Lasers in ophthalmology


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brief note on lasers usedin ophthalmology.

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Lasers in ophthalmology

  2. 2.  Introduction. History . Laser physics. Classification . Laser tissue interactions. Uses – therapeutic.- diagnostic. Complications.
  3. 3. LASER is an acronym for: L : Light A : Amplification (by) S : Stimulated E : Emission (of) R : RadiationTerm coined by Gordon Gould.Lase means to absorb energy in one form and to emit a newform of light energy which is more useful.
  4. 4.  1960 : The first laser was built by TheodoreMaiman using a ruby crystal medium. 1963 : The first clinical ophthalmic use of laserin humans. 1968 : L Esperance developed the argon laser. 1971 : Neodymium yttrium aluminum garnet(Nd.YAG) and Krypton laser develop. 1983 : Trokel developed the eximer laser.
  5. 5. LASER LIGHT Stimulated emission Monochromatic. Highly energized Parallelism Coherence Can be sharply focussed. Spontaneous emission. Polychromatic. Poorly energized. Highly divergence Not coherent Can not be sharplyfocussed.
  6. 6.  Coherency Monochromatism Collimated Constant Phasic Relation Ability to be concentrated in short time interval Ability to produce non linear effects
  7. 7.  Light as electromagnetic waves, emitting radiant energy in tinypackage called ‘quanta’/photon. Each photon has acharacteristic frequency and its energy is proportional to itsfrequency. Three basic ways for photons and atoms to interact: Absorption Spontaneous Emission Stimulated EmissionHOW LASER WORK ???
  8. 8. Contd. …
  9. 9. Pulsed – energy delivered in briefbursts, more powerExamples: Nd YAG, Excimer lasersContinuous – Argon, krypton lasers, diodelasers, and dye lasers
  10. 10.  Solid StateRubyNd.YagErbium.YAG GasIonArgonKryptonHe-NeonCO2 Metal VapourCuGold DyeRhodamine ExcimerArgon FluorideKrypton FluorideKrypton Chloride DiodeGallium-AluminumArsenide (GaAlAs)
  11. 11.  Haemoglobin: Argon Green are absorbed , Krypton yellow. Theselaser are found to be useful to coagulate the bloodvessels. Xanthophyll: Present in inner and outer plexiform layers of macula. Maximum absorption is blue. Argon blue is notrecommended to treat macular lesions. Melanin: RPE, Choroid Argon Blue, Krypton Pan Retinal Photocoagulation, and Destruction of RPE
  12. 12.  Class-I : Causing no biological damage. Class-II : Safe on momentary viewing but chronicexposure may cause damage. Class-III : Not safe even in momentary view. Class-IV : Cause more hazardous than Class-III.LASER SAFETY REGULATION: Patient safety is ensured by correct positioning. Danger to the surgeon is avoided by safety filter system. Safety of observers and assistants.
  13. 13. LASER VARIABLE: Wavelength Spot Size Power DurationTISSUE VARIABLE: Transparency Pigmentation Water Content
  14. 14. This is the amount of power delivered to aunit area of tissue.To prevent creating very intense burn.Decrease in the spot size should beaccompanied by decrease in power.
  15. 15. LASERTISSUEThermalEffectPhoto-chemicalIonizingEffect Photocoagulation  Photoradiation Photodisruption  Photoablation Photovaporization
  16. 16. (1) Photocoagulation:Laser LightTarget TissueGenerate HeatDenatures Proteins(Coagulation)Rise in temperature of about 10 to 20 0C will cause coagulation oftissue.
  17. 17. (2) Photodisruption: Mechanical Effect: Laser LightOptical BreakdownMiniature Lightening BoltVaporQuickly CollapsesThunder ClapAcoustic ShockwavesTissue DamageContd. …
  18. 18. (3) Photoablation: Breaks the chemical bonds that hold tissue togetheressentially vaporizing the tissue, e.g. PhotorefractiveKeratectomy, Argon Fluoride (ArF) Excimer Laser.Usually -Visible Wavelength : PhotocoagulationUltraviolet Yields : PhotoablationInfrared : PhotodisruptionPhotocoagulationContd. …
  19. 19.  Vaporization of tissue to CO2 and water occurs when itstemperature rise 60—100 0C or greater. Commonly used CO2Absorbed by water of cellsVisible vapor (vaporization)Heat Cell disintegrationCauterization Incision
  20. 20. PHOTORADIATION (PDT): Also called Photodynamic Therapy Photochemical reaction following visible/infrared lightparticularly after administration of exogenous chromophore. Commonly used photosensitizers: Hematoporphyrin Benzaporphyrin Derivativese.g. Treatment of ocular tumour and CNV
  21. 21. Photon + Photosensitizer in ground state (S)3S (high energy triplet stage)Energy TransferMolecular Oxygen Free RadicalS + O2 (singlet oxygen) Cytotoxic IntermediateCell Damage, Vascular Damage , Immunologic DamageContd. …
  22. 22.  Highly energized focal laser beam is delivered on tissueover a period of nanosecond or picoseconds and produceplasma in target tissue. Q Switching Nd.YagIonization (Plasma formation)Absorption of photon by plasmaIncrease in temperature andexpansion of supersonic velocityShock wave production Tissue Disruption
  23. 23. iridotomy
  24. 24.  A Laser Mediume.g. Solid, Liquid or Gas Exciting Methodsfor exciting atoms or molecules in the mediume.g. Light, Electricity Optical Cavity (Laser Tube)around the medium which act as a resonator
  25. 25.  Continuous Wave (CW) Laser: It deliver their energy in acontinuous stream of photons. Pulsed Lasers: Produce energy pulses of a few tens of micro tofew mili second. Q Switches Lasers: Deliver energy pulses of extremely shortduration (nano second). A Mode-locked Lasers: Emits a train of short duration pulses(picoseconds). Fundamental System: Optical condition in which only one typeof wave is oscillating in the laser cavity. Multimode system: Large number of waves, each in a slightdifferent direction ,oscillate in laser cavity.
