Week 4 - RGP Fitting Problems and Solutions

Question 1

What are 4 MAIN symptoms of poor fit?

Answer 1

1. Flare
2. Blurred vision
3. Burning (solution or dirty)
4. Spectacle blur

Question 2

What will a px experience with flare? 2

Answer 2

streaming
halos

Question 3

What can cause flare? 3

Answer 3

small optic
large pupil
corneal edema

Question 4

What could cause blurry vision? 5

Answer 4

• Lens switched
• Dirty/coated or smudged lens
• Retinoscope (radiuscope)
  (gives irregular reflex-due to greasy lens)
• Corneal edema
  -scratched lens

Question 5

If the patient is feeling a burning sensation soon afrer lens insertion. What could be the problem? 2

Answer 5

wetting agent sensitivity
dirty lens

Question 6

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?

Answer 6

Poor blinking
poor fitted lens

corneal edema

Question 7

What is spectacle blur?
How long on average does it last?

Answer 7

-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

Question 8

How to determine if flare is due to small optic zone or decentration? 2

Answer 8

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

Question 9

When is spectacle blur considered normal?

Answer 9

if it lasts less than 30 mins

Question 10

If the patient is experiencing spectacle blur in excess of 0.50D (over refracting) what do we need to do?

Answer 10

check the fit of the lens

Question 11

How does the diameter of the lens affect spectacle blur?

Answer 11

large diameter the more prominent spectacle blur is

Question 12

How does the thickness of the lens affect spectacle blur?

Answer 12

Thicker lens greater the duration of blur

Question 13

What can cause excessive blur while wearing and not wearing CLs ?

Answer 13

-Caused by corneal edema

Question 14

Why does corneal edema cause excessive blur?

What do we do with the RGP/PX if they are suffering with corneal edema?

Answer 14

Edema will cause changes in the curvature of the cornea thus px wanting more minus

refit/refer

Question 15

Who are more likely to suffer from spectacle blur, hyperopia/myopia?

Answer 15

Hyperopia as the centre of the lens is thicker

Question 16

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)

Answer 16

• Reduce diameter
• Blend lenses better
• Flatten and extend the
  peripheral curve
• Switch to thin lens
• Fix by using higher Dk material

Question 17

What are common causes of mucus (common complaint) on the lens? 2

Answer 17

-make up
-poor edge design bumping into Meibomian glands secretion and lid irritation

Question 18

Poor edges account for most problems. T/F

Answer 18

TRUE

Question 19

What can poor edges causes? 5

Answer 19

Corneal abrasions,
lid irritation,
dirty lens,
photophobia,
low lens tolerance

Question 20

If a lens is warped what can it cause?

Answer 20

Can cause large amounts of induced astigmatism and
can be permanent
(found when astig changes or overrefracting)

Question 21

What can we do to help someone having symptoms from a warped lens?

Answer 21

refit after patient stop contact lens use for a
day to allow cornea to go back to normal

Question 22

What can cause 3 o’clock and 9 o’clock staining? 4

Answer 22

Tight lens,
poor blinks,
poor tear exchange
corneal edema

Question 23

If the lens is too steep what will we observe during a fluorescein test? 2

Answer 23

Fluorescein pattern shows band
around periphery of cornea and central pooling (review picture)
-Likely to see air bubbles

Question 24

How will a steep RGP lens move?

Answer 24

little to no movement

Question 25

If the lens is riding too low due to its steepness how can this affect the cornea? 3

Answer 25

-apical edema
-inferior corneal erosion
-3 o’clock and 9 o’clock staining

Question 26

What could be the cause of an RGP lens being too steep? 4

Answer 26

-Steep base curve
-Steep peripheral curves
-Decentered lens
-large lens

Question 27

What will a px experience is the lens is too steep? 4 (initially, vision, tolerance, feeling)

Answer 27

Initially comfortable but as worn longer-
hazy vision,
not able to tolerate lens,
burning sensation

Question 28

If the lens is too flat what will we observe during a fluorescein test? 3

Answer 28

Not conforming to cornea
shadow around peripheral - edge lift
more flurorescein around the edge

Question 29

How will a flat RGP lens move?

Answer 29

Excessive movement

Question 30

What can the px experience with a flat RGP lens? 2

Answer 30

-foggy vision
-spectacle blur

Question 31

If the lens is riding too high due to flattness of the lens how can this affect the cornea? 2

Answer 31

corneal irritation
corneal edema

Question 32

What could be the cause of an RGP lens being too flat?

Answer 32

BC is too flat

Question 33

If the lens is decentered low, how should we accurately assess the fit and fluorescein pattern ?

Answer 33

put the lens back to the center

Question 34

What are the causes of a low riding lens? 2

Answer 34

• Absence of peripheral band
• BC too steep

Question 35

What are good characteristics of a well fitting RGP lens? 4

Answer 35

*Corneal alignment
*Weight distributed in large as possible area
*Good tear exchange (movement)
*Good vision

Question 36

What does BOZR stand for?

Answer 36

Back Optic Zone Radius

Question 37

What does TD mean?

Answer 37

Total diameter

Question 38

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

Answer 38

TRUE

Question 39

In Practice the higher the power the larger the diameter. But why?

Answer 39

for lens stability

Question 40

In Practice the high astigmatism should have a smaller diameter. But Why?

Answer 40

to avoid excessive edge stand off in steep meridian