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Contact Lens Theory > Week 3 - Fitting Soft Contact Lenses > Flashcards

Week 3 - Fitting Soft Contact Lenses Flashcards

1
Q

Inserting contact lenses adversely affect tear lens (change how the tears work).
What 4 changes to do with CLs and fitting CLs can cause this?

A
  • Contact lens surface/ design
  • Tear of wearer
  • Drops / saline solution
  • Indicates px suitability
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2
Q

What 4 things do you do during the slit lamp evaluation?

A

-overall view of eye - sit lamp illuminations
-tarsal plate assessment (lid eversion)
-FBUT (fluorescein break up time)
-choose appropriate lens design

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3
Q

What do we need to consider when choosing the appropriate lens design? 3

A

-material (DK/T value)
-lens design (BC/Diameter)
-surface of the lens (surface coats which affect dry eye)

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4
Q

If power is under +/- 4.00D it does not need to be vertexed. T/F

A

TRUE

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5
Q

what are the 4 steps to designing a soft contact lens?

A
  1. Make sure prescription is in MINUS FORM.
  2. Draw optical cross
  3. Vertex Lens
  4. Determine power, base curve and diameter
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6
Q

Determine is the soft contact lens requires a toric or sphere.
What are the 2 conditions?

A
  1. The sphere: cyl > 3:1 - the sphere power is greater than or equal to 3 times the cyl power.
  2. CL RX cyl is < -1.00D - the cyl power is equal to or less than -1.00D.

If both conditions exist then we use a spherical equivalent if NOT go to soft toric

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7
Q

After -/+6.00D the steps go up in 0.50 D increments. T/F

A

TRUE
-6.50D to -12.00D
+6.50D to +8.00D
BE CAREFUL IN TESTS AS WILL TRY AND TRICK

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8
Q

Toric options for contact lenses are usually found in these powers ………. (5)

A

-0.75
-1.25
-1.75
-2.25
-2.75

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9
Q

What is the rule of thumb when considering the diameter of a contact lens?

A

the contact lens should fit 1mm larger than the cornea (overlapping the limbus) although often we are bound to what the manufacture makes

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10
Q

What is the common diameter ranges ?

A

14.00 mm to 14.50 mm

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11
Q

For a steep cornea, if there is only one BC option should we chose the larger diameter or smaller diameter lens?

A

Smaller -
the steeper the cornea the smaller the diameter = larger saggital depth
the flatter the cornea the larger the diameter = smaller saggital depth

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12
Q

What do most Base Curves come in? (range)

A

8.2 - 9.0 mm

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13
Q

The steeper the keratometer reading the lower the base
curve number. T/F

A

TRUE

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14
Q

BC for steep K (OVER 45.00D) reading?

A

8.3mm

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15
Q

BC for medium K (42.00D to 45.00D) reading?

A

8.6mm

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16
Q

BC for flat K (UNDER 42.00D) reading?

A

8.9mm

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17
Q

What vertex distance do we assume if nothing is specified?

A

12mm

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18
Q

ALWAYS use an optical cross to determine what CL rx is needed when cyl is present. T/F

A

TRUE

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19
Q

What material has dominated the CLs market?

A

Silicone Hydrogel

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20
Q

What are 2 ways to increase DK (oxygen permeability) in a HYDROGEL lens?

A
  1. Decrease lens thickness.
  2. Increase water content.
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21
Q

How is oxygen transported through a HYDROGEL lens?

A

Through the water channels

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22
Q

What are the 4 groups of material for hydrogel?

A
  1. Lower Water content & non-ionic polymers
  2. High water content & non-ionic polymers
  3. Lower Water content & ionic polymers
  4. High water content & ionic polymers
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23
Q

If the K readings have a difference of more then or equal to 2.00D what do we recommend?

A

Rigid Gas Permeables

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24
Q

More Water Content = more breathable lenses as more oxygen transmission T/F

A

TRUE

25
Q

What is a benefit of the Night and Day Lenses (Lower Water content & non-ionic polymers) ?

A

generally show lower levels of protein deposits

26
Q

What do you not want to use with the Proclear lens (High water content & non-ionic polymers) ?

A

sorbic acid found in certain solutions might cause discoloration

27
Q

What can happen with a Acuvue (High water content & ionic polymers) ? 2

A

-Highest level of protein deposit
-avoid sorbic acid as
disinfectant due to discoloration

28
Q

What can happen with a PureVision lens (Lower Water content & ionic polymers)? 2

A

-Balance Oxygen permeability and durability
-more protein deposits

29
Q

Ionic polymers are more sensitive to temperature and the composition of care products. T/F

A

TRUE - they also attract higher levels of deposits from tears

30
Q

Does a low water content lens have a longer lifespan and less breakage?

