Laser Vision Flashcards
What do lasers do
Evaporate, melt, break down tissue
The light emitted from a laser is _____________, that is, of one wavelength (color)
Monochromaticity
Properties of laser
- monochromatic
- directional
- coherent
What are we concerned about in the 4 basic interactions of light when it comes to lasers?
Absorption
What is the number one ability of the ophthalmic lasers
Ability to be focused and absorbed by collagen
What are some things lasers are used for in ophthalmology
- corneal refractive surgery
- retina (photocoagulation)
- lens (cataract)
- Iris (glaucoma)
To open up an pacified lens capsule resulting from prior extracapsular cataract surgery
Posterior capsulotomy
Removal of corneal tissue by high energy photon directly breaking molecular bonds with sufficient photon energy
PhotoAblation by Excimer Laser
What is the photon energy of Excimer Laser
193nm, 6.4 eV energy
Biggest risk of lasers
Not reversible
Importance of pulsed laser
Molecular breakdown
The nano-second pulsed laser
Makes craters here, doesn’t melt!
What does lasik stand for
Laser-assisted-in-situ keratomileusis
Steps of LASIK
- Flap created in 100 microns of cornea
- Lift flap
- Excimer laser ablation
Why is LASIK better for the patient than PRK?
LASIK goes underneath the epithelium and then puts the epithelium back over it for protection. PRK strips the top most layer, causing a lot of pain for patient in the first few days
What does SMILE stand for
Small-incision lenticulate extraction
Steps of SMILE
- Lamellar cut
- Lenticular creation
- Lenticular separation
- Lenticule removal
- Reshape cornea
NO LASER
To correct myopia, we want
Less optical power
Less corneal power means
Decreased corneal curvature (flatter)
What we want when you correct myopia with laser-vision correction
Less optical power and decreased curvature
What we can do to correct myopia in laser-vision correction
Flatten the cornea
Remove the central tissue
What part of the eye do we hit with the laser?
Optical zone
What is the golden standard for laser surgery
Ablation depth= (optical zone)^2 x ((myopia correction)/3)
To correct myopia we want
Less optical power
Less corneal power means
Decreased corneal curvature (flatter)
What do we want when correcting myopia
Less optical power Decreased curvature (center)
What can we do to correct myopia
Flatten the cornea
Remove the central tissue
What part of the cornea do we want to flatten when laser correcting for myopia
Optical zone that is the size of a scoptopic pupil
What shape do we move from the cornea when we correct for myopia
Positive meniscus, reduced optical power
Munnerlyn formula
Ablation depth= (optical zone)^2 x ((myopia correction)/3)
For hte same myopia correction, consider increasing the optical zone by a factor of the square root of 2. The maximum ablation depth…
Increases by a factor of 2
Two myopic eyes, -2.00 and -6.00. The maximum ablation depth in the -6.00 eye, compared to the -2.00 eye is
More by a factor of 3
Pre op and post op LASIK corneal curvature in myopia
Post op the corneal curvature will be flatter in someone being corrected for myopia
To correct hyperopia, we want
More optical power
More corneal power means
Increased corneal curvature (steeper)
What do we want when correcting for hyperopia?
More optical power Increased curvature (center)
What can we do when laser correcting for hyperopia
Steepen the cornea
Remove peripheral tissue
What is the shape of the tissue that is removed from the hyperopic eye during laser correction?
Minus meniscus
What does the ablation profile look like in hyperopia post op
Doughnut
What happens to the CCT in hyperopia after laser surgery?
Nothing, the CCT is the same because the peripheral tissue is what was removed
The corneal curvature went from 41.5 to 49.9, what is the degree of hyperopia that was corrected?
6-7 degrees of hyperopia
