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226 Cards in this Set
- Front
- Back
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Energy level Property of Laser Theory
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Atoms & molecules have distinct energy levels. Electrons can occupy one or more of these levels and move from one level to another. see graph.
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Population Inversion Property of Laser Theory
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For laser action to occur, it is necessary to excite a MAJORITY OF THE ELECTRONS in the GROUND STATE to an EXCITED METASTABLE STATE. see graph.
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Simulated Emission Property of Laser Theory
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-An incident photon stimulates an excited to EMIT A PHOTON.
-Monochromatic Radiation -Coherent Radiation |
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Why is Monochromatic radiation produced?
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-The energy of the incident photon must be equal to the energy of the photon released when the excited electron drops to the lower energy level
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Why is Coherent radiation generated?
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The two photons are in phase with each other
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Active medium
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-Gas (e.g., Ar, Kr, HeNe, CO2, ArF)
-Liquid (e.g., Rhodamine dye used in a tunable dye laser) -Solid (e.g., Neodymium [Nd], GaAlAs diode) |
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What is Electrical Pumping?
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excitation by passing an electric current through gas or semiconducto
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What is Optical Pumping?
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excitation by absorption of photons from intense light source
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Radiant energy
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Output of a pulsed laser in energy terms (Joules)
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Radiant Power:
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Output of CW laser in power terms (Watts)
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Radiant Exposure (Fluence):
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Ratio of total emitted ENERGY v. cross-sectional area of the beam (Joules/square cm)
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Irradience:
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Ration of emitted POWER v. cross-sectional area of beam (Watts/square cm)
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Beam Size:
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Defines exposure parameters & assesses safety of beam
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Beam Waist
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Region of beam with smallest diameter
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Beam Boundary:
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AKA Beam Diameter
Can be denoted by Solid Angle, 1/e diameter, or 1/e2 |
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Solid Angle:
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For Converging/Diverging Beams, rays from the edge of the laser aperture to the focal point form a solid angle. The diameter of a cross-section of this solid cone (at any distance) will equal the beam diameer.
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1/e diameter
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-For a Gaussian fundamental mode laser beam, the intensity of the beam at the center is 1, the radius of the beam can be determined where the intensity distribution has fallen off to 1/e.
-Used for Laser Safety Calculations -63% of total power is contained within th 1/e beam |
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1/e2 diameter
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-86.5% of the total power can be measured within the 1/e2
-Used by manufacturers to describe output of lasers |
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Beam Divergence:
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Measure of the rate of increase in beam diameter with the distance from the laser.
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Angular Aperture (Cone Angle):
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-Beam emitted by Nd Yag converges to a focus (beam waist), and then diverges
- Convergence ~16 degrees -Can be compomised by wide & smaller angles |
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How can a wide angle compromise the angular aperture?
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Wide angles will MAXIMIZE:
-Spatial stability of breakdown region -The decrease in power density at points beyond focus -Aiming/focusing ability |
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How can a small angle compromise the angular aperture?
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Small angles MINIMIZE...
-ANY beam path obstruction |
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3 unique characteristics of LASER RADIATION:
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Coherent
Monochromatic Collimated |
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COHERENT Laser Radiation means:
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-A photon hits an atom, and another photon is emitted (due to STIMULATION EMISSION).
-Both photons are IN PHASE with each other. Thus, they are coherent. |
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MONOCHROMATIC Laser Radiation mean that...
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-Each of the photons have the same energy & same wavelength.
-Monochromatic output eliminates chromatic abbe & allows for selective tissue damage (b/c of selective tissue absorption) |
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COLLIMATED Laser Radiation means that...
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-The cascade process (amplification) will ONLY occur for photons moving paralled to the LONG axis of the RESONANCE CAVITY
-EMERGING rays will run paralled to each other -Usually 1 mrad |
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What two characteristics of Laser Radiation allow us to focus down to a diffraction limited spot size
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Monochomatic & Collimated
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Laser Transmission
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No interaction with tissue
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Laser Reflection:
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Specular or Diffuse
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Elastic Scattering of Laser Radiation:
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No energy is lost to tissue
Laser wavelength is unchanged |
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Inelastic Scattering of laser radiation:
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Small amt of energy is either lost
Wavelength shifted slightly to red or blue |
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Absorption of Laser radiation:
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For radiation to damage a tissue, it must be absorbed by atoms in tissue
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Absorbers of Laser radiation;
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Chromatophores
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UV absorbers
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Nucleic acids (UV-C & IR), DNA, & RNA
Proteins (UV-C & IR) Melanin |
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Visible Light Absorbers
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Hemoglobin (red absorbs least)
Xanthophyll (blue absorbs most) Melanin (Abs dec, wavelength inc) Exogenous Chromophores (Psorlens) |
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IR Absorbers
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Water due to strong vibrational bands
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What does the depth of penetration depend on?
