Case 15: Refractive Surgery Flashcards
Why are large pupils a relative contraindication for refractive surgery?
Dim light may result in an increase in aberrations & halos, esp when driving at night when the pupil size becomes larger than the tx optic zone
Why is DM a relative contraindication for CRS?
Uncontrolled blood glucose levels may experience fluctuations in their refractive error, also DM results in poor corneal wound healing
Why is lattice a relative contraindication for CRS?
Increase the risk of retinal breaks during or after refractive surgery
Why is pre-existing dry eye disease a relative contraindication for CRS?
May be exacerbated by refractive surgery as the corneal nerves are temporarily damaged during the procedure. Pts may have reduced vision due to dry eye disease.
Why is uncontrolled primary open-angle glaucoma a relative contraindication for CRS?
IOP elevates as high as 65 mmHg during placement of the suction cup during surgery, which may be dangerous in pts w/ uncontrolled or advanced glauc
What are absolute contraindications of CRS?
- Pts <18 yo 2. unstable refractive error (>0.50 D change) w/i the last year 3. Refractive error outside of tx zone 4. Inadquate corneal thickness (minimum of 250 microns residual stroma for LASIK, and 400 microns for PRK) 5. unrealistic expectations of need for glasses and/or contact lens after LASIK; pts should expect a decreased dependence but NOT complete freedom from corrective lenses 6. pregnancy 7 keratoconus, active herpes simplex or zoster keratitis or CL induced corneal warpage 8. CT tissue disease, collagen vascular disease, or immunocompromised disease
In LASIK the flap is approx _____ microns thick if created by the microkeratome, and _____ microns thick if created w/ laser (Intralasik)
160-200, 120
The ablation depth for LASIK is ____ um/diopter
15
Radial keratotomy
No longer performed. Radial incisions in corneal stroma w/ diamond knife to flatten the cornea & reduce myopia. Was common for pts to end up w/ hyperopic RE
PRK
Corneal epi is completely removed & excimer laser used to directly ablate the anterior stroma to reshape the corneala tissue & correct for myopia, hyperopia and/or astig
What is the tx range for PRK?
-8 D to +4 D & up to 4 D of cyl
What tissue is removed to correct for hyperopia?
mid-peripheral corneal tissue
What are the results of PRK?
Laser creates a corneal abrasion, resulting in extremely poor vision in the immediate post-op period, slow recovery (the entire corneal epi must regrow, more post-op discomfort compared to LASIK. Pts monitored & treated w/ topical opthal steroids that are slowly tapered over a couple weeks
What are 6 advantages of PRK over LASIK?
- no flap 2. less risk of corneal ectasia 3. requires less corneal thickness 4. less post-op higher order aberrations 5. decreased risk of post-op dry eye disease 6. less expensive
LASIK
corneal epi flap is created w/ a microkeratome, an excimer laser is used to ablate the underlying anterior corneal stroma & epi flap is folded back in place
What is the tx range for LASIK?
-10 D to +4 D & up to 5 D of cyl
___ ___ ____ can be performed on a pt whose refractive errors exceed the tx range of LASIK
Clear lens extraction
What are advantages of LASIK over PRK?
Heal faster (1-2 days), experience less pain, & have less post-op corneal haze compared to pts who receive PRK
Intralasik
Same procedure as LASIK, except corneal epi flap is made w/ laser instead of microtome
What are advantages of Intralasik?
The corneal flap created by a femtosecond laser is thinner, leaving more tissue behind for ablation; also assoc w/ decreased post-op dry eye disease
LASEK
Same procedure as LASIK, but the corneal epi flap is creased using dilute alcohol instead of microkeratome
Epi-LASIK
same procedure as LASIK but blunt plastic blade used to create corneal epi flap
Intrastromal Corneal Rings (ICR) - INTACS
PMMA rings are inserted in the peripheral corneal stroma in order to flatten the cornea (shortens corneal arc length)
ICR is approved for the tx of what?
Keratoconus
What is the tx range for ICR?
