Refractive Surgery Flashcards
what are 3 types of incisional refractive surgeries?
radial keratotomy (RK), astigmatic keratotomy (AK), relaxing incisions (limbal or peripheral)
what are 2 types of thermal refractive surgeries?
laser thermal keratotomy (LTK) and conductive keratoplasty
what are 4 types of excimer laser refractive surgeries?
PRK, LASEK, epi-LASIK and LASIK
what are 2 types of intraocular surgeries?
phakic IOL’s and refractive lens exchange
which procedure steepens the cornea and which one flattens the cornea?
incisional = flattens
thermal = steepens
what 3 types of cuts will result in more flattening of the cornea?
larger, central and deeper cuts
How is radial keratotomy performed and what is it used for?
diamond blade - radial/tangential incisions used for myopia and astigmatism correction
what are some con’s for radial keratotomy?
fluctuating vision, hyperopic shift over time, and corneal integrity is permanently weakened
when is astigmatic keratotomy performed?
during cataract surgery - limbal relaxing incisions or post PKP
what results did the PERK study find with radial keratotomy?
43% of eyes experienced a hyperopic shift of 1.00D or more at 10-year follow-up
what are intrastromal corneal ring segments made of and why are they used?
made of PMMA implanted in deep stroma to modify corneal curvature (keratoconus)
what is the minimum corneal thickness needed for intrastromal corneal ring segments and what are 2 ways to create the pockets?
450 microns (inserted 70-80% corneal thickness) diamond blade pocket creator or femtosecond infrared laser Nd: glass laser
what are the two types of intrastromal corneal ring segments and how are they different?
Intacts = hexagonal shape
Ferrara rings = triangular shape
how is laser thermal keratoplasty performed?
a series of radial treatment spots are placed outside the visual axis with a Holmium: YAG laser
what is laser thermal keratoplasty used for?
causes shrinkage of stromal collagen - steepens cornea to treat hyperopia or presbyopia (effect regresses within several years)
what is conductive keratoplasty? what is the advantage over thermal keratoplasty?
a probe applanates the corneal surface - radio waves heat/shrink collagen less risk of irregular astigmatism and regression
what type of laser is used in excimer refractive surgery?
argon-fluoride gas laser (emits cool, UV pulses = 193nm and vaporizes tissue at 1/4000mm/pulse)
which procedures use excimer lasers? what does it correct?
PRK, LASEK, epi-LASIK and LASIK can correct refractive errors and higher order aberrations
what happens in photoreactive keratectomy (PRK)?
corneal epithelium is mechanically removed (blade or ethanol) - excimer laser photoablates Bowman’s and anterior stroma - either flattens or steepens cornea
what are some indications for PRK?
thin cornea, cost, mild-moderate refractive errors, dry eyes, residual refractive errors (cataract sx, PKP, refractive surgery), and PTK (therapeutic keratomy)
what are some primary issues with PRK?
significant post-op discomfort, delayed VA recovery, and development of stromal corneal haze (2-3 weeks)
what can you put on the cornea during surgery to reduce the risk of corneal haze?
Mitomycin- C
how is LASEK performed?
alcohol is used to loosen the epithelium - cells are harvested - rolled back into place after treatment (similar to PRK but less discomfort and quicker VA recovery)
how is epi-LASIK performed?
an epi-microkeratome is used to remove the corneal flap (less discomfort than PRK and more cells survive than with LASEK)
how is LASIK performed?
incision is made with either microkeratome (blade) or fematosecond (laser) into corneal stroma creating a flap
NOT surface ablation - goes deep into stroma
what layers does the flap consist of in LASIK?
epithelium, bowman’s, and anterior stroma (ablation occurs deeper into stroma so there is less wound healing from keratocytes)
which method, microkeratome or fematosecond laser creates very high IOP?
microkeratome creates more suction during procedure - very high IOP
what does conventional LASIK correct for vs. WaveFront or CustomCornea LASIK?
conventional = myopia, hyperopia, astigmatism custom = also spherical aberrations
what are some indications for LASIK?
