Flashcards in CL 2-2: GP Parameters 2014 Deck (55):
GP Manufacturing: (1) Polymerization
1. It's a Combination of what 2 THINGS?
2. The Final Products are what?
a. What can these then be cut into?
3. What are these put through at this point?
a. How does this Process work?
1. of Monomers and other ADDITIVES (like TINTS)
3. an ANNEALING PROCESS
a. Heat the material to a VERY HIGH TEMP in an Oven, then cool it VERY SLOWLY; You get a MORE HOMOGENOUS END PRODUCT
GP Manufacturing: (2) Machining
a. Which surface is CUT FIRST?
b. Cannot produce EXCESSIVE HEAT: WHY? (what will happen to the CL)?
c. Does Manufacturing of the MATERIAL get more difficult with a HIGHER/LOWER Dk?
2. Base curve is cut with what tool?
a. Base Curve Surface is then what?
1. a. CONCAVE first, then Convex
b. It will cause DISTORTION
c. HIGHER Dk = More difficult to manufacture
2. a LATHE
GP Manufacturing: (3) Blocking
1. Lens mounted back on LATHE
a. They then use what?
b. This product has three properties or things it does...
2. Slide 13: Ask: Are ALL GPs a NON-WETTING LENS???
1. a. Use of "PITCH" (WAX)
b. i. Vegetable Tar Product
ii. Low Melting Point
iii. Leaves Residue
GP Manufacturing (4): FRONT CURVE Cutting and Polishing
1. Similar to BASE CURVE, except what kind of surface is created?
2. The Blank is reduced to its what...? (2)
3. Polishing is SIMILAR to what?
2. it's FINAL THICKNESS and POWER
3. to BACK SURFACE
GP Manufacturing (5): Finishing
1. Lens is cut down to DESIRED DIAMETER (how much larger though to Allow for Edge Shaping and Polishing?)
2. What Curves can now Be Applied?
3. Soft Pad is used to do what 2 things?
4. What is the FINAL STEP before INSPECTION?
1. about 0.1-0.2 mm larger
2. Peripheral Curves
3. Polish and BLEND PERIPHERAL CURVES
4. EDGE POLISHING
1. What are the 3?
1. Modulus (Resistance to deformation)
2. Specific Gravity (Weight)
3. Oxygen Transmissibility
GP: Properties (2): Modulus
1. Modulus = ?
2. What does the slope of this refer to?
3. Stiffness of a Material is the Ability of a GP to do what?
4. How do you figure it out for a GP?
2. the Stiffness measured in MEGAPASCALS (MPa)
3. to MASK CORNEAL ASTIGMATISM (resistance to flexure)
4. APPLY FORCE (stress) to a lens until it begins to deform (Strain)
GP: Properties: (3): Specific Gravity
1. Weight of a GP lens at a given temperature divided by what?
a. What is LOW?
d. What does this affect?
1. by weight of an Equal Volume of Water at the SAME TEMPERATURE
a. Less than or EQUAL to 1.10
b. 1.11 - 1.20
c. more than 1.20
d. LENS position on the eye
GP: Properties (4): Oxygen
1. Dk = ?
2. Dk/t = ?
3. Equivalent Oxygen Percentage (EOP) = ?
4. Higher Oxygen Permeability does what?
3. Measured in vivo
4. Makes the Lenses more flexible (Material chemistry is a major contributing factor to flexibility)
1. PMMA = ?
2. PMMA + Silicone & Fluorine = ?
3. Silicone Acrylate/ Fluorosilicone Acrylate = ?
1. Very stiff (High Modulus)
2. Less Stiff
3. Higher Dk GP materials have a LOWER MODULUS than their Lower Dk Counterparts.
(This is the opposite from SCLs)
1. What is Wettability/Wetting Angle?
1. Helps us know how well a CL will wet and Stay wet when placed and worn on the Eye
1. Contact Angle: It's a quantitative measure of what?
1. of the Wetting of a solid by a liquid. It's found at the angle formed by a liquid at the 3 phase boundary where a liquid, gas, and solid intersect.
1. Sessile Drop
2. Classic Sessile Drop
3. Dynamic Sessile Drop
4. Captive Bubble
1. Drop of liquid on lens material. Measure CONTACT POINT b/w Liquid and Solid (OLDEST METHOD)
2. Gives us an ADVANCING ANGLE
3. Gives us an ADVANCING ANGLE (liquid being added) and a RECEDING ANGLE (liquid being removed)
4. Bubble of Air trapped against the surface of the GP to determine Contact angle (MORE Repeatable: Less Dehydration of material) (Very wettable for the SMALLER Angle measured from Lens material to Gas)
1. What 4 Factors Affect the Sessile Drop Test? (TESS)
1. Time of Measurement
3. Size of Drop
4. Surface Dehydration
GP Wettability: Wilhelmy Plate
1. Static or Dynamic Test?
2. Dipping GP material in what?
3. Measuring Contact Angle between what?
1. Dynamic Test
2. in and out of a test solution
3. b/w Lens material and Solution
Dynamic Contact Angle (CA)
1. Contact Angle (CA) Hysteresis = ?
1. Advancing CA - Receding CA
Wetting Angle vs. On-eye Wettability
1. Wetting Angle measurements are NEEDED for GP lens Testing and FDA Approval. However, do these tests have a CORRELATION with on-eye Wetting/Comfort?
