Lasers in ophthalmology


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Lasers in ophthalmology

  1. 1. ROLE OF LASERS IN OPHTHALMOLOGY Presenter : Dr. Ajay Gulati
  2. 2. HISTORY  Dates to 400 BC, when Plato described the dangers of direct sun gazing during an eclipse  Czerny and Deutschmann, in 1867 and 1882, respectively, focused sunlight through the dilated pupils of rabbits  Meyer-Schwickerath undertook the study of retinal photocoagulation in humans in 1946 using the xenon arc lamp  The first functioning laser was demonstrated by Maiman in 1960. The active laser material was a ruby which emitteda radiation of 649 nm (red light) pulsed with a xenon flash lamp  First clinical ophthalmic use of a laser in humans was reported by Campbell et al. in 1963 and Zweng et al. in 1964  Argon laser was developed in 1964, L’Esperance conducted the first human photocoagulation with it  He also introduced the frequency-doubled neodymium:yttrium- aluminum-garnet (Nd:YAG) and krypton lasers in 1971 and 1972, respectively  Q-switched , mode-locked , tunable dye laser , semiconductor infrared diode laser were other sequential discoveries
  3. 3. INTRODUCTION  LASER stands for Light Amplification by Stimulated Emission of Radiation  The basic laser cavity consists of an active medium in a resonant cavity with two mirrors placed at opposite ends. One of the mirrors allows partial transmission of laser light out of the laser cavity, toward the target tissue. A pump source introduces energy into the active medium and excites a number of atoms. In this manner, amplified, coherent, and collimated light energy is released as laser energy through the mirror that partially transmits. The various lasers differ mainly in the characteristics of the active medium and the way this active medium is pumped
  4. 4. Properties of laser light that make it useful to ophthalmologists  Monochromaticity  Spatial coherence  Temporal coherence  Collimation  Ability to be concentrated in a short time interval  Ability to produce nonlinear tissue effects
  5. 5. Laser physics
  6. 6. TYPES Carbon Dioxide Neon Helium Krypton Argon Gas Nd Yag Ruby Solid State Gold Copper Metal Vapour Argon Fluoride EXCIMER Dye Diode LASERS
  7. 7. Tissue Interactions Carbon Dioxide (Photo vaporisation) Neon Helium Krypton (Photo coagulatn) Argon (Photo coagulatn) Gas Nd Yag (Photo coagulatn) (Photo disruption) Ruby (Photo coagulatn) Solid State Gold (Photo dynamic) Copper Metal Vapour Argon Fluoride (Photo ablation) EXCIMER Dye (Photo coag.) (Photo dynamic) Diode (Photo coag.) LASERS
  8. 8. DELIVERY SYSTEMS  Slit-lamp biomicroscope : most common, delivery is transcorneal, with or without the aid of contact lenses  Indirect ophthalmoscope : condensing lens , transcorneal  Endolaser probes : fiber-optic probes used within the eye  Exolaser probes : fiber-optic probes used trans- sclerally
  9. 9. PARAMETERS AND TECHNIQUES  Wavelength: choice of optimal wavelength depends on the absorption spectrum of the target tissue  PRINCIPAL WAVELENGTHS OF COMMONLY USED LASERS  193 nm - Excimer (Cornea)  488 - 514 nm - Argon (Retina)  532nm - Frequency doubled Nd:YAG  694.3 nm - Ruby  780 - 840 nm - Diode  1064 nm - Nd Yag (Capsule)  10,600 nm - Carbon dioxide (Skin)
  10. 10. Other Parameters  Power  Exposure Time  Spot Size
  12. 12. PHOTORADIATION (PDT):  Also called Photodynamic Therapy  Photochemical reaction following visible/infrared light particularlyafteradministration ofexogenous chromophore.  Commonly used photosensitizers:  Hematoporphyrin  Benzaporphyrin Derivatives
  13. 13.  Photon + Photosensitizer in ground state (S)  high energy triplet stage  Energy Transfer   Molecular Oxygen Free Radical S + O2 (singlet oxygen), Cytotoxic Intermediate   Cell Damage, Vascular Damage , Immunologic Damage
  14. 14. Photoablation:  Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy, Argon Fluoride (ArF) Excimer Laser.