A

YES

31
Q

What is the disadvantage to a low water content lens?

A

less breathable lens - more chance of vascularization

32
Q

The high water content materials have faster adaption with comfort and wearing time. T/F

A

true

33
Q

What is a disadvantage to high water content materials? 4 (lifespan/stability/issues?2)

A
  • shorter lifespan
    -more deposits
    -dry eye issues
    -less stable
34
Q

What are the advantages of THIN HYDROGEL LENSES? 4 (conditions 3/patient)

A
  • Lower incidence of edema
  • Reduced lid sensation because of thinner edges
  • Reduced limbal irritation because of thinner edges and
    larger total diameter
  • Safer if the patient falls asleep
35
Q

What are the disadvantages of a THIN HYDROGEL LENSES? 5 (handling, breakage, lifespan, vision, effect on eye)

A
  • Handling is more difficult
  • Higher breakage rate then standard thickness lenses
  • Shorter life span
  • VA may not be as sharp with toric corneas
  • Dehydrates on eye
36
Q

What group does Silicone Hydrogel fall into?

A

FDA Group V - five

37
Q

What are advantages of Silicone Hydrogel lenses? 2 (adaption/good for who?)

A

-high Dks with rapid adaptation
-good for patient with vascularization and mild dry eyes.

38
Q

What are disadvantages of Silicone Hydrogel lenses? 2 (conditions?3)

A

-greater incidence of GPC and arcuate
staining in certain materials
-more likely to have mucin balls

39
Q

The lower the Dk value the less breathability. The more the DK value the more breathability. T/F

A

TRUE

40
Q

How do we now if a lens is well fitting? 3

A
  • Good centration with full corneal coverage in all direction of gaze
  • Sufficient movement to allow tear exchange under the lens during the blink (0.1 to 0.5 mm is generally
    considered optimal)
  • Satisfactory Push-Up Test
41
Q

What is a tight fitting lens also known as?

A

Steep Lens fit

42
Q

What is a loose fitting lens also known as?

A

flat Lens fit

43
Q

When a contact lens is too tight or too steep what should we expect from the movement of the lens during blinking?

A

insufficient/ no movement during the blink in primary or upward gaze

44
Q

How will a tight lens react in the push up test if it is too tight? 3

A
  • resist movment
  • on upward nudge the lens may remain decentered
  • on upward nudge the lens may return slowly to its orginal position
45
Q

What are 6 signs and symptoms of a tight/steep fitting lens? (centration/comfort/vision3/physical sign)

A
  • Good centration
  • Good comfort
  • Fluctuating vision between blinks
  • Poor visual acuity
  • Temporary improvement on blinking
  • Blanching/ lens indentation
46
Q

When a contact lens is too loose or too flat what should we expect from the movement of the lens during blinking?

A

Excessive lens movement during the blink in primary or upward gaze

47
Q

How will a loose lens react in the push up test if it is too tight? 2

A
  • Lens will readily move
  • Lens may drop back inferiorly quickly
48
Q

What are 6 signs and symptoms of a loose/flat fitting lens? (comfort/ centration2/ vision2/ physical sign)

A
  • Vision may be blurred after the blink
  • Comfort of fit is poor
  • Poor centration
  • Post blink movement is >0.4mm
  • Peripheral edge standoff
  • Vision is variable
49
Q

What could a loose/flat fitting lens be mistaken for?

A

Inverted lens - check to see if the lens is inverted if signs and symptoms of a loose lens occur.

50
Q

What can happen to the edges of a loose/flat lens?

A

edge stand off

51
Q

What can happen to the edges of a tight/steep lens?

A

conjunctival indentation

52
Q

After the characteristics of a well-fitted lens have been satisfied
* Conduct a spherical over-refraction to determine the proper lens power to be dispensed. T/F

A

TRUE

53
Q

What is the relationship between saggital depth, and steep/looseness of a contact lens?

A

Saggital depth –
-greater the depth of the lens - the steeper the lens
- the lower the depth of the lens - flatter the lens

54
Q

When over refracting what prescription do we start with?

A

Plano - +0.25D
then
Plano- -0.25D

55
Q

If we keep the BC the same what do we do to the diameter to steepen the fit?

A

to steepen the fit we select a larger diameter

56
Q

If we keep the diameter the same what do we do to the BC to steepen the fit?

A

to steepen the fit we select a smaller BC

57
Q

If we keep the BC the same what do we do to the diameter to flatten the fit?

A

to flatten the fit we select a smaller diameter

58
Q

If we keep the diameter the same what do we do to the BC to flatten the fit?

A

to flatten the fit we select a larger BC

Contact Lens Theory (27 decks)

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