Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Contact lenses year 3 > Contact lens verification > Flashcards

Contact lens verification Flashcards

1
Q

give 5 reasons why you will bother with CL verification

A
  • Check quality of manufacturing
  •  Ensure matches the CL spec you have ordered
  •  If the px mixes up the right and left lenses
  •  To confirm current pair of lenses worn
  •  Verify trial lens (fitting) set

We have a obligation to check that lens we are giving to the px is correct

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

list 9 things about a lens you should check

A
  • Base curve: BOZR, (central and peripheral
  • Diameter (TD,BOZD)
  • Power (BVP, FVP)
  • Centre thickness
  • Edge thickness
  • Edge form
  • Surface quality
  • Colour
  • Special features
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what can be used to check the power of a CL

A

focimeter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

which power of the lens are you using a focimeter to check
what is a disadvantage to using this and what can you do that will help
what can be done to the focimeter to make it better to use with CLs and why

A
  • Back vertex power
  • Image quality may be poor due to lens surface e.g. scratches or deposits - so make sure lens is clean and dry before use
  • Better to use a small aperture:
    usually the aperture stop is too large for CLs when it is set up for glasses
    Because:
    as the CL is very steep it cannot align with the aperture stop as the aperture stop of the focimeter is not in the centre of the lens
    so it does not measure the correct area of the power of the lens which will be in the middle
    so you can attach a small aperture stop on the focimeter to see through the power of the centre of the CL and measure it correctly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

instruct how you will check the BVP of a RGP lens using a focimeter

A
  • Make sure lens is clean and dry
  • Concave side down on the focimeter stop
  • Focus mires and take reading
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

instruct how you will check the BVP of a SCL using a focimeter and what you need to be careful of

A
  • Set the focimeter scale at the expected reading (if known)
  • Rinse lens and dry with lint-free tissue (no kleenex)
  • But SCLs have a tendency to dry out, so take the reading quickly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

instruct how you will check the FVP using a focimeter

and what can you do with the FVP measurements

A
  • Procedure is same as for BVP except the convex side is placed downwards
  • Can convert FVP measurements to BVP if centre thickness and BOZR is known
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how can you measure the peripheral curve width PCW

A

the difference between TD and BOZD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what 3 instruments can be used to verify TD of a CL

A
  • V-guage
  • Magnifier
  • Projection magnification with scale
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

instruct how you will use a V-guage to verify a TD of a lens

A
  • It is a ruler with a slot in it
  • Ensure lens is dry
  • Pop lens in and push down until it doesn’t go down any further
  • Don’t force lens-it will break or edges will be damaged
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what 2 parameters of a CL can a magnifier measure
what power does it use
which types of CL can be used

A
  • BOZD and TD
  • Approx. x10 mag
  • RGP or SCL
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

describe how a magnifier is used to check the BOZD and TD of a CL
what must you ensure for a RGP
what must you ensure for a SCL

A
  • Magnifier provides light
  • For BOZD: look for the markings of the optic zone seen inside the concentric line and line up that marking where the BOZD begins with the 0 on the scale and measure
  • For TD: exactly the same way but from edge to edge of the lens
  • Look through eyepiece and measure
  • RGP: ensure lens is dry
  • SCL: lens is placed in a wet cell = a thin CL case where can put saline in
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what 2 things must you be careful of when using a magnifier to measure the TD and BOZD a SCL

A
  • be careful of cross contamination when using the case to hold the SCL in the wet cell
    and
  • take into account of refractive index of saline
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what can you also measure off in a multifocal lens using a magnifier

A

can line up the seg of the bifocal part and measure the near zone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q 
what 2 parameters of a CL can you use to measure using a projection magnification with scale
which 2 types of CL can you measure 
describe how you will carry this out 
what must you ensure with a RGP 
what will a SCL require
A
  • BOZD and TD
  • RGP or SCL
  • Light up the lens with a strong light and shadow of lens will be shown
  • Line up lens with scale
  • Ensure it’s in focus
  • RGP: ensure lens is dry
  • For a SCL, would require lens to be held in wet cell with saline
    solution
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

as well as BOZD and TD which are the main uses of a projection magnification with scale, what else can you check about a CL

A

can use it to check the lens quality = good way to show px if theres lots of deposits etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

which 3 instruments can be used to measure base curve

A
  • Radiuscope
  • Keratometer
  • Photokeratoscope (topographer)
18
Q

describe how you will measure a CL BC with a radiuscope and which principle does it use

A
  • uses the drysdale principle
  • Clean and dry lens
  • Use saline in holder
  • Focus aerial image
  • You get th first image into focus and carry on until you see the bulb/filament and keep going until you see the 2nd image of the spoke
  • Ensure it reads zero on dial
  • Focus on front lens surface
  • BC = difference between the first and the second image
  • Read dial
  • Repeat 2-3 times
  • Tilt lens to measure peripheral curves
19
Q

how is a radiuscope used to measure the BC os a toric lens

A
  • either no spokes get into focus
  • or one of them might be bit clearer
  • what you aiming for is to get one of them very sharp
  • you may have to rotate the lens to get it into focus
  • keep going until the perpendicular one get into focus
20
Q

how is a keratometer used to measure BC of a CL
what does it require
what can be included for a SCL
what will you do to measure the peripheral BC