  15. 15. Photocoagulation: Laser Light  Target Tissue  Generate Heat  Denatures Proteins (Coagulation) Rise in temperature of about 10 to 20 0C will cause coagulation of tissue.
  16. 16.  Photovaporization  Vaporization of tissue to CO2 and water occurs when its temperature rise 60—100 0C or greater.  Commonly used CO2  Absorbed by water of cells  Visible vapor (vaporization)   Heat Cell disintegration   Cauterization Incision
  17. 17. Photodisruption: Mechanical Effect: Laser Light  Optical Breakdown  Miniature Lightening Bolt  Vapor  Quickly Collapses  Thunder Clap  Acoustic Shockwaves  Tissue Damage
  18. 18. MODES OF OPERATION  Continuous Wave (CW) Laser: It deliver the energy in a continuous stream of photons.  Pulsed Lasers: Produce energy pulses of a few tens of micro to few mili second.  Q Switched Lasers: Deliver energy pulses of extremely short duration (nano second).  Mode-locked Lasers: Emits a train of short duration pulses (picoseconds) to femtoseconds  Pulsed pumping
  19. 19. Safety Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is  Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players.  Class II/2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power, for example laser pointers.  Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.  Class IIIb/3B can cause immediate eye damage upon exposure.  Class IV/4 lasers can burn skin, and in some cases, even scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.
  20. 20. Warning symbol for lasers
  22. 22. DIAGNOSTIC  Scanning Laser Ophthalmoscopy  Laser Interferometry/ Optical Coherence Tomography  Wavefront Analysis
  23. 23. Scanning Laser Ophthalmoscopy  In the scanning laser ophthalmoscope (SLO), a narrow laser beam illuminates the retina one spot at a time, and the amount of reflected light at each point is measured. The amount of light reflected back to the observer depends on the physical properties of the tissue, which, in turn, define its reflective, refractive, and absorptive properties. Media opacities, such as retinal hemorrhage, vitreous hemorrhage, and cataract, also affect the amount of light transmitted back to the observer. Because the SLO uses laser light, which has coherent properties, the retinal images produced have a much higher image resolution than conventional fundus photography.  study retinal and choroidal blood flow  microperimetry, an extremely accurate mapping of the macula’s visual field.
  24. 24. Tests Performed on the Scanning Laser Ophthalmoscope  Scanning Laser Acuity Potential (SLAP) Test: The letter E corresponding to different levels of visual acuity (ranging from 20/1000 to 20/60) is projected directly on the patient’s retina. The examiner directs the test letters to foveal and/or extrafoveal locations within the macula, and determines a subject’s potential visual acuity. This is especially helpful in individuals who have lost central fixation but still possess significant eccentric vision.
  25. 25.  Microperimetry / Scotometry : The SLO could visualize a particular area of the retina and test its sensitivity to visual stimuli, thereby generating a map of the seeing and non-seeing areas.