  26. 26. Transpupillary: - Slit lamp- Laser IndirectOphthalmoscopyTrans scleral : - Contact- Non contactEndophotocoagulation.
  27. 27. Most commonly employed mode foranterior and posterior segment. ADVANTAGES:Binocular and stereoscopic view.Fixed distance.Standardization of spot size is moreaccurate.Aiming accuracy is good.
  28. 28.  Advantages : Wider field(ability to reach periphery). Better visualization and laser application inhazy medium. Ability to treat in supine position.(ROP/EUA) Disadvantage : difficulty in focusing. Difficulty to standardize spot size. Expensive. Un co-operative patient. Learning curve.
  30. 30. CORNEA:Laser in Keratorefractive Surgery: Photo Refractive Keratectomy (PRK). Laser in situ Keratomileusis (LASIK). Laser Sub epithelial Keratectomy (LASEK). Epi Lasik.Laser Thermal Keratoplasty .Corneal Neovascularization.Retrocorneal Pigmented Plaques.
  31. 31. High energy UV laser.Excited dimer.Argon fluoride(193nm) most commonlyapplied for corneal surgeries.Photoablation.
  32. 32. Laser removes approximately 0.25micronsof corneal tissue with each pulse.Amount of tissue to be ablated derivedfrom ―munnerlyn equation”Central ablation depth in microns=dioptersof myopia*(ablation zone diameter in mm)23
  33. 33. PRK LASIK
  34. 34. ADVANTAGES: Flap are more accurate and uniform in thickness. Centration of flap is easier. Better adherence to underlying stroma. Patient are more comfortable.DISADVANTAGES: Suction break Costly
  35. 35. Contd. …
  36. 36.  Laser Iridotomy. Laser Trabeculoplasty (LT) Selective Laser Trabeculoplasty Trabecular ablation Gonioplasty (Iridoplasty, Iridoretraction) Pupilloplasty Sphincterotomy Iridolenticular Synechiolysis Goniophotocoagulation Goniotomy
  37. 37. Peripheral Iridectomy Argon LaserIridoplastyArgon Nd:YAGLight Irides Dark IridesSpot size (μm) 50 50 Fixed 200–500Spot duration (seconds) 0.2 0.02–0.05 Fixed(nanoseconds)0.2–0.5Power (mW) 1000 1000 3–8 mJ 200–400Number of spots perquadrant15–25 25–100 1–5 shots (eachburst consists of1–3 pluses)4–10Wavelength Argon green Argon green 1064 nm Argon greenContact lens Abraham Wise Abraham, Wise,or Lasag CGIGoldmannPretreatment PilocarpineandapraclonidineorbrimonidinePilocarpineandapraclonidine orbrimonidinePilocarpine andapraclonidine orbrimonidinePilocarpine
  38. 38. PUPILLOPLASTY2-3 rows of burnscircumferentially 1mmaway from the pupillarymargin.Innermost row:8spots,200micron size, 200-400mW.Outer row:10-12spots,400micronsize,300-500mW
  39. 39. Laser parameters aresame for photomydriasis.Burns are placed alongthe inferior margin.
  40. 40. ARGON LASER TRABECULOPLASTYMechanism ofaction:Mechanical.Biological.
  41. 41. Parameters Argon laser trabeculoplastySpot size (μm) 50Spot duration (seconds) 0.1Power (mW) 200–800Number of spots perquadrant20–25Wavelength Argon greenContact lens GoldmannAnesthetic TopicalPretreatment Apraclonidine or brimonidineArgon laser trabeculoplasty
  42. 42.  Laser Filtration Procedures (sclerostomy): Ab Externosclerostomy (Holmium) Ab Internosclerostomy (Nd.YAG)Contact Non-contact Cyclodestructive Procedures (cyclophotocoagulation) Transscleral Cyclophotocoagulation Trnaspupillary Cyclophotocoagulation Diode Laser EndophotocoagulationContd. …
  45. 45.  Posterior capsulotomy Laser phacoemulsification Phacoablation. Laser in Lacrimal Surgery: Laser DCR.LASER IN VITREOUS Vitreous membranes Vitreous traction bands
  46. 46.  Diabetic Retinopathy Retinal Vascular Diseases Choroidal Neovascularization (CNV) Clinical Significant Macular Edema (CSME) Central Serous Retinopathy (CSR) Retinal Break/Detachment Tumour
  47. 47.  ARMD Retinal Vein Occlusion Eale’s Disease Coats Disease Peripheral Retinal Lesion Retinopathy of prematurity.Contd. …
  48. 48. Patient should be explained about thepossible complications to avoid legalproblems to the treating physician later.
