GP contact lenses Flashcards
General rule for RGP
For every 0.05mm the RGP BC is changed, the tear lens increase or decreases by 0.25D
OR
For every 0.1mm the RGP BC is changed, the tear lens increase or decreased by 0.50D
How to decrease lens flexure?
Increase CT
What should TD be for RGP
1.4MM less than HVID
How much movement in RGP
1 to 1.5mm w/ each blink (oxygen exchange / removes debris)
How much edge clearance should RGP have
less than 1mm width
When increasing lens diameter what change does it have to RGP fit
Sag increases
-Fit is tighter/ steeper
When decreasing lens diameter what does it do to the fit?
Sag decreases
Fit is looser / flatter
When decreasing base curve what does it do to the fit>?
Fit is tighter/steeper
When increasing BC what does it do to the fit?
Fit is looser / flatter
GP candidates
-Astigmatism
-Borderline dry eye
-Refits (not satisfied with SOFT CL)
-Irregular cornea
-Presbyopia
-OrthoK / Myopia control
decentration complications
-reduced VA and flare
-limbal irritation / 3 n 9 staining
-lens dislocation
-lens awarness
Appical bearing
Central part of lens touches the apex (highest part of conrea)
-loose fit
Appical clearnence
Lens rests on mid periphery of cornea
Seal off
Peripheral edge of lens is too steep
Mid periphery bearing
Touches the cornea in the mid periphery
-Flat fit?
What can cause poor comfort in a GP
-excessive movement
-excessvie edge clearance
-edge to thick
-FB
-damaged lens design
-astigmatic cornea
-pt sensitivity
-poor wetting
What can cause poor vision in RGP
-refractive change
-corneal shape change
-RA
-flexure
-deposits
-surface scratches
-poor wetting
what is the cause of a continually high, not dropping after blink RGP fit
-flat peripheral zone
-widen peripheral zone
-too large TF
-lens to thick
-WTR cyl
remedy for a continually high, not dropping after blink fit
-steepen the periphery
-narrow the periphery
-reduce TD
-toric periphery design
cause of continually low/rapid drop after blink fit
-lens too small
-lens too thick
-no lid attachment
how to fix a continually low, rapid drop after blink fit
increase TD
reduce Tc
add peripheral negative carrier
BEOFRE INSERTING GP MAKE SURE YOU CHECK..
-MAKE SURE THERE ARE NO DEPOSITS
-MAKE SURE THERE ARE NO CHIPS ( free of defects)
