Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
54 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
3 Types of Laser-Tissue Interaction effects
|
1. Thermal
2. Ionizing 3. Photochemical |
When you're blow drying your hair, use heat, ionic blow dryer to make your hair photogenic
|
|
|
2 major thermal laser-tissue interaction effects and their general characteristics
|
1. Photocoagulation
- pigment dependent - creates burn - denatures protein 2. Photovapourization - pigment dependent - make holes - localized microexplosion |
|
|
|
Ant and post segment ophthalmic laser procedures using photocoagulation and what the procedure is for
|
- PRP (saves best supply for retina)
- focal retinal photocoagulation (finding leaks in BV in DM) - laser iridoplasty (ACG) - laser trabeculoplastic (increases AH flow) |
|
|
|
Comment on photocoagulation is largely pigment-dependent
a. exception b. type of light used c. how wavelength is selected |
a. unless the laser is at a very high setting, it generally only coagulates tissue pigment
b. UV and IR lasers c. depends on absortption characteristics of pigment in target tissue. Lower frequency (longer wavelength) penetrates deeper than short |
|
|
|
Comment on the laser of these ocular pigments:
a. melanin b. Hb c. xanthophyll |
a. most commonly targeted in the eye
b. selectively avoided or targeted avoided --> laser through vitreous hemorrhage targeted --> vascularizzed lesions in veseels c. avoided because macula |
|
|
|
Comment on photocoagulation creates burns
|
- pigment absorbs laser energy and converts to heat
- heat sink effect causes pain in some laser therapies (PRP) - avoid increased energy and longer exposure time b/c will thermal effect will spread to surrounding non-targeted tissue - when laser is on high power and long exposure, tissue response changes to photocarbonization wwhere tissue becomes charred |
|
|
|
Comment on photocoagulation denatures proteisn
|
- protein denaturation seen as tissue whitening
- moderate inflammation is induced and can be beneficial to make desired scarring and adhesion as collegan contracts - desirable in laser trabeculoplastic and BPI - undesirable at other times - tissue around the burn atrophies and decreases oxygen demand (PRP for DR) |
|
|
|
Example of photocoagulation of retinal BV
|
- blood coagulation --> thrombus
- Collagen contraciton --> BV closes |
|
|
|
Photovapourization
|
- pigment dependent
- thermal alser - melanin targed - high-pwoered laser light in brief bursts - tissue vaporized by light (CO2 and H20) - localized microexplosiong - tissue change before heat dissipation into adj. structure can occur - make holes in argon LPI |
|
|
|
Ionizing laser-tissue interaction effect
|
Photodisruption AKA optical breakdown
- ionizes target tissue by strippping them of their electrons - Tissue reduced to plasma |
|
|
|
Photodisruption
- thermal/non-thermal - describe process |
- non-pigment dependent
- TONS of energy, highly localized and brief pulse (um, picosec) - Em light --> ionizing radiation - high energy photons hit target tissue and converted to thermal and kinetic energy - instantaneous, highly localized heat raise - ionization of tissue - acceleration e' collide and knock out of orbit "e' avalanche" - free e' and plasma (ions) expands, gnereating fluid and acoustic forces (sound wave), shearing tissue in all direction - quick with NO outward disspiation of heat |
|
|
|
What is photodisruption used for? example
What is photodisruption not associated with? |
1. Cleave undesired membranes in the eye
ex. Posterior capsulotomy 2. Blast holes through tissues Nd: YAG laser peripheral iridotomy - BV coagulation --> causes intraocular bleeding |
|
|
|
Where does plasma formation occur? What are the undesirable types of plasma formation?
