SCL Flashcards
Two classes of SCLs
HEMA
SiHy - protein-attracting in and of itself, hydrophobic
three terms to use when evaluating SCLs
centration, coverage, movement
Water content range __-__%
-what’s considered “low”? “high”?
25-75%
low: 50%
Which is true for LOW water content TRADITIONAL SCLs: (lower/higher) Dk, (lower/higher) modulus, (less/more) deposits, used (more/less) for daily CLs
- lower Dk
- higher modulus (stiffer) - made THINNER
- smaller pores/deposits
- used MORE for dailies
Which is true for HIGH water content TRADITIONAL SCLs: (lower/higher) Dk, (lower/higher) modulus, (less/more) deposits, used (more/less) for daily CLs
- higher Dk
- lower modulus- poorer durability/handling, made thicker
- more deposits, faster dehydration
- not daily! –>extended wear
Dk = ?
- what does the D mean? The K?
- determined by the content of what 2 things? Which is more permeable?
oxygen permeability
- D = diffusion
- K = solubility
- 1) water, 2) silicone - MORE permeable
What is Dk/T?
HOW MUCH O2 is actually getting to the eye
-remember: higher water content lenses need to be made THICKER
Silicone is hydro___, but it is paired w/ hydrogel which is hydro____ to greatly improve ____ permeability
phobic
philic
oxygen permeability - Dk
SCL CT is between 0.-0.
0.07-0.09mm (GP was .14)
Air optix N+D and dailies total 1 have suuuper high what?
Dk
4 lenses approved for 7 days/6 nights EW?
biofinity, ultra, air optix, acuvue oasys
modulus = ____
- give two high modulus lenses
- 2 low modulus?
stiffness
- high mod (uncomfortable): N+D, PureVision (~1.50)
- low mod (slippery, comfortable): AV2, AV oasys (~.30)
higher water content = (higher/lower) index of refraction?
lower (1.38-1.42)
- ionic surfaces: (better/worse wettability)
- nonionic surfaces: (better/worse) deposit resistance
ionic: better wettability
- BUT: tend to attract proteins
nonionic: better deposit resistance
(lower/higher) wetting angles = better surface wettability?
lower
total one lens - (high/low) Dk SiHy core w/ hydro(philic/phobic) polymer chains bound to the core
high Dk, hydrophilic chains
MoistureSeal: grows ___ around silicone polymer chains
PVP: HIGH Dk, LOW modulus
FDA group 1 - water/ionicity?
-do they attract excess deposits? How about dryness?
Group 1: LOW water, NON-ionic
-NO: deposit-resistant, least dehydrating
FDA group 2 - water/ionicity?
Group 2: HIGH water, NON-ionic
-dry out faster
FDA group 3 - water/ionicity?
Group 3: LOW water, ionic
-PureVision, basically
FDA group 4 - water/ionicity?
-GREATEST attraction to _____
Group 4: HIGH water, ionic
-greatest attraction to protein
4 methods of manufacturing SCLs?
spincasting, lathe cutting, cast molding, lightstream technology
spincasting: faster spin results in a more (minus/plus) lens
minus - THINS it, makes it larger, more minus
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?
true
true - wicked expensive
-CONVENTIONAL (the old ones that last forever with a bunch of complications)
Cast molding: two states?
dry: molded, polymerized, hydrated
wet: molded, polymerized, NOT hydrated - lower cost/reproducible
Lightstream: mainly which company/lens?
ciba dailies - like the total one
-polymerized w/ UV light - falls off and has nice clean edge
a lens with a LOW water content usually has a (lower/higher) modulus - this allows it to be made (thinner/thicker)?
HIGHER modulus - it has less water so it’s more rigid by nature! Allows it to be made THINNER
a lens with a ____ modulus is easier to handle
HIGH - more rigid!
an SCL with HIGH water content evaporates _____ than a lens with LOW water content
FASTER - counter-intuitive. but there’s more water available to evaporate in a high-water-content lens
BASE CURVE: tend to be (flatter/steeper) than GPs
-what’s the range?
FLATTER. (compensate for increased diameter)
8-9.2mm
LD: DIAMETER: usually what range? usually how much LARGER than HVID?
What’s the OZD, usually? Depends on what?
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
CT range? Is it thicker or thinner for plus powers?
-Does CT increase or decrease w/ higher water content materials?
- 03-0.10; THICKER for plus powers
- INCREASES
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?
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
4 reasons for using tints? (HEP-C)
Handling
Enhancing colors
Prosthetics
Cosmetics (opaques)
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?)
combine, new
-nighttime when pupil dilates: may see BLUR around edges
what are some things you can mask/create w/ prosthetic tints?
corneal scars, iris defects, pupil occluders (amblyopes)
-VERY expensive/long production time - may be prism ballasted to maintain position
Inversion markers should be looked at from the (outside/inside)?
OUTSIDE; otherwise they’ll put ‘em in the opposite eye
what are the three replacement modalities? [CFD]
Conventional
Frequent replacement
Disposable
what’s the problem w/ conventional lenses? What’s their typical replacement schedule? Do they require more/less cleaning?
more deposits - older lens type! they’re custom (little glass jars) - MORE DEPOSIT PRONE, but lower cost. MORE cleaning
frequent replacement lenses: how often do you change them?
-LOWEST _____ rate
planned schedule - 2wks-3 mos, worn DW or EW
-lowest COMPLIANCE rate
Disposable: can be DAILY (one day)
- EW: how long?
- Continuous wear: how long?
EW: one week, then chuck em
continuous wear: 1 month nonstop (N+D), then chuck
(disposable) dailies - avg WT/day? can you nap?
10-14 hrs. No…i mean, 50% more likely for infection
(disposable) EW lenses - max day/night WT?
- what additional requirement is inherent in these lenses?
7 days/6 nights
-gotta be FDA approved.
(disposable) continuous wear - up to how many days max?
- lenses have to be WHAT material to qualify here? Must have a high ___
30 days, nonstop
-Silicone Hydrogel - high DK req’d.
generally, SiHy lenses have a (higher/lower) wetting angle
HIGHER - silicone repels water - which is why they use different processes to make it hydrophilic again