  26. 26.  Hi-Speed FA / ICG  Fluorescein and Indocyanine Green Angiography (FA/ICG) performed using the SLO is recorded at 30 images per second, producing a real- time video sequence of the ocular blood flow
  27. 27. Optical Coherence Tomography  diode laser light in the near-infrared spectrum (810 nm)  partially reflective mirror used to split a single laser beam into two, the measuring beam and the reference beam  measuring beam is directed to the retina , laser beam passes through the neurosensory retina to the retinal pigment epithelium (RPE) and the choriocapillaris. At each optical interface, some of the laser light is reflected back to the OCT’s photodetector  reference beam is reflected off a reference mirror at a known distance from the beam splitter, back to the photodetector. The position of the reference mirror can be adjusted to make the path traversed by the reference beam equal to the distance traversed by the measuring beam to the retinal surface. When this occurs, the wave patterns of the measuring and reference beams are in precise synchronization, resulting in constructive interference. This appears as a bright area on the resulting cross-sectional image. However, some of the light from the measuring beam will pass through the retinal surface and will be reflected off deeper layers in the retina. This light will have traversed a longer distance than the reference beam, and when the two beams are brought back together to be measured by the photodetector, some degree of destructive interference will occur, depending on how much further the measuring beam has traveled. The amount of destructive interference at each point measured by the OCT is translated into a measurement of retinal depth and graphically displayed as the retinal cross-section.  OCT images are displayed in false color to enhance differentiation of retinal structures. Bright colors (red to white) correspond to tissues with high reflectivity, whereas darker colors (blue to black) correspond to areas of minimal or no reflectivity. The OCT can differentiate structures with a spatial resolution of only 10 μm
  28. 28. Wavefront Analysis and Photorefractive Keratectomy  Lasers are used in the measurement of complex optical aberrations of the eye using wavefront analysis  Hartmann-Shack aberrometer
  29. 29. Therapeutic Uses • Lids and Adnexae • Anterior Segment & Posterior Segment
  30. 30. Lids and Adnexae Skin: (usually CO2 laser)  Lid Tumors : carbon dioxide laser ,benign and malignant ,bloodless but scarring, lack of a histologic specimen, and inability to assess margins.  Blepharoplasty (carbon dioxide or erbium:YAG laser )  Xanthalesma ( green laser)  Aseptic Phototherapy  Pigmentation lesion  Laser Hair Removal Technique  Tattoo Removal  Resurfing
  31. 31. Lacrimal Surgery  Endoscopic Laser Dacryocystorhinostomy
  32. 32. Anterior Segment  Conjunctival / Corneal Growths, Neovascularization  Refractive Surgery  Laser in Glaucoma  Laser in Lens
  33. 33. Refractive Surgeries  Photorefractive keratectomy  Laser subepithelial keratomileusis (LASEK)  Laser-assisted in situ keratomileusis (LASIK)
  34. 34. Photorefractive keratectomy  low myopia (up to 6D) and low hyperopia (up to 3D)
  35. 35. LASIK jjj  2 to 9 D  lamellar dissection with the microkeratome  refractive ablation with the excimer laser  IntraLASIK/Femto-LASIK or All-Laser LASIK ( corneal flap is made with Femtosecond laser microkeratome)
  36. 36. Suction Ring Microkeratome Flap Removed LASIK Flap replaced Post operative
  37. 37. Femto lasers in cataract surgery  LenSx Lasers (ALCON)  new level of precision and reproducibility  The Laser creates a) Corneal incisions with precise dimensions and geometry. b) anterior capsulotomies with accurate centration and intended diameter, with no radial tears. c) lens fragmentation (customized fragmentation patterns)
  38. 38. Lasers in Glaucoma  Laser treatment for internal flow block  Laser treatment for outflow obstruction  Miscellaneous laser procedures
  39. 39. Laser treatment for internal flow block  Laser peripheraLiridotomy &  Laser iridopLasty (GoniopLasty)
  40. 40. Laser peripheraLiridotomy
  41. 41.  ND:YAG Laser iridotomy : Q-switched Nd:YAG lasers (1064 nm)  2–3 shots/burst using approximately 1–3 mJ/burst  opening of at least 0.1 mm.
