SCL

Question 1

Two classes of SCLs

Answer 1

HEMA

SiHy - protein-attracting in and of itself, hydrophobic

Question 2

three terms to use when evaluating SCLs

Answer 2

centration, coverage, movement

Question 3

Water content range __-__%

-what’s considered “low”? “high”?

Answer 3

25-75%

low: 50%

Question 4

Which is true for LOW water content TRADITIONAL SCLs: (lower/higher) Dk, (lower/higher) modulus, (less/more) deposits, used (more/less) for daily CLs

Answer 4

• lower Dk
• higher modulus (stiffer) - made THINNER
• smaller pores/deposits
• used MORE for dailies

Question 5

Which is true for HIGH water content TRADITIONAL SCLs: (lower/higher) Dk, (lower/higher) modulus, (less/more) deposits, used (more/less) for daily CLs

Answer 5

• higher Dk
• lower modulus- poorer durability/handling, made thicker
• more deposits, faster dehydration
• not daily! –>extended wear

Question 6

Dk = ?

• what does the D mean? The K?
• determined by the content of what 2 things? Which is more permeable?

Answer 6

oxygen permeability

• D = diffusion
• K = solubility
• 1) water, 2) silicone - MORE permeable

Question 7

What is Dk/T?

Answer 7

HOW MUCH O2 is actually getting to the eye

-remember: higher water content lenses need to be made THICKER

Question 8

Silicone is hydro___, but it is paired w/ hydrogel which is hydro____ to greatly improve ____ permeability

Answer 8

phobic
philic

oxygen permeability - Dk

Question 9

SCL CT is between 0.-0.

Answer 9

0.07-0.09mm (GP was .14)

Question 10

Air optix N+D and dailies total 1 have suuuper high what?

Answer 10

Dk

Question 11

4 lenses approved for 7 days/6 nights EW?

Answer 11

biofinity, ultra, air optix, acuvue oasys

Question 12

modulus = ____

• give two high modulus lenses
• 2 low modulus?

Answer 12

stiffness

• high mod (uncomfortable): N+D, PureVision (~1.50)
• low mod (slippery, comfortable): AV2, AV oasys (~.30)

Question 13

higher water content = (higher/lower) index of refraction?

Answer 13

lower (1.38-1.42)

Question 14

• ionic surfaces: (better/worse wettability)

- nonionic surfaces: (better/worse) deposit resistance

Answer 14

ionic: better wettability
- BUT: tend to attract proteins
nonionic: better deposit resistance

Question 15

(lower/higher) wetting angles = better surface wettability?

Answer 15

lower

Question 16

total one lens - (high/low) Dk SiHy core w/ hydro(philic/phobic) polymer chains bound to the core

Answer 16

high Dk, hydrophilic chains

Question 17

MoistureSeal: grows ___ around silicone polymer chains

Answer 17

PVP: HIGH Dk, LOW modulus

Question 18

FDA group 1 - water/ionicity?

-do they attract excess deposits? How about dryness?

Answer 18

Group 1: LOW water, NON-ionic

-NO: deposit-resistant, least dehydrating

Question 19

FDA group 2 - water/ionicity?

Answer 19

Group 2: HIGH water, NON-ionic

-dry out faster

Question 20

FDA group 3 - water/ionicity?

Answer 20

Group 3: LOW water, ionic

-PureVision, basically

Question 21

FDA group 4 - water/ionicity?

-GREATEST attraction to _____

Answer 21

Group 4: HIGH water, ionic

-greatest attraction to protein

Question 22

4 methods of manufacturing SCLs?

Answer 22

spincasting, lathe cutting, cast molding, lightstream technology

Question 23

spincasting: faster spin results in a more (minus/plus) lens

Answer 23

minus - THINS it, makes it larger, more minus

Question 24

T/F: Lathe cutting involves a button (like in GPs)
T/F: Water only touches/expands the lens after its manufacture
-which type of lenses are typically lathe-cut?

Answer 24

true

true - wicked expensive
-CONVENTIONAL (the old ones that last forever with a bunch of complications)

Question 25

Cast molding: two states?