thicker corneas, keloid formers, higher corrections (>-6D), rapid restoration of vision and almost painless
what are some LASIK complications?
flaps (button hole, lost, aborted, epithelial ingrowth, DLK, and striae), corneal ectasia or irregular astigmatism
how can you help prevent corneal ectasia during LASIK?
keep a residual corneal thickness of 275 microns (250-300)
only perfom up to -10.00D myopia
what are some indications for phakic IOL’s?
high refractive errors (20D myopia/hyperopia or 7.5D astigmatism) and thin corneas
what are some general risks to phakic IOL’s?
endophthalmitis, residual refractive error, glare and glaucoma/cataract
which phakic IOL can cause glaucoma and which can cause a cataract?
anterior chamber lens = glaucoma
posterior chamber lens = cataract
what is the minimum anterior chamber depth for an anterior chamber phakic IOL?
minimum 3.2mm (problem for hyperopes - smaller AC depth)
what type of patients get refractive lens exchange?
for patients who are not good candidates for other refractive surgeries (similar to cataract removal)
what are 3 considerations for refractive lens exchange?
PVD/retinal detachment, presbyopia, and stability of refractive error
what percentage of patients had visual symptoms that were extrememly bothersome in the LQOLCP study?
4% of subjects without correction at 3 months
what percentage of patients had new dry eye symptoms in the LQOLCP study?
30%
what are some medical history/conditions that would not be good for refractive surgery?
autoimmune/collagen vascular disease (lupus, rosacea, sjogren’s, ehler’sdanlos, RA), diabetes, pregnancy, immunodeficiency, personality disorder and medications (Amiodarone HCL, Isotretinoin - Accutane)
what are some ocular history’s that would not be good for refractive surgery?
corneal ulcers, viral infections - post tx, steroid responder, lagophthalmos, floppy lid syndrome and eye dominance
why do you need to know the patient’s CL history before refractive surgery?
need to know if they like the CL or if they are non-compliant = good candidate
if they do not like monovision or multifocals = bad candidate dry eyes = bad candidate
why do you perform a cycloplegic refraction prior to refractive surgery?
you do not want to overestimate their Rx
what are some risk factors for dry eye history?
females, over 50 y/o, Asians, higher myopes and hyperopes, medications and cigarette smoking
what are the risk factors for ectasia according to the Randleman study (in order)?
abnormal topography, residual stromal bed thickness, age, pre-op corneal thickness and refractive error
what are the absolute surgical contraindications?
under 18 y/o, pregnant or nursing, dx with collagen vascular disease, autoimmune or immunodeficiency, taking accutane and/or amiodarone and keratoconus
what are the relative surgical contraindications?
diabetes, connective tissue/atopic disease, immunocompromise status, herpes simplex/zoster, keratitis sicca and glaucoma
what are the pre-op medications/treatments?
omega 3, doxycycline, restais, antibiotics, artificial tears, lid massage, plugs
what are some potential complications with the laser or microkeratome?
*worst complications may be postponed irregular flap healing
can cause corneal distortion perforation of cornea could occur with devastating consequences
what are some potential complications of refractive surgery?
mild or severe infection is possible, could develop keratoconus, increased light sensitivity/glare, dry eyes, over/under correction, fragile cornea, pain/FB sensation and vision could regress over time
what are the day 1 pot-op clinical tests?
history, UCVA, slit lamp, review drops and RTC in 1 week
what are some clinical findings at the 1 day post-op appointment that would indicate they return to the surgical center?
dislodged flap, flap striae, infections
what clinical tests are different at the 1 week appointment?
do a dry Rx BCVA, use NaFl with slit lamp and RTC in 3 weeks
what clinical findings at the 1 week appointment would indicate the patient to return to the surgical center?
infection and loss of BCVA
what clinical tests are performed at the 1 month post-op exam?
history, UCVA, dry refraction, slit lamp with NaFl, and RTC in 8 weeks
what are the symptoms of post-LASIK dry eye?
visual fluctuation, dryness, irritation, and pain (refract with little hyperopia and WTR cylinder)
can dry eyes cause a regression towards the pre-LASIK refractive state?
