XM 1 Flashcards
What are the 3 types of effects that occur as a result of use of therapeutic lasers?
- Thermal effects
- Ionization effects
- Photochemical effects
What FDA class of lasers are the lasers used for eye procedures?
Class IV
What FDA class of lasers are those used in printers, CD players, and DVD players?
Class I
What FDA class of lasers are those used in barcode scanners?
Class II
What FDA class of lasers are pointers?
Class III
Starting with which FDA class of lasers are immediate skin and eye injury possible?
Class III
What is considered the “safe” limit of laser power?
5 mW
Interactions of light on biological tissue depend on what 3 characteristics?
- Wavelength
- Pulse duration
- Irradiance (power per unit area)
What is the end result of photocoagulation caused by laser light?
Denatured proteins
What rise in temperature will cause photocoagulation of tissue?
10-20 degrees Celsius
(results in tissue temperature between 50 and 60 C
What effect of therapeutic lasers is associated with the “thunderclap” and results in tissue damage?
Photodisruption (Ionizing Effect)
What temperature range does photovaporization occur in?
60-100 degrees Celsius
What temperature range does photodisruption occur in?
100-305 degrees Celsius
What are 2 examples of thermal effects?
- Photocoagulation
2. Photovaporization
What is 1 examples of an ionization effect?
Photodisruption
What are 2 examples of photochemical effects?q
- Photoradiation
2. Photoablation
What are 6 modes of laser operation?
- Continuous wave (CW) lasers
- Pulsed lasers
- Q-switched lasers
- Mode-locked lasers
- Fundamental systems
- Multimode systems
At what temperature do visual changes begin occurring in the retina?
60 degrees Celsius
Blanching begins to occur due to coagulation
At what temperature does a smoke plume result in the retina?
100 degrees Celsius
What is PDT?
Photodynamic Therapy
Same thing as photoradiation
What does photoablation do in layman’s terms?
Vaporizes the tissue by breaking bonds that bind the tissue together
What are 2 examples of lasers that interact with photothermal effects?
- Argon laser
2. Nd: YAG Laser
What is 1 example of a laser that interacts with photoablation?
Excimer laser
What is 1 example of a laser that interacts via photoradiation?
Photodynamic therapy
What is 1 example of a laser that interacts with tissue via photodisruption?
Nd: YAG laser (Q-Switched)
What are 3 methods of laser delivery?
- Biomicroscope (Slit Lamp)
- Binocular Indirect Ophthalmoscope (BIO)
- Endophotocoagulation (enter through pars plana)
What is an argon blue-green laser composed of?
70% blue (488 nm)
30% green (514 nm)
What is the wavelength of a green argon laser?
514.5 nm
What is the wavelength of an Nd-YAG laser?
532 nm
What is the wavelength of a yellow laser?
577 nm
What is the wavelength of a krypton red laser?
647 nm
What is the wavelength of a diode laser?
805-810 nm
What is a large benefit of the MicroPulse laser design?
Long off times allow tissue to cool which results in less thermal damage to the retina
What does duty cycle mean as applied to MicroPulse lasers?
Example: 5% duty cycle
On for 5 units of time, off for 95 units of time
What is a major advantage of the green argon laser?
No absorption by macular pigment
What laser is preferred over green argon lasers to treat choroidal neovascularization?
Yellow argon laser
What are the 10 layers of the retina from inner (vitreous) to outer (choroid)?
- (ILM) Internal limiting membrane
- (NFL) Nerve fiber layer
- (GCL) Ganglion cell layer
- (IPL) Inner plexiform layer
- (INL) Inner nuclear layer
- (OPL) Outer plexiform layer
- (ONL) Outer nuclear layer
- (ELM) External limiting membrane
- (PR) Photoreceptors
- (RPE) Retinal pigmented epithelium
What membrane lies directly outside of the RPE?
Bruch’s membrane
For the laser to remain effective, an increase in spot size needs an increase in what?
Increase in power
What are the 2 types of laser delivery system?
- Parfocal system
2. Defocus system
Where will a parfocal system be focused for treatment?
On the retina
As parfocal spot size increases, does the diameter of the laser at the cornea increase or decrease?
Decreases
More risk of damage
Where will a defocus system be focused for treatment?