1. How is it done?
2. What does it remove from Manufacturing?
3. Wettable Surface without what?
4. So what does it IMPROVE?
5. What is the LIMITATION?
1. Lenses Placed in a VACUUM chamber and Bombarded w/Plasma Gas
2. RESIDUALS from manufacturing
3. w/o Extra Cleaning before dispensing
4. Improves wettability
5. It's unknown how long the Tx lasts.
Silicone Acrylate (SA)
1. What does Adding Silicone do to O2 Permeability?
2. What 3 things does SILICONE DECREASE?
3. Charge on SA Surface?
a. What does this ATTRACT?
1. Increases it
2. Decreases Wettability, Stability, and Deposit Resistance
3. Negative Ionic Charge
a. Protein Deposits
Fluorosilicone Acrylate (FSA)
1. Why would we introduce Fluorine?
2. What does Fluorine do to O2 permeability?
3. What does FLUORINE DECREASE (3 things)
4. Is Fluorine Hydrophobic/Hydrophilic?
a. What does it Resist?
b. What does it Attract?
1. Because you can only add so much silicone BEFORE compromising Lens Properties
2. Increases it
3. Wettability, Stability, and Deposit Resistance (But not as much as silicone)
a. Protein Deposits
b. ATTRACTS LIPIDS!!
1. Less than or EQUAL to 50
3. More than or EQUAL to 100
Choosing a Material
1. Low Dk
a. Best for what kind of Astigmatism?
b. DW, FW, EW?
c. What 2 things are OPTIMUM?
2. High Dk
a. Best for what?
b. DW, FW, EW and for whom? (2)
c. They also include what Design?
3. Hyper Dk
a. Best for what?
1. a. Myopia
c. Wettability and Stability
2. a. Hyperopia
b. Flexible Wear (Hyperopia), and EW (Myopia)
c. Prism Ballasted Lens designs
3. a. Hyperopia
but can be done for EW (myopia and hyperopia)
GPs and DK/t
1. GPs are LESS Dependent on O2 Transmissibility than what?
1. Than SCL. Why....IDK LISTEN to lecture...
1. GP exchange % of underlying tear layer per blink?
2. SCL will promote only what?
3. The SCL-Wearing Cornea DEPENDS on what?
2. only MINIMAL, if any, tear exchange
3. on the Dk/t for Oxygen
Parameters Specified for GP Rx
1. What 5 things are the MINIMUM things you need?
2. to design your own lens, what would you need? (5)
1. POWER, OAD, BCR, Color, MATERIAL
2. On top of the five things listed above, you would need, OZD, PCR, PCW, CT, and BLEND
1. What Properties are measured to 1 decimal place?
2. What are Peripheral Curves?
a. how are they listed?
3. Bicurve Lens
4. Tricurve Lens
5. Properties Measured to 2 DECIMAL PLACES?
1. OAD, OZD
2. Fitting portion of the Lens
a. PCR x PCW ...Have to Add the Width of all PCs to the OZD and Blend to get the OAD
3. BCR + Peripheral Curve
4. Base Curve (BCR) + Intermediate Curve + Peripheral Curve
5. PCR and PCW (1-2 decimal places)
1. The Curvature of a CL gets Progressively Steeper/Flatter as we move out from Base Curve to 2ndary Curve to Tertiary Curve to Peripheral Curve....
Determining Number of Curves
1. Standard Spherical GP Lenses are Generally what curve(s)?
2. If a Cornea has Higher/Lower Eccentricity, MORE CURVES will be needed
a. Ex: Irregular Corneas...?
b. Why is this?
1. BICURVE or TRICURVE
a. That's sufficient for Normal Corneal Eccentricity
a. Like Keratoconus
b. More PCs allow for a more gradual Transition
1. Curves are blended together to do what?
2. 3 types of blend?
3. Heavier the Blend, the Harder it is to what?
**Remember: OAD = ?
1. to Smooth transition b/w Them
2. Light, Medium, Heavy
3. the Harder it is to visualize the distinction b/w curves
**OZD + 2PCW (Don't forget to add all peripheral Curves)
2. Found in or outside of OZ?
3. Specified: Important for what?
4. Can be determined by Lab for what kind of cornea?
1. Fitting Only
2. Outside Optic Zone
3. for Atypical Corneal Eccentricities
4. for an AVG Cornea
Empirical vs. Diagnostic Fitting. What's the difference?
Empirical: Call in order for starting lens based on Calculations using PATIENT PARAMETERS (Ks and Rx)
2. Diagnostic: Put on a Diagnostic Lens from Fitting set and go from there!
GP Replacement Schedule?