several studies show that regression following hyperopic and myopic LASIK is correlated with dry eyes
how is post LASIK ectasia diagnosed?
delayed acquired astigmatism, loss of BCVA, elevation topography and aberromtey (elevated vertical cornea)
what are the treatments for ectasia?
specs, soft CL, RGP CL, hybrid CL, Intacts, collagen cross linking, keratoplasty (PKP)
which LASIK treatment has been shown to cause more dry eyes?
microkeratome (had 46% corneal staining vs. femto 8%)
what happens to contrast sensitivity with LASIK?
decreases initially - by 3 months patients regain normal cycles/degree
what did the cyclosporin and corneal sensitivity study find?
Restasis helps dryness and makes a better corneal bed for the healing process (most patients benefit)
what medications are patients on post LASIK?
antibiotic 1 week, Pred Forte QID 1 week, Restasis BID 1 month, AT’s QID 1 month, omega 3, punctal plugs
what is diffuse lamellar keratitis (sands of the Sahara)?
LASIK complication - interface inflammation, WBCs (neutrophils) but no infection noticed first 12-72 hours
will patients have symptoms if they have grade 1 DLK?
usually no - treat before they have symptoms = use steroid more frequently (q1h for 24 hours) will see at first or 1 week visit
what are the signs of diffuse lamellar keratitis?
no conjunctival injection, no AC inflammation, no NaFl stain
what causes diffuse lamellar keratitis?
no precise etiology - suspected autoimmune response
what happens if you do not treat DLK?
if not treated aggressively it can cause a stromal interface melt - neutrophils release proteolytic enzymes that digest or melt the stroma
what happens in grade 2 DLK?
may have mild ocular discomfort, BCVA is reduced by 1-2 lines, hyperopic shift is seen and the risk of corneal melt is higher
what happens in grade 3 DLK?
(should never get to this state) - patients complain of extremely blurred vision and glare (BCVA is drastically reduced), large hyperopic/astigmatic shift, dense infiltration and can resemble severe PRK haze
how do striae stain?
fluorescein makes it easier to see as valley’s and mountains with negative staining
when is striae after LASIK a concern?
only is there is loss of BCVA or subjective quality of vision, glare or halos
what are the treatments for striae?
mechanical problem = caro ball smoothing, flap lift and stretch, flap lift with epithelial debridement/hypotonic saline, flap suture and therapeutic PTK
why would fematosecond provide less epi-ingrowth than blades (microkeratome)?
blades all have tapered or gradual entry into cornea -all FSL had either a 65 or 70 degree side cut from the lamellar dissection to the anterior surface of the cornea
what is the most common infection in laser vision correction?
MRSA
when will patients complain of a MRSA infection?
day 1 looks normal and then the patient calls in pain between 2-4 days
what are some characteristics of MRSA infections after LASIK?
slow to heal, significant pain, and non-healing peripheral infiltrates
which patients are more at risk of developing MRSA?
health care workers, known carriers of MRSA, and patients with blepharitis
what do you give patients pre-op for prophylaxis for MRSA?
aggressive treatment for blepharitis to reduce lid colonization by staphylococcus, hot compress, lid hygiene, regular Zymar or Vigamox QID for 5-7 days or Tobradex ST
what can you give to patients during the LASIK procedure to reduce MRSA?
regular Betadine lid prep
what can you give patients post-op for MRSA prophylaxis?
regular Zymar or Vigamox QID, add polytrim or Neosporin QID and consider Tobradex ST
what is the treatment protocol for corneal infiltrates post refractive surgery?
Assume MRSA infection is resistant to Zymar/Vigamox until culture, lift flap (LASIK) and culture (PRK, LASIK) Irrigate Vancomycin 25mg/ml under flap increase Zymar/Vigamox q1h add vancomycin 25mg/ml 130min (or bacitracin/polytrim/neosporin) follow up every 12-24 hours
what complication is seen in this photo?
epithelial ingrowth (starts in periphery vs. DLK which starts centrally)
progressive
what complication is seen in this photo?
significant epithelial ingrowth