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Absorption-wavelegth
Scattering-wavelegth & size Reflection-specular or diffuse |
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What gives the DEEPEST Depth of penetration?
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Infrared
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What will be the depth of penetration for a wavelength LESS THAN 1400?
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Longer wavelength = Greater transmission = Deeper Penetration
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What will be the depth of penetration for a wavelegth GREATER THAN 1400
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Shallow = Less penetration because there is an INCREASE in water absorption
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What UV light is absorbed in the Cornea?
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All UV-C (100-280) & some UV-A & UV-B
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What UV light is absorbed in the Lens?
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Most UV-A & UV-B (that gets past cornea)
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What light is transmitted through the cornea & lens?
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Visible (400-780)
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What absorbs the visible light that reaches the retina?
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Hb, xanthophyll, & melanin
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Which type of IR is absorbed mostly in the retina?
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IR-A (780-1400)
Loves the melanin in RPE & choroidal melanocytes |
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Which type of IR is absorbed in the lens?
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Some IR-A & a small amt of IR-B
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WHICH TYPE OF IR IS ABSORBED IN THE CORNEA?
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MOST OF IR-B & IR-C
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What can the energy of UV & visible photons cause?
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Electronic excitation
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What can the energy of infrared photons cause?
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Not high enough to cause electronic excitation
Can only increase vibration & rotation of the molecules |
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How can selective coagulation be obtained?
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Match the laser wavelength to the wavelength of maximum absorption
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What will happen to the tissue that is hit by a CO2 laser wavelegth of 10,600nm in the far IR-C range?
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Since IR-C is highly absorbed by water, the 1st cells hit will be absorbed by most of the beam.
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Where is the penetration depth the highest?
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IR-A region and the depth falls off to either side of that region
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Which will penetrate water the deepest?
A. Nd Yag with output of 1064nm B. CO2 laser in IR-C region C. Argon laser in 488 region |
Nd Yag
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How can energy be converted from an excited state to the vibrational & rotational states of the molecule?
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Internal Conversion
-Absorption of laser must raise an e- to an excited state |
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How can you INCREASE the stored kinetic energy (temperature) of a molecule?
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Two ways:
1. Internal Conversion: raising an e- to an excited state by absorption of photon 2. Direct absorbtion of the energy of an absorbed photon into vibrational & rotational states |
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What histopathologic changes are involved in Photocoagualtion (PRP) of a px with Diabetic Retinopathy?
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1. Cell Shrinkage
2. Nuclear Pyknosis 3. Hyperchromatism 4. Membrane rupture 5. Bifringence changes in collagen & Muscle |
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What are the six types of thermal damage?
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1. Photocoagualtion
2. Photovaporization 3. Photocarbonization 4. Photoshortening 5. Photowelding 6.Hyperthermia |
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Photocoagulation is defined as...
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- A 10-20o C or more rise can lead to denaturation of the tissue proteins.
- Increasing the temperature to 50-100° C can lead to coagulation (i.e., fluid tissue is changed to a gel or a solid). |
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Photovaporization is defined as...
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-As the temperature increases to 100° C and water is vaporized, hot pockets of steam create vacuoles that enlarge & rupture explosively
-"popcorn effect" |
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What type of photothermal damage is being used when a CO2 laser removes Basal cell carcinoma from a px lid?
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Photovaporization
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Photocarbonization is defined as...
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As long as there is water in the tissue, the temperature cannot climb above 100 degrees.
Once water is vaporized the temperature can rise, and the remaining tissue vaporizes & CHARS. |
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What is Laser thermokeratoplasty?
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Photoshortening of collagen fibrils to change the refractive state of the cornea
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Photoshortening is defined as...
