A. Optics 2 Lasers Lec #2 (1).pptx

Light characteristics Laser light- Tissue Interactions Light and the spectrum/Wavelengths UV -light a. UV-C b. UV-B c. UV-A d. Visible light /Colors e. IR-A f. IR-B g. IR-C Light can undergo…… Reflection Absorption Transmission Scattering a. Elastic b. Inelastic c. Raleigh /relationship to wave...

Light characteristics Laser light- Tissue Interactions Light and the spectrum/Wavelengths UV -light a. UV-C b. UV-B c. UV-A d. Visible light /Colors e. IR-A f. IR-B g. IR-C Light can undergo…… Reflection Absorption Transmission Scattering a. Elastic b. Inelastic c. Raleigh /relationship to wavelength d. Mie/relationship to wavelength Reflection and scattering of light Raleigh Scattering Raleigh Scattering Mie Scattering Raleigh and Mie Scattering Mie Scattering Raleigh and Mie Scattering Raleigh Scattering Raleigh Scattering Scattering and the eye Raleigh(Tyndall )/Mie and the… 1. Eye color a. Brown, Green ,Blue vs Grey 2. Lens cataracts  Mie in the ant part of the eye 1. Anterior chamber 2. Cornea Absorption a. tissue damage b. Energy/wavelegth of the photons Tissue depth penetration/transmission a. depends on the wavelength b. depends on the absorption c. depends on the scattering b. 1400nm is the limit Absorption characteristics Spectrum wavelengths a. UV-C b. UV-B c. UV-A d. Visible light e. IR-A f. IR-B g. IR-C  Absorptive properties by tissue consistency a. nucleic acids and amino acids b. skin and eye pigment c. macular pigment d. hemoglobin Absorption properties of ocular structures a. Cornea >> UV and IR b. Lens >> UV and IR c. Retina >> IR and UV Damage Mechanisms  Amount of absorption by the tissue  Penetration depth  Type of damage mechanism is wavelength related Types of damage mechanisms  1.Photothermal  2.Photochemical  3.Photomechanical  Heat production >>> Thermal damage mechanism a. Internal conversion b. Kinetic energy c. Temperature  Thermal damage classification (Types) 1. Photocoagulation A. protein chains B. increase in temp >>denaturation C. higher temp.>>>coagulation 1. cell shrinkage 2. membrane destruction 3. changes in collagen and muscle fibers 4. hyperchromatism D. examples of photocoagulation E. Photoshortening a. collagen fibrils b. temperature rise c. tissue change Photothermal ablation or Photovaporization a. Temperature rise b. vacuoles formation c. popcorn effect d. tissue rupture e. example 3.Photocarbonization 4. Melting 2. Thermal damage characteristics Heat conduction Exposure time Thermal relaxation time Spot size Selective photothermolysis Photochemical damage Type of light causing photochemical damage Photochemical interactions by Photosensitizers and release of toxic products (free radicals) Types of Photochemical reactions a. Photodissociation b. Dimerization c. Photoinduced Isomerization Isomers Cis to Trans Retinal Isomerization Requirements for a photochemical reaction/damage Dose dependent No threshold of energy BUT…… Delayed onset /Duration exposure Temperature factor Examples or Types of Photochemical Therapies Photoradiation by photodissociation/PDT Photothrombosis /PDT Photochemical ablation Controversy about purity of procedure Photomechanical damage/Photodisruption Ionization/Plasma formation Methods of plasma formation a. Thermionic emission b. Multiphoton absorption Plasma characteristics a. Multiple ionization b. temperature c. Fluence and/or Irradiance dependent d. pulse duration States of Matter Plasmas and the Universe Plasmas and the Universe Plasmas in life Plasma induced ablation a. Ionization>> plasma>>tissue disruption >> plasma growth >> multiple plasmas>> secondary tissue disruption >> induced tissue ablation Photodisruption /secondary effects a. Shock waves by plasma expansion >>> sound b. Tissue Thermal expansion >> tissue breakage >> spallation c. Cavitation d. spark emission Factors influencing the severity of the tissue damage in the eye 1. Type of tissue exposed 2. Wavelength 3. Duration of exposure a. >> than 10sec b. 10 microsec to 10 sec c. less than 10 microsec 4. Energy absorbed by the retinal tissue in the eye when treating - Factors: cornea ,pupil,beam, tx spot area or spot size