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how do radial incisions affect astigmatism of the cornea
flatten the cornea at the meridian of the incision AND 90 degrees away
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how do arcuate limbal relaxing incisions affect astigmatism of the cornea
"flatten the cornea at the meridian of the incision, steepen the cornea 90 degrees away"
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what is coupling ratio?
amount of flattening induced by an incision divided by the amount of steepening 90 degrees away
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what is the coupling ratio of LRI and arcuate incisions? Transverse incisions (straight incisions parallel to the limbus)
1 (spherical equivalent remains unchanged); >1 (induces hyperopic shift)
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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"
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wahts an ideal patient for intacs (intrastromal ring segments)
low myopic keratoconus patients
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what do intacs do for KC
reverse lower myopia and flatten the cornea (allowing for possible c/l use)
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which multifocal IOL are refractive? Apodized diffractive? What are downsides to refractive?
ReZoom; Restore and Tecnis; higher incidence of glare
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what time period after HSV/VZV infection should you avoid lasik?
1-2 years
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"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"
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"in myope, what is the shape of the post-lasik cornea? For hyperopes?"
oblate (steeper peripherally than centrally); prolate (steeper centrally than peripherally)
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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"
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what is photoablation effect? Give example
break carbon-carbon and carbon-nitrogen bonds; eg. Excimer laser
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"in pellucid marginal degeneration, where is the area of thinning"
below the protrusion
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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)"
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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)
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what is the ideal vault of a posterior chamber phakic IOL from the natural lens
550 (1 corneal thickness)
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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
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what is Munnerlyn's formula
amount of cornea tissue removed for LASIK = (optical zone squared * spherical power of myopia) / 3
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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
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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"
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what meds associated with delayed cornea stromal healing
"accutane, amiodarone"
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what meds asscoatied with delayed epi healing
"anihistatmines, sumatriptans, hormone replacement therapy"
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what wavelength of light is used by excimer laser (argon)? Yag? Femtosecond?
193; 1064; 1053
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what wavelenght of light is rhodopsin most sensitive to?
510
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what is the best choice for lasik vs prk for embd patient
prk
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why is iol calculation for cataract person hard after lasik procedure
the topography overestimates corneal curvature
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who is ideal candidate for intrastromal corneal ring patients
low myopic keratocnous patients; the rings flatten thte cornea to allow KC patients to use RGPs
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what is lasik CI in trab patients
"microkeratome can cause dramatic rise in IOP, sunction ring has difficulty grasping eye in presence of bleb, IOP may be falsely law after procedure"
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what is the complication of intralase for flap creation
diffuse lamellar keratitis
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what happens in lasik if you irrigate stroma with bss prior to ablation? Leave stroma unattended for a logn period of time prior to ablation?
undercorrects the result because extra water is absorbed and prevents adequate ablation; overcorrects because cornea dehydrates and laser ablates too much
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"when you sleep at night, what happens to your cornea in RK patients"
"cornea tends to absorb water between the incisions, swell, and flattens causing hyperopic shift"
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how do wavefront optimized lasers help to smooth the transition from optical zone to the periphery
smooth the transition from the optical zone to the periphery which helps keep prolate shape of cornea
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when can you do lasik after stopping soft CL?hard card?
3-14 days; 2-3 weeks
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"after lasik, what complications are diabetics at higher risk for?"
"corneal anesthesia, epi ingrowth, epi defect (no higher risk of dlk in diabetics)"
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what pupil size do you get halos and and glare after refractive surgery
7mm (most lasers use optical zone of 6.5mm)
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what are Cis to lasik?
"PDR, pregnant and nursing mothers (can have unstable refractions, wait 3 months after nursing), patients taking accutane (prevents corneal wound healing); surprisingly keloid formers do well"
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what happens if you decrease steroids after lasik
can reduce the treatment effect (may want to do this if you overcorrect)
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how does size of flap hinge affect corneal nerves
"the larger the flip hinge, the less corneal nerves are cut"
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what medications are associated with meibomian gland destruction
"accutane, amiodarone"
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what are the ways in which lasers deliver energy to the cornea
"flying spot (uses spots in alternating sizes), braod beam laser, slit beam laser"
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what can you put in nondominant eye of prescryopic patients wanting monovision
"alloplastic corneal inlay (acufocus), "
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why is aids a relative CI for lasik?
chance of corneal infections
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when does dlk and infectious keratitis occur post-lasik?
without 24 hours; usually 2-3 days postop
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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"
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"you see epi ingrowth after lasik, what should you do first"
"observation first, most epi ingrowth doesnt affect vision"
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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"
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what is the optic power of the posterior cornea
minus 6d
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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"
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are patietns with inactive autoimmune disease good candidates for refractive surgery
"relatively speaking yes, must be aware of risks"
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what should you do if you get superiorly decentered ablation
go to canada for topography guideed lasik or prk
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what is the minium stromal bed that should be left after refractive sx
250
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what should you do to reduce astigmatism in a patient with corneal graft
arcuate keratotomy in the graft
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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"
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at what axis is the astimagtmism in pellucid marginal degeneration
180
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what is epi-lasik
using blunt microkeratome to remove only the epithelium and then ablating the stromal bed
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how does hyperoipc lasik work
flattens the peripheral cornea which steepens the central cornea and increases dioptic power by making cornea more prolate
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"in phaco, what is cavitation"
formation of bubbles at the phaco tip resultign in lens breakdown
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"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
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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"
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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"
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what cataracts associated with myotonic dystrophy? DM?