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Heating collagen fibril to a temperature range of 58-76 degreed C, in order to break H bonds, to shrink the fibrils up to 1/3 of there original length
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Photowelding is defined as...
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Glueing soft tissues together by localized heat
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What photothermal mechanism would best describe closing corneal wounds by using localized heat?
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Photowelding
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How do photochemical changes occur?
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-UV or visible radiation is absorbed into tissue
-IR, esp. C & B, does not have enough energy to cause a photochemical effect |
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What are photosensitizers?
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-Absorbed photon raises molecule from ground state to excited singlet state
-Short singlet state has little time to interact with surrounding molecules -Molecule returns to ground state by emitting a long-wave photon or... Intersystem crossing can take place |
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How can a intersystem crossing result in a photosentizer?
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-Electron must change its spin state to a excited triplet state
-Spins are parallel -Triplet state lasts longer than Singlet state -Give more time to interact with surrounding molecules |
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Type I Photosensitizer Interaction:
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-Direct Interaction of the triplet state of the photosensitized molecule with a nearby substrate or solvent
-Results in atom/electron transfer, which yields radicals. |
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Type II Photosensitizer Interaction:
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-Interaction involves transfer of energy from triplet to singlet, which easily interacts with nearby substrates
- Results in oxidized products that are toxic to cells |
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Examples of Photochemical Rxn:
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1. Photodissociation
2. Dimerization 3. Photo-induced isomerization |
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Characteristic Features of Photochemical RXN:
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1. No threshold
2. Dose-dependent 3. Reciprocity between threshold irradiance and exposure duration 4. Delayed onset 5. Thermal enhancement |
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How can photodynamic PDT kill a tumor cell?
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Photosensitzing Drug is injected and selectively taken up by tumor. Then, laser (tuned to max absorption of drug) is focused on drug. Absorption of laser radiation by drug leads to generation of toxic species (singlet o2 or free radical). Toxic species destroys tumor.
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Photoablation is...
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The use of short pulses of UV radiation to break molecular bonds and fragment molecules
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Bio-stimulation is...
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the use of low level red light to produce analgesia and enhance wound healing.
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What process causes high irradiance of a beam to strip off electron from atoms/molecules leaving behind positive ions & free radicals?
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Dielectric Breakdown
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What is the mixture of positive ions & free radical that result from dielectric breakdown called?
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Plasma (4th state of matter): this state has some characteristics from each state of matter
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How does plasma formation occur?
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1. Ionization creates free electrons and ions
2. Plasma is the fourth state of matter with characteristics of gases and metals 3. Laser can increase temperature of the tissue up to 15,000 C (more than 2x temp. of sun), but since the energy only lasts a short time, it doesnt diffuse to surrounding tissue. NOT clinically significant!! 4. Plasma shielding - plasma can absorb some of the laser beam leading to a shielding effect of structures behind plasma |
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After a posterior capsulotomy, what will happen to the number of photons in the retina after plasma has formed behind the capsule?
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The number of photons will DECREASE behind the retina
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T/F: The formation of plasma is an all-or-none phenomenon, meaning that it must reach a certain threshold value before it can occur
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True
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What forms pressure waves?
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Plasma Expansion, Phase Changes, & Thermal Expansion
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What is it called when electrons recombine with ions?
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Spark emission
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What process is characterized by a unstable gas bubble that expands & contracts with decreasing diameter, in order to to expel microbubbles & debris?
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Cavitation
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What body organ is most susceptable to damage by a laser?
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The Eye
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What is the extent of damage from a laser a function of?
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1. Organ exposed
2. Wavelength 3. Duration of exposure 4. Energy absorbed |
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If the duration of laser exposure is > 10sec...
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photochemical damage
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If the duration of laser exposure is 10 sec...
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Photothermal damage
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If the duration of exposure is less than 10 usec
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Photodisruption
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How does the iris affect beam size?
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Larger beams may become clipped by iris
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How does spot size affect energy absorption?
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focusing to a smaller spot INCREASES energy density
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How can Nd Yag laser cause mechanical damage?
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Plasma expansion causes a "shock wave" to form, which results in an audible snap (mini-thunder)
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What is a Nd Yag laser composed of?
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Laser rod
High-relectance mirror Output coupler mirror Q-switch shutter Mode-limiting aperture |
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What is the damage mechanism of an Nd Yag Laser?