Answer 25

dry: molded, polymerized, hydrated wet: molded, polymerized, NOT hydrated - lower cost/reproducible

Question 26

Lightstream: mainly which company/lens?

Answer 26

ciba dailies - like the total one | -polymerized w/ UV light - falls off and has nice clean edge

Question 27

a lens with a LOW water content usually has a (lower/higher) modulus - this allows it to be made (thinner/thicker)?

Answer 27

HIGHER modulus - it has less water so it's more rigid by nature! Allows it to be made THINNER

Question 28

a lens with a ____ modulus is easier to handle

Answer 28

HIGH - more rigid!

Question 29

an SCL with HIGH water content evaporates _____ than a lens with LOW water content

Answer 29

FASTER - counter-intuitive. but there's more water available to evaporate in a high-water-content lens

Question 30

BASE CURVE: tend to be (flatter/steeper) than GPs | -what's the range?

Answer 30

FLATTER. (compensate for increased diameter) | 8-9.2mm

Question 31

LD: DIAMETER: usually what range? usually how much LARGER than HVID? What's the OZD, usually? Depends on what?

Answer 31

LD: 13.5-15.0mm; 1-3 (or 2-3) LARGER than HVID (want 1-1.5mm around limbus) OZD: 8-10mm, depends on CLP

Question 32

CT range? Is it thicker or thinner for plus powers? | -Does CT increase or decrease w/ higher water content materials?

Answer 32

0. 03-0.10; THICKER for plus powers | - INCREASES

Question 33

T/F: All SCLs are lenticulated. T/F: The MORE lenticulated a lens is, the LARGER the OZD will be. -two major aspects affected by edge design?

Answer 33

TRUE. They have to be in order to maintain a thin profile. FALSE. There's less space for the OZD b/c you put it on the edge! -comfort, lid interaction

Question 34

4 reasons for using tints? (HEP-C)

Answer 34

Handling Enhancing colors Prosthetics Cosmetics (opaques)

Question 35

Enhancing tints c____ with your natural eye color, while opaque tints create a whole ___ color. -what's the problem with opaque tints (you should warn your pt, hint: night?)

Answer 35

combine, new -nighttime when pupil dilates: may see BLUR around edges

Question 36

what are some things you can mask/create w/ prosthetic tints?

Answer 36

corneal scars, iris defects, pupil occluders (amblyopes) | -VERY expensive/long production time - may be prism ballasted to maintain position

Question 37

Inversion markers should be looked at from the (outside/inside)?

Answer 37

OUTSIDE; otherwise they'll put 'em in the opposite eye

Question 38

what are the three replacement modalities? [CFD]

Answer 38

Conventional Frequent replacement Disposable

Question 39

what's the problem w/ conventional lenses? What's their typical replacement schedule? Do they require more/less cleaning?

Answer 39

more deposits - older lens type! they're custom (little glass jars) - MORE DEPOSIT PRONE, but lower cost. MORE cleaning

Question 40

frequent replacement lenses: how often do you change them? | -LOWEST _____ rate

Answer 40

planned schedule - 2wks-3 mos, worn DW or EW -lowest COMPLIANCE rate

Question 41

Disposable: can be DAILY (one day) - EW: how long? - Continuous wear: how long?

Answer 41

EW: one week, then chuck em | continuous wear: 1 month nonstop (N+D), then chuck

Question 42

(disposable) dailies - avg WT/day? can you nap?

Answer 42

10-14 hrs. No...i mean, 50% more likely for infection

Question 43

(disposable) EW lenses - max day/night WT? | - what additional requirement is inherent in these lenses?

Answer 43

7 days/6 nights | -gotta be FDA approved.

Question 44

(disposable) continuous wear - up to how many days max? | - lenses have to be WHAT material to qualify here? Must have a high ___

Answer 44

30 days, nonstop | -Silicone Hydrogel - high DK req'd.

Question 45

generally, SiHy lenses have a (higher/lower) wetting angle

Answer 45

HIGHER - silicone repels water - which is why they use different processes to make it hydrophilic again