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Choroidal neovascularization, retinal vascular anomaly
– Laser induced endovascular thrombosis
– Heat induce vessel wall contraction

55. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Nonvascular intraocular tumor
– Retinoblstoma
» Amelanotic  poorly absorb laser
» Heavy, confluent laser photocoagulation  Close
surround retinal vascular blood supply  tumor
necorsis
– Choroidal malignant melanoma
» Heavy, confluent laser photocoagulation  Close
surround choroidal vascular blood supply
» Focal laser destruction  tumor necrosis

56. Laser-tissue interaction
1. Photocoagulation
– Photocoagulation mechanism
• Retinal break
– Laser and cryotherapy  adhesion and scar
– Adhesive force generate within 24 hours  several weeks
to its maximum strength
– Laser > Cryotherapy
» Less breakdown of blood retinal barrier
» ↓Risk proliferative vitreoretinopathy

57. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

58. Laser-tissue interaction
1. Photocoagulation
– Practical aspect
1. Lens
• Lesion location, patient anatomy, desired field of view,
image magnification, working distance
1) Contact lens
– All purpose fundus contact lens
» Goldmann contact lens
» Macular, retinal periphery
» Virtual, erect image
» Look away from mirror  more anterior

59. Laser-tissue interaction
1. Photocoagulation
1) Contact lens
– Contact lens for macular photocoagulation
» Mainster high magnification, Volk Area Centralis, Mainster
Standard lens
» Real, inverted image
– Contact lens for peripheral photocoagulation
» Rodenstock Panfundoscopic, Mainster wide field, Volk
Superquad 160 lens
» Real, inverted image
2) Non contact lens
– Lens 60,78,90 D  Spot magnification 0.92,1.15,1.39

60. Laser-tissue interaction
1. Photocoagulation
– Practical aspect
2. Laser setting
• Slit lamp magnification
• Wavelength selection
– Retinal vascular lesion
» Argon green, Nd:YAG green, Dye yellow
– CNV
» Argon green, Nd:YAG green, Dye yellow, Dye red, Krypton
red, Diode
– Scatter photocoagulation
» Argon green **
» Red, Diode  Cataract, VH

61. Laser-tissue interaction
1. Photocoagulation
– Practical aspect
2. Laser setting
• Spot size
– Macular photocoagulation = 50-200 µm
– Peripheral photocoagulation = 200-1000 µm
– Shorter wavelength  higher intraocular scattering 
Larger, less focused retinal burn

62. Laser-tissue interaction
1. Photocoagulation
– Practical aspect
2. Laser setting
• Power, Duration
– Burn intensity
• Burn intensity
Light Barely visible retinal blanching CSC, Grid
Mild Faint white
Moderate Dirty white Scatter PRP, RB
Heavy Dense white Choroidal melanoma
Burn intensity α (Burn duration)(Power)
Spot size

63. Laser-tissue interaction
1. Photocoagulation
– Practical aspect
Panretinal Photocoagulation for PDR
:Pattern Scan Laser VS Argon Laser
Am J Ophthalmol 2012

64. Background
• Traditionally laser burns have been placed one by
one in a grid pattern
100-500 µm
100-200 ms
Total spots ≥ 1500 spots
Several sessions

65. Background
Blumenkranz MS
PASCAL (PAttern SCAn Laser)
• A new frequency doubled 532 nm
Nd:YAG laser
• Delivering arrays up to 56 spots
over less than 0.6 sec following a
single foot step
• Less painful and safer alternative to
argon laser for both PRP and
macular photocoagulation

66. Background
Pattern scan laser
• Short pulse duration result in a quicker PRP procedure
• As pulse durations < 50 ms
X Thermal energy
 Mechanical rupture
• because of transient vapor formed adjacent to
melanosomes
• Without thermal energy
– laser-induced damage is limited to RPE and
photoreceptors, sparing choroid and inner retina

67. Background
Pattern scan laser
• Decrease perception of pain
– Mechanical rupture effect do not diffuse to sensory neuro
rich choroid as seen in Argon laser
• Safe
– Inner retina and choroid are spared
– However, as pulse duration < 50 ms
– Smaller safety margin when titrating power of the PASCA

68. Background
• However, they are not aware of any study that has
compared clinical outcomes for the 2 lasers when treating
high-risk PDR
• This retrospective comparative study evaluates efficacy
between PASCAL and traditional argon laser in treating
newly diagnosed high-risk PDR

69. Methods : Procedure
Argon laser
• 514-nm (green) pulses
• 1 burn width apart
• Indirect headset
• Slit-lamp microscope with contact
lens
• spot-size magnification factor
of 2x
• Pulse duration 200 ms
• Spot size 200-300 µm
• Power 200 mW increased by
10-20 mW until a gray/white
lesion
• 2 or 3 sessions
(37% completed PRP in 1 session)
PASCAL
• 1 burn width apart
• Small or larger array was
determined by operator
• Slit-lamp microscope with contact
lens
• spot-size magnification 2x
• Pulse duration 20 ms
• Spot size 200 µm
• Power 200 mW increased
until gray/white lesion
• 2 or 3 sessions
(44% completed PRP in 1 session)

70. Discussion
• PASCAL has greater speed and comfort
• When both lasers were applied with similar number and
size of laser spots in similar patients
– PASCAL treatment was less effective in inducing regression
and preventing recurrence of NV in high-risk PDR
• Inherent difference in properties of PASCAL and argon
lasers
– Limits efficacy of PASCAL when used in context of traditional
argon laser treatment parameters