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Photodisruption
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T/F: With a Nd Yag laser, Optical breakdown is linear.
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False. Optical breakdown is nonlinear with Yags.
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What focus is most desirable when working with a Nd Yag?
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At or close to threshold energy density
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With an Nd Yag, what can working above threshold trigger?
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Unwanted plasmas anterior to target
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Why is a small cone angle not recommended for Yags?
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Smaller beams produce more anterior breakdown
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In Yags, what does a large cone angle do?
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Localizes the plasma formation closer to focus
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When is a Posterior Capsulotomy indicated?
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Opacified posterior capsule resulting in decreased VA, glare, photophobia, and loss of CS
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When is a Posterior Capsulotomy contraindicated?
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Uncontrolled IOP
Glass IOL Active Intraocular Inflammation (increase risk of CME) Corneal edema Before 3 mo post-cataract surgery |
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What must be obtained prior to Posterior Capsulotomy?
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Informed written consent:
Detailing procedure, risks, & alternatives |
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How much energy should be used to perform a Posterior Capsulotomy? How many Shots?
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Minimum energy necessary (0.6-1.5mJ)
Minimum # of shots (3-123) |
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How would u perform a crucial opening (if feasible) on a posterior capsulotomy?
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Begin 12 oclock
Progress down to 6oclock Cut across from 3-6 oclock Clean up residual tags Avoid large free floating fragment of capsule material Continue until opening is central and 3-4mm in diamtere |
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What should you do if IOL marking is ocurring during a posterior capsulotomy?
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Make a Xmas tree shaped opening from 12oclock to 430 & 730
Move focus further behind capsule |
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If Purkinje images interfere with a PC?
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Adjust the SL beam and redirect patients gaze to one side
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What is the post-op procedure for PC?
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Aproclonidine x 1 drop
Steroid x 4 days Followup: 1-4 hrs, 1 day, 1 week, Routine |
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At 1-4 hrs post-op PC, what should be checked?
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VA, IOP
HA within 2hrs - Use Analgesic HA > 2hrs - Recheck IOP Educate px on RD & Acute glaucoma |
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What are complication of PC?
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IOL pits & cracks
IOP spike Persistant IOP increase CME RD Uveitis Rupture of Hyaloid face Vitreous prolapse Iris heme Macular hole Corneal damage |
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Large IOL pits
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can cause glare & reduce VA
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IOP spike:
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Increase of >10mmHg
Occurs 4 hrs post-treatment Declines over next 24 hrs |
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Persistant IOP increase RF
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HX of glaucoma & IOP>20mmHg
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Retinal Detachment RF:
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Axial Myopia
Hx of RD in fellow eye Lattice Degeneration Vitreous prolapse Young White Males |
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What are the wavelengths for Argon Laser?
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Blue (488 nm) ~ 70%
Green (514.5 nm) ~ 30% |
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What is the output mode for Argon Laser?
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CW
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What are the fxns of Laser Lenses?
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To increase spot size in periphery
To allow tx of angle structure & retinal periphery |
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What are types of contact lenses used with Argon laser?
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Goldman: macula to periphery
Eisner funnel: periphery Rodenstock: PRP Mainster: More Magnified Rodenstock |
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What is the active medium is an Nd Yag?
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Neodymium (Nd)
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What is the crystal rod matrix in the Nd Yag?
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Yitrium
Aluminum Garnet |
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What is the output from a Nd Yag?
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Near infra-red (1064nm) Invisible
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What does eximer laser mean?
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"excited dimer"
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What is used in an eximer laser?
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Argon flouride (193 nm UV)
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What laser is used for photoablation in PRK?
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Eximer laser
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Characteristics of eximer laser:
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Highly energetic photons
Disintegration of irradiated molecules into fragments Flame-like pattern of luminance/flourescence Minimal collateral damage with tissue removal |
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What is the output of a THC: Yag?
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2.1 um (mild infrared)
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How do you steepen the cornea with a THC YAG?
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8-16 concentric spots shrinks collagen fibrils to 1/3 their original size
Will correct for hyperopia No structural damage |
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What is the active mediums in CO2 lasers?
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1. CO2-radiation emitter
2. Nitrogen-Inceases efficacy of CO2 (Excites CO2 to upper laser level) 3. Helium-Increases efficacy of CO2 (lower vibrational to ground state) |
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Where are the two principal laser transition in a CO2 laser?
