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Contact Lens I > Contact Lens 1: CL Optics and Material Properties > Flashcards

Contact Lens 1: CL Optics and Material Properties Flashcards

1
Q

Contact Lenses

  1. Optically, CLs are considered what type of lenses?
  2. Their Thickness, relative to what, is Optically Significant?
A
  1. THICK Lenses

2. Relative to their SHORT RADII of Curvature.

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2
Q

Power

  1. F Thin = ?
  2. Fv Thick = ?
A
  1. F1 + F2

2. (F1)/(1-t/(nF1)) + F2

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3
Q

Vertex Distance

  1. It’s the Distance b/w what 2 things?
  2. Spectacles –> Depends on what?
    a. Asian Vertex distance?
    b. Caucasian?
    c. Refractions done at what?
  3. Contact lenses?
A
  1. the Lens and Eye
  2. on Fit of the Frame on the Face
    a. 10-14 mm
    b. 12-15 mm
    c. about 13.75 mm
  3. It’s on the Eye
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4
Q

Effective vs. Compensated Power

  1. Effective Power: Define
  2. Compensated Power: Define
A
  1. Power that’s Effectively delivered to the Eye based on the Distance at which a Lens is Placed
  2. Power that’s used to Compensate for Effective Power in order to deliver the Proper Rx to the Eye
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5
Q

Effective Power

  1. When a (+) Lens is Brought CLOSER to the Eye, it becomes what?
  2. When it’s moved away from the eye, it becomes what?
A
  1. Less Powerful

2. MORE POWERFUL

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6
Q

Effective Power

  1. F effective = ?
A
  1. F/(1+dF)

+) d when lens is Moved TOWARDS the Eye. (- in opposite situation

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7
Q

Effective Power

  1. Lenses, no matter whether they’re plus or minus, become EFFECTIVELY more what, as they’re brought CLOSER to the EYE?
A
  1. Effectively more (-)
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8
Q

Compensated Power

  1. In order to compensate for Effective power, what do we do?
A
  1. We change the power of a lens depending on what distance we intend to use it at.
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9
Q

Hyperopic Eye

  1. f1 is what to f2?

1/f1 is what to 1/f2?

A
  1. f1 < f2

1/f1 > 1/f2

f1 (closest to eye (CL)) Needs MORE Power to Place its focal point on the Far Point.

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10
Q

Compensated Power

  1. F compensated = ?
A
  1. F/(1-dF)
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11
Q

Vertex Distance Calculation

  1. F contact lens = ?
  2. When is it clinically necessary to vertex a spectacle prescription? Why? (Listen to Lecture at slide 26)
A

F(spectacle Sphere Power)/ (1-d(vertex distance in m)*F(spectacle sphere power)

  1. When it’s >or equal to +/- 4.00D

Because vertexing anything under +/-4.00D will result in less than 0.25D change in power from spectacle to corneal plane.

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12
Q

What about a Sphero-Cylindrical Rx?

A

Need to put Rx on a Power Cross first. Then, Vertex any meridian that’s greater than or equal to +/- 4.00

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13
Q

Refractive Index

  1. of a SCL refers to that of a material’s what?
  2. n Has what relationship w/WATER Content for HYDROGEL LENSES?
A
  1. Material’s Fully Hydrated State; n is a property of the polymer and its cross-linking
  2. An INVERSE LINEAR RELATIONSHIP
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14
Q

RI’s of CL Materials

  1. PMMA?
  2. GP?
  3. SCL?
A
  1. 1.49
  2. 1.44-1.53
  3. 1.38-1.44
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15
Q

% H2O/RI Relationship

  1. Well established relationship b/w RI and H2O Content does NOT Hold as well for what materials?
A
  1. For SILICONE HYDROGEL Materials. (Why…cuz these and Hydrogel have Different Material Chemistries)
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16
Q

CL Wettability

  1. The Wettability of a lens is measured by its ability to support what?
  2. A Lens w/Limited Wettability can cause what 3 problems?
  3. 1 of the C’s Industry’s Major investments involves developing lens Surfaces that are highly what?
A
  1. To Support a Continuous and Rupture-resistant tear film on its surface
  2. Discomfort, Ocular Physiological Changes and/or Reduced Visual Performance
  3. Highly Wettable in the eye
17
Q

Wettability

  1. Contact Angle: What is it?

**Listen to lecture @ Slide 45…About Wettability

A
  1. Theta c. Quantitative Measure of the wetting of a solid by a liquid. DEFINED Geometrically as the ANGLE formed by a liquid at the 3 phase boundary where a Gas, Liquid, and Solid Intersect
18
Q

Three methods of measuring Contact Angle?

A
  1. Sessile Drop
  2. Captive Bubble
  3. Wilhemy Plate
19
Q

Sessile Drop

  1. Drop of Liquid placed where?
  2. Measure Contact point b/w what?
  3. Method?
A
  1. on the Surface
  2. Solution and Material
  3. OLDEST and LEAST ACCURATE Method
20
Q

Classic Sessile Drop

  1. Classic Sessile drop test gives us what kind of angle?
A
  1. An ADVANCING ANGLE
21
Q

Dynamic Sessile Drop

  1. Gives us what kind of Angle(s)?
A

An ADVANCING (Liquid being added) and a RECEDING ANGLE (Liquid being removed)

22
Q

Advancing vs. Receding

  1. Advancing Angle
    a. Tendency of a liquid to spead over what?
    b. This is similar to the eyelid closing and what happening?
  2. Receding Angle
    a. Tendency of a liquid to do what?
    b. This is analogous to the eyelid being open and what happening?q
A
  1. a. over a Lens surface
    b. And tear film spreading over the lens
  2. a. to withdraw
    b. and tear film breaking up over the lens
23
Q

Contact Angle Hysteresis

  1. CA Hysteresis is the difference b/w what 2 things?
A
  1. Advancing and receding angles.

CA Hysteresis = advancing - receding

24
Q

Captive Bubble

  1. Bubble of air introduced into the liquid environment to evaluate how much the liquid does what?
  2. Avoids what?
A
  1. Recedes from the solid

2. Avoids Material Dehydration

25
Q

Advancing and Receding Angles

  1. The Contact Angle thru Liquid during bubble expansion yields what?
    a. Tendency of liquid to withdraw from what?
  2. Contact angle thru liquid during bubble contractions yields what?
    a. Tendency of liquid to coat what?
A
  1. Receding Angle
    a. from the Lens surface
  2. the Advancing Angle
    a. to Coat Lens Surface
26
Q

Captive bubble

  1. What angle size is VERY WEttable?
A
  1. The Smaller Angle.
27
Q

Wilhelmy Plate

  1. Kind of test?
  2. Dipping GP Material how?
  3. Measuring Contact Angle b/w what?
A
  1. Dynamic test
  2. in and out of liquid
  3. Lens material and liquid
28
Q

Advancing vs. Receding

  1. Advancing Contact Angle is measured as what happens?
  2. Receding Contact Angle is measured as material is what?
A
  1. As the fluid is moved over a previously unwet surface

2. is Withdrawn from the liquid

29
Q

Contact angle hysteresis

A

Advancing CA tends to be larger than the Receding CA (CA Hysteresis = Advancing CA - Receding CA)

30
Q

Wetting Angle on Eye

  1. WEtting Angles DO NOT Correlate well with what?
  2. Tear Film is comprised of many components. What 4 are there?
  3. Biofilm forms over lens, acting as what?
A
  1. with ON EYE Wettability
  2. Lactoferrin, Lipids, Lysozyme, and Mucin
  3. Acting as a Natural Wetting Agent

Contact Lens I (4 decks)

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