71. Discussion
-PRP scars following treatment with argon laser are larger size than with
PASCAL
-Total area of PRP scars in the argon-treated patient exceeds that of the
PASCAL-treated patient by an order of magnitude

72. Discussion
• Increasing rate of recurrence NV experienced in the
PASCAL-treated patients
– Given equivalent number of treatment spots, PASCAL created smaller
total burn area results in a significant decrease in efficacy compared to
Argon laser
– Either additional lesions or larger spot sizes may be required to
achieve comparable efficacy with PASCAL

73. Conclusion
• PRP with PASCAL less effective than traditional
argon green laser in high-risk PDR to achieving
treatment goals when using traditional argon
green laser parameters
• Increasing number, spot size, or duration of laser
burns may improve efficacy of PASCAL as
measured by rates of regression and recurrence
NV

74. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

75. Laser-tissue interaction
1. Photocoagulation
– Clinical use
Transscleral cyclophotocoagulation
(TSCPC)
• Diode laser : less pain & inflammation
• Power 1.5-2 W, Duration 2 sec, 180-270 °
Endoscopic cyclophotocoagulation
(ECP)
• Argon laser

76. Laser-tissue interaction
1. Photocoagulation
– Clinical use
Laser
trabeculopl
asty (LTP)
• Argon

77. Laser-tissue interaction
1. Photocoagulation
– Clinical use
Laser iridectomy
• Angle closure
• Argon laser
• Iris colour effect
• P.800-1000 mW, D 0.02-0.1 sec,
Spot size 50 µm
• Q-switch Nd:YAG laser
• Abraham, Wise lens
• P. 2-8mJ

78. Laser-tissue interaction
1. Photocoagulation
– Clinical use
Laser suture lysis
• Hoskins lens, Ritch lens
• Argon laser
• P. 300-800 mW, D. 0.02-0.1 sec,
Spot size 50-100 µm
Panretinal Photocoagulation

79. Laser-tissue interaction
1. Photocoagulation
– Clinical use
Grid laser
Focal laser
• RB, Lattice

80. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

81. Laser-tissue interaction
2. Photodisruption
High peak power pulsed laser
(Nd:YAG, Er:YAG)
Ionize target tissue and increase tissue temperature
to exceed vaporization threshold
Vapor bubbles
Rupture tissue within zone of bubbles

82. Laser-tissue interaction
2. Photodisruption
– Clinical use
Neodymium : Yttrium-
Aluminum-Garnet Laser
Capsulotomy (Nd:YAG)
• Posterior capsule opacification
• Infrared light 1064 nm
• P.0.8-2.0 mJ, aim slightly
behind capsule

83. Laser-tissue interaction
2. Photodisruption
– Clinical use
Refractive surgery
• Femtosecond laser (10 -15)
• Infrared 1053 nm
• Create corneal epithelial flap

84. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

85. Laser-tissue interaction
3. Photochemical
– Nonthermal light induce chemical reaction
• Photosynthesis in plants
• Phototransduction in photoreceptor
• Photodynamic therapy (PDT)

86. Laser-tissue interaction
3. Photochemical
– Photodynamic therapy (PDT)
• CNV, ocular and nonocular tumor
Photosensitizer (Porphyrin derivative : Verteporfin) IV
Blood stream, retina, choroid
Accumulate in LDL receptor in NV
Photon in porphyrin absorpt Far-red peak laser(688-691nm)
-Lower sensitivity to
retina
-Superior choroid
penetration

87. Toxic singlet oxygen and free radical
Endothelial cell damage, photothrombosis, closure NV

88. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

89. Laser-tissue interaction
4. Photoablation
– High-powered ultraviolet laser etch cornea like
synthetic polymer
Excimer laser
• Excited dimer (Rare
gas+Halide)
• ArF (193 nm)
• Photon break covalent bond
strength of cornea
• Remove submicron layer of
cornea without damage
adjacent tissue  absence of
thermal injury

90. Outline
• Principle
– Laser physics
– Properties of laser light
• Monochromaticity
• Directionality
• Coherence
– Laser interferometer
– OCT
• Polarization
• Intensity
– Laser system
– Laser interactions and its
clinical use
– Photocoagulation
• Basic
• Choice of wavelength
• Photocoagulation mechanism
• Practical aspect
• Clinical use
– TSCPC
– ECP
– LTP
– LPI
– Laser suture lysis
– Photodisruption
• Nd:YAG capsulotomy
• Femtosecond laser
– Photochemical
• Photodynamic therapy
– Photoablation
• Excimer laser

91. Reference
• Daniel Palanker, Mark S. Blumenkranz, John J. Weiter. Chapter 21 Retinal
laser therapy : Biophysical basis and application. Retina. Forth edition.
Elsevier Mosby
• Steven M. Bloom, MD, Alexander J. Brucker, MD. Laser surgery of the
posterior segment. Second edition. Philadelphia: Lippincott-Raven; 1997.
• American academy of ophthalmology : section 12 Retina and vitreous,
Basic and clinical science course, 2010-2011
• American academy of ophthalmology : section 10 Glaucoma, Basic and
clinical science course, 2010-2011
• Antonia M. Joussen, Thomas W. Gardner, Bernd Kirchhof, Stephen J.
Ryan. Retinal vascular disease. New York: Springer
• Aimee V. Chappelow, Kevin Tan, Nadia K. Waheed, Peter K. Kaiser.
Panretinal photocoagulation for proliferative diabetic retinopathy : Pattern
scan laser versus Argon laser. Am J Ophthalmol 2012;153:137-142

92. "The important thing is not to stop
questioning.
Curiosity has its own reason for
existing."
Albert Einstein

93. Thank you