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10.6 um line
9.6 um line |
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What two pumping modes can cause excitation in a CO2 Laser?
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1. Direct current discharge (discharge-excited)
2. Radio freq controlled disharge (Rf-excited) |
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What are the instrument parameter of a CO2 laser?
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Operating wavelength 10.6um
Temporal mode - CW Power range: up to 50 W |
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What is a "sealed tube" CO2 laser?
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classic glass tube filled with gas
Mirrors are at both ends of tube |
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What is a "waveguide" CO2 laser?
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Have a small cavity lined with metal or dielectric materials
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What are "axial slow flow" Co2 lasers?
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unsealed lasers that pass gas slowly in one end and out the other end
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What are "fast axial flow" CO2 lasers?
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Gas is pumped more rapidly in one end and out the other
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What is the damage mechanism of a CO2 laser?
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Photothermal
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Where is a CO2 laser absorbed at?
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-Water
-1st 20um of tissue |
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With a small spot size, focused beam, & small pulse, what type of photothermal damage is used for cutting?
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Photovaporization (100C)
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With a large spot size, defocused beam, and long pulse, what type of photothermal damage is used for cutting?
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Photocoagualtion
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What are some opthalmic uses of CO2 lasers?
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Oculoplastic surgery:
-microsurgery in highly vascularized areas -remove superficial tumors -superficial tissue destruction |
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What is the active medium in a dye laser?
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flourescent organic medium dissolved in salt
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Why are dye lasers tunable?
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Due to interactions among the electonic, vibrational, and rotational energy levels
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What is the temporal mode for a dye laser?
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CW or pulsed
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What are clinical uses of a dye laser?
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1. Retinal Photocoagulation (PRP in DR)
2. PDT |
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What is the active medium in a tunable solid state laser?
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an impurity embedded in the crystalline host matrix
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Why is a tunable solid state laser "vibronic"?
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electronic energy levels spread out due to superimposed vibrational sublevels
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What is a commercially available tunable solid stat laser?
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Titanium doped sapphire laser
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When would a visual field defect occur with glaucoma?
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After the loss of 25-35% of retinal ganglion cell
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What precedes visual field loss?
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Optic nerve damage
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What is the major limitation to making an ealry Dx of glaucoma?
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the normal variation of the optic disc & RNFL parameters
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What type of laser is used in cSLO?
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Diode laser
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How is Retinal tomography (cSLO) useful?
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Detects Macular Edema & Holes
Evaluation of rNFL |
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How is Optic Nerve tomography (cSLO) useful?
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May provide an earlier dx of glaucoma
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How is Autoflouresence tomography (cSLO) useful?
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Assess macular holes
Detection of Ealry Macular dystrophies |
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What are advantages of cSLO?
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Can be used on miotic pupils
Can be used with correction Clarity of media is not important Reproducible & Reliable 3D images Real time analysis Monochromatic Illumation |
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What are disadvantages of cSLO?
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Abbe on cornea & lens limit resolution
Lateral & avial measurement are magnification dependent Variablity in normal eyes No age/ race database yet |
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Why does fluctuation in optic disc tomography occur?
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1. IOP & cardiac pulsation
2. Misalignment b/t px & instrument |
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What RE will decrease the sensitivty, specificity, & diagnostic precision in HRT results?
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Large Myopic eyes
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What characteristics of the optic disc cause Moorefield's regression analysis to perform poorly in an HRT?
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Small or tilted discs
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Why is there significant variablity in normal eyes in HRTs?
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Large variability in the number of nerve fibers in the ON
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What are commercial instrument that use confocal scanning laser Opthalmoscopes?
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HRT I, II, III
HRA |
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What is the radiation source in a GDx?
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GaAIA diode laser
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What makes the rNFL birefringent?
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Retinal Ganglion Cell Microtubules
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How does retardation occur in a GDx?
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Incident beam splits two rays with different velocities
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What is retardation proportional to in a GDx?
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rNFL thickness
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What are the clinical uses of a GDx?
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Glaucoma & Optic Neuropathies
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What are advantage of the GDx?
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Noncontact
No pupil dilation Rapid measurement Normative Databases exist Good reproducibilty |
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Why is the new GDxVCC better than the old GDx?
