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This document provides an overview of fundamental laser ophthalmology. It begins with laser physics, describing the principles of stimulated emission and population inversion required for laser action. It then discusses the properties of laser light including monochromaticity, directionality, coherence, polarization and intensity. The document outlines different laser systems used in ophthalmology and laser-tissue interactions, focusing on photocoagulation. It explains the basic mechanism of photocoagulation, factors in choosing the appropriate wavelength, and discusses photocoagulation in the clinical context of conditions like diabetic macular edema and retinal neovascularization.

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Fundamental laser ophthalmology 5 November 2012 Mallawee Charatcharungkiat, MD Instructor Nawat Watanachai, MD
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
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
Laser physics • “Light amplification by stimulated emission of radiation”
Laser physics • “Light amplification by stimulated emission of radiation” • 1917 • Atomic transposition process – Absorption – Spontaneous emission – Stimulated emission Albert Einstein
Laser Physics • Absorption Unexcited atom (E0 : Ground state) Photon Excited atom (E1 : Excited state)
Laser Physics • Spontaneous emission Unexcited atom (E0 : Ground state) Photon Excited atom (E1 : Excited state)
Laser Physics • Stimulated emission Unexcited atom (E0 : Ground state) 2 Photon Excited atom (E1 : Excited state)
Laser Physics
Laser Physics • After absorption – Spontaneous emission • Majority • Incoherent – Stimulated emission • Few • Coherent Laser Laser
Laser Physics • Element of laser 1. Active medium 2. Energy input 3. Optical feedback
Laser Physics • Element of laser 1. Active medium • Allowed stimulated emission • Particular atomic energy transition Wavelength of the emission E = hv = hc /λ
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)
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”
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)
Laser Physics • Element of laser 3. Optical feedback • Promote stimulated emission, suppress spontaneous emission • Spontaneous emission  not amplify • Stimulated emission  Coherent laser
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
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
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)
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
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
Properties of laser 3. Coherence – Ability of 2 light beams, or different parts of the same beam, to produce interference – Interference
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
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
Properties of laser 3. Coherence • OCT ½ light ½ light
Properties of laser 3. Coherence • OCT
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
Properties of laser 5. Intensity – Power in a beam of given angular size – Most important property – “Brightness” • Intensity / unit area
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
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
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
Properties of laser 5. Intensity – Continuous laser • Argon, Krypton  watts – Pulsed laser • Nd:YAG  joules • Average, peak power
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
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
Laser system • Types of medical laser
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
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)
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
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
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
Laser-tissue interaction 1960, Theodore Maiman built the first successful laser with ruby crystal medium 1927-2007
Laser-tissue interaction 1. Photocoagulation Target tissue absorb light energy Convert to thermal energy Tissue Temperature > 65 °C Tissue protein denaturation and coagulative necrosis
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
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
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
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
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
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
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
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
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
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
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
Laser-tissue interaction 1. Photocoagulation – Photocoagulation mechanism • Choroidal neovascularization, retinal vascular anomaly – Laser induced endovascular thrombosis – Heat induce vessel wall contraction
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
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
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
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
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
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
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
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
Laser-tissue interaction 1. Photocoagulation – Practical aspect Panretinal Photocoagulation for PDR :Pattern Scan Laser VS Argon Laser Am J Ophthalmol 2012
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
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
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
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
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
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)
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
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
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
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
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
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
Laser-tissue interaction 1. Photocoagulation – Clinical use Laser trabeculopl asty (LTP) • Argon
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
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
Laser-tissue interaction 1. Photocoagulation – Clinical use Grid laser Focal laser • RB, Lattice
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
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
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
Laser-tissue interaction 2. Photodisruption – Clinical use Refractive surgery • Femtosecond laser (10 -15) • Infrared 1053 nm • Create corneal epithelial flap
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
Laser-tissue interaction 3. Photochemical – Nonthermal light induce chemical reaction • Photosynthesis in plants • Phototransduction in photoreceptor • Photodynamic therapy (PDT)
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
Toxic singlet oxygen and free radical Endothelial cell damage, photothrombosis, closure NV
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
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
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
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
"The important thing is not to stop questioning. Curiosity has its own reason for existing." Albert Einstein
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Nw2014 laser fundamenal01

  • 1.
    Fundamental laser ophthalmology 5November 2012 Mallawee Charatcharungkiat, MD Instructor Nawat Watanachai, MD
  • 2.
    Outline • Principle – Laserphysics – 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 – Laserphysics – 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 • “Lightamplification by stimulated emission of radiation”
  • 5.
    Laser physics • “Lightamplification by stimulated emission of radiation” • 1917 • Atomic transposition process – Absorption – Spontaneous emission – Stimulated emission Albert Einstein
  • 6.
    Laser Physics • Absorption Unexcitedatom (E0 : Ground state) Photon Excited atom (E1 : Excited state)
  • 7.
    Laser Physics • Spontaneousemission Unexcited atom (E0 : Ground state) Photon Excited atom (E1 : Excited state)
  • 8.
    Laser Physics • Stimulatedemission Unexcited atom (E0 : Ground state) 2 Photon Excited atom (E1 : Excited state)
  • 9.
  • 10.
    Laser Physics • Afterabsorption – Spontaneous emission • Majority • Incoherent – Stimulated emission • Few • Coherent Laser Laser
  • 11.
    Laser Physics • Elementof laser 1. Active medium 2. Energy input 3. Optical feedback
  • 12.
    Laser Physics • Elementof laser 1. Active medium • Allowed stimulated emission • Particular atomic energy transition Wavelength of the emission E = hv = hc /λ
  • 13.
    Laser Physics • Elementof 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 • Elementof laser 2. Energy input • Make majority of atom are in higher energy state than ground state • “Population inversion” • “Pumping” • “Light amplification”
  • 15.
    Laser Physics • Elementof 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 • Elementof laser 3. Optical feedback • Promote stimulated emission, suppress spontaneous emission • Spontaneous emission  not amplify • Stimulated emission  Coherent laser
  • 17.
    Outline • Principle – Laserphysics – 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 Chromaticaberration – 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 Sunhas power 10 26 watts, but emits in all direction Helium neon laser 1 mW has 100 x radiance of sun
  • 34.
    Outline • Principle – Laserphysics – 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 • Typesof medical laser
  • 36.
    Laser system • Typesof 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 • Typesof 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 • Contactlens – 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 – Laserphysics – 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 – Laserphysics – 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, TheodoreMaiman built the first successful laser with ruby crystal medium 1927-2007
  • 42.
    Laser-tissue interaction 1. Photocoagulation Targettissue 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 – Laserphysics – 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 – Laserphysics – 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 – Laserphysics – 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 laserburns 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 (PAtternSCAn 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, theyare 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 Argonlaser • 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 hasgreater 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 followingtreatment 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 rateof 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 withPASCAL 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 – Laserphysics – 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 – Laserphysics – 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 Highpeak 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 – Laserphysics – 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 oxygenand free radical Endothelial cell damage, photothrombosis, closure NV
  • 88.
    Outline • Principle – Laserphysics – 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 – Laserphysics – 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 thingis not to stop questioning. Curiosity has its own reason for existing." Albert Einstein
  • 93.