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OPTOM 430 - Keratoconus Questions & answers
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OPTOM 430 - KeratoconusHow do RGPs improve visual optics? - CORRECT ANSWER-They are able to fill
the gaps and neutralise corneal irregularity.
What is the first diagnostic clue to keratoconus? - CORRECT
ANSWER-Observations made during retinoscopy
-Scissoring reflex
-Charleux oil droplet sign
How to do retinoscopy on a keratoconic patient? - CORRECT ANSWER-Use any
portion of the ret-reflex that seems to be more distinct/brighter and attempt to
neutralise it.
How to refract a keratconic patient? - CORRECT ANSWER--Use LARGE steps
according to just noticeable difference.
-Use techniques to control accommodation.
-+/-1.00DC JCC often needed.
-Cycle through rounds of sphere then cyl, checks and if VA improves reduce the
step used, and repeat.
-Consider balance is relevant and method of balancing.
When to not use Humphriss balancing for a keratoconic patient? - CORRECT
ANSWER-If there is a large difference in VA between the eyes.
How to find cyl in a keratoconic patient if normal JCC doesn't work? - CORRECT
ANSWER-1. Insert a 1D or 2D and ask patient to rotate axis dial "until things look
the best". Use a larger letter.
2. Perform a power check.
3. Find cyl power, use big power step jumps.
4. If a few dioptres of change occur, check VA.
5. If improve in VA return to sphere check then cyl check using an appropriate
smaller steps.
6. Further refine the axis by finding the range of cyl axis, then placing the axis in
middle of range.
,How to decide the prescription for spectacles in keratoconic patients? -
CORRECT ANSWER--Place rx in trial frame and test outside clinic room.
-Don't automatically cut cyl for adaptation.
-Don't automatically assume the patient can wear the full correction either.
-If VA is better than 6/15, can prescribed full rx.
What parameters to empirically start with in a keratoconic patient RGP fitting? -
CORRECT ANSWER--Diameter.
-Central back optic zone radius (base curve).
-Design.
What parameters to consider during fitting in a keratoconic patient RGP fitting? -
CORRECT ANSWER--Peripheral curves.
-Peripheral design/OZ.
-Back vertex power.
How to empirically design a base curve for a RGP for a keratoconic patient? -
CORRECT ANSWER-Topographically consider the steepest and flattest values
(normalise map view). Select the BC that is flatter than the steepest value.
-Go 1/3 flatter for moderate to advanced (yellow-orange).
-Go 1/4 flatter flatter for mild to moderate (yellow-green).
What is the mm to dioptre conversion for base curves in the 6.0mmm range? -
CORRECT ANSWER-0.75D per 0.1mm.
What is the mm to dioptre conversion for base curves in the 5.0mmm range? -
CORRECT ANSWER-1.00D per 0.1mm.
Advantages of fitting an RGP with high clearance on a keratoconic patient. -
CORRECT ANSWER-Minimise corneal compression and damage at corneal
apex.
Disadvantages of fitting an RGP with high clearance on a keratoconic patient. -
CORRECT ANSWER-Poor VA due to insufficient masking of irregular corneal
astigmatism and residual astigmatism.
, Advantages of fitting an RGP with central touch on a keratoconic patient. -
CORRECT ANSWER-Increase VA through squishing the cornea.
Disadvantages of fitting an RGP with central touch on a keratoconic patient. -
CORRECT ANSWER-Not ideal for long-term ocular health.
What do we want the fitting of a RGP on a keratoconic patient to look like? -
CORRECT ANSWER-Like a spherical fitting.
What is the peripheral curve design like for keratoconic patients as compared to
normal RGPs? - CORRECT ANSWER-Will incorporate a greater peripheral curve
flattening rate, therefore would be more likely to exhibit higher edge lift and show
signs of looseness and instability.
How to assess peripheral RGP lens fitting on a keratoconic patient? - CORRECT
ANSWER--Assessment of the elevation map to determine lens clearance and
potential lens positioning.
-Diagnostically.
How does the peripheral curve of a RGP lens for a keratoconic patient tend to
affect fitting? - CORRECT ANSWER-Tend to travel towards lower elevation
and/or there will be more edge lift or tear volume in this area.
How is BVP of a RGP for a keratoconic patient determined? - CORRECT
ANSWER--Diagnostically through over-refraction with the contact lens on eye.
-Over refraction added to the trial lens BVP for the given BC.
What to do if BC is changed in a keratoconic RGP from the diagnostic on eye
BC? - CORRECT ANSWER-A calculation of the tear layer power change needs
to be factored in.
Advantages of RGPs of standard diameters for keratoconic patients. -
CORRECT ANSWER--Fairly straight forwards fitting process.
-Lens fitting reasonably easy to judge.
-Tear exchange allows for good ocular health prognosis.
-Over-refraction to determine best CL BVP so makes it easy to consider sphere
equivalent or if switching to front surface toric.
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