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basics in laser

  1. 1. BASICS IN LASER Dr P shilpa
  2. 2. Objectives • What is Laser ? • LASER history.. • LASER Properties. • How LASER is produced ? • Effects of laser. • Application of LASERs in Ophthalmology. • LASER Safety.
  3. 3. What is Laser? LASER 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.
  4. 4. LASER history • 1917 -Sir Albert Einstein created the foundations for the laser. • 1958 - C.H. Townes, A.L. Schawlow: Theoretical basis for lasers.
  5. 5. 1960 - Theodore Maiman : Built first laser by using a ruby crystal medium .
  6. 6. • 1963 - C. Zweng: First medical laser trial (retinal coagulation). • 1965 - W.Z. Yarn: First clinical laser surgery. • 1970- The excimer laser was invented in by Nikolai Basov • 1971 -Neodymium yttrium aluminum garnet (Nd.YAG) and Krypton laser developed.
  7. 7. Lasers have many important applications. • Common consumer devices such as DVD players, laser printers, and barcode scanners. • laser surgery and various skin treatments, • Industry - cutting and welding materials. • Military and law enforcement devices marking targets and measuring range and speed. • Laser lighting displays
  8. 8. Laser physics • Laser light differs from “ordinary” light in several important ways. • These differences are a direct result of the manner in which laser light is generated Fig. 1. “White” light is composed of all wavelengths, traveling in all directions. Fig. 2. Ordinary monochromatic light consists of light of approximately the same wavelength. However, the light is not traveling in one direction.
  9. 9. PROPERTIES OF LASER LIGHT • Monochromatic (emit only one wave length) • Coherence (all in step with one another-improve • focusing ) • Polarized (in one plane-easy to pass through media) • Collimated (in one direction & non spreading ) • High energy (Intensity measured by Watt J/s)
  10. 10. LASER Vs. LIGHT LASER LIGHT  Simulated emission  Monochromatic.  Highly energized  Parallelism  Coherence  Can be sharply focussed.  Spontaneous emission.  Polychromatic.  Poorly energized.  Highly divergence  Not coherent  Can not be sharply focussed.
  11. 11. How LASER is produced ? Light is a form of energy at which the human eye is sensitive
  12. 12. 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. • When light is passed through certain kinds of materials, the photons may excite electrons around certain atoms into the next higher energy level
  13. 13. 3 Mechanisms of Light Emission 1. Absorption 2. Spontaneous Emission 3. Stimulated Emission Therefore 3 process of light emission:
  14. 14. Absorption . A photon of the “right” energy can be absorbed and “bump” an electron into a higher energy level. E2
  15. 15. Spontaneous Emission An excited electron falls back to its lower energy level, releasing a photon in a random direction.
  16. 16. Stimulated Emission A photon strikes an excited electron. The electron falls to its lower energy level, releasing a photon that is going in the same direction as, and is in exact phase with, the original photon. Note that whereas only one photon strikes the atom, two photons leave it—the original photon plus the emitted photon.
  17. 17. Background Physics • Stimulated emission is the basis of the laser action. • The two photons that have been produced can then generate more photons, and the 4 generated can generate 16 etc… etc… which could result in a cascade of intense monochromatic radiation. • The natural state of matter -most electrons - lowest energy levels.
  18. 18. • One requirement - most “elevatable” electrons must be at their higher energy level before the light enters the medium. • Such a situation is called a population inversion. • To create a population inversion-energy must be supplied to the medium • External flashes of light (surrounding the solid crystal with a helical flash tube) • Electric current passing through the gas
  19. 19. THREE BASIC COMPONENTS • A Laser Medium e.g. Solid, Liquid or Gas • Exciting 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
  20. 20. The Resonator- • The energy of the emitted laser beam - increased still further by causing the light beam to traverse the material multiple times. • This is accomplished by placing a mirror over each end of the crystal or gas tube so that the distance between them is an even multiple of the laser light’s wavelength. • The coherent light beam is reflected back and forth becoming more and more intense. If the “exciting” energy is supplied in brief pulses, laser output of higher energy levels (in pulses) can be obtained.
  21. 21. LASER INSTRUMENTATION Three Main Components – • Console: laser medium and tube, power supply and laser control system. • Control Panel: dials or push buttons for controlling various parameters & standby switch as a safety measure. • Delivery System
  22. 22. Delivery systems • Transpupillary: - Slit lamp - Laser Indirect Ophthalmoscopy • Trans scleral : - Contact - Non contact • Endophotocoagulation.
