what factors increase risk of ectatic disorder after lasik?
"thin corneas, high K values, young age, residual stromal bed after ablation less than 300, assymetric bowtie astigmatism, areas of superior or inferior thinning"
wahts an ideal patient for intacs (intrastromal ring segments)
low myopic keratoconus patients
what do intacs do for KC
reverse lower myopia and flatten the cornea (allowing for possible c/l use)
which multifocal IOL are refractive? Apodized diffractive? What are downsides to refractive?
ReZoom; Restore and Tecnis; higher incidence of glare
what time period after HSV/VZV infection should you avoid lasik?
"in lasik, why do you perform central ablation for myopes and peripheral ablation for hyperopes "
"in myopic ablation, central ablation will flatten the cornea and maek the cornea less dioptrically powerful; for hyperic, peripheral ablation will steepen the cornea and make it more dioptrically powerful"
"in myope, what is the shape of the post-lasik cornea? For hyperopes?"
oblate (steeper peripherally than centrally); prolate (steeper centrally than peripherally)
what is photodisruption? Give example
"applying laser to cornea tissue and turning it into plasma, which then creates microscopic tissue expansion and creation of tiny cavity; eg. Femtosecond laser, yag for capsuolotomy"
what is photoablation effect? Give example
break carbon-carbon and carbon-nitrogen bonds; eg. Excimer laser
"in pellucid marginal degeneration, where is the area of thinning"
below the protrusion
describe the stages of diffuse lamellar keratitis
"stage 1 (peripheral faint infiltrates), stage 2 (central faint infiltrates), stage 3 (dense central infiltrates), stage 4 (dense central infiltrates with flap melting)"
what are risks of flat corneas and steep corneas with lasik
free caps for flat corneas (flat corneas you dont have enough cornea for microkeratome to make flap); button hole caps for steep corneas (steep corneas are brittle)
what is the ideal vault of a posterior chamber phakic IOL from the natural lens
550 (1 corneal thickness)
how does MMC prevent corneal haze after surface ablation
reduces number of keratocytes and enzymatic activity (activatio of keratocytes leads to haze by laying down collagen and GAGs
what is Munnerlyn's formula
amount of cornea tissue removed for LASIK = (optical zone squared * spherical power of myopia) / 3
what is the PERK study and what were its findings
Prospective evaluation of Radial Keratotomy -> 43% of patietns who underwent RK had 1 diopter of hyperopia shift over 10 years
what is conductive keratoplasty and what is it used for
"radiofrequency probe is used to heat points along peripheral cornea to shrink collagen and cause central cornea steepening, resulting in cornea with more refractive power; this procedure can only correct low hyperopia without astigmatism ; used in low hyperope presbroypes to create monovision"
what meds associated with delayed cornea stromal healing
what can you put in nondominant eye of prescryopic patients wanting monovision
"alloplastic corneal inlay (acufocus), "
why is aids a relative CI for lasik?
chance of corneal infections
when does dlk and infectious keratitis occur post-lasik?
without 24 hours; usually 2-3 days postop
how do you distinguish dlk from infectious keratitis post-lasik?
