UNIT FIVE - GP Flashcards

1
Q

What are the three lens design goals necessary for GP lenses?

A

Optical ( clarity & stability)
Physiological ( maintain ocular integrity)
Comfort

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2
Q

What are some key factors when looking at the optical design goal for GP lenses?

A
Good centralization 
Minimum post blink movement
Adequate optical zone
Minimum lens flexure
Deposit resistance
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3
Q

What are some factors when looking at the physiological design goal for GP lenses?

A

Adequate transmissibility
Sufficient movement ( waste products & oxygen
Minimum corneal bearing

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4
Q

What are some factors when looking at the comfort design goal for GP lenses?

A

Minimum lid interaction

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5
Q

Tear layer thickness ( Vault)

A

CPC (B.C. Radius)

POZ diameter

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6
Q

Power of Tear layer ( lacrimal lens)

A

SAM - steeper add minus

FAP - flatter add plus

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7
Q

What does the acronym SAM stand for?

A

Steeper add minus

( when referring to the lacrimal lens or power of tear layer) 

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8
Q

What does the acronym FAP stand for?

A

Flatter add plus

(when referring to the lacrimal lens or power of tear layer)

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9
Q

Why is a peripheral curve necessary?

A

Allows fresh reservoir of tears to collect around the lens between blinks.
Allows tear exchange between blinks.
Permits lens to glide over flatter peripheral regions of cornea.

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10
Q

What are some of the determining factors for peripheral curves?

A

Lens diameter, POZ diameter, CPC radius, corneal shape.

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11
Q

What does center thickness effect?

A

Transmissibility
Centering and movement (gravity)
Lens Flexure
Edge Thickness (hyperflange, myoflange) 

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12
Q

What are some of the determining factors for center thickness?

A

Prescription
Lens diameter
Lens material
Lens design

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13
Q

What are the General rules for rigid lens design? (3 total)

CPC OR BC

A

1) as the degree of astigmatism increases, a steeper base curve is needed for centralization.
2) as the size of the OZ increases, The CPC must be made flatter to maintain the correct vault.
3) increasing the vault causes the lens to fit tighter and reduces movement.

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14
Q

What are the General rules for rigid lens design? (3 total)

LENS DIAMETER

A

1) large (11.5mm), flat (<42.00D) corneas require large lenses.
2) Large palpebral apertures (>10mm) require larger lenses.
3) less than a +2mm upper lid position may require a larger lid attachment design or an inter-palpebral design.

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15
Q

What are the General rules for rigid lens design? (2 total)

OPTICAL ZONE DIAMETER

A

1) large pupils (>4mm) require larger optical zones.

2) the optical zone usually varies with the lens diameter.

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16
Q

What are the spherical rigid power rules ? (5 steps)

A

1) Transpose into - cyl
2) compare RX cyl to K readings and calculate residual astigmatism
3) if residual astigmatism is 1.00D or less, IGNORE. (CAP)
4) compensate for vertex is > +/- 4.00D
5) compare CPC in diopters to flat K and adjust power by difference (FAP or SAM)

17
Q

SPHERICAL RIGID LENS POWER RULES EXAMPLE !!!!

Rx: -3.00 +1.00 x 090
K reading: 42.00/43.00 @90

A

1) Convert to - cyl:
- 2.00 -1.00 x 180
2) Both RX and K are at 1.00 WTR ( difference between 43 and 42) ( -1.00 cyl @180)
3) CRA (residual astigmatism) is the difference between 1.00 WTR for both so 1.00-1.00= 0 CRA
4) CPC = 0.50D steeper than Flat K (flat K is 42) so CPC= 42.00+ 0.50 = 42.50
5) order lens power : -2.50 ( 0.50 steeper than -2.00)

18
Q

Paragon spherical GP design steps

A

1) lens diameter

2) CPC or BC

19
Q

Paragon Nomogram:

Use the nomogram to find the correct Lens diameter for:

K: 42.00/42.50@90

A

9.0–9.5 mm

If flat K is 42.00D, The guide indicates a diameter of 9.0–9.5 mm

20
Q

Paragon Nomogram:

Use the Nomogram to determine the CPC or BC for:

K: 42.00/42.50@90
Corneal cylinder: 0.50D
Diameter: 9.0-9.5mm

A

Flat K or 0.25D steeper

(first you must find the diameter in millimeters based off the flat is K, then you must find the corneal cylinder. Based off of those two numbers, the monogram shows the guided recommendations for the spherical GP design.)

21
Q

Summit Aspheric Periphery Design:

Using the summit table, convert BC to radius of curvature of:

K: 42.00/42.50@90
Corneal cylinder= 0.50D

A

8.08mm

First find the initial BC:
42.00 - 0.25: 41.75 (0.25 flatter than K)
Use the formula to convert:
r=337.5/D
r=337.5/41.75
r=8.08mm
22
Q

What are the three steps for diagnostic lens fitting?

A

1) Select diagnostic lens (CPC, POZ, and diameter are most important. Power should be within +/- 2.00D of Rx)
2) Inspect & Insert diagnostic lens.
3) Evaluate position & movement. (Interpalpebral and lid attachment)

23
Q

For diagnostic lens fitting, what should the power parameters be within?

A

+/- 2.00D of RX

24
Q

What are the steps when we are evaluating the lens and corneas relationship?

A

1) install fluorescein ( add color)
2) check the lens periphery
3) check for corneal patterns/CPC
(Alignment, steep, or flat)
4) problem solving

25
Q

What is the point of using fluorescein when evaluating the lens and cornea relationship?

A

The use of color or fluorescein can detect corneal patterns.

( alignment, steep, or flat cornea)

26
Q

What type of attachment is this ?

A

Lid attachment

27
Q

What type of attachment is this?

A

Interpalpebral

28
Q

What type of attachment is shown ?

A

Alignment GP pattern Spherical cornea

Looks smooth

29
Q

What type of attachment is shown ?

A

Steep GP Pattern Spherical Cornea

30
Q

What attachment is shown here ?

A

Flat GP pattern spherical cornea

31
Q

What type of attachment is this?

A

Alignment WTR

32
Q

What type of attachment is shown?

A

Steep WTR

33
Q

What are some problems that need solving when it comes to contact lenses?

A
Tight lens
No movement 
Loose lens
Low/high riding lens
3-9 staining 
Flare
Poor VA (Flexure)
34
Q

PROBLEM SOLVING BREAKDOWN SHEET

A
35
Q

What kind of problem does this image show ?

A

Low riding / loose

36
Q

What kind of problem does this image show ?

A

3:00 & 9:00 staining with Dellen

37
Q

What kind of problem does this image show ?

A

Flare