LASERS IN OPHTHALMOLOGY

LASERS IN OPHTHALMOLOGYMODERATOR: DR. S. KALPANA PRESENTER: DR. ANJALI

Brief outlineIntroduction.History .Laser physics.Classification .Laser tissue interactions.Uses therapeutic. - diagnostic.Complications.

INTRODUCTIONLASER is an acronym for:L: Light A: Amplification (by)S: Stimulated E: Emission (of)R: Radiation Term coined by Gordon Gould. Lase means to absorb energy in one form and to emit a new form of light energy which is more useful. 3HISTORY1960 :The first laser was built by Theodore Maiman using a ruby crystal medium.1963 : The first clinical ophthalmic use of laser in 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. LASER Vs. LIGHT LASER LIGHT Stimulated emissionMonochromatic.Highly energizedParallelismCoherenceCan be sharply focussed.Spontaneous emission.Polychromatic.Poorly energized.Highly divergenceNot coherentCan not be sharply focussed.PROPERTIES OF LASER LIGHTCoherency MonochromatismCollimated Constant Phasic RelationAbility to be concentrated in short time intervalAbility to produce non linear effects LASER PHYSICS Light as electromagnetic waves, emitting radiant energy in tiny package called quanta/photon. Each photon has a characteristic frequency and its energy is proportional to its frequency.Three basic ways for photons and atoms to interact:AbsorptionSpontaneous EmissionStimulated Emission HOW LASER WORK ???

HOW LASER WORK ???Contd.

Continuous and pulsed lasers Pulsed energy delivered in brief bursts, more powerExamples: Nd YAG, Excimer lasers

Continuous Argon, krypton lasers, diode lasers, and dye lasers

CLASSIFICATION OF LASERSolid StateRubyNd.YagErbium.YAG

GasIonArgonKryptonHe-NeonCO2Metal VapourCuGoldDyeRhodamineExcimer Argon FluorideKrypton FluorideKrypton Chloride DiodeGallium-Aluminum Arsenide (GaAlAs)

THREE TYPE OF OCULAR PIGMENTHaemoglobin:Argon Green are absorbed , Krypton yellow. These laser are found to be useful to coagulate the blood vessels. Xanthophyll:Present in inner and outer plexiform layers of macula. Maximum absorption is blue. Argon blue is not recommended to treat macular lesions. Melanin:RPE, ChoroidArgon Blue, Krypton Pan Retinal Photocoagulation, and Destruction of RPEABSORBTION SPECTRUM

ELECTROMAGNETIC SPECTRUM

LASER SAFETY Class-I :Causing no biological damage.Class-II :Safe on momentary viewing but chronic exposure may cause damage.Class-III : Not safe even in momentary view.Class-IV :Cause 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. LASER TISSUE INTERACTIONLASER VARIABLE:WavelengthSpot SizePowerDurationTISSUE VARIABLE:Transparency PigmentationWater Content

Power density.This is the amount of power delivered to a unit area of tissue.

To prevent creating very intense burn. Decrease in the spot size should be accompanied by decrease in power.LASER TISSUE INTERACTIONLASERTISSUEThermal EffectPhoto-chemicalIonizing Effect Photocoagulation Photoradiation Photodisruption Photoablation Photovaporization THREE BASIC LIGHT TISSUE INTERACTIONS (1) Photocoagulation:Laser Light Target TissueGenerate HeatDenatures Proteins (Coagulation)Rise in temperature of about 10 to 20 0C will cause coagulation of tissue. THREE BASIC LIGHT TISSUE INTERACTIONS (2) Photodisruption:Mechanical Effect: Laser LightOptical Breakdown Miniature Lightening Bolt Vapor Quickly Collapses Thunder Clap Acoustic Shockwaves Tissue DamageContd. THREE BASIC LIGHT TISSUE INTERACTIONS (3) Photoablation:Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy, Argon Fluoride (ArF) Excimer Laser.Usually - Visible Wavelength:PhotocoagulationUltraviolet Yields:Photoablation Infrared:Photodisruption Photocoagulation Contd. PHOTOVAPORIZATIONVaporization of tissue to CO2 and water occurs when its temperature rise 60100 0C or greater.Commonly used CO2Absorbed by water of cells Visible vapor (vaporization) HeatCell disintegration Cauterization Incision PHOTOCHEMICAL EFFECTPHOTORADIATION (PDT):Also called Photodynamic TherapyPhotochemical reaction following visible/infrared light particularly after administration of exogenous chromophore. Commonly used photosensitizers:Hematoporphyrin Benzaporphyrin Derivatives e.g. Treatment of ocular tumour and CNVPHOTOCHEMICAL EFFECTPhoton + Photosensitizer in ground state (S)3S (high energy triplet stage) Energy Transfer Molecular OxygenFree Radical S + O2 (singlet oxygen) Cytotoxic Intermediate Cell Damage, Vascular Damage , Immunologic Damage Contd. IONISING EFFECTHighly energized focal laser beam is delivered on tissue over a period of nanosecond or picoseconds and produce plasma in target tissue.Q Switching Nd.YagIonization (Plasma formation) Absorption of photon by plasma Increase in temperature and expansion of supersonic velocity Shock wave production Tissue Disruption