-0.75 D to -3 D & less than 1 D of cyl. Reversible
Clean Lens Extraction
remove lens for IOL that will alter the refractive power -> cataract surgery w/o cataract. No accomm after surgery
Phakic IOL
An intraocular lens is implanted into the phakic eye-> alteration of the eye’s refractive power w/o removing the ability to accommodate. Surgical peripheral ididectomy is required to prevent angle closure
Astigmatic keratotomy
Circumferential corneal incisions are made in order to relax the cornea in the steepest meridian to minimize corneal astigmatism
Conductive Keratoplasty
Radio frequency energy is applied to the peripheral cornea, causing collagen fibers to shrink & central cornea to steepen
What is the tx range for conductive keratoplasty?
+0.75 D to +3.00 D. May also be used to treat <0.75 D residual astig after previous intraocular surgeries. Regression expected 2-3 yr
Wave-front guided ablation
Custom corneal surgery that reduces higher order aberrations in addition to correcting the refractive error. Can be performed w/ LASIK or PRK results in better quality vision w/ improved contrast, improved acuity & decreased glare
Diffuse lamellar keratitis
Inlammatory, non-infectious reaction at the lamellar interface (between the corneal flap & corneal stroma). Most commonly present w/i 2-3 days after surgery.
Sx of DLK
Blurred vision, photophobia, pain, FB sensation
Etiology of DLK
In response to toxins during surgery (blade debris, microkeratome oil). Less common w/ disposable microkeratomes
Signs of DLK
Fine, granular, sand-like infiltrates. May lead to severe vision loss secondary to corneal scarring and/or corneal melting
DLK tx
Mild cases treated w/ topical opthal steroids (Pred Forte Q1H or Durezol Q2H. Severe tx w/ oral steroids and/or the flap is lifted & irrigated
What is the MC SE of CRS?
Dry eye, typically resolves 1-2 mo.
What makes sx of glare & halos worse?
Smaller ablation zones, larger pupils, monovision correction, higher refractive errors
When does infection post-op most commonly occur
1-3 days after surgery
Risk of infection w/ PRK? LASIK?
PRK= 1/1000-1/3500. LASIK= 1/5000
What are the MC causative bacteria of CRS infection?
gram (+) microorganisms or mycobacteria
Post-op infection tx
Lifting the flap & irrigate w/ topical opthal antibiotics
When will corneal haze appear?
Will present for several weeks following PRK as the corneal epi heals, rare following LASIK. Risk increases w/ higher refractive error
Corneal haze Tx
topical opthal steroids, dosage titrated as corneal haze improves
Corneal ectasia
Abnormal bulging forward of a thin cornea- more likely to occur in high myopes or in pts w/ undetected keratoconus or forme fruste keratoconus
Corneal ectasia tx
RGP contact lenses, Intacs, or penetrating keratoplasty
Required thickness of the residual stromal bed is ____ microns for LASIK and ____ microns for PRK
250, 400
Free caps
More commonly occur w/ very flat corneas, inadequate amount of cornea in the ring causes the microkeratome blade to cut the hinge of the flap
Button holes
More commonly occur in very steep corneas or deep set eyes. Steep cornea can buckle in the ring, resulting in a hole in the flap w/ the pass of the keratome
Macrostriae
Full-thickness w/ undulating, parallel, stromal folds; they are commonly due to slippage or malpositioning during surgery
Microstriae
Fine, multi-directional folds in Bowman’s membrane that result in optical irregularities, typically resolve on their own
Epithelial ingrowth
Most commonly presents @ 1 mo. post-op. White milky deposits at the flap interface
When can enhancement procedures be performed?
can be performed as early as 3mo. but a 6 mo. wait period is preferred to allow for stabilization of the RE
3 Recommended Tx criteria
- RE >/= 0.75 D from the target refraction in an unhappy pt. 2. Uncorrected VA = 20/30 in the distance eye in an unhappy pt 3. Astig >0.75 D causing sx
What is considered a success in RE surgery?
20/40 or better. 75% of pts achieve 20/25 or better
Removal of the corneal tissue results in a falsely _____ IOP
Low