A
  • Special lens mount (can’t just hold CL in front) - lens is put on top of a prism
  • Requires modified scale
  • Clean and dry lens
  • Add saline to holder
  • Can include wet cell for
    soft lenses to stop it from drying out
  • For periphery BC-tilt lens
21
Q

how does a photokeratoscope (topographer) measure the BC of a CL

A
  • lens is put on a special holder
  • take image of the CL
  • the machine uses special software to work out the power of the lens
  • it produces a power profile map of the lens
22
Q

when placing a SCL in a saline immersion/wet cell to measure BC on all instruments, what needs to be done to get the true BC/BOZR value

A
  • readings are multiplied by the
    refractive index of saline to calculate the BOZR
  • can use a radiuscope or ultrasonic measurement
23
Q

what 2 instruments can be used to verify the thickness of a CL

A
  • dial thickness gauge

- electronic thickness gauge

24
Q

down to which value can a electronic thickness gauge measure a CL

A

100th of a mm

it doesn’t mean this machine is more accurate, it just measures down to that

25
Q

describe how you will use either a dial thickness gauge or electronic thickness gauge to measure the thickness of a RGP CL and what must you be careful of whilst doing this

A
  • for central thickness tc - you want to measure along the optic/geometric axis
  • central thickness is also referred to as the axial thickness
  • to measure the edge thickness te - rotate the lens and move it along the edge
  • edge thickness is also referred to as radial thickness

be careful not to damage the lens

26
Q

what is central thickness of a lens also referred to as

what is edge thickness of a lens also referred to as

A

axial thickness

radial thickness

27
Q

what 4 different thickness gauges can you use to measure the thickness of a SCL

A

Variety of gauges you can use:

  • Electronic thickness gauge
  • Pressure controlled gauge
  • Electrical thickness gauge
  • Radiuscope (modified)
28
Q

what 2 instruments can be used to check edge profile

why will you want to check this

A
  • microscope
  • slit lamp

to examine the CL and make sure of no defects which can cause inflammation or discomfort

29
Q

how will you use a slit lamp or microscope to check the edge profile of a lens

A
  • Dark (lights off)
  • Rotate lens to inspect edges
  • Increase magnification
30
Q

what 3 different types of edge shapes are there

A
  • knifepoint
  • chisel
  • round
31
Q

other than looking fr the edge shape, what else may you want to find out about a edge profile of a CL and what can’t cause this

A
  • edge quality
  • can be a torn lens
  • damaged by case or nails
32
Q

what 2 instruments are used to measure surface quality of a CL

A
  • microscope

- slit lamp

33
Q

what 5 things will you be look out for when checking surface quality of a CL
how will you carry this out

A

You are looking out for

  • Manufacturing errors
  • Mottling
  • Lathe marks
  • Scratches
  • Pitting
  • Focus eyepieces
  • Use magnification dials
  • Rotate and examine lens
34
Q

list 6 special features you can look for when verifying a CL and what 4 things you can use to do this

A
  • Engravings
  • Lab codes
  • Fenestrations: how many? Where? Size?
  • Carrier design
  • Prism ballast?
  • Truncation?

Magnifying 10x loupe
Naked eye
Microscope
Slit lamp

35
Q

which 3 colours are used to verify tints/colour of a CL and what does each colour stand for

why is this used
what 3 instruments can be used to check this
what is the best way to do it

A
  • Grey = right eye
  • Green = right eye
  • Blue = left eye
    Rule: second letter of colour
  • Naked eye
  • Slit lamp
  • Band magnifier
  • View against white paper
36
Q

what is the reality about SCL checking

A

In reality, most lenses are in sterile pre-packed blister packs and are verified by the manufacturer

We usually just check the packet to confirm lens power, diameter, base curve, date of expiry, brand, material etc

37
Q

list all the things about a CL the a slit lamp and microscope can be used for to measure/check

A
  • edge profile
  • surface quality
  • special features
  • CL colour/tint
38
Q

what is the BS code for an RGP

the parameters it includes and their tolerances

A
  • BS 7208: part 1: 1992
  • ISO 8321-1:1991

BOZR - ± 0.05
BOZD - ± 0.20
TD - ± 0.10
Centre thickness - ± 0.02

39
Q

what is the BS code for a SCL

the parameters it includes and their tolerances

A
  • BSEN ISO 8321-2:2000
  • BS 7208-24:2000

BOZR - ± 0.05
sag (at specified diameter) - ± 0.05
TD - ± 0.20
Centre thickness (unto 0.1mm) - ± 0.01 +10%

40
Q

which instrument used to verify BOZD and TD is mainly used in lab

A

projection magnification with scale

41
Q

which is a more practical instrument to use in clinic to measure BC/BOZR

A

keratometer (more practical than radiuscope)

Contact lenses year 3 (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions