Lec 4 RGP Fitting Troubleshooting

Question 1

Effect of large diameter lenses

Answer 1

Tighter

Move less

Higher edge lift

More lid attachment

Overall really stable

Question 2

Effect of smaller diameter lenses

Answer 2

Looser

Move more

Lower edge lift

Less lid attachment

Overall less restrictive to tears/oxygen to cornea

Question 3

What happens if low edge clearance

Answer 3

Less tears

Less debris and metabolic removal

Limited movement

Corneal indentation

Discomfort and hard to remove

Question 4

What happens if edge clearance is too wide

Answer 4

Excess tears Under lens

Discomfort

Epithelial compromise

Question 5

How to increase edge lift

Answer 5

Increase SCR OR PCR

Increase SCW OR PCW (while decreasing OZ diameter)

Increase total diameter along with OZD

Question 6

What brings a CL up

Answer 6

Pulling lid forces

Larger lenses

Question 7

What brings a CL down

Answer 7

Pushing lid forces

Smaller lenses

Plus power lenses/thicker lenses

Flatter BC

Gravity

Question 8

When will a lens move off to the side

Answer 8

Loose lens So flat or small

ATR astig As it slides along steep meridian

Decentred corneal apex

Question 9

How to fix an decentration problem

Answer 9

Add a -3/-6minus carrier if inferior displace or if they have problems with the lid then add a plus lenticular

Question 10

Basic RGP materials include

MMSFHC

Answer 10

Methy methacrylate

Methacrylic acid

Silicone

Fluorine

Hema

Cross linking agents

Question 11

Function of

Methy methacrylate

Methacrylic acid

Silicone

Answer 11

Methy methacrylate helps Mechanical and optical stability

Methacrylic acid Optical stability and wetting agent

Silicone helps Transmits 02

Question 12

What’s function of

Fluorine

Hema

Cross linking agents

Answer 12

Fluorine transmits 02 and improves surface quality for wearing

Hema is wetting agent for comfort

Cross linking agent makes CL more rigid

Question 13

What’s special about fluoro silicone acrylate

Answer 13

Adding fluorine increases DK by 30-70s and makes it more wettable and deposit resistant

Less deposits as masks negative surface charge and hydrophobic surface

Helps minimise protein binding

Question 14

What’s the techniques to measure wet ability

Answer 14

Sessile drop

Captive bubble

Wilhelmy plate

Question 15

Describe sessile drop

Answer 15

Put drop of moisture on material and using high mag watch how this droplet/bubble spreads

If bubble spreads more (small angle) then means more wettable

Question 16

Describe wilhelmy plate

Answer 16

High mag video records lens submerging in solution and record this advancing

Pull lens up and see how solutions draws against edge of lens and record receding angle

advancing angle is bigger than receding

Question 17

Describe captive bubble technique

Answer 17

Lens submerged into bowl of water

Bubble put into water with straw and as it floats up look at the tangent the bubble has with surface of lens

Receding angle should be bigger than advancing

Question 18

Problems in measuring wetting angle

Answer 18

Different techniques and measurements lead to poor standardisation

Question 19

How to reduce lens surface deposits

Answer 19

Lower dk means less affinity for proteins and lipids

Question 20

How to troubleshoot a high rx or thick lens

Answer 20

Increase refractive index

Question 21

How to make a RGP more flexible

Answer 21

Increase DK of material