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Localized thinning of the rNFL is more visible with the new GDxVCC
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What is the Nerve Fiber Indicator?
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Analagous to the number in the old GDx
Derived from AI to recognize glaucomatous px |
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What is the radiation source in a OCT?
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Superluminescent diode
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With a OCT, a high speed, fiber optic ____ is mounted onto a modified SL. This has a ____ & ____. The ____ is scanned back and forth creating a DOPPLAR SHIFT.
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Michelson interferometer
Reference & Sample arm Reference Arm |
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In an OCT, reflections from the eye travel back through the ____arm, and combine with the _____arm. Then, both arms are measured by a photodetector.
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Sample
Reference |
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The OCT signal strength is strongest when the ____
Low Coherence Interferometry ensures that the signal amplitude falls off rapidly as the delay become ____ |
reference & sample paths are equal
Mismatched |
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What is a single longitudinal scan called?
What is it analagous to? |
Optical coherence domain radiometry
Ultrasound B scan |
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What are advantages to OCT?
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Non-invasive, Noncontact
High resolution & sensitivty Topographical imaging Good reproducibitlity Normative database exists |
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What are disadvantages of OCT?
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Requires pupil dilation
Impaired Performance with CS & PSC Poor fixation leads to problems Specific retinal layers cannot be delineated |
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The acronym LASER is derived from the process of stimulated emission. What is a good example of stimulated emission?
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Pumping energy into a laser medium such that excited state electrons are induced to drop back to ground state, thereby emitted photons that have a uniform wavelength
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The process of cavitation during a Nd YAG photodisruption and in a lightning strike causes a shock wave that produces physical tissue effects. Cavitation is best described as...
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A transient gas bubble that rapidly expands and collapses emitting shock waves in the form of sound and energy in the form of light
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OCT can do all of the following except...
A. Image retina & ONH B. Measure corneal thickness C. Measure ACD D. Measure the local rate of retinal BF |
D. Measure the local rate of retinal BF
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What type of laser uses a solid lasing medium doped into a lasing cavity comprised of crystaline matrix?
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Nd YAG
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A Q-switch is used in a Nd YAG and can be described as...
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An output coupler that holds back and then time-focuses laser emission to maximize peak delivery power of the laser beam
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In a capsulotomy, to minimize damage to an IOL, one can do all of the following except...
A. limit the laser energy B. Increase the number of pulse/burst C. Use a CL to better focus the laser D. De-focus toward the px |
B. Increase the number of pulses/burst
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The output of an ArF eximer laser is in the ____ region.
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UV (193)
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T/F: IOL pits formed by a Nd YAG laser usually degrade VA
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False. IOL pits only degrade VA if they are large, and this happens rarely.
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Opticla interfaces and debris in front of a target such as the iris can decrease the threshold of plasma formation. This produces the situation where unexpected plasma formation may occur _____.
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Upstream (closer to the laser output)
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What laser output wavelength range is most absorbed by the macular yellow xanthophyll pigment?
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Argon Blue
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What is an example of an eximer laser excited by electrical current in a gas?
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Argon gas
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Which of the following laser temporal emissions has the shortest duration?
A. Q-switched B. Pulse C. CW |
Pulse (but remember that mode-locked has the shortest)
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The irradiance of a laser beam on the retina is described as the power density. This parameter directly affects the burn intensity, which can be altered by changing the power or spot size. Which of the following has the highest irradiance for an ARGON laser retina treatment, when delivered at the same duration of 100 ms?
A. 200mW, 50 micron spot B. 200mW, 100 micron spot C. 100mW, 50 micron spot D. 100 mW, 100 micron spot |
200mW, 50 micron spot
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Laser radiation can produce damage only if it is _____
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Absorbed by the tissue
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The Hc: YAG laser operates at appoximately 2 microns. When this is applied to the ocular surface it can selectively damage only the:
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Cornea
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Compared to yellow macular xanthophyll and red Hb, melanin pigment is black, and therfore will have what shape of absorption curve?
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Flat
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Treating choroidal melanoma or subretinal neo with a laser after injection of a special photosensitizing dye is often referred to as PDT. Which is consistant with what tissue damage mechanism?
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Photochemical
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Most of the tissue effect caused by a Q-switched Nd Yag is produced directly by which part of the total photodisruption process?