"christmas tree cataracts, sometimes PSC; PSC for dm"
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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"
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how does tecnis multifocal work
ring segments extend to periphery so therefore not as dependent on pupil for near vision
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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)"
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what disease can cause ectopia lentis with lenses dislocated inferonasally?
homocystinuria
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what is risk of general anesthesia on patietns with homocystinuria?
thromboembolic events like PE
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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"
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what do you leave nondominant eye to create monovision with lasik
-1.75
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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"
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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"
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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)"
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where do you place the intacs in KC
where cornea is steep so you can flatten it
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what is threshold for stability in refraction over the years
less than .5 change in refraction per year is stable
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"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
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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
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what are Ses of ICL
"lens decentration (16%), cataract (0.4%), RD and sustained rise in IOP are very rare"
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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
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what tyep of astigmatism do young people have?
"with the rule, tight eyelid causes steepening alogn 90 degree axis- eyelid loosens with age"
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"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
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what type of laser-tissue interaction does excimer laser get? Femtosecond? Yag for laser thermokeratoplasty? Yag for capsulotomy
photoablation; photodisruptive; photothermal; photodisruptive
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what gases are used in excimer laser
argon and fluorine; argon is stimulated to form dimers with fluorine
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how would you correct a +2.25 D astigamatism with toric IOL
"(+3.00 lens, remember that +2.06 cylinder on the spherical plane translates to +3 diopter on IOL plane and you never want to flip axis of astigmatism by overcorrecting "
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how do you quickly diagnose epithelial downgrowth
"argon laser used to turn the membrane white if its downgrowth, brown if its iris"
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how much does yag capsulotomy increase risk of RD
4x
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when should you stop taking flomax before cataract surgery
about a month
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"in endolphthalmitis study, what was the most commonly cultured organism"
staph epidermydis(70%)
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what causes oil droplet cataracts? Sunflower cataracts? Christmas tree cataracts?
"1. galactosemia 2. intraocular copper foreign body, wilsons disease 3. myotonic dystrophy"
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what are some rarer causes of psc cataracts
"steroid use, radiation exposure (brachytherapy), chronic uveitis, NF2, RP"
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what is the historical method of corneal power calculation calculation for cataract surgery lens calculation
post op K = preop K + preop spherical equivalent refraction - postop spherical equivalent refraction
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when is fuchs dystrophy worse?
"in the morning, because during the day, the surface moisture may evaporate and corneal deturgescence may occur"
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what type of cataract do you get after PPV? Silicone oil?
"NS, PSC"
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what are complications of PPV
"NS, 10-20% get OAG, cataract surgery is difficult given minimal vitreous support, zonular loss"
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what is average dioptric power of lens
15-20
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how long can you leave dropped nuclear material in vitreous before getting CME
3 weeks
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what are complications of COPD patients for cataract surgery
"positive posterior pressure which can lead to shallow AC, capsulorhexis running out, vitreous loss"
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where does the lens dislocate in marfans? Homocysturinuria
"superotemporal location, inferonasal (think marfan is tall bball player dunking, uria is towards the penis)"
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what should you do if you are in the middle of cataract surgery and you get suprachoroidal hemorrhage
"close wound immeidately to prevent expulsion of intraocular contents, then can consider doing posterior sclerotomies (controversial)"
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do patients with PSC cataracts have better distance of near vision
better distance because pupil will enlarge
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what is cause of PSC
due to swollen epithelial cells in the equator migrating to the posterior capsule (wadl or bladder cells)
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how does yag contact lens benefit the procedure
"stabilizes the eye, reduces depth of focus, reduces pitting of the lens"
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which breakdown pathway is the primary pathway of energy production in lens
anaerobic glycolysis
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where are the Na-K ATPase pump in the lens and how do they work
"anterior surface of lens, pushes Na out and K in"
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what are the stages of diffuse lamellar keratitis
stage 1: faint peripheral infiltrates stage 2: faint central infiltrates stage 3: dense central infiltrates stage 4: dense central infiltrates with flap melting
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how do you treat diffuse lamellar keratitis
"with stage 2, you can give frequent steroid drops and possible lifting and irrigating the flap if not improved; stapge 3 and 4 you want to lift and irrigate the flap"
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what lasik situation gives the highest risk of epi ingrowth? What can help reduce the risk?
retreatments; contact lens placement after retreatment can decrease risk
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what has been assocaited with DLK after lasik?
"beta-iodine, solutions used to clean microkeratome, gram negative endotoxin, meibomian gland secretions, laser ablation debris, RBCs in the interface"
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what structure in the eye has greatest refracting power
air-tear film interface
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what is chatter during phaco
chatter describes how nuclear fragments is repelled by phaco tip
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what suture do you use for iris or scleral sutured IOL?
9-0 prolene
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how do you calculate power of the lens by SRK formula
P (power) = A constant - 2.5*(axial length) -0.9*(avg dioptric power of cornea)
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what are manifestatiosn myotonic dystrophy
"diffuclty releasing grip from door handle, cardiac concudction defects, early balding and infertility , low IOP, ptosis (not lid retraction), pigmentary retinopathy, CPEO"
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what piggyback lens situation in the postcapsular bag would most likely develop an interlenticular membrane
two acrylic lens in the capsular bag
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where are Aks performed on the cornea (astigmatic keratotomy)
"parallel to the limbus done at least 1mm toward the apex of the cornea, done on the steep axis to reduce astigmatism and generally more effective than LRI"
-
"how often is medical tx (intense mydraisis and cycloplegics, aqueous suppressants, hyperosmotics) successful for malignant glaucoma"
50% of the time
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what results when lens vesicle fails to properly separate from the surface ectoderm
peters anomaly
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what is the ddx for cloudy cornea at birth
"STUMPED: sclerocornea, trauma (forceps), Ulcer, Mucopolysaccharidoses, peters anomaly, endotheial (CHED), dermoid"
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"while doing lasik, where does the pupil move under the bright lights of laser operating field"
superonasally (pupillary constriction causes pupil to shift superonaslly)
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