Contact Lenses III MT 2 - Keratoconus

Terms Definitions
K-conus = inflam or non-inflam?
Where is K-conus localized?
Ectasia in central or inferior cornea
T/F - CLEK was an experimental study funded by the NEI involving an 8-year follow-up.
False - observational study
K-conus age of onset?
K-conus progressive until...
3rd to 4th decade
Earlier onset of K-conus = (more/less) severe?
K-conus more prevalent in males or females?
Relatively equal incidence (CLEK sample = 56.4% male, 43.6% female)
K-conus = symmetrical or asym?
CLEK survey = __% diagnoses between ages __ and __ years.
90%, 10, 39
CLEK survey: mean age of diagnosis = ___.
27.3 ± 9.5 yrs
CLEK survey: __% of sample less than 50 years of age.
K-cone VA: __% were 20/__ or better thru CLs__% were 20/__ or better through manifest refraction.
88%, 20/4058%, 20/40
What pigmentation is involved with K-cones?
Fleischer's Ring - usually at base of cone, iron deposit; easier to find when dilated
What three main signs are involved with K-conus?
- Fleischer's Ring: iron deposits at base of cone- Vogt's Striae: "stretch marks", different from striae in edema b/c mostly (not always) vertical and see few.- Scars: cause unk (possibly eye rubbing or cone itself?)
What is the most common bilat sign of K-conus?
Fleischer's ring (bottom left pg 3)
What is the most common unilat sign of K-conus?
Vogt's Striae (bottom left pg 3)
What is the hereditary pattern of K-conus?
AD w/ variable penetrance
CLEK study sample showed __% reported a family Hx of K-conus at baseline (parent, sibling, child, aunt, or uncle)
What behavior is commonly assoc w/ K-conus? What is the prevalence of this behavior in K-cones?
Eye rubbing49% both eyes1.8% rub only one eye vigorously3.2% unsure whether they rubbed their eyes
CLEK study: Hay fever or allergies = __%
CLEK study: Asthma = __%
CLEK study: Atopic dermatitis = __%
What is the prevalence of atopy in the general population?
What is Munson's Sign?
When the cornea of a K-cone pushes enough on the lower lid to make the lid protrude when looking down.
T/F - Blindness can occur with K-conus.
Average age of Dx K-conus = __ years old, based on CLEK.
T/F - LASIK is ok for K-cones.
False - cannot do LASIK in K-cones due to thin cornea
What is the NKCF?
National Keratoconus Foundation
What is the primary mode of correction for mild K-conus?
T/F - CLs can stop the progression of K-conus.
What RGP fitting philosophy is best for achieving a "successful" fit with K-cones?
Fit flat - touch cone apex
Which RGP fitting philosophy is best for less disruption to the cone apex in K-cones?
Fit steep - less rubbing on apex therefore less scarring
Which RGP fitting philosophy is best for longer wear time in K-cones?
Fit flat - more peripheral clearance allows better tear exchange vs fitting steep
T/F - An "ideal" RGP fit on a K-cone involves a sag height of BC that is less than the sag height of the cornea.
False - sag height of BC to EQUAL or SLIGHTLY EXCEED sag height of cornea
T/F - An "ideal" RGP fit on a K-cone involves no excessive areas of tear/debris pooling under the OZ.
What does FDACL stand for in K-cone RGP fitting? What is the significance?
First Definite Apical Clearance Lens - want to find the flattest lens that will result in AC (then eventually fit the steepest AT lens).
What are the three main goals for K-cone RGP fits?
1) Feather "three point" touch2) Minimize tear pooling3) Maximize periph clearance
How do you extend your keratometer's range for a K-cone?
Use +1.25 D and add 8.00-9.00D to the drum reading.(+2.25D add = ~16.00D to drum reading)
T/F - It is possible to judge the amount of bearing (e.g. "1.00D flat") based on the FP in K-cone RGP fits.
False - can't tell if too flat since the amount of bearing can be very similar between two lenses of different BCs (due to shape of cone apex)
What is a good strategy to minimize the area of tear pooling around the base of the cone?
Decrease the OZ (see figure middle right pg 8)
K-cone RGP power is usually (plus/minus)?
K-cone RGP OAD is usually (smaller/larger) vs typical RGPs? Why?
smaller (better for tear exch)
K-cone RGP OZ is usually (smaler/larger) vs typical RGPs?
How do you determine the SCr in K-cone RGPs?
Typically given as normal since mid-periph and periph usually unaffected, but change SCr based on amount of periph clearance seen (want to maximize)
What kind of blend is indicated for K-cone RGPs?
What Dk is typical for K-cone RGPs?
DK ≥60
T/F - There is usually no relation between your subjective refraction and CLP in K-cone RGPs.
True - but typically CLP is more minus
T/F - The Rose K RGP design minimizes the amount of tear pooling around the base of the cone.
In rose K, OZ (incr/decr) as BC is prescribed steeper.
For Rose K fits, what BC should you start with when fitting your K-cone patient?
Avg K to 0.2mm steeper for initial lens
In Rose K, the BC is (sphere/aspheric), and the PC is (sphere/aspheric)
sphere, aspheric
Rose K2 typically has (smaller/larger) OZs. What is the significance of this?
larger; improved night vision, decr image ghosting and aberrations
What K-cone RGP involves computer-assisted fitting?
Keratoconus Bi-Aspheric (KBA)
What is the OAD of KBA?
10.2 mm
T/F - Prism-ballasted front-surface torics can work with K-cones.
False ("Nah!")
Why is a bitoric design "tempting" to use with K-cones?
Irregular astigmatism thus no particular corneal toricity. Even if periph cornea is toric, bitoric design is more apt to peripheral seal-off.
What benefits and problems are assoc w/ large OADs when fitting K-cones?
- Benefit = centration not an issue- Problems = harder to avoid excess areas of clearance and bubbles under OZ; adequate edge clearance more of a challenge
When is a large OAD for K-cones indicated?
- Decentered cone apex- Enhance initial comfort
T/F - Ortho-K is contraindicated for K-cones.
What is the problem with K-cone SCLs?
Tend to be thick therefore poor O2 transmissibility.
When is a piggy-back lens indicated for K-cones?
For initial comfort, 3-9 staining, or bandage
SynergEyes Hybrid Cl is approved for what conditions?
- Post-surgical- K-cones- Multifocal
SynergEyes Hybrid CL (fill-in):- OAD = ___mm- Center = ___mm- Center material = ___- Center Dk = ___- ___% water soft skirt
14.5 mm OAD8.2 mm centerParagon HDS 100 Dk rigid center30% water soft skirt
T/F - Can use piggyback if see 3-9 staining in your K-cone patient.
Name the steps in the Game-Day Game-Plan for K-cones.
1) Measure K curvature2) Select first trial lens BC3) Eval apical FP4) Observe pooling under OZ5) Eval edge lift/PC6) Sphero-cyl OR
Your first trial lens BC in fitting K-cone RGPs should be...
somewhere between steep K finding and avg K value (fudge toward steep K)
T/F - Bubbles are acceptable in K-cone fits since there is a moderate amount of clearance around the cone.
False - want the steepest apical touch lens, but avoid bubbles.
You see minimal periph clearance when fitting your K-conus pt with your DxCL; what parameter should be changed in your order and how?
Order flatter SCr
What SCr is typically suitable for K-cones?
8.50 mm (range from 8.00-9.00)
You should do a sphero-cyl OR on a K-cone with which of the following trial lenses:1) Steepest touch2) Flattest clearance3) Steepest clearance4) Flattest touch
1) Steepest touch
There tends to be a (+/-) TL in K-cone RGP fits?
T/F - In K-cone RGP fits, an increase in BC (in D) typically means a decreased OZ.
T/F - K-conus does not typically affect the mid-peripheral and peripheral corneal topography.
Center thickness in K-cone RGP fits are typically (thinner/same/thicker) vs. normal RGPs. Why?
slightly thicker, even though high minus CLP, because of relatively flat periph curve system.
Why do a blend in K-cone RGP fits?
Makes periph curve system more "aspheric"
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