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6 CU MCQ REVISION > ALL about RGP > Flashcards

ALL about RGP Flashcards

1
Q

Indication of RGP

A

High astig / irregular cornea
Orthokeratology
Dry eyes patient
Unsuccessful SCL wearer

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2
Q

Contraindication of RGP

A

Contact sport
Dusty environment
Occasional wearer

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3
Q

Advantages of RGP

A

Correction of astig
Low risk of CL complication
Suitable for extended wear
Less hydration

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4
Q

disdvantages of RGP

A

Require adaptation
Easier to dislodge from cornea
Complaint of flare

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5
Q

SA: comparing Silicon acrylate with FSA

A 
Older 
Lower dk
Less wettability 
Less flexure 
e.g Boston II
  • only suitable for daily wear

Material: PMMA +silicon

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6
Q

FSA: comparing flourousilicon acrylate with SA

A 
Deposit resistant 
Very high dk
More wettability 
More flexure 
e.g boston xo2 and menicon z
  • suitable for both daily and extended wear
    material: PMMA + silicoon
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7
Q

RGP design and its respective example

A
  1. Tricurve design e.g oculus rgp
  2. Centre spherical with aspheric peripheral zome e.g minicon ex and za
  3. Aspheric rgp – entire back surface is aspheric e.g menicon z, tinu, boston envision
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8
Q

what is lens flexure

A

blur vision after blink (due to the presence of silicon)

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9
Q

what is plasma effect and which lens is plasma applied?

A
  1. High energy plasma particles bombard the lens surface to remove lens impurities that contaminate final lens surface during manufacturing process
  2. Plasma will rearrange to attract water so that water can spread over the surface very quickly
  3. Smooth, clean and wettable lens = enhance initial comfort
  4. Effect is not permanent due to thin layer of plasma and wearing out of plasma on day to day basis

applied to all menicon lens and some SiHy lens

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10
Q

Dk ranking of CL material

A 
Low <12 
Medium 15-30
High 31-60
Super high 61-100
Hyper >100
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11
Q

tear exchange in RGP

A

RGP is able to exchange tear 10x or more compared to SCL hence, medium Dk of SA material is still prescribe nowadays as it will still give more oxygen as compared to SCL of higher Dk value.

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12
Q

4 step for trial lens selection

A
  1. design selection
  2. bc selection
  3. diameter selection
  4. power selection
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13
Q

trial lens design selection

A
  1. Spherical – cyl <1.5D
  2. Aspherical – cyl >1.5 <3.5D
  3. Toric RGP- cyl 3.5D or more
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14
Q

trial lens BC selection

A

in 0.05 step

Flattest K – 1/3 (Flattest – steepest K)

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15
Q

trial lens diameter selection

A

Diameter: HVID -2 in 0.4 steps (9.2,9.4,9,6)

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16
Q

trial lens power selection

A

Power: 3 and 6 D available pick the closest to px power

17
Q

lens fitting assessment

A
  1. Centration and pupil coverage
  2. Movement (primary gaze post blink movement and lag)
  3. NaFl pattern (static fit) – observe the post lens tear film thickness between the RGP lens back surface and the anterior cornea *intensity of green increase with the thickness of post lens tear film
    - Evenly green – lens BC is aligned to cornea curvature – pre and post parallel
    - Absence of green (touch) = minimal space between lens and cornea / lens is touching cornea
    - Excessive green (pool ) = large space between lens and cornea
18
Q

characteristic of optimum fitting

A 
Decentration 	<0.5
Movement 	1-2
Dynamic of movement 	Fast up and down
Lag	Do not cross  limbus 
Centre	Evenly green 
Mid periphery 	Evenly/slight touch 
Edge clearance 	0.3-0.5
19
Q

characteristic of flat fit

A 
Decentration 	>0.5
Movement 		>2
Dynamic of movement 	Apical rotation 
Lag		cross limbus
Centre	touch 
Mid periphery 		Pool 
Edge clearance 	>0.5
20
Q

characteristic of steep fit

A 
Decentration : <0.5
Movement : 1
Dynamic of movement : slow, up and down
Lag: do not cross limbus 
Centre: pool
Mid periphery : touch 
Edge clearance : <0;3
21
Q

what is tear lens

A

form by back surface of rgp and front surface of cornea - account for astig <3.5 ca cyl as it neutralise 90 percent of regular and irregular astig

22
Q

tear lens value:

A

Steep = - tear lens
Flat = + tear lens
On k = pl tear lens
Every 0.05 diff from the rgp size and the flattest k = 0.25 diff

23
Q

what is the manufacturing method of rgp

A

computerized lathe cut.
1 Grind the diameter and base curve required,
2 Cut off the rod
3 Block the lens on the lens holder
4 Trim the lens to right thickness and generate the lens power

24
Q

what is a dumbbell pattern

A

when spherical rgp is fitted on astig cornea

25
Q

when do patient complain of flare

A
  • small bozd
  • significant lens decentration
  • large pupil size in dim condition
  • tear film deficiency
  • poor lens wettability
26
Q

how to determine the final lens power

A

sum of trial lens power +over refraction

6 CU MCQ REVISION (6 decks)

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