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Optics to Memorize > Contact Lenses > Flashcards

Contact Lenses Flashcards

1
Q

How is the equation for Shape factor different from the Equation for Back Vertex Power

A

Both use F1 in the denominator but the Shape Factor Equation has a numerator of 1 and the Fv equation has a numerator of F1

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2
Q

Contact Lenses are _____ lenses so to find their power use the equation for _______

A

Thick; Back Vertex Power

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3
Q

When using the Effective Vergence equation going from CL to Specs or vise versa do you have to adjust the vertex distance?

A

NO!!
You only have to adjust the vertex distance when calculating Power Factor of SM because it is measured to the entrance pupil

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4
Q

How does power in the LL change per every 0.1mm change in BC?

A

0.50D

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5
Q

Residual Astigmatism Equation

A

Spec Cyl - K Cyl

-remember to vergence SRx if >4.00

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6
Q

Javals Rule

A

Estimate of refractve cyl based on K readings

Refractive cyl = 1.25 (K cyl) + (-0.50 x 090)

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7
Q

Parameter: Optical Zone Diameter (OZD)

A

Usable area of optics
Adjust in steps of 0.4mm (adjust BC by 0.25D)
-Increase OZD -> increase Sag -> steeper

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8
Q

Parameter: Overall Diameter (OAD)

A

Adjusted in steps of 0.4mm (Adjust BC by 0.25D)

Chosen to minimize flare, lid attach and maximize comfort (bigger)

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9
Q

Parameter: Peripheral Curves

A

Contribute to alignment b/t edge and peripheral cornea

- prevents bearing on K, promotes tear exchange, and centration

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10
Q

Parameter: Edge Thickness

A

Ideal is similar to a -3.00 lens

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11
Q

Parameter: Edge Lift

A

Change in steps of 1.00mm
Too little edge lift: Traps debris, no movement
Too much edge lift: decreased centration, increased 3 & 9 desication

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12
Q

Parameter: Center Thickness

A

Change in steps of 0.03mm
Thinner = better oxygen transmission
Higher Dk materials need a thicker CL to minimize flexure

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13
Q

Parameter: Center of Gravity

A

More posterior = Better centration

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14
Q

Describe fluorescein pooling in WTR vs ATR

A

Dumbell pattern corresponds to touch
WTR: horizontal
ATR: vertical

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15
Q

When to fit Bitoric

A

When K cyl is > 2.50D AND spec cyl =/= 1.5Kcyl

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16
Q

When to fit front surface toric

-How to adjust for rotation

A

K cyl is < 2.50D but Rx cyl is high

Prism Ballasting with BD prism helps prevent rotation

17
Q

When to fit Back Surface Toric

A

Corneal cyl is > 2.50D and spec cyl is = 1.5Kcyl

-usually used in ATR corneas

18
Q

Bitoric Fitting philosophies

A

Saddle Fit: both meridians fit equally flat (usually 0.25)
-used for ATR corneas
Low Toris Simulation: fit one meridian 0.25 flat and the other 0.75 to 1.00 flat to give a WTR tear film
-used for WTR corneas, most used

19
Q

Advantages and Disadvantages of Aspheric GP CLs

A

Advantages: better centration and comfort, decreased spherical aberration
Disadvantage: decreased tear exchange

20
Q

Types of Aspheric CLs

A

Back Surface: Typically Distance center, GPs, and more positive aberrations
-High, ATR, or irregular K astigmatism
Front Surface: Typically Near center, Soft, and more negative aberrations
-Excessive residual astigmatism (most fits are these)

21
Q

Lens Designs of MF CLs

A

Simultaneous: increases aberration but also increases depth of focus (Aspheric lenses give functional fuzzy vision at all distances)
Translating: move up as pt looks down, prism ballasted for rotation
(usually IP fit and spheric lenses -> good optics)

22
Q

Lens flexure is a GP lens _____ the eye and contributes to ______

A

ON; Residual astigmatism (provides less cyl correction via LL)

23
Q

Warpage is ______ of a GP lens ________ the eye that occurs due to _______

A

Permanent toricity; ON and OFF; excessive digital cleaning

24
Q

Equation for Oxygen Transmission through a CL

A

Dk/t

t in cm

25
Q

Compare vergence in CL vs glasses for Myopes and Hyperopes

A

Hyperopes converge LESS in CLs due to less BO prism

Myopes converge MORE in CLs due to less BI prism

26
Q

Compare accommodation in CL vs glasses for Myopes and Hyperopes

A

Hyperopes Accommodate LESS in CLs

Myopes Accommodate MORE in CLs

27
Q

Compare Magnification in CL vs glasses for Myopes and Hyperopes

A

Hyperopes have a SMALLER retinal image size with CLs

Myopes have a LARGER retinal image size with CLs

28
Q

Which Group classification of soft CLs is most likely for deposits?

A

4

29
Q

Label Soft Contact Lens Classification Groups 1-5

A

1: low water, non-ionic
2: high water, non-ionic
3: high water, ionic
4: low water, ionic
5: SiHy

30
Q

How can you change the fit to lessen corneal edema

A

Loosen the fit

31
Q

GP lens materials

A

PMMA: Dk = 0
Silicone Acrylate: Better Dk but can lead to warpage, deposits and poor wetting
Fluro-Silicone Acrylate: better wettability, less deposits and warpage

32
Q

Which surface is toric in a Soft CL?

A

Front

33
Q 
Ways to minimize rotation with Soft CLs
Prism Ballasting
Periballasting
Dynamic Stabilization
Eccentric Lenticulation
Truncation
A

Prism Ballasting: BD prism
Periballasting: BD prism outside OZD only
Dynamic Stabilization: thin inferior and superior portions
Eccentric Lenticulation: thin inferior and superior portions outside OZD only (combo of Periballisting and Dynamic Stabilization)
Truncation: lower portion of CL removed to sit on LL

34
Q

10 degrees of rotation gives how much cyl power

A

1/3

  • 20 degrees gives 2/3
  • 30 degrees gives full cyl
35
Q

Describe the OR on a tight vs loose fit toric lens

A

Tight fit: shows a stable OR corresponding to a tight fit

Loose fit: more rotation give an unstable OR

36
Q

Describe the assessment of a good fitting CL

A

Extends 1.5 mm beyond the limbus 360, moves 0.25-1mm with blink in primary gaze, 1mm of lag

37
Q

Base Curve Selection for a Soft CL

A

Normal K (41-45): If two options, go for flatter. If three options, go for middle
Flat <41: Flatter option
Steep >45: Steeper option

38
Q

Diameter Determination for a Soft CL

A

Measure HVID and add 3 to give 1.5mm overage on each side

Optics to Memorize (9 decks)

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