Week 4 - RGP Fitting Problems and Solutions Flashcards
What are 4 MAIN symptoms of poor fit?
- Flare
- Blurred vision
- Burning (solution or dirty)
- Spectacle blur
What will a px experience with flare? 2
streaming
halos
What can cause flare? 3
small optic
large pupil
corneal edema
What could cause blurry vision? 5
- Lens switched
- Dirty/coated or smudged lens
- Retinoscope (radiuscope)
(gives irregular reflex-due to greasy lens) - Corneal edema
-scratched lens
If the patient is feeling a burning sensation soon afrer lens insertion. What could be the problem? 2
wetting agent sensitivity
dirty lens
If a patient is feeling a burning sensation hours after insertion. What could be the problems? 2
And what can these symptoms also be linked it?
Poor blinking
poor fitted lens
corneal edema
What is spectacle blur?
How long on average does it last?
-blurry vision after taking RGPs out while wearing gls
-Lasts from only a few
minutes to a few hours after the lens has been removed
How to determine if flare is due to small optic zone or decentration? 2
If due to decentration - the flare will appear as an arc
If due to small optic zone - the flare will appear as a full halo
When is spectacle blur considered normal?
if it lasts less than 30 mins
If the patient is experiencing spectacle blur in excess of 0.50D (over refracting) what do we need to do?
check the fit of the lens
How does the diameter of the lens affect spectacle blur?
large diameter the more prominent spectacle blur is
How does the thickness of the lens affect spectacle blur?
Thicker lens greater the duration of blur
What can cause excessive blur while wearing and not wearing CLs ?
-Caused by corneal edema
Why does corneal edema cause excessive blur?
What do we do with the RGP/PX if they are suffering with corneal edema?
Edema will cause changes in the curvature of the cornea thus px wanting more minus
refit/refer
Who are more likely to suffer from spectacle blur, hyperopia/myopia?
Hyperopia as the centre of the lens is thicker
How could we fix excessive blur caused by corneal edema? 5 (change of the lens size 3/ kind of lens change/ change to what material)
- Reduce diameter
- Blend lenses better
- Flatten and extend the
peripheral curve - Switch to thin lens
- Fix by using higher Dk material
What are common causes of mucus (common complaint) on the lens? 2
-make up
-poor edge design bumping into Meibomian glands secretion and lid irritation
Poor edges account for most problems. T/F
TRUE
What can poor edges causes? 5
Corneal abrasions,
lid irritation,
dirty lens,
photophobia,
low lens tolerance
If a lens is warped what can it cause?
Can cause large amounts of induced astigmatism and
can be permanent
(found when astig changes or overrefracting)
What can we do to help someone having symptoms from a warped lens?
refit after patient stop contact lens use for a
day to allow cornea to go back to normal
What can cause 3 o’clock and 9 o’clock staining? 4
Tight lens,
poor blinks,
poor tear exchange
corneal edema
If the lens is too steep what will we observe during a fluorescein test? 2
Fluorescein pattern shows band
around periphery of cornea and central pooling (review picture)
-Likely to see air bubbles
How will a steep RGP lens move?
little to no movement
If the lens is riding too low due to its steepness how can this affect the cornea? 3
-apical edema
-inferior corneal erosion
-3 o’clock and 9 o’clock staining
What could be the cause of an RGP lens being too steep? 4
-Steep base curve
-Steep peripheral curves
-Decentered lens
-large lens
What will a px experience is the lens is too steep? 4 (initially, vision, tolerance, feeling)
Initially comfortable but as worn longer-
hazy vision,
not able to tolerate lens,
burning sensation
If the lens is too flat what will we observe during a fluorescein test? 3
Not conforming to cornea
shadow around peripheral - edge lift
more flurorescein around the edge
How will a flat RGP lens move?
Excessive movement
What can the px experience with a flat RGP lens? 2
-foggy vision
-spectacle blur
If the lens is riding too high due to flattness of the lens how can this affect the cornea? 2
corneal irritation
corneal edema
What could be the cause of an RGP lens being too flat?
BC is too flat
If the lens is decentered low, how should we accurately assess the fit and fluorescein pattern ?
put the lens back to the center
What are the causes of a low riding lens? 2
- Absence of peripheral band
- BC too steep
What are good characteristics of a well fitting RGP lens? 4
*Corneal alignment
*Weight distributed in large as possible area
*Good tear exchange (movement)
*Good vision
What does BOZR stand for?
Back Optic Zone Radius
What does TD mean?
Total diameter
The total diameter is normally 2mm smaller than the HVID and smaller than the palpebral aperature, but it does depend on the pupil diameter. T/F
TRUE
In Practice the higher the power the larger the diameter. But why?
for lens stability
In Practice the high astigmatism should have a smaller diameter. But Why?
to avoid excessive edge stand off in steep meridian
