Final Review Flashcards
what does LASER stand for
Light amplification of stimulated emission of radiation
Characteristic properties of photons
- in the interaction of radiation with matter, radiation behaves like particles called photons. PHOTONS=PARTICLES
- photons are always moving with the speed of light in a vacuum. Attempt to stop a photon=absorption
- photons travel in straight lines
- photons have a zero rest mass but never occur at rest
Electron volt
Energy carried by a single photon
-the amount of energy that an electron gains while moving through a potential difference of 1 V
Electrons that orbit the atomic nucleus exist
ONLY IN DISCRETE ENERGY LEVELS
Bohr atom model
An electron can jump to a _____ energy level by emitting a photon
Lower
Bohr
A electron can jump to a _____ energy level by absorbing a photon
Higher
Bohr
Spontaneous emission
- An electron that stays in an excited state for <8-10s and then jumps to a LOWER LEVEL emitting a photon in the process
- an atom will absorb only photons whose energy is the exact amount needed to raise electrons up by 1 energy level and will release that same wavelength of enegery as we photon
Stimulated emission
If a photon of the precise wavelgnth passes Ana electron in an elevated energy level of equal gain in energy, that electron will emit a photon of that same wavelgnth, direction, phase, coherence, and polarization
Two photons will leave for each photon that enters=amplifying the beam
Fluorescence and Phosphofluorescence
- stand out because the luminous flux EMITTED at the fluorescent wavelengths by a fluorescent substance may be FAR GREATER than the luminous flux INCIDENT at those wavelengths
- the energy that drives the fluorescent radiation comes from an incident HIGHER FREQUENCY radiation (UV)
- when a metastable state with a long lifetime is populated by incident radiation, the material may continue to glow or emit radiation long after the original source is removed
What is the distinction between fluorescence and phosphofluoresence
Matter of time
Population inversion: electrons at LOWER energy levels ____protons
Absorb
Population inversion: electrons at HIGHER levels _____protons
Emit
Application occurs when
Mor eeelctrons are at an elevated state than at a lower energy state
Cavity oscillator
- optical cavity
- 2 parallel Mirrors=feedback loop with active medium between the mirrors. Mirrors have optical coating-reflective proptosis
- builds the strength of the avalanche
- stimulated emission causes application of the signal within the optical resonator
Q switching
- NANOSECOND DURATION
- higher power intensity
- shutter or light modulator
- energy builds and is then released in sudden bursts
- plasma formation
- PHOTODISRUPTIVE EFFECT
- less affected by pigmentation
Laser light characteristics
Coherence
Monochromatic
Collimated
Photochemical effects
Photoradiation
Photoablation
Photoradiation
- Photochemical
- IV administration of photosensitizing agent taken up by target tissue-free radicals
- PDT therapy
Photoablation
Photochemical
- pigment independent
- higher energy UV light=excimer laser (cleaves bonds)
- NON THERMAL
Photothermal effects
Photocoagulation
Photovaporization
Photocoagulation
Phototheramal
- ALT
- targets melanin and hemoglobin
- denatures protein, contracts collagen, coagulates blood
- 10-20 decrease C increase in temp
Photovaporization
Photothermal
- targets melanin
- water turned into steam, tissue turned to CO2 and H20
- 60-100* C increase in temp
Mechanical disruption
Photodisruption
Photodisruption
- mechanical disruption
- YAG CAP/LPI/VITREOLYSIS
- reduces tissue to plasma, modules stripped of electron. NO COAGULATION** (why there is blood on LPI with Nd:YAG 1064 vs using Argon)
- PIGMENT INDEPENDENT
- explosive force
- pulse travels back towards surgeon
- 15,000* C increase in temp