"DLK starts at flap periphery, inflammation generally confined to flap interface and doesnt extend beyond flap edge, inflammation is more diffuse"
"you see epi ingrowth after lasik, what should you do first"
"observation first, most epi ingrowth doesnt affect vision"
what should you do if you get visually significant slipped flap after lasik
"refloat immediately since epithelium can grow under flap -> lift and irrigate under the flap, use cannula to stroke flap over striae"
what is the optic power of the posterior cornea
when can you take out all sutures after PK and when can you do lasik after PK
"1 year (sufficient scarring at the host graft interface), then wait 4 more months for refractive surgery since taking out sutures can induce changes"
are patietns with inactive autoimmune disease good candidates for refractive surgery
"relatively speaking yes, must be aware of risks"
what should you do if you get superiorly decentered ablation
go to canada for topography guideed lasik or prk
what is the minium stromal bed that should be left after refractive sx
what should you do to reduce astigmatism in a patient with corneal graft
arcuate keratotomy in the graft
what are risk factors for abrasions after lasik
"old age, topical anesthetic use > 5 mins before procedure, use of microkeratome over femtosecond, keepign sunction on during the reverse pass of microkeratome"
at what axis is the astimagtmism in pellucid marginal degeneration
what is epi-lasik
using blunt microkeratome to remove only the epithelium and then ablating the stromal bed
how does hyperoipc lasik work
flattens the peripheral cornea which steepens the central cornea and increases dioptic power by making cornea more prolate
"in phaco, what is cavitation"
formation of bubbles at the phaco tip resultign in lens breakdown
"with RGP overrefraction, how do you calculate the true power of the cornea"
true power = base curve of RGP + power of contact lens + overrefraction - spherical equivalent of refraction without contact lens
which viscoeleastic agent is dispersive? What are the properties
"viscoat- better coating ability to protect endothelium, more difficult to remove, causes less of IOP spike if left in the eye due to lower molecular weight"
what are cohesive agents? What are their properties
"healon/amvisc/provisc- tend to clump more due to high surface tension, easily removed from the eye, high molecular weight, more likely to cause IOP spike due to high molecular weight when left in the eye"
what cataracts associated with myotonic dystrophy? DM?
"christmas tree cataracts, sometimes PSC; PSC for dm"
how does restor multifocal implant work
"by diffraction and refraction, series of apodized rings which create a diffraction pattern, central rings are for near vision and diffracts light; and once pupils dilate past central rings, out outside refractive lens focuses the majority of light for distance; light is lost by diffraction in central rings, so patietns have difficulty seeing close in dim light at near"
how does tecnis multifocal work
ring segments extend to periphery so therefore not as dependent on pupil for near vision
what complications in CE do you get with fuchs heterochromic uveitis?
"anterior chamber hemorrhges, since fuchs associated with large and friable vessels that cross the angle and insert high into the angle, which is frequently knicked by the keratome (recommend more anterior placement of the wound)"
what disease can cause ectopia lentis with lenses dislocated inferonasally?
what is risk of general anesthesia on patietns with homocystinuria?
thromboembolic events like PE
what is orthokeratology and what are Ses
"using flat contact lens at night to push down on the central cornea and make it flatter to treat low order myopia; 73% had discomfort, also corneal edema occurred"
what do you leave nondominant eye to create monovision with lasik
what is epikeratophakia
"taking a graft cornea stroma, carving a myopic or hyperopic shape and suturing it onto recipient cornea onto bowmans layer; not effective because carving exact shape into graft was difficult, risk of epi ingrowth"
how long should you not wear soft CL before lasik? Soft toric CL? Hard CL?
"3days-2weeks; 2 weeks; 2-3 weeks, sometimes an additional month for every decade of CL use; need to get topography before lasik to make sure it normalizes"
how should you treat blood in the flap after lasik?
"if patietn 20/20 and no inflammation then observe; if inflammation or reduced vision, can lift the flap and irrigate (lifting flap risks loss of vA)"
where do you place the intacs in KC
where cornea is steep so you can flatten it
what is threshold for stability in refraction over the years
less than .5 change in refraction per year is stable
"after lasik, do you want to leave person mypopic or hyperopic"
young people love to be slightly hyperopic since they can easily focus and get sharp vision
what is root-mean-square error
deviation of wavefront averaged over the entire wavefront in laser; gives a quantifiable number to a patient's degree of higher order aberrations
what are Ses of ICL
"lens decentration (16%), cataract (0.4%), RD and sustained rise in IOP are very rare"
what are Se of clear cornea incision during cataract surgery in post-RK patient
hyperopic shift since cornea incision can risk hydration of cornea; recommend sclerocorneal tunnel incisions and aim for -1.00 sphere
what tyep of astigmatism do young people have?
"with the rule, tight eyelid causes steepening alogn 90 degree axis- eyelid loosens with age"
"after lasik, what type of organisms causes infections in first 10 days? After 10 days?"
gram positive bacteria; atypical mycobacteria or fungus after 10 days
what type of laser-tissue interaction does excimer laser get? Femtosecond? Yag for laser thermokeratoplasty? Yag for capsulotomy