  23. 23. 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.
  24. 24. Laser indirect ophthalmoscope. • Advantages : • Wider field(ability to reach periphery). • Better visualization and laser application in hazy medium. • Ability to treat in supine position. • Disadvantage : difficulty in focusing. • Difficulty to standardize spot size. • Expensive. • Un co-operative patient. • Learning curve.
  25. 25. MODES OF LASER OPERATION • Continuous Wave (CW) Laser: deliver - 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.
  26. 26. CLASSIFICATION OF LASER • Solid State Ruby Nd.Yag Erbium.YAG • Gas Ion Argon Krypton He-Neon CO2 • Metal Vapour Cu Gold  Dye Rhodamine  Excimer Argon Fluoride Krypton Fluoride Krypton Chloride  Diode Gallium-Aluminum Arsenide (GaAlAs)
  27. 27. LASER TISSUE INTERACTION : TISSUE VARIABLE:  Transparency  Pigmentation  Water Content LASER VARIABLE
  29. 29. THREE TYPE OF OCULAR PIGMENT Effective retinal photocoagulation depends – • how well light penetrates the ocular media • how well the light is absorbed by pigment in the target tissue • Haemoglobin:  Argon Green are absorbed - 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, Choroid  Argon Blue, Krypton  Pan Retinal Photocoagulation, and Destruction of RPE
  31. 31. Light - tissue interactions light Thermal effectsPhotochemical effects Ionizing effects Photoradiation eg. Dye laser Photoablation eg. Excimer laser Photocoagulation Argon, krypton,dye,Nd:YAG Photovapourization CO2 laser Photodisruption eg. Nd:YAG laser
  32. 32. Thermal Effects (1) Photocoagulation: Laser Light  Target Tissue  Generate Heat -Tissue temp.:increases from 37 deg c to 50 deg. C or higher  Denatures Proteins (Coagulation) Risein temperature of about 10 to 20 0C will cause coagulation of tissue.
  33. 33. Panretinal photocoagulation (PRP) ctd 1. Proliferative diabetic retinopathy with high risk characteristics 2. Neovascularisation of iris 3. Severe non proliferative diabetic retinopathy associated with-poor compliance for follow up-before cataract surgery-renal failure-one eyed patient and-pregnancy 4. central retinal vein occlusion, branch retinal vein occlusion, 5. sickle retinopathy, 6. Eales disease and IRVAN (idiopathic retinal vasculitis, aneurysms, and neuroretinitis ) Indications
  34. 34. Thermal Effects (2)Photovaporization LaserLight  TargetTissue  increasetemp of cellular and extacellular water to 100 degree  steam and (vaporization)   Heat Cell disintegration   Cauterization Incision eg..Femtosecond laser
  35. 35. • The carbon dioxide laser used photovaporization and photocautery. • Advantage - bloodless incision by sealing blood vessels and lymphatic tissue in its path. • Intravitreal photocautery -used • Mainly used in Laser iridotomy. • Complication- Bruch’s membrane rupture → CNV.
  36. 36. FEMTOSECOND LASER Mode-locking -pulses of light of extremely short duration, on the order of picoseconds (10−12s) or femtoseconds (10−15s). Indications 1. Clear Corneal Incisions in LASIK it replaces a mechanical device (microkeratome) to create a precise corneal flap, also in cataract surgery to create the incision 1. Capsulotomy 2. Phacofragmentation
  37. 37. Photochemical effcts Photoablation: • Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy, Argon Fluoride (ArF) Excimer Laser. Contd. … Is a form of ultraviolet laser • Used in delicate surgeries such as eye surgery eg ;LASIK
  38. 38. PHOTOCHEMICAL EFFECT Photoradiation OR Photodynamic therapy (PDT) • 42°C and 52°C temp • Photoradiation by red (630 nm)- cytotoxic free radicals in a tumor previously sensitized by a hematoporphyrin-derived uptake. • The most common - PDT. • This new treatment modality combines low-power diode lasers (689 nm) with an infusion of verteporfin to ablate subretinal neovascular membranes and treatment of various tumors. • The advantage -over conventional photocoagulation -lower energy levels result in much less damage to adjacent normal tissue E.G. Treatment of Ocular tumours and CNV
  39. 39. Photodisruption: Extremely high irradiance delivered - very short exposure - small spot  electrons - energized from molecules - target tissue (microscopically localized temp. rise from 37 deg. c to 1500degc)  collection of free electrons and ions – plasma  Rapid expansion of the plasma creates acoustic and shock waves  combines with latent tissue stress, incise the target tissue  Tissue damage Contd. …
  40. 40. Nd:YAG laser • (neodymium-doped yttrium aluminum garnet) is a crystal that is used as a lasing medium for solid-state lasers. • Nd:YAG lasers typically emit light with a wavelength of 1064nm, in the infrared. Applications • Correct posterior capsular opacification • Peripheral iridotomy in patients with acute angle-closure glaucoma. • Frequency-doubled Nd:YAG lasers (wavelength 532 nm) are used for pan-retinal photocoagulation in patients with diabetic retinopathy.