1. 1-2 yrs or prn.
usually for Scratched or Cracked Lenses, or Stubborn Deposits
GP Wearing Schedule
1. 2 types
2. When new to GPs or SCLs, adaptation wearing schedule?
1. DW and EW (any overnight wear)
2. Day 1: 4 hrs then +2 hrs each day.
1. 3 Purposes
2. Right eye vs. Left eye color?
3. 2 other methods of identification?
1. Visibility (aid handling); Enhancing (enhance natural eye color);
2. Differentiation (b/w right and left lens): RIGHT = gReen and Left = bLue
3. Dot or Drill Dot
Verifying GP CLs
1. What 4 things?
1. Power, OAD, BCR, CT
1. When we refer to power, we refer to which one?
2. Most CL labs use what power?
1. Back Vertex Power
2. Front Vertex Power
Back Vertex Power
1. Measured by placing CL w/which SIDE towards us?
2. BVP = ?
1. CONVEX SIDE
2. F1/(1- (t/n)*F1) + F2
Front Vertex Power
1. Opposite of Back
1. CONCAVE side towards me
FVP = F1 + F2/(1-(t/n)*F2)
FVP vs. BVP
1. When CT is THIN, is there a difference b/w them?
2. What about High Plus Rxs?
2. CT becomes more significant and thus BVP and FVP can differ (establish your lab's convention)
Types of GPs
2. Front Surface Toric
3. Back Surface Toric
1. 1 Power
2. Spherical Back surface, Toric front surface
4. Both front and back surfaces are toric
GP Power Verification Conventions
1. Front Surface Toric: How do you write it?
2. Back Surface/Bitoric GP: What do you do?
1. Sphero-cyl Rx (like Spec Rx)
2. Read straight off the lensometer (drum power)
Ex: -3.00/-6.00 (MOST PLUS POWER COMES FIRST!)
1. What three things?
1. Hand held magnifier, Projection magnifier, or V-gauge (measure to nearest 0.1 mm)
Hand Held Magnifier
1. How do you measure it?
1. Place Posterior Lens surface on Scale; Look thru eyepiece at a fluorescent light; Center Lens Vertically
*Can also verify OZD: Look for demarcation b/w Optic Zone and Peripheral Curves to the nearest 0.1 mm
1. Lens is projected onto what?
1. Onto Screen and diameter is read off.
V-Channel Gauge: how does it work
Channel down center gets progressively smaller; Insert lens and let gravity slide lens down
THEN read off AT MIDPOINT of GP!
1. Average for normal Corneas (Overall diameter)
2. Affects what else?
1. 9.0 to 9.6 is average (can go MUCH bigger for IRREGULAR Corneas)
2. Affects Sagittal Depth: LARGER Lens w/Given BCR will FIT STEEPER than SMALLER LENS in same BCR
1. Base Curve Radius (BCR/BC) is what?
a. Sometimes called what?
2. This is measured to what?!
3. Verified in what instrument?
1. Radius of Curvature of the POSTERIOR SURFACE OPTIC ZONE
a. the Back Optic Zone Radius (BOZR)
2. in mm to 2 DECIMAL PLACES (to the nearest 0.01 mm; contrast to SCL??)
3. Using a RADIUSCOPE
Toricity of GP Contact Lenses
1. How do you provide different Powers 90 degrees apart (Toricity)?
a. If found on FRONT SURFACE?
b. Back Surface toric?
2. How do you verify GP BC?
b. Front surface toric
c. Back surface/Bitoric GP
1. Curvature of the lens is different in each major meridian
a. 2 curves on front
b. 2 curves on back
c. 2 curves on FRONT and the BACK!
2. a. 1 BC
b. 1 BC
c. 2 BCs: BC FLAT/ BC STEEP (Ex: -7.67 / 7.37)
How many Base Curves?
1. Base Curve refers to what?
2. Any lens that has a SPHERICAL SURFACE will only HAVE what?
3. Any lens that HAS a TORIC BACK SURFACE will have what?
1. the back surface
2. 1 BASE CURVE (Spherical GP; Front Surface Toric GP)
3. have 2 BASE CURVES 90 degrees APART (Back surface toric GP and Bitoric GP)
Base Curve Radii
1. Lenses of Equal Diameter
1. a. BC = 8.5 mm
b. BC = 9.5 mm
BCR in mm vs. Diopters
1. BCR can be converted to m from D and vice Versa: How?
1. (n' - n)/r
n' = 1.3375 (standard corneal refractive index)
n = 1 (Air)
Curvature in Diopters
How to convert to Diopters from Meters and from mm?
m: 0.3375/r (in meters)
mm: 337.5/r (in mm)
1. MOST common and MOST accurate
2. Keratometer must be recalibrated; and Needs Special Attachment
1. Must include what?
a. Measured to NEAREST what?
b. Verified USING what?
1. Leading ZERO
a. 0.01 mm
b. using a CT Gauge