  42. 42.  Argon or Solid-State Laser iridotomy: Photocoagulative (lower energy & longer exposure) Iris color (pigment density) is the most imp factor Iris color can be divided into three categories: a) light brown : 600–1000 mW with a spot size of 50 µm and a shutter speed of 0.02–0.05 second b) dark brown: 400–1000 mW , spot size of 50 µm and a shutter speed of 0.01 second c) blue iris: 200- µm spot, 200–400 mW, 0.1 Second to anneal the pigment epithelium to the stroma , Then the spot size reduced to 50 µm and power increased to 600–1000 mW at 0.02–0.1 second to perforate
  43. 43. Complications of Laser iridotomy  Iritis  Pressure elevation  Cataract  Hyphema  Corneal epithelial injury  Endothelial damage  Failure to perforate  Late closure  Retinal burn
  44. 44. Laser Iridoplasty (Gonioplasty)  Plateau iris & Nanophthalmos: 100–200- µm spot size , 100–30 mW at 0.1 second , 10- 20 spots evenly distributed over 360º
  45. 45. Laser treatment for outflow obstruction  Laser Trabeculoplasty  Excimer Laser Trabeculostomy  Laser Sclerostomy
  46. 46.  Laser trabeculosplasty (LTP) : a) Argon laser trabeculoplasty (ALT) : 50 µm spot size and 1000-mW power for 0.1 second , 3–4° apart 20–25 spots per quadrant b) Selective Laser trabecuLopLasty (SLT) : Q- switched, frequency-doubled 532-nm Nd:YAG laser 400-µm spot , 0.8 mJ , 180° with 50 spots or 360° with 100 spots , 3–10 ns
  47. 47.  COMPLICATIONS Iritis Pressure elevation Peripheral anterior synechiae Hyphema
  48. 48. Excimer Laser Trabeculostomy((ELT)  precise and no thermal damage to surrounding tissues  ab-interno (used intracamerally) : 308-nm xenon- chloride (XeCl) excimer laser delivers photoablative energy
  49. 49. Laser sclerostomy  Nd:YAG laser, the dye laser, 308-nm XeCl excimer laser, argon fluoride excimer laser, erbium:YAG laser, diode lasers, the holmium:YAG laser etc .  Ab-externo : probe applied to the scleral surface under a conjunctival flap.  Ab-interno : through a goniolens
  50. 50. Miscellaneous laser procedures  Cyclophotocoagulation  Laser suture lysis (LSL)  Reopening Failed Filtration sites  Laser synechialysis  Goniophotocoagulation  Photomydriasis (pupilloplasty)
  51. 51. Cyclophotocoagulation  Trans-scleral Cyclophotocoagulation A) Noncontact Nd:YAG laser cyclophotocoagulation B) Contact Nd:YAG laser cyclophotocoagulation C) Semiconductor diode laser trans-scleral cyclophotocoagulation  Endoscopic cyclophotocoagulation (ECP)
  52. 52. Laser suture lysis (LSL) When lasering sutures, the flange of the Hoskins laser suture lens holds up the lid. The suture is located under the laser slit lamp lens is pressed steadily against the conjunctiva, displacing edema until a clear image of the suture is seen . The suture usually is treated near the knot. The long end of the suture will then retract into the sclera
  53. 53.  Laser synechialysis : lyse iris adhesions  Goniophotocoagulation: anterior segment neovascularization , rubeosis , fragile vessels in a surgical wound  Photomydriasis (pupilloplasty) : enlarge the pupillary area by contracting the collagen fibers of the iris
  54. 54. Lasers In Lens  Posterior Capsular Opacification : (Nd:YAG) laser posterior capsulectomy
  55. 55. Laser posterior capsulectomy Cruciate pattern Circular pattern
  56. 56. Posterior Segment  Laser in vitreous  Laser in Retinal vascular diseases  Other Retinal diseases
  57. 57. Laser in vitreous  Vitreolysis in cystoid macular edema  Viterous membranes & traction bands
  58. 58. Laser Photocoagulation In Vascular Diseases  Panretinal Laser Coagulation a) Full Scatter Panretinal Laser Coagulation b) Mild Scatter Panretinal Laser Coagulation  Focal Laser Application  Subthreshold Laser Coagulation for Retinal Disease