|
a. most likely at laser's focal point, but can occur anywhere along the beam's path
b. Plasma shielding - too high laser energy plasma before focal point. - dissipates laser energy and causes undesired damage to adjacent tissues and structures (IOP pits/cracks during posterior capsulotomy) |
|
|
|
Photochemical Effects
a. when does it occur b. three major types |
a. occur when light triggers the formation of or breaks moecular bons
b. photoablation, photodynamic therapy and photosynthesis/bleaching of rhodopsin |
|
|
|
Photoablation
- dependent/nondependent - laser wavelength used - mechanism |
- non-thermal dependent
- non-pigment dependent - uses short UV wave - cleaves -C bons in cornea and removes tissue in LASIK and PRK |
|
|
|
Process of photoablation
|
- high energy, brief pulse, highly localized
- non-thermal - tissue reduced to molecular fragments - "plume" or puff of smoke - tissue removed one molecular layer at a time with submicron precision and no damage to surrounding tissue |
|
|
|
use of excimer laser
|
- produces far UV light for photoablation
- cornea absorbes far UV light well - no damage to collateral tissue - photoablation does not incite an inflammatory healing reaction |
|
|
|
Photodynamic Therapy - characteristics
|
- laser treat tissue INdirectly
- laser activates drug to destroy neovas/cancerous tissue |
|
|
|
Process of Photodynamic Therapy
|
1. Photosensitizing drug
Light-activated drug introduced to living tissue 2. Tissue irradiation Tissue exposed to UV radiation, which activates drug - neither the drug/laser along can exert effect |
|
|
|
Step 1: Photosensitizing drug
|
- IV drug binds to cell lipoprotein
- drug contains porphyrins (component of Hb der. fr animals) - absorb light and tansfer this energy to surroudning oxygen |
|
|
|
Ideal drug for photodynamic therapy
|
- selectively accmulate in the target tissue
- activated by a wavelength capable of penetrating deeply through tissue/blood - cear quicly from body to reduce skin phototoxicity |
|
|
|
Step 2 of Photodynamic therapy
Tissue irradiation |
- porphyrins uses laser energy to produce toxic oxygen species
- light catalyzes conversion of O2 into signlet oxgen and free radicals - damaged by radicals, cancer cell dies |
|
|
|
Why use laser for phtoodynamic therapy?
- restriction |
- hjghly selective (monochromatic)
- precised focused - intense (short tx time) - restr: as long as tissue is accesible to laser light |
|
|
|
Ex. of a photosensitizing drug
- what does it treat - which wavelenght activates it? |
Visudyne
- treats WET ARM - activated by 689nm laser light (red diode laser) |
|
|
|
What must be considered when choosing the best laser for a surgical procedure?
|
- tissue type
- media the laser must pass through - desired action |
|
|
|
Laser variables
|
1. wavelength
2. cumulative energy delievered 3. spot size 4. mode of operation |
|
|
|
Tissue variables in the way laser light affects ocular tissue
|
- transparency of ocular tissues and media
- ocular pigments - how loss of trasnrency affect light absorption |
|
|
|
Parts of Visible and Near-visible EM spectrum
|
Near visible
UVC (far UV) 100-290 UVB (med UV)290-320 UVA (near UV) 320-400 Visible 400-750 Near Visible IR A (near IR) 750-1400 IR B (med IR) 1400-3000 IR C (far IR) 3000-10000 |
|
|
|
Spectrum transmission of transparent vs. non-transparent ocular tissue/media
|
transparent
- similar to water - transmit wavelengths <1000nm - increase absor'n 1000-1400 - total absor'n at >1400nm Non-transparent ocular structures - depends on absoprtion char of their pigments |
|
|
|
Type of light and tissue affected
|
UVC+UVB
- cornea - when epithelium slough of, photokeratitis; seen in welder's flash or snow blindness - never reach the AQ in AC UVA - increasingly transmit by cornea - through AQ and absorbed by lens - culprit of cataract Visible light - completely trasmitted to lens, vitreous body - wavelength used to treate pigmented structures in the eye Near IR - some IR completed transmitted also and treat pigmented structures - near IR 1000--> 1400nm, lens increasingly absorbes radiation Medium and Far IR - mainly absorbed by lens (causes Glassblower's cataract) - min absorbed by cornea >1900nm --> absorbed by cornea and causes corn burns - cannot treat retina |
|
|
|
What type of light must be blocked by cataract IOL?