iridotomyTHREE BASIC COMPONENTS A Laser Medium e.g. Solid, Liquid or GasExciting Methods for exciting atoms or molecules in the medium e.g. Light, Electricity Optical Cavity (Laser Tube)around the medium which act as a resonator MODES OF LASER OPERATION Continuous Wave (CW) Laser: It deliver their energy in a continuous stream of photons.Pulsed Lasers: Produce energy pulses of a few tens of micro to few mili second. Q Switches Lasers: Deliver energy pulses of extremely short duration (nano second).A Mode-locked Lasers: Emits a train of short duration pulses (picoseconds).Fundamental System: Optical condition in which only one type of wave is oscillating in the laser cavity. Multimode system: Large number of waves, each in a slight different direction ,oscillate in laser cavity. Delivery systemsTranspupillary:- Slit lamp - Laser Indirect Ophthalmoscopy

Trans scleral:- Contact - Non contact

Endophotocoagulation.Slit lamp biomicroscopic laser delivery Most commonly employed mode for anterior and posterior segment.ADVANTAGES:Binocular and stereoscopic view.Fixed distance. Standardization of spot size is more accurate.Aiming accuracy is good.Laser indirect ophthalmoscope.Advantages :Wider field(ability to reach periphery).Better visualization and laser application in hazy 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.USESTHERAPEUTIC.

DIAGNOSTIC.

LASER IN ANTERIOR SEGMENT 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. EXCIMER LASERHigh energy UV laser.Excited dimer.Argon fluoride(193nm) most commonly applied for corneal surgeries.Photoablation.

EXCIMER LASER(contd)Laser removes approximately 0.25microns of corneal tissue with each pulse.Amount of tissue to be ablated derived from munnerlyn equationCentral ablation depth in microns=diopters of myopia*(ablation zone diameter in mm)2 3

PRKLASIK FEMTOSECOND LASERADVANTAGES: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 FEMTOSECOND LASER

Contd. LASER IN GLAUCOMA Laser Iridotomy.Laser Trabeculoplasty (LT)Selective Laser TrabeculoplastyTrabecular ablation Gonioplasty (Iridoplasty, Iridoretraction)Pupilloplasty Sphincterotomy Iridolenticular Synechiolysis Goniophotocoagulation Goniotomy

Peripheral IridectomyArgon Laser IridoplastyArgonNd:YAGLight IridesDark IridesSpot size (m)5050Fixed200500Spot duration (seconds)0.20.020.05Fixed (nanoseconds)0.20.5Power (mW)1000100038 mJ200400Number of spots per quadrant15252510015 shots (each burst consists of 13 pluses)410WavelengthArgon greenArgon green1064 nmArgon greenContact lensAbrahamWiseAbraham, Wise, or Lasag CGIGoldmannPretreatmentPilocarpine and apraclonidine or brimonidinePilocarpine and apraclonidine or brimonidinePilocarpine and apraclonidine or brimonidinePilocarpine LASER IRIDOTOMY

PUPILLOPLASTY

2-3 rows of burns circumferentially 1mm away from the pupillary margin.Innermost row:8spots, 200micron size, 200-400mW.Outer row:10-12spots,400micron size,300-500mWStretching the updrawn pupil

Laser parameters are same for photomydriasis.

Burns are placed along the inferior margin.

ARGON LASER TRABECULOPLASTYMechanism of action:Mechanical. Biological.Parameters Argon laser trabeculoplastySpot size (m)50Spot duration (seconds)0.1Power (mW)200800Number of spots per quadrant2025WavelengthArgon greenContact lensGoldmannAnestheticTopicalPretreatmentApraclonidine or brimonidineArgon laser trabeculoplasty

LASER IN GLAUCOMA Laser Filtration Procedures (sclerostomy):Ab Externosclerostomy (Holmium)Ab Internosclerostomy (Nd.YAG) Contact Non-contact Cyclodestructive Procedures (cyclophotocoagulation)Transscleral Cyclophotocoagulation Trnaspupillary Cyclophotocoagulation Diode Laser Endophotocoagulation Contd.

SCLEROSTOMYAB INTERNO SCLEROSTOMY

LASER IN LENSPosterior capsulotomyLaser phacoemulsificationPhacoablation.