  59. 59. Full Scatter Panretinal Laser Coagulation  Diabetes : four accepted indications for a dense (full scatter) panretinal laser coagulation are a) Presence of vitreous or preretinal hemorrhage b) Location of new vessels on or near the optic disk (NVD) c) Presence of new vessels “elsewhere” (NVE) d) Severity of new vessels (proliferation area greater than one-fourth of the optic disk size) exposure times 100–200 ms ,a spot size of 500 μm. The laser application should lead to a mild white retinal lesion. The distance between the laser spots 0.5–1 laser spot. range of laser spots varies between 1,000 and 2,000 . It is recommended to apply laser lesions in Two to four sessions, 2 weeks apart , Regression expected after 4–6 weeks
  60. 60.  Central Retinal Vein Occlusion: main complications of a central vein occlusion apart from macular edema are neo-vascularizations of the retina and of the iris  no effect of prophylactic pan-retinal laser coagulation to prevent neovascularizati-ons of the iris. But if neovascularizations of the retina or of the iris exist,the treated eyes clearly benefit from full scatter panretinal laser coagulation
  61. 61.  Branch Retinal Vein Occlusion: characterized by macular edema and vitreous hemorrhage from retinal neovascularizations  Retinal laser coagulation done not earlier than 3–6 months.  done only if retinal hemorrhage has significantly cleared.  For the treatment of macular edema, exposure times of 100 ms and a spot size of 100 μm are recommended. The distance of 2–3 spot diameters. The area of the edema should be treated in a dense grid. After occurrence of neovascularizations a sector retinal laser coagulation is indicated.
  62. 62. Mild Scatter Panretinal Laser Coagulation  For Non-proliferative diabetic retinopathy  risk factors for treating non PDR  The 4:2:1 rule a) If either intraretinal bleeding occurs in 4 quadrants b) Or if venous beading occurs in at least 2 quadrants c) Or if intraretinal microvascular abnormalities (IRMA) occur in at least one quadrant 600 laser spots of 500 μm ,exposure times 100–200 ms spots more spaced than full scatter.
  63. 63. Focal Laser Application  Clinically significant macular edema (CSME)  It is present and should be treated by focal laser coagulation if: a) There is a clinical retinal thickening within 500 μm distance from the center of the macula b) There is hard exudation within 500μm distance from the center of the macula with retinal thickening in the bordering retina c) There is a retinal thickened area by the size of at least one papilla diameter within the distance of one papilla diameter from the center of the macula
  64. 64.  Placement of the laser coagulation spots has to be decided by fluorescein angiography  exposure times 100ms and a spot size of 100 μm with beginning power of 70–80 mW.  leads to a mild gray retinal lesion.
  65. 65. Subthreshold Laser Coagulation for Retinal Disease  Selective treatment of the RPE  Diabetic macular edema  Central serous retinopathy (CSR)  Drusen in age-related macular degeneration (AMD)
  66. 66. Focal diabetic macular edema before treatment by SRT
  67. 67. The same fundus 2h after SRT–the lesions are visible only in the fluorescein angiogram and show the pattern of treatment
  68. 68. Fundus image 6 months after SRT. The hard exudates have resolved
  69. 69. Photodynamic therapy (PDT)
  70. 70. Indications  CNVs due to age-related macular degeneration, pathologic myopia, angioid streaks and presumed ocular histoplasmosis syndrome  Retinal capillary hemangioma  Vasoproliferative tumor  Parafoveal teleangiectasis
  71. 71.  For age-related macular degeneration and pathologic myopia : i.v Verteporfin at 6mg/m2 BSA over 10 mins. Five minutes after the cessation of infusion, light exposure (laser emitting light of 692 nm) with an irradiance of 600 mW/m2 is started, delivering 50 J/cm2 within 83 s .  Angiod Streaks: light dose of 100 J/cm2 over an interval of 166 s
  72. 72. Other Uses Of Lasers in Post. Segment  Drainage of subretinal fluid / haem
  73. 73.  Retinal Breaks or Tears
  74. 74.  Intraocular tumors (RB , Melanomas )
  75. 75. THANK YOU