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CLs 2 ilyas > SCL Fitting 3 > Flashcards

SCL Fitting 3 Flashcards

1
Q

What properties affect the comfort of RGPs?

A
  • Oxygen permeability
  • Oxygen transmissibility
  • Wettability
  • Modulus
  • Water content
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2
Q

Assuming that the lenses fit well, what are sorts of things are you expecting to find during a contact lens assessment if px complains of comfort?

A
  1. Incomplete blink
  2. Corneal staining inferior due to dryness – Conjunctival staining from tight fit
  3. Reduced TBUT (< 10sec)
  4. MGD (less lipids means more evaporation)
  5. Reduced Schirmer’s test (< 15mm after 5 min)
  6. Reduced central tear prism height (< 0.2mm) – Normal central 0.2 to 0.4mm – Normal periphery 0.1 to 0.2mm
  7. Reduced vision
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3
Q

What is Schirmer’s test?

A

Basically where you put a little bit of paper touching the eye and see how much of it gets wet in a set period of time - it is an indication of tear volume

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4
Q

Which stain, lissamine green or rose bengal, do px prefer?

A

Lissamine green as it is not associated with stinging or pain

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5
Q

What do rose bengal and lissamine green stain?

A

Dead and degenerate cells

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6
Q

What does circum-limbal (i.e. where the edges of a CL would be) staining indicate?

A

Lens is too tight or edge is too sharp

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7
Q

What is the TBUT like in a px with dry eye?

A

It is reduced

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8
Q

When are RGPs a great option for a px with dry eye?

A

If the dry eye is NOT a result of insuffiicient tear volume.

-RGPs are insufficient if dry eye is caused by reduced tear prism

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9
Q

What is tear prism?

How is it measured?

A

Height of tears pooled at the bottom of the eye.

Make a spot of 1mm/0.5mm and see how much of that spot the tear height gets to

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10
Q

Judging from the name of a material how can we infer that it is a hydrogel material?

A

Hydrogel materials end with the suffix ‘filcon’

[RGP materials end with the suffix ‘focon’]

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11
Q

What is the relationship between ionic hydrogels and protein deposition?

A

Ionic hydrogels tend to have a negatively charged surface which makes it sensitive to chnages in pH and osmolarity and therefire more likely to attract tear proteins.

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12
Q

What are non-ionic hydrogels?

A

Ionic hydrogels that have been treated to remove the ionic charge

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13
Q

What are FDA groupings?

A

Groups that are allocated according to water content and whether the material is ionic or not

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14
Q

What are the disadvantages of having a higher water content?

A

Dehydration - lens dries out

Mechanically weaker - lower modulus

More likely to attract Deposits

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15
Q

What are the disadvantages of an ionic SCL material?

A

More likely to attract deposits

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16
Q

What is the relationship between water content and Dk?

A

Increased H2O will increase Dk

[– More oxygen→healthier]

17
Q

What are the advanatges and disadvantages of having a low modulus?

A

Advantages:

  • Easy to fit
  • Increased initial comfort
  • Reduced mechanical induced ocular complications

Disadvantages:

  • Difficult to handle
18
Q

What is a disadvanatge of a high modulus?

A

Material is stiffer and so more uncomfortable.

Linked to a foreign body sensation

19
Q

True or False- Lenses in FDA group 4 tend to attract more protein deposits than any other group

A

True

20
Q

What does the Fifth FDA group consist of?

A

Silicone hydrogels

21
Q

What are the advanatges of Silicone hydrogels and why were they created?

A

They were created for continuous wear. They have a high oxygen transmissability.

Advantages of Silicone hydrogels are that because of its increased oxygen transmissability hypoxia is less likely to occur and as a result the following symptoms are less likely to occur:

  • – Hyperemia
  • – Limbal injection
  • – Vascularization
  • – Corneal edema
  • – Myopic creep (-0.25 to -0.50D more myopia)

Silicone hyrdogels arguably provide better comfort than hydrogels

22
Q

Why do silicone hyrdogels arguably provide better comfort than hydrogel lenses?

A

Lower water content of silicone hydrogel materials cause slower dehydration

– SiH materials are treated to enhance wettability and comfort to make up for the hydrophobic nature of the silicone component

23
Q

Why is oxygen flux a better parameter to judge by than Dk/t?

A

Dk/t tells us about the materials oxygen transmissibility but not necessarily how much oxygen reaches the cornea udring a set period of time ( like oxygen flux does).

24
Q

True or False- There is a strong corrolation between oxygen transmissibilty ans corneal oedema

A

True - – Low-Dk hydrogel lenses cause approx 7% to 15% corneal swelling overnight (as a pose to the 3-4% of corneal swelling that occurs naturally overnight).

25
Q

True or False- The amount of overnight swelling induced by SiH lenses is close to normal values

A

True - SiH materials induce significantly less overnight corneal swelling (ranging from 2% to 5%) • These values are similar to overnight (closed-eye) corneal swelling without contact lens wear

26
Q

What is the relationship between silicone content and water content of silicone hydrogel lenses (first generation)?

A

Increased Si content results in decreased H2O content

27
Q

How does water content affect modulus?

A

Decreased H2O content results in higher modulus

28
Q

True or False- Second generation SiH lenses are formulated in such a way that they have a highh water content and low modulus

A

True

29
Q

What are disadvanatges of Silicone hydrogels?

A

Mechanical irritation from a stiffer silicone hydrogel material – Increased incidence of Superior epithelial arcuate lesions (SEALs) and mucin balls

• Increased lipid based deposits – May slide around on the lens surface: affecting vision and comfort dynamically – Conventional SCL materials more protein based

30
Q

How do flexibility and vision affect one another?

A
  • Comfort can best be achieved from a flexible CL that drapes easily over the cornea and has minimal interaction with the eyelids during blinking
  • But a high degree of flexibility can be a disadvantage when trying to achieve optimum vision – The optical performance of a lens will be significantly improved if it can mask corneal astigmatism – An increase in stiffness or rigidity will achieve this but at the expense of initial comfort
31
Q

Describe the differences between RGPs and SCLs

A
32
Q

What are mucin balls?

How long do they take to resolve?

A

Mucin balls are speherical and translucent bodies sandwiched between a contact lens and the cornea - they can be observed minutes after you insert a lens and can become embedded into the cornea.

They take 24 hours to resolve

33
Q

Are mucin balls associated with decreased comfort?

A

No

34
Q

Deposits on the lens can could worsened vision, if vision is still bad/foggy after having removed the lens what may we suspect?

A

The possibility that the px is experiencing corneal oedema

35
Q
A

CLs 2 ilyas (18 decks)

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