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Shock wave
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Changing the duration of the laser delivery can change the dominant damage mechanism. Nd YAG photodisruption is produced when laser duration is in the ______range.
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Nanosecond = photodisruption
(Photochemical = second) (Photothermal = Microsecond) |
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What is the most important factor when deciding on using a Nd YAG?
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The level of subjective interference with px daily visual needs
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What occurs immediately after an Nd YAG capulotomy?
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Mild transient IOP rise
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The GDx NFL analyzer uses what type of optical effect?
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Polarimetry
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The GDx VCC was developed to compensate for what error producing factor?
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Corneal birefringence
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The laser treatment that effectively yields an optical section of the retina analoagous to the SL cornela optic section is _____.
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Retinal thickness Analyzer
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What is analagous to a Bscan?
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OCT
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What is analogous to an Ascan?
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Optical coherence domain reflectometry
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What cLSO creates a topographical image of the ONH that is an integrated map of up to 32 images taken at different depths?
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HRT-II
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Which of the following is NOT an anatomical RF for a Narrow angle attack?
A. Shallow ACD B. Anterior Iris insertion C. Small corneal Diameter D. Long axial length |
D. Long axial length (actually short axial length)
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What is the name of the lenses used in a capsulotomy/Iridotomy to control eye movement and lid closure as well as focus the beam better on the target tissue?
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Abraham
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In a px with blue irides, Nd YAG is performed without any pre-tx by an argon laser. When dark brown irides are similarly tx, they are usually pre-tx with argon because it is needed to....
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Thin the iris
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The mechanism of iridotomy in resolving narrow angle glaucoma...
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reduces peripheral iris bombs by creating an alternate channel for the flow of aqueous from posterior to anterior chamber
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Non-invasive, CL delivered, pressure lowering tx of the trabeculum can be performed with any of the following lasers EXCEPT...
A. Argon B. Diode C. Eximer D. 532 frequency doubled Nd YAG in SLT mode |
C. Eximer
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When is a laser iridotomy contraindicated...
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1. When the cornea is too hazy to perform the procedure
2. When the ACD is too shallow 3. PAS |
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What is the most appropriate iridotomy procedure for brown irises?
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Combin Argon + Nd YAG photodisruptive procedures
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When perfroming Nd YAG iridotomy on a blue iris, one should place the plasma in the _____/
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Crypt
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What is the best setup for an Argon photocoagulative iridotomy "chipping" procedure?
A.1.0 W, 50 micron spot, 50 ms B.1.0 W, 500 micron spot, 50 ms C. 200 mW, 50 micron spot, 100 ms D. 200 mW, 250 micron spot, 100 ms |
1.0 W, 50 micron spot, 50 ms
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What anti-glaucoma medication is best as a pre- & post-iridotomy pressure management?
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Apraclonidine (iopidine)
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The mechanism of pressure lowering in a trabeculotomy is thought to be due to all of the following except....
A. trabecular puncture B. Local trabecular tighting C. Circumferential trabecular tightning D. Activation of trabecular enzymes |
Trabecular puncture
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What is the immediate goal of a retinal photocoagulation burn in treating a retinal break?
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Tissue inflammation that will later heal
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Refreactive surgery for a reduction of myopia using an exolmer laser for ablation under a ALK flap is called....
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LASIK
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The most significant complication of LASIK is...
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Corneal haze and power regression
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What laser absorbs in water, and therefore can be used to create a glaucoma filtering bleb?
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Ho YAG
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Laser goggles provide what safety measure?
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Personal protective device
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Which of the following is an engineering control (i.e. a safety feature built into the design of the laser) in a laser safety program?
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Laser Key Switch
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Laser signage for class 4 laser must read....
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Danger (also for class 3b)
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Laser signage for class 2 lasers must read....
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Class 2 = caution
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What government agency mandates the development of a laser safety program in the workplace?
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OSHA
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Opthalmic surveillance refers to....
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Checking workers prior to commencing laser activity to rule out pre-existing retinal lesions (or any other pre-existing conditions)
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Class I lasers:
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<.4mW
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Class 2 Lasers:
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< 1mW
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Class 3 lasers:
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3a: < 5 mW
3b: <500mW |
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Class 4 Lasers
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> 500 mW
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