  49. 49.  Light : Barely visible retinal blanching Mild : Faint white retinal burn Moderate : Opaque dirty white retinal burn Heavy : Dense white retinal burn
  50. 50. TYPE OF RETINOPATHY THERAPYBackgroundControl of diabetes, regularreviewMaculopathyCSMEFocal photocoagulationDiffuse leakage around macula Grid laserCircinate Focal photocoagulationPre-proliferative Retinopathy Frequent reviewProliferative retinopathy Pan retinal photocoagulationAdvanced diabetic eye diseaseVitreoretinal surgery withphotocoagulationContd. …
  51. 51. Step 1Step 2
  52. 52. Step 3Step 4
  53. 53. Laser settingsWavelength :argongreen, Nd YAG,dyeyellow red , diode.Duration :0.1-0.2seconds.Retinal spot size: 200-500microns.Intensity : moderateretinal whitening
  54. 54.  Indication:Photocoagulationtechnique.Initial destruction of thesurrounding choroidalblood supply-1-2rows -200-500 microns 0.5-1sec-intense burn.Direct tumourphotocoagulation-lowenergy burns longduration5-30sec.
  55. 55.  Visudyne (Verteporfin) Selective Damageof SRNVM. Costly.
  56. 56. 1. Dye dose = 6 mg/m2 body surface area2. Intravenous infusion over 10 min3. Treatment at 15 min after start of dyeinfusion4. Laser light wavelength of at 689 nm,irradiance of 600 mW/cm2and fluence of 100 J/cm2
  57. 57.  Thermotherapy can involve using ultrasound, microwave, or infrared radiation todeliver heat to the eye. Retinoblastoma -application of diode (infrared)laser to the tumor surface in regions of diseaseactivity. Goal- cause tumor cell death by raising thetemperature of tumor cells to above 45°C for ~1min, thus reducing blood supply and producingapoptosis.
  58. 58. Retinoblastoma afterthermotherapy
  59. 59. Lens Uses ImageSpotMagnificationField of viewGoldmannMaculaEquatorPeripheryVirtualErect1.08 360VolkSupermacula 2.0MaculaRealInverted2.15 700MainsterHighMagnificationMaculaRealInverted1.34 750Volk AreaCentralisMaculaEquatorRealInverted1.13 820
  60. 60. Lens Uses ImageSpotMagnificationField ofviewMainsterStandardMaculaEquatorRealInverted1.03 900PanfunduscopicEquatorPeripheryRealInverted0.76 1200VolkTransequatorEquatorPeripheryRealInverted0.75 1220MainsterWide FieldEquatorPeripheryRealInverted0.73 1250
  61. 61. Lens Uses ImageSpotMagnificationField ofviewVolkQuadrAsphericEquatorPeripheryRealInverted0.56 1300MainsterUltra FieldPRPEquatorPeripheryRealInverted0.57 1400VolkSuperQuard160EquatorPeripheryRealInverted0.56 1600
  62. 62.  The PASCAL Photocoagulator is an integrated semi-automatic pattern scan laser photocoagulation systemdesigned to treat ocular diseases using a single shot orpredetermined pattern array. Laser source :Nd:YAG laser. Delivery device: slit lamp or laser indirectophthalmoscope (LIO) Control system for selecting power and duration Method for selecting spot size.
  63. 63. Scanning Laser Ophthalmoscopy allows for high-resolution, real-time motionimages of the macula without patientdiscomfort. SLO angiography: to study retinal andchoroidal blood flow. May be used to perform microperimetry, anextremely accurate mapping of the macula’svisual field.
  64. 64. Uses diode laser light in the near-infraredspectrum (810 nm) to produce high-resolution cross-sectional images of theretina using coherence interferometry.
  65. 65.  General complications: Pain Seizures. Anterior segment complications: Elevated IOP. Corneal damage. Iris burns. Crystalline lens burns. IOL and PC damage. Internal opthalmoplegia.
  66. 66. Choroidal detachment and exudative RD.Choroidal ,subretinal and vitreoushemorrhage.Thermal induced retinal vascular damage.Preretinal membranes.
  67. 67. Ischaemic papillitis.Paracentral visual field loss and scotoma.Photocoagulation scar enlargement.Subretinal fibrosis.Iatrogenic choroidal neovascularisation.Accidental foveal burns.
  68. 68.  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…...
  70. 70. Thank you