  41. 41. [ - The most common laser source used is the Nd:YAG 1064-nm. Methods of pulsing and Nd:YAG laser:- 1)Q- switching 2)mode- locking
  42. 42. LASER IN ANTERIOR SEGMENT CORNEA: Laser in Keratorefractive Surgery: • Photo Refractive Keratectomy (PRK) • Laser in situ Keratomileusis (LASIK) • Laser Subepithelial Keratectomy (LASEK) • Epi Lasik Laser Thermal Keratoplasty Corneal Neovascularization Retrocorneal Pigmented Plaques Laser Asepsis
  43. 43. PRK LASIK
  44. 44. LASER IN GLAUCOMA  Laser Iridotomy, Laser Iredectomy  Laser Trabeculoplasty (LT)  Selective Laser Trabeculoplasty
  45. 45. ARGON LASER TRABECULOPLASTY Mechanism of action:Mechanical. Biological.
  47. 47. LASER IN LENS • Posterior capsulotomy(YAG) • Laser phacoemulcification • Phacoablation LASER IN VITEROUS • Viterous membranes • Viterous traction bands
  48. 48. Posterior capsulotomy(YAG)
  49. 49. LASER TREATMENT OF FUNDUS DISORDERS  Diabetic Retinopathy  Retinal Vascular Diseases  Choroidal Neovascularization (CNV)  Clinical Significant Macular Edema (CSME)  Central Serous Retinopathy (CSR)  Retinal Break/Detachment  Tumour
  50. 50. Retinoblstoma before treatment Retinoblastoma after thermotherapy
  51. 51. DIAGNOSTIC USE OF LASERS • Scanning 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 macula’s visual field.
  52. 52. 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.
  53. 53. Complications • General complications: • Pain • Seizures. • Anterior segment complications:  Elevated IOP.  Corneal damage.  Iris burns.  Crystalline lens burns.  IOL and PC damage.  Internal opthalmoplegia.
  54. 54. Complications(contd…) • Choroidal detachment and exudative RD. • Choroidal ,subretinal and vitreous hemorrhage. • Thermal induced retinal vascular damage. • Preretinal membranes.
  55. 55. Complications(contd..) • Ischaemic papillitis. • Paracentral visual field loss and scotoma. • Photocoagulation scar enlargement. • Subretinal fibrosis. • Iatrogenic choroidal neovascularisation. • Accidental foveal burns.
  56. 56. PREVENTION OF LASER HAZARDS  Engineering Control Measure: laser housing filters and shutter for safe observer viewing  Personal protective devices, like protective eye wear or goggles with side shields, protective clothes may be included.
  57. 57. New Developments Pattern Scan Laser:(pascal)
  58. 58. PASCAL PATTERN SCAN LASER:(Pascal) Offering multiple, patterned burns in a single-session procedure.  Improved precision  Safety  Patient comfort  Significant reduction in treatment time.
  59. 59. CONCLUSION Light Amplification by the Stimulated Emission of Radiation). PROPERTIES  Simulated emission  Monochromatic.  Highly energized  Parallelism  Coherence  Can be sharply focussed MECHANISM:1 Absorption 2 Spontaneous Emission 3 Stimulated Emission • THREE BASIC COMPONENTS • A Laser Medium • Exciting Methods • Optical Cavity (Laser Tube)
  60. 60. Light - tissue interactions light Thermal effectsPhotochemical effects Ionizing effects Photoradiation eg. Dye laser Photoablation eg. Excimer laser Photocoagulation Argon, krypton,dye,Nd:YAG Photovapourization CO2 laser Photodisruption eg. Nd:YAG laser
  62. 62. Thank you