Laser in Lacrimal Surgery:Laser DCR.LASER IN VITREOUSVitreous membranesVitreous traction bands

LASER TREATMENT OF FUNDUS DISORDERS Diabetic Retinopathy Retinal Vascular DiseasesChoroidal Neovascularization (CNV)Clinical Significant Macular Edema (CSME)Central Serous Retinopathy (CSR)Retinal Break/DetachmentTumour LASER TREATMENT OF FUNDUS DISORDERS ARMDRetinal Vein Occlusion Eales DiseaseCoats DiseasePeripheral Retinal Lesion Retinopathy of prematurity. Contd. Informed consentPatient should be explained about the possible complications to avoid legal problems to the treating physician later.CLASSIFICATION OF CHORIORETINAL BURN INTENSITYLight :Barely visible retinal blanchingMild :Faint white retinal burnModerate:Opaque dirty white retinal burnHeavy :Dense white retinal burn

Pathogenesis of diabetic macular edema

DIABETIC RETINOPATHYTYPE OF RETINOPATHYTHERAPYBackground Control of diabetes, regular review Maculopathy CSMEFocal photocoagulation Diffuse leakage around maculaGrid laserCircinate Focal photocoagulation Pre-proliferative RetinopathyFrequent review Proliferative retinopathyPan retinal photocoagulation Advanced diabetic eye diseaseVitreoretinal surgery with photocoagulation Contd.

Step 1Step 2

Step 3Step 4Retinal hemorrhage

Retinal breaks and tears

Laser settingsWavelength :argon green, Nd YAG,dye yellow red , diode.Duration :0.1-0.2seconds.Retinal spot size: 200-500microns.Intensity : moderate retinal whiteningChoroidal melanoma

Indication: Photocoagulation technique.Initial destruction of the surrounding choroidal blood supply-1-2rows -200-500 microns 0.5-1sec-intense burn.Direct tumour photocoagulation-low energy burns long duration5-30sec.

What is PDT ? Visudyne (Verteporfin) Selective Damage of SRNVM. Costly.

Standard Clinical Treatment Parameters for Visudyne PDT1. Dye dose = 6 mg/m2 body surface area2. Intravenous infusion over 10 min3. Treatment at 15 min after start of dye infusion4. Laser light wavelength of at 689 nm, irradiance of 600 mW/cm2and fluence of 100 J/cm2Transpupillary thermotherapyThermotherapy can involve usingultrasound, microwave, or infrared radiation to deliver heat to the eye. Retinoblastoma -application of diode (infrared) laser to the tumor surface in regions of disease activity. Goal- cause tumor cell death by raising the temperature of tumor cells to above 45C for ~1 min, thus reducing blood supply and producing apoptosis.

Retinoblstoma before treatment

Retinoblastoma after thermotherapyLensUsesImageSpot MagnificationField of viewGoldmannMaculaEquatorPeripheryVirtualErect1.08360Volk Supermacula 2.0MaculaRealInverted2.15700Mainster High MagnificationMaculaRealInverted1.34750Volk Area CentralisMaculaEquatorRealInverted1.13820LensUsesImageSpot MagnificationField of viewMainster StandardMaculaEquatorRealInverted1.03900PanfunduscopicEquatorPeripheryRealInverted0.761200Volk TransequatorEquatorPeripheryRealInverted0.751220Mainster Wide FieldEquatorPeripheryRealInverted0.731250LensUsesImageSpot MagnificationField of viewVolk QuadrAsphericEquatorPeripheryRealInverted0.561300Mainster Ultra Field PRPEquatorPeripheryRealInverted0.571400Volk SuperQuard 160EquatorPeripheryRealInverted0.561600PAttern SCAn Laser(PASCAL)The PASCAL Photocoagulator is an integrated semi-automatic pattern scan laser photocoagulation system designed to treat ocular diseases using a single shot or predetermined pattern array.

Laser source:Nd:YAG laser.

Delivery device:slit lampor laser indirect ophthalmoscope (LIO)

Control system for selecting power and durationMethod for selecting spot size.

DIAGNOSTIC USE OF LASERSScanning Laser Ophthalmoscopy allows for high-resolution, real-time motion images of the macula without patient discomfort.

SLO angiography: to study retinal and choroidal blood flow.

May be used to perform microperimetry, an extremely accurate mapping of the maculas visual field.80Optical Coherence TomographyUses diode laser light in the near-infrared spectrum (810 nm) to produce high-resolution cross-sectional images of the retina using coherence interferometry.

Complications General complications:Pain Seizures.

Anterior segment complications:

Elevated IOP.Corneal damage.Iris burns.Crystalline lens burns.IOL and PC damage.Internal opthalmoplegia.

Complications(contd) Choroidal detachment and exudative RD.Choroidal ,subretinal and vitreous hemorrhage.Thermal induced retinal vascular damage.Preretinal membranes.

Complications(contd..) Ischaemic papillitis.Paracentral visual field loss and scotoma.Photocoagulation scar enlargement.Subretinal fibrosis.Iatrogenic choroidal neovascularisation. Accidental foveal burns.Lasers can. Save a childs 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...

References YANOFF AND DUKER OPHTHALMOLOGY- 3rd edition.

LASERS IN OPTHALMOLOGY A practical guide-AIIMS.

LASER SURGERY OF THE POSTERIOR SEGMENT- Steven M. BloomThank you