Pigment dependent lasers
Argon
Diode
Pigment independent laser
Nd:YAG 1064nm
Femtosecond
Excimer
Nd:YAG characteristics
- 1064nm
- solid state laser (level 4)
- Q switched
- continuous or short pulsed
- neodymium YAG
- photodisruptive
Nd:YAG 532
- 532nm
- Freqyency doubling and Q switches
- photocoagulation/sublethal photostimualtion pigment dependent
UV range
200-400
UVC
200-280
UVB
280-315
UVA
315-400
Visible light
400-780
IRA
780-1400
IRB
1400-3000
IRC
3-1000um
Near infrared
IRA
780-1400nm
Far infrared
IRB and IRC
1400-3000nm
3-1000um
UV light absorbed within the
Cornea
<400nm
Visible light absorbed with in the
Retina
400-700
Near infrared light absorbed within the
Retina
700-1400
Far infrared light absorbed within the
Cornea
1400nm+
Tissue variables
Melanin
Hemoglobin
Xanthophyll
Melanin
- absorbs across entire visible spectrum
- absorbers infrared less effectively
Hemoglobin
Absorbed green and blue wavelengths very well
Xanthophyll
Absorbs blue well
Use red or IR for macula
Class I ANSI standard
Very low powered laser (<0.5 uW)
- no eye or skin hazard from full day exposure
- no labeling requirements are needed
- lasers inside CD/DVD players
Class II ANSI standard
Low powered laser (<1mW)
- no eye hazard from intrabeam exposure within short period of time
- basic laser pointers/surveying lasers
Class IIIa
- visible beam with power <5mW
- damage on accidental exposure through optical aid
- more powerful laser pointers
Class IIIb
- Eye and skin hazard
- viewed only through diffuse reflection from distance over 50mm for <10s with diffuse image diameter greater than 5.5mm
Class IV lasers
- eye andskin hazard from intrabeam and diffuse relcfection
- fire hazard
What class is an Nd:YAG 532nm (freq doubled)
Class IIIb
Which class of lasers is an Nd:YAG 1064
Class IV
Laser safety
Governing bodies and professional organizations
-ANSI,FDA, OSHA
Administrative controls
-laser safety officer
Practice guidelines
-american society for laser medicine and surgery (ASLMS)
Protective equipment
-warning signs, skin protection, smoke evacuation
What grading system uses Roman numerals to describe the degree to whch the angle is closed
Sheie’s system
Which grading system uses numeral to describe the degree to which the angle is open
Shaffer
Which are pathological? Iris processes or peripheral synechiae
Synechiae
What is the general mechanism of action for a laser trabeculoplasty
Increase Aqueous outflow mainly through the TM
Indications for laser trabeculoplasty
POAG NTG OHTN PDG PSG
Positive predictors for laser trabeculoplasty
<40yo
Moderate to heavy TM pigment
Clear cornea
Thermal relaxation time
Time required by melanin to convert electromagnetic energy into thermal
-1 MICROSECOND
Argon laser trabeculoplasty: mechanical or biological MOA?
Both
What are the pre op drops for ALT and SLT
Alphagan 15-30m prior
Proparacaine
Can you repeat an ALT
Highly recommended NOT to-increases complication and 50% need filtration surgery to lower IOP within 6 months of repeated ALT
SLT: mechanical or biological MOA?
Biological only
Is SLT a cold or hot laser and why
Cold
Thermal relation time is not met, so no burns occur
Is SLT a safe and effective initial therapy?
Yes
-based upon multiple studies
SLT laser settings
Energy-0.8-1.2mJ Spot size-400microns fixed Duration-3ns fixed Pulses-1 Amount of burns ~100/360
What are the post opt drops of SLT
Alphagan
NO STEROIDS!! Oral Tylenol PRN or optical NSAID if absolutely needed
What is the time frame for an SLT to be the most successful
12-60m
-80% @ 1 yearand 50% at 5 years
Will an SLT be successful if the patient DI not repsond to a PGA
No
Alvarados insights
Should you perform an SLT on patient’s with pigment dispersion syndrome/glaucoma?
Yes-be more cautious
-10-20* at a time-test area
Can you repeat an SLT
Yes
-no as effective the second time