|
UVA
|
|
|
|
Application of Medium IR in laser
|
Laser Thermal Keratoplasty (LTK) - create a pattern of corneal burns
Laser Presbyopia Reversal - thin sclera |
|
|
|
General rule of thumb re: pigment absorption and light penetration
|
- less tissue absorption, the deeper the light can penetrate
|
|
|
|
Location of melanin
Darker fundus Tessellated fundus |
- TM
- CB - Iris stroma and pigment epithelium - RPE and choroid Darker fundus - easier to photocoagulate Tessellated funus - uneven melanin distribution in RPE |
|
|
|
Absorption char of melanin
|
- absorbs visible spectrum
--> orange/red less than G/Y - absorbs near IR but less effectively than visible light G/Y/O light --> shallow/intermediate/deep intra-retinal burns Red and IR light --> subretinal and choroidal burns |
|
|
|
Absorption char of Hb
|
- effective absorbs B/G/Y <575nm
- poorly absorbs >575 (O/R/IR) therefore, use red/IR to photocoagulate melanin-pigmented targets deep to regions of hemorrhage |
|
|
|
Absorption char of xanthophyll
|
- completely transmits wavelengths > 514 nm (green)
B and B-G laser will therally damage foveal cones (central soctoma) Y/O/R/IR --> treats subfoveal retinal lesions safely |
|
|
|
How Loss of transparency affects light transmission in cornea, AQ/VH, lens
|
Cornea
- scarring, infiltrates, edema, dystrophies, degenerations - reduce laser light transmission - risky to do anterior segment laser procedure (LPI) when the cornea is edematous (acute angle clusre attack) and predisposes px to corneal burns AQ/VH - inflammatory cells, flare, hyphema, and vitreous hemorrahge - heating denatures and coagulates protein-rich ocular fluids Lens - cataract, nuclear sclerosis and brunescences - cannot perform reitnal laser surgeies and can speed up cataract progression |
|
|
|
Laser Variables - UV wavelengths
|
Wavelengths
- UVC UVB --> absorbed by cornea; excimer lasers that emit UVC at 193nm to ablate the cornea in LASIK/PRK, epi-LASIK procedures UVA - partially cornea and aq, mostly lens not used in eye care |
|
|
|
Laser variables - visible light char
|
Visible lgiht
- transmitted by ocular media - photocoagulation |
|
|
|
Laser variables - Blue
|
Blue
- poor penetration through opacities - absorbs well by all 3 ocular pigments --> cannot be sued on or near macular - not a popular wavelength |
|
|
|
Laser variables - Green
|
Green
- poor penetration through media opcacities - some absorption by xanthophylls - absorbs well by melanin and hb - most popular for anterior segment photocoagulation (LPI and laer trabeculoplasty) and retinal photocoagulation procedures (focal and PRP) but not used at the macula |
|
|
|
Laser variables - Yellow
|
Yellow
- slightly better penetration through media opaciites - poorly absoprbed by xanthophyll --> can be used for macular photocoagulation absorbed very well by hb -->but cannot treat hemorrhage absorbs well by melanin --> good choice for a pale fundus - used fo retinal photco. procedures and will treat at deeper level than green light |
|
|
|
Laser variables - Orange
|
Orange
- fairly good penetration through opacities - used for macular photocoagulation and photocoagulation at deeper level than yellow light - poorly absorbed by Hb --> treat deeper retina even with vitreous hemorrhage - ok melanin absorption but not good choice for a pale fundus |
|
|
|
Laser variables - red
|
- macular photocoagulation, treat retina at deeper level than orange light
- used in photodynamic therapy to activate Visudyne - good penetration thru opacities - very poorly absorbed by xanthophyll |
|
|
|
Laser variables - Near Infrared
|
750-1000nm
- excellent transmiattion by clear ocular tissues, media and media opocities - poorly absorbed by xanthophyll and Hb - absobes by melanin <red --> not a good choice for a pale fundus - treats reitna at a deeper level than red light, but not as strong 1000-1400nm - lens increasing absorbs radiation, not reach retina effectively - Q switched Nd:YAG laser has a radiation output in this range (1064nm) used for non-pigment dependent (photodisruptive) procedures like posterior capsulotomy and LPI |
|
|
|
Laser variables - Med and Far IR
|
- not used for retinal photocoagulation since these wavelengths do not reach the pigmented structures in the retina
- risks are in the cornea and cataract - used in LTK to create corneal burns and in LPR to thin the sclera |
|
|
|
Laser variables - Cumulative Energy Delivered
Power/Energy Level Number of Applications Duration of Applications/Exposure Time |
Cumulative energy determines laser-tissue interaction will be thermal, ionizing, or photochemical
Increase impact on target and surrounding tissue with - increased energy level - increased # applications - longer exposure time - all incrases cummulative energy |
|
|
|
Best application of laser energy
|
- lowest effective energy setting
- fewer number of shots - shortest duration pulses |
|
|
|
Laser variables - spot size
|
Nd:YAG have fixed spot size
Argon has variable spot size - cornal CL (Lgodlmann) decreases spot size. Focused spots are more intense and must decrease power to avoid over-treatment |
|
|
|
Laser variables - mode of operation
|
Pulsed
Continous wave Q-switched |
|
|
|
Pulsed laser
|
AKA long pulse laser
- beam lasts ms pump is usually a flash lamp multiple flashes= multi pulses |
|
|
|
Laser Variable - Continuous wave laser
|
- pump must be continous and typically electric current
|
|
|
|
Laser Variable - Q-switched laser
|
- emitted as an extremely brief, powerful pulse of light
- during light amplifaction, light is held back insdier the cavity by a shuttter Q-switch until high amounts of energy builds up - enough energy accum. in resonator --> shutter opens and coherent photons are released - intense pulse ns - usually inoizing lasers and produce photodisruptive effect on tissue Q = quality factor (how well energy is being stored) |
|
