Refractive Flashcards
why do pple who had RK have fluctutaions in vision?
b/c with diurnal variations in IOP, the swelling in the K causes vision changes
What is LASEK?
Remove all epi and leave hinge at the limbus and try to save the epi to put back after stromal ablation
When does DLK occur?
24-72 hrs post LASIK
What is DLK?
Inflammation of the LASIK flap. The inflammation is in the flap interface only
whats a bug that may cause keratitis post-lasik?
atypical mycobacteria- treat w amikacin
what do you do if you have macrostriae in lasik flap?
refloat the flap
what happens if you get a buttonhole in the flap?
abort the procedure. Put the flap down and put on a BCL.
how much stromal tissue do you have to ablate to correct 1D of myopia?
10-12 microns
whats the minimum stromal bed necessary to do lasik?
250 microns
what’s “coma”
a third order “higher” aberration in which light doesn’t enter pupil evenly. Pple perceive a comet shaped image
what is a lower order aberration?
myopia, hyperopia and regular astigmatism that can be corrected with glasses
what’s “higher order aberration” mean?
shit that cant be corrected with glasses, like coma, trefoil and irregular astigmatism
whats the femtosecond laser used for in LASIK and how does it work?
used to make the flap, works by photodisruption (burst of plasma breaks bonds)
whats the wavelength of the excimer photoablative laser?
193nm
who is a candidate for INTACS?
low myopia. works by flattening the central K. Or KCN pt with super steep Ks can have INTACS
Whats “prolate” mean?
steep in center
whats “oblate” mean
flat in center and steep in periphery
whats microstriae and how to treat?
striae in bowmans layer of the flap, will go away on its own
whats MACROstriae and how do you treat?
striae in full thickness of flap, need to refloat flap
whats the flap consist of?
goes through stroma! cuts K nerves therefore post-op dry eye
what is pressure induced stromal keratitis?
Looks like DLK. Usually caused by PF. High iop causes fluid to be trapped under flap interface. But when you applinate IOP will be falsely low b/c pf that fluid!!!! D/C PF
how does conductive keratoplasty work?
make burns in peripheral K 360 causes local shrinkage and central steepening (THIS PROCEDURE TREATS HYPEROPIA ONLY)
Whats the main downside of doing conductive keratoplasty?
the effect wears off
does RK last forever?
NO. overtime most pts have hyperopic shift
whats a risk of a piggyback IOL placed in sulcus in already pseudophakic eye?
adhesions can form between the IOLS. Treatment is to explant both IOLs
How do you treat stage 1-3 DLK?
PF Q1
How do you treat stage 4 DLK (sands of sahara?)
re-float the flap
who usually gets phakic intraocular lenses?
super high myopes who are not candidiates for any other type of refractive procedure
what causes the lasik flap to stick back on?
endothelial pump activity
what’s DLK actually consist of?
sterile inflammation of the flap
whats the risk if the suction doesn’t work properly while making the flap?
incomplete flap
what type of K is at high risk for a buttonhole flap?
very steep k can easily buttonhole
whats the worst SE of multifocal IOL
glare, halos , ghosting
what do you do if you “free cap” a lasik flap?
put it in BSS and put it on after you do the stromal ablation
why is doing post-lasik IOL calc so fucked up?
b/c relationship between the anterior and posterior K has changed and the keratometer relies on that
how to treat post-PRK pt with persistent epi defect?
lubricante! and put in PP if necassary
what type of refractive procedure should you do on a pt with EBMD?
PRK- Wipe off that shitty epi
what does “coupling” mean?
a principle used w LRI- if you relax in one meridian, you steepen the meridian 90 degrees away. Hence, the total spherical equiv does not change even if you do LRI
How do RK scars effect the cornea? Steepens or flattens?
Flattens K at incision and 90 degrees away through optical zone. Treats myopia
how do you tell the difference between DLK and infectious keratitis?
depth and location.
DLK- in flap interface only (ie at flap/K jxn)
INFECTION- all over flap
what happens to depth if you make a wider ablation zone?
the ablation goes DEEPER
How long should pple be off CL before LASIK?
SCL- 2d-2 wk
toric scl- 2 weeks
HCL- 2-4 wks
how does INTACS cause corneal necrosis/erosion?
loss of nutrition from underlying K to stroma above the INTACS ring
what med reduces post-op prk haze?
MMC- by reducing the number of keratocytes
1)How are lasik “touch-ups” done? 2) what if the residual stromal bed is <250 microns?