On the retina or behind the retina
What would occur if a defocus system was focused in front of the retina?
Vitreous damage or lens damage
What is an advantage to the defocus system and when would it be utilized?
Corneal beam density decreases as spot size increases (Lower risk of damage)
Useful for when large spot size is required
What is the scale of photocoagulation lesions graded as? Which is most mild? Most severe?
1-4
1 is most mild (light, minimal constriction)
4 is most severe (heavy, total constriction, charring)
How are punctate and streaked coagulation patterns different?
Punctate style patterns appear as dots
Streaked style patterns appear as dashes
What is the anatomic center of the fovea known as?
Umbo
What is the molecule that causes neovascularization in diabetic retinopathy?
VEGF
What is the name of the laser treatment for diabetic retinopathy?
Panretinal Photocoagulation
What do black spots in the retina after laser treatment signal?
RPE has been damaged
What is peripheral laser iridotomy used to treat?
Either primary or secondary angle closure glaucoma
What 2 types of lasers are useful for performing Peripheral Laser Iridotomy procedures?
- Argon lasers
2. Nd: YAG lasers
What type of laser is used to perform PRP?
Argon Green
PASCAL (Pattern Scanning Laser)
What is the purpose of the PLI procedure?
Creates an opening in the peripheral iris to allow aqueous to pass through
Where is the opening in the iris typically made in peripheral laser iridotomy?
Underneath the upper lid
What is the purpose of laser trabeculoplasty?
To treat the trabecular meshwork to improve the outflow of aqueous
What are the 4 types of laser trabeculoplasty?
- (ALT) Argon Laser Trabeculoplasty
- (SLT) Selective Laser Trabeculoplasty
- (MLT) Micropulse Laser Trabeculoplasty
- (TSLT) Titanium Sapphire Laser Trabeculoplasty
Which type of laser trabeculoplasty is not commonly used anymore because of trabecular meshwork damage?
Argon Laser Trabeculoplasty (ALT)
When is laser trabeculoplasty typically performed?
As a last resort, once patient is on maximum medical therapy.
What is the purpose of ALT?
To scar the trabecular meshwork to increase the amount of aqueous outflow
Where is the ALT laser aimed, and how many degrees around is the first treatment?
Junction of pigmented and nonpigmented TM
180 degrees
What is the target and goal of SLT treatment?
Targets melanin in pigmented TM
Recruits macrophages to help with outflow
Does previous ALT treatment have any effects on the results of SLT treatment?
No
IOP reduction is not influenced by previous ALT
How long after SLT do the biochemical changes take place?
4-6 weeks
Delayed response
What is the main goal of MLT?
Simulate a biological response in the TM while minimizing damage to the tissue
Between ALT, SLT, and MLT, which procedure involves the smallest laser spot size?
ALT
About 50 microns
How does the spot size of MLT compare to that of SLT?
Slightly smaller
300 microns as opposed to 400 microns
Allows access to narrower angles
Is ALT a repeatable procedure?
No
Are MLT and SLT repeatable procedures?
Yes
Where is the laser focused in a YAG laser capsulotomy?
Slightly behind the lens in the vitreous
What is the purpose of YAG laser capsulotomy
Opens the opacified posterior capsule to improve patient VA and allow easier viewing of the fundus
Is an IOP spike normal to see following YAG laser capsulotomy?
Yes
What is the normal size of the opening of the posterior capsule created in YAG laser capsulotomy?
4mm
What is the average number of laser spots per eye in panretinal photocoagulation?
1200 laser spots per eye
Topical anesthesia allows for the delivery of about how many laser spots with PRP?
500-600 spots
What type of anesthesia allows for the delivery of a full treatment (1200) of laser spots in PRP?
Retrobulbar anesthesia
What is the purpose of PRP?
Kill/destroy living retina that is releasing VEGF due to being in a hypoxic state
How far around the posterior pole (macula and optic disc) are the laser spots delivered with PRP?
3 disc diameters around posterior pole and extend to the equator
What is the purpose of lasering around a retinal break?
Seals off the progression of sub-retinal fluid (SRF) that would lead to macular involvement
What is a risk of laser treatment of retinal tears?
Vitreous shrinkage may tear the retina farther
Shrinkage may occur with opacities present