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6 CU MCQ REVISION > ALL about SCL > Flashcards

ALL about SCL Flashcards

1
Q

indication for SCL

A
  • Spherical cornea with spherical refraction
  • Toric cornea with astigmatism refraction
  • Toric cornea with spherical refraction
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2
Q

FDA grouping and its example

A 
1 e.g soflen38 -	Non ionic, low water
2 e.g biotrue -	Non-ionic, high water 
3  -	                           -Ionic, low water
4 e.g biomedic-       Ionic, high water
5 e.g acuvue oasys - SiHy
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3
Q

Advantage of hydrogel

A
  • Excellent initial comfort
  • Minimal adaptation time
  • Occasional wear possible
  • Disposable
  • Low incidence of oedema, lacrimation, flare, photophobia
  • Long wearing times
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4
Q

Disadvantage of hydrogel

A
  • Reduced va with uncorrected astig due to lower modulus as compared to SiHy
  • Deposit prone
  • Oxygen transmission with hydrogel is lower than those of SiHy and rgp
  • lens water content have to be maintained
  • Increase risk of bacteria contamination
  • Corneal vascularization with thicker or low water content lenses
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5
Q

Advantage of SiHy

A
  • Excellent high oxygen permeability
  • Very low risk of vascularization
  • Suitable for extended wear
  • Less hydration because lower water content
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6
Q

disadvantage of SiHy

A
  • Greater incident of arcuate staining
  • More liable to lipid deposit
  • More expensive
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7
Q

Comparing SiHy and hydrogel

A

SiHy :

  • higher DK
  • water content 33-56
  • higher modulus
  • less wettable (attract lipids )

Hydrogel

  • Lower dk
  • water content 30-78
  • lower modulus
  • more wettable
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8
Q

5 property of SCL

A
  1. Dk and Dk/t
  2. water content
  3. ionic content
  4. wettability
  5. modulus
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9
Q

what is dk and dk/t

A
  • Dk is the oxygen permeability of the material (relating to the material)
  • Dk/t is the oxygen transmissibility (relating to lens thickness)
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10
Q

what is water content

A
  • the higher the water content the higher the Dk

* the higher the water content = higher amount of tear quantity is needed to maintain the lens

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11
Q

what is ionic content and what is proteins and lipid

A
  • Nonionic – less protein and lipid attracted
  • Ionic – more protein and lipid attracted
  • Protein and lipid; lysozyme, lactoferrin and lgA
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12
Q

what is wettability and what is SiHy and Hyrdrogel respective wettability (high/ low)

A

how quickly water can spread over the surface

  • SiHy – less wettability – more lipid deposit
  • Hydrogel – more wettability – more protein deposit
  • High contact angle = low wettability
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13
Q

what is modulus

A

ability of lens material to align to the ocular surface and resist deformation under tension.
• Low = softer, harder to handle, more comfortable
• High = stiffer, easier to handle, less comfortable

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14
Q

what kinds of SCL is there

A

daily, biweekly, monthly

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15
Q

what is keratometry

A
  • measure shape and power of cornea
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16
Q

what is total ocular astigmatism

A

Total ocular astigmatism = corneal astigmatism + lenticular astigmatism

17
Q

what is the product detail formula

A

product name/ BC/ DIA / POWER

18
Q

production selection for trial lens

A

decide between SiHy and hydrogel , frequency of wear, patient expectation , tear quality and quantity etc.

19
Q

selection of trial lens bc and diameter

A

conventional:
bc = flattest K + 8 (in 0.3 steps)
diameter : HVID +2 (in 0.5 steps)

disposable:
bc and diameter = one size fits all

20
Q

how do we select trial lens power

A

convert subjective rx into corneal plane - select closest power (power, before 6 is in 0.25 steps and after 6, is in 0.5 step )
- astig= 0.75 and above then use astig lens

21
Q

what do we use for astig less than 0.75

A

SE = sphere + 1/2 astig

22
Q

Cyl and axis value in toric SCL

A

-0.75 ,-1.25, -1.75,-2.25

axis in 10 degree step

22
Q

Cyl and axis value in toric SCL

A

-0.75 ,-1.25, -1.75,-2.25

axis in 10 degree step

23
Q

trial lens evaluation

A

a) Comfort
b) Vision
c) Corneal coverage (should be adequate in all direction): incomplete coverage: too loose/ too small lens
d) Centration – decentration can cause blur vision and decrease lens comfort
e) Movement – should move about 0.5mm. inadequate movement = tight fit(does not allow adequate tear exchange, cause a build up of debris and metabolic waste behind the lens )
f) Lag on up gaze
g) Push up test

24
Q

what are some of the characteristic of tight fit lens?

A

vision blurred between blinks and clear after blinking (accompanied by conjunctiva indentation blood vessel closure and the lens edge may lead to inflammation, cornea neovas, acute red eye reaction )

25
Q

what are some of the characteristic for loose fit lens

A

excessive movement, decrease comfort, blur vision and decentration. Vision clear between blink and clear after blink

26
Q

what is the importance of having an optimum SCL fitting

A
  • Prevent cellular deris and waste product from accumulating beneath the lens
  • Supplement the oxygen supply to cornea through tear exchange
27
Q

lens fitting assessment : comfort level for optimum, tight and loose fit

A

(10-15 mins in the eye), grade level from 1-10

Optimum fit – 9-10
Loose fit – 8 and below (hint to indicating discomfort due to excessive movement and lens edge stand off)
Tight fight – 9-10 but the lens wouldn’t move☹

28
Q

lens fitting assessment: centration , optimum, tight and loose fit

A

– lens resting position after blinks superior, positive, nasal positive (anything more than 0.5)
Optimum fit – well centered, slightly decentered
Loose fit- ride high or low on cornea
Tight fit well centered

29
Q

lens fitting assessment: what is the respective post blink movement , for optimum, tight and loose

A 
shift in the lens after each blink
•	Primary gaze – blink as normal
•	Upgaze  - look up and blink 
Optimum – 0.2 -0.5 
Tight is less than 0.2 
Loose is more than 0.5
30
Q

lens fitting assessment: what is no blink movement for optimum, tight and loose

A 
•	Lag – look side 
•	Sag – look up
Optimum – 0.2-0.5
Tight – less than 0.2 
Loose is more than 0.5
31
Q

lens fitting assessment: what is PUT and its optimum, tight and loose

A 
•	PUT – nudge the lens with thumb over the lower lid
100	 – very tight 
0 - Very loose 
Acceptable 30-70
Optimum -50
32
Q

lens fitting assessment : impact on lens periphery

A

Lens edge stand off – loose fitting

Conjunctival indentation – tight fitting

33
Q

types of disposable toric scl

A
  • prism ballast
  • peri ballast
  • thin zone
34
Q

when do we compensate lens rotation

A
  • If vision is 6/7.5-2 or worse compensate lens rotation with LARS rule on the subjective refraction axis
  • Pick the closest axis to the subjective rx axis.
35
Q

what is the manufacturing method and steps of scl

A

cast moulding
1 Making top and bottom mould
2 Inject liquid monomers into bottom mould
3 Applying top mould to shape the lens back surface
4 Polymerization with UV light
5 Remove lens from mould before sending for hydration

36
Q

how to perform over refraction on scl

A
  • TAKE va with lens in eye
  • Bvs
  • Add + then minus
  • Maximum plus
  • End with binocular bvs

6 CU MCQ REVISION (6 decks)

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