1) lift flap and reablate
2) do PRK over flap
whats the worst possible outcome with DLK?
corneal melt
how does conductive keratoplasty work?
radiofrquency applied to K stroma, creates local heat, returns through wire to THE LID SPECULUM, used to treat mild hyperopia only
whats “bioptics?”
putting in a phakic PCIOL followed by LASIK
Why would someone get a phakic IOL?
not a candidate for other types of refractive sx
eg K too thin, h/o herpes etc
what makes more glare, refractive or diffractive multifocal iols?
refractive
whats an example of a diffractive multifocal IOL?
ReStor (buy DIFFRerent things at the STORe)
What an example of a refractive multifocal IOL?
ReZOOM
Is DLK more common after microkeratome or intralase?
intralase
how far from natural lens should a phakic iol sit?
550 microns away (1 k thickness away)
whats the difference between wavefront analysis and topography?
wavefront just tells you if theres a higher order aberration, but doesn’t give you steepness map
which 2 drugs cause delayed STROMAL K healing after LASIK?
Amiodorone and accutaine
Whats the refracting power of the anterior and posterior surface of the K?
48 front, -5 back therefore 43!
what’s the most common cause of coma?
decentered ablation
whats the most common size of the optical zone?
6.5mm
whats the smallest possible optical zone before you start getting halos etc?
6.0mm
who is at risk for a free cap?
flat cornea
What are the steps in calculating post lasik K by “historical” method
1) take an avg of the pre-op ks
2) pre-op sph evquiv-post-op sphere equivalent
3) pre-op K - change in sph equiv
what type of “surprise” refraction do you often get after post-lasik ce?
hyperopic surprise. b/c k readings are falsely steep (ie myopic) so you put in a hyperopic lens
whats the most common complication of PRK?
HIgh IOP
WHat kind of visual disturbance does “spherical aberration cause? (its a type of higher order aberration?)
night myopia- bc light falls partly on retina and partly behind retina
which multifocal iol is best for pple w tiny pupils?
technis multifocal (NOT RESTOR)
what did the PERK study show? (looked at post-RK pts)
43% had hyperopic shift over time
what’s epi-lasik?
making a flap only through epi!
which type of topography map gives best estimation of central K power?
axial map (goes thru visual axis)
which type of topography map gives best estimation of peripheral K power?
instantaneous map
whats the crystalens?
accommodating IOL that moves w CB
what’s munnerlyn’s formula for calculating ablation in myopia?
optical zone^2 *sph / 3
what’s the typical optical zone in lasik?
6.5mm
what type of pupil is at risk for post-op halos?
large pupil size (ie a pupil that dilates larger than the ablation zone, so if your abl zone is 6.5 and your pupil dilates to 7, you are at risk of halos. Similarly, if you make a small ablation zone, smaller than a typical pupil diameter, you are at risk of halos)
how are the spots applied in conductive keratoplasty?
8 spots around the cornea for 0.5D
then 8 more inside them for more correction of hyperopia up to 32 spots for correction of +3D
how does the femtosecond laser work?
photodisruption (like the yag)
how does the excimer laser work?
photoablation
how long after PKP do you
1) remve sutures
2) can perform refractive surgery on the graft?
1) 12 mo
2) 16 mo
what do you do if there is blood at the lasik interface?
leave it alone!
but if there is inflammation you should lift flap and irrigate it
whats the accufocus cornea inlay?
an inlay you put in under the lasik flap, uses pinhole effect to give greater depth of focus
What are the 4 stages of DLK?
1) scattered WBC confined to perph K- steroids
2) scattered WBC in central K- steroids
3) clumped WBC in central K w scarring- lift flap
4) sands of sahara- lift flap
why should you never irrigate after removing epi in PRK?
bc the water gets absorbed, the K thickens and you underorrect
what factor may effect how well an LRI works?
age of pt
where do you do LRI?
At the steep point
the eye excyclotorts when you lie down, how does that effect cyl correction
it will be undercorrected
why is reSTOR crappy for reading at night time?
bc the pupil dilates and light enters thru the “refractive” outer rings that are meant for distance viewng
excimer lasers, iols and intraocular solutions are what class fda approval?
class 3 (pose considerable risk)
how do you manage epithelial ingrowth under the flap?
observe unless its crossing visual axis or irritating then you can lift flap and irrigate
how do radial incisions effect the K
flatten in that meridian AND flattens in the meridian 90 degrees away (as opposed to LRI or arc incisions flatten at the meridian and steepen 90 degrees away)
high myope s/p ablation may regress, whats the mech?
epi remodeling and scarring
stupid q- what the most common complication of prk
high iop from steroid use
absolute contraindications to lasik
uncontrolled RA/lupus pregnancy HIV KCN Accutane/amiodorone use
relative contraindications
h/o HSV diabetes (K sensation) dry eye allergies uveitits
how thick is the K epi?
50 microns
