Post-Surgical CL Fitting Flashcards
What’s the OLDEST (1898) procedure of refractive surgery?
- still performed?
- amt of myopia being corrected determines parameters of what?
RK - radial keratectomy - NOT performed today (plenty of pts still w/ post-RK stitches)
-length, number, depth of incisions - TRANSVERSE ones made for astigmatic correction
how does RK correct refractive error?
incisions in the MIDPERIPHERY weaken the mid-peri cornea.
-IOP then pushes midperi out, effectively FLATTENING central cornea (diurnal variations in VA)
physiological changes seen w/ RK? (got good ones)
-visual side effects w/ RK?
physiological: uneven tear film, transient EBMD/erosions, sensory denervation, neo
visual: irregular astig, fluctuating VA, anisometropia, linear opacities from scars (flare/glare)
PRK: uses an e___ laser (argon fluoride) of ___nm
- what happens to the tissue?
- what variable (related to the laser) controls refractive error correction?
excimer laser of 193nm
-ablates central 5.5-7.0mm of the cornea
- vaporized - very precise
- DEPTH of the laser/ablation determines Rf treatment zone
post-op PRK: initial partial regression/___opic shift
3 types of would healing responses; describe them
-which is at highest risk of OVERcorrection?
hyperopic
1: MAJORITY: trace haze @ 1 month, dissipates
2: UNDERhealer: clear-tr haze @ 3-6 months, at risk of OVERcorrection (d/c steroid to allow wound healing)
3: OVERhealer: severe haze; increase steroid use
what is the MOST common corneal refractive procedure?
- uses what to create flap?
- name a few pertinent complications
LASIK
blade/microkeratome or femtosecond laser (current)
-DLK (sands of the sahara), flap striae, epi ingrowth, increased risk of infection (MRSA)
how will topo change s/p PRK/LASIK? (central zone, transition zone, peripheral zone?)
central - flatter
transition - steeper (“knee”)
peripheral - unchanged
what might topo look like on an over-corrected Rf surgery patient?
- which 2 procedures may lead to central islands?
- which procedure results in FLUCTUATING vision?
central GREEN (over-flattened) area
island: PRK, LASIK
fluctuating: RK
how long after each of the three major surgeries can CL lenses be used (if needed)?
-RK, PRK, LASIK
RK: 6 months
PRK: 9-12 months
LASIK: 2-4 weeks
lens selection for post-surgical pts must be CAREFUL; requires close monitoring of every ~__-__ months
-4 aspects of proper lens selection for a SCL?
3-6 months
1) Sihy is a MUST - esp for RK
2) thin as possible
3) LOW modulus (stiffness)
4) >14.0 LD (LARGE, d/t increased likelihood of decentration from central flattening)
T/F: SCLs are the go-to choice for post-RK patients
false. Sihy may be acceptable, but GP is preferable d/t decreased likelihood of NEO
parameters of an appropriate GP LENS for use post-surgery? (mid-peri, LD, OZD).
Should the lens be compensated to be more PLUS or MINUS after surgery?
- mid-peri: alignment
- LARGE LD (increase centration)
- relatively SMALL OZD
more MINUS: increased central clearance creates a (+)LL; compensate w/ (-)
although it’s ONLY A STARTING POINT, what should your BC selection be for:
-post-op RK readings (for RK, PRK, LASIK)
post-op RK: 1.50D STEEPER (or 1.00D FLATTER than pre-op)
- post-op PRK: 1.00-1.50 STEEPER than post-op (but variable depending on the study)
- post-op LASIK: ~1.00D STEEPER
- bottom line: these are VARIABLE; you’ll use the FP (fl pattern) to determine final parameters
GP fitting goals post-RK:
- central pooling?
- mid-peri bearing?
- peri clearance?
central pooling - low to moderate (have to have some d/t the surgery)
- mid-peri bearing - clearance/even
- peri clearance? mod
-don’t forget: minimize central staining, corneal edema, neo
Reverse geometry lenses: most useful with higher PRE-op _____
- relatively (large/small) lens diameters, and (large/small) OZDs
- BC selection?**
myopia (greater effect of central flattening)
- large LD, small OZD
- BC: 1D STEEPER THAN POST-OP K (starting point)
what other types of lenses can you fit on unhappy post-refractive surgery patients?
sclerals, hybrids, piggyback
which lens would you use FIRST for:
- RK patient:
- PRK/LASIK patient:
- pt w/ poor GP stability/comfort
- pt w/ extreme central flattening?
RK: GP
PRK/LASIK: Sihy SCL
poor stability: scleral or hybrid
central flattening: RGL
Post-penetrating Keratoplasty - COMPLETE removal of full-thickness corneal tissue with replacement graft- conditions that require this?
(just a few) - pseudophakes, KC, Fuch’s, trauma, AI dz, infection
about how many diopters of cyl do patients have post-PK?
4-5DC (diopters of cyl) - but they’re ok w/ that b/c their previous vision was likely >20/40
-success rate: 90%
Wait at least ___ months before fitting pt to CLs (for tx of refractive error, or epi defects, or SPK, etc.)
4 months
-note: complete healing may take up to 18 months
“normal” topo s/p PK is usually ___ centrally, and then ____ toward periphery.
-____ astigmatism is common. Preferred lens to treat?
steep centrally, flat peripherally
IRREGULAR astig common; GP preferable (or high Dk SCL)
5 types of grafts/comparisons to host cornea? Which lens to use for each?
[one nipple pretty tiny eye]
Oblong: graft FLATTER than host. Use conventional/RGL GP
Nipple-like: graft STEEPER than host. Use nml/KC design
Proud: graft STANDS OUT from host. Use large dia/RGL GP
Tilted: variations b/w thicknesses. Use large dia, BST, or SCL
Eccentric: graft is OFF CENTER. Use large diameter GP or BST
Which lens type should you START with post-PK?
start simple: sph or aspheric
if needed: then do toric, reverso geometry, scleral, hybrid
2 contraindications/contraindicated lens types post-PK?
PMMA, Sihy EXTENDED WEAR (risk of graft rejection, neo, infection)
endgoals of proper post-PK fitting:
good vision, comfort, wearing time
-good corneal physiology
