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.
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.
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.
Coherency Monochromatism Collimated Constant Phasic Relation Ability to be concentrated in short time interval Ability to produce non linear effects
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 ???
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
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.
(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. …
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
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
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. …
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
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
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.
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.
High energy UV laser.Excited dimer.Argon fluoride(193nm) most commonlyapplied for corneal surgeries.Photoablation.
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
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
Patient should be explained about thepossible complications to avoid legalproblems to the treating physician later.
Light : Barely visible retinal blanching Mild : Faint white retinal burn Moderate : Opaque dirty white retinal burn Heavy : Dense white retinal burn
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. …
1. Dye dose = 6 mg/m2 body surface area2. Intravenous infusion over 10 min3. Treatment at 15 min after start of dyeinfusion4. Laser light wavelength of at 689 nm,irradiance of 600 mW/cm2and fluence of 100 J/cm2
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.
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.
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.
Uses diode laser light in the near-infraredspectrum (810 nm) to produce high-resolution cross-sectional images of theretina using coherence interferometry.
General complications: Pain Seizures. Anterior segment complications: Elevated IOP. Corneal damage. Iris burns. Crystalline lens burns. IOL and PC damage. Internal opthalmoplegia.
Choroidal detachment and exudative RD.Choroidal ,subretinal and vitreoushemorrhage.Thermal induced retinal vascular damage.Preretinal membranes.
Ischaemic papillitis.Paracentral visual field loss and scotoma.Photocoagulation scar enlargement.Subretinal fibrosis.Iatrogenic choroidal neovascularisation.Accidental foveal burns.
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…...
YANOFF AND DUKEROPHTHALMOLOGY- 3rd edition.LASERS IN OPTHALMOLOGYA practical guide-AIIMS.LASER SURGERY OF THE POSTERIORSEGMENT- Steven M. Bloom