Week 1.03 CLs Materials

Question 1

What does permeability mean Dk

Answer 1

Rate of O2 flow through unit of CL material when under a unit pressure difference

Question 2

What is Dk/t

Answer 2

Transmissibility of oxygen
Rate of oxygen flow under specified conditions through a contact lens of specified thickness when subjected to unit pressure differences

Based on material permeability
Related to material thickness in cm

Question 3

What can low o2 transmissibility cause

Answer 3

• epithelial microcysts
• endothelial ploymegathism
• oedema
• endothelial blobs
• corneal staining
• limbal hyperaemia
• microbial keratitis

Question 4

How much o2 does cornea need

Answer 4

Dk/t = 18 for 0% daily wear oedema
Dk/t = 65 for extended wear (<4% overnight oedema)

Question 5

Define oxygen flux

Answer 5

Volume of oxygen passing through a specified area of a contact lens per unit time when on the cornea

Question 6

PMMA

Answer 6

Polymethyl methacrylate

• no o2 content no permeability

Question 7

Conventional hydrogel CLs

Answer 7

Low water content hydrogels:
Dk/t too low despite lenses being thin - HEMA
38% water doesn’t allow much oxygen through

High water content hydrogels:
Evaporation of free water can lead to desiccation of cornea (drying) Dk~35 ISO units but lens needs to be thicker so Dk/t improvement limited

Question 8

Filcon

Answer 8

Soft lenses

Question 9

Focon

Answer 9

Rigid lenses

Question 10

Group suffix

Answer 10

1 <50% water content non ionic
2 >50% water content non ionic
3 <50% water content ionic
4 >50% water content ionic
5 enhanced oxygen permeable materials (SiH material)
5A ionic
5b >50% non ionic
5c <50% non ionic

Question 11

What’s an example of conventional hydrogel

Answer 11

Bio true
High water to match cornea
Dk/t 42 fatt
O2 93%
Surface mimics lipid layer of tears

Question 12

Water gradient lens example

Answer 12

Dailies total 1
Silicone hydrogel
33% water - low dehydration
Increases to 86% at surface
High lubricity

Question 13

RGP material groupings

Answer 13

Group 1: no silicone or fluorine
Group 2: silicone no fluorine
Group 3: silicone and fluorine
Group 4: fluorine but no silicone

Question 14

Daily disposable hydrogels

Answer 14

Acuvue moist J&J
Bio true B&L
Proclear cooper vision

Question 15

Daily disposable silicone hydrogels

Answer 15

Trueye J&J
Cooper vision my day
Cooper vision clarity 1 day
Dailies total 1

Question 16

Replacement lenses sih

Answer 16

SiH:
Acuvue oasys
Acuvue advance
Air optic aqua
Pure vision
Biofinity
Clarity monthly