wk2: CL/M - Nomenclature and Verification of CLs

Question 1

Why is CL verification necessary? (4)

Answer 1

To confirm lens received is as ordered
To identify parameters of lens prescribed elsewhere
Confirm parameters of trial lenses
Ensure that the lens meets ISO standard

Question 2

Define BOZR

Answer 2

Back Optic Zone Radius

Question 3

Define BOZD

Answer 3

Back Optic Zone Diameter

Question 4

Define BPR

Answer 4

Back Peripheral Radius

Question 5

Define BPZD

Answer 5

Back Peripheral Zone Diameter

Question 6

Define TD

Answer 6

Total Diameter

Question 7

Define FOZR

Answer 7

Front Optic Zone Radius

Question 8

Define BVP

Answer 8

Back Vertex Power

Question 9

Define CT

Answer 9

Centre Thickness

Question 10

Define ET

Answer 10

Edge Thickness

Question 11

Define Dk

Answer 11

Oxygen permeability

Question 12

Define Dk/t

Answer 12

Oxygen transmissability

Question 13

What tool is used to verify the BOZR/BC in RGPs?

Answer 13

Radiuscope (optical microspherometer)

Question 14

What techniques can be used to verify the BOZR/BC in SCLs? (3)

Answer 14

Template method
Radiuscope
Spherometer (optimec device)

Question 15

What is the “Drysdale’s principle”?

Answer 15

For a curved mirror, an image is formed in the same plane as the objectwhen the object is at the centre of curvature of the mirror

Question 16

Briefly explain how a radiuscope (optical microspherometer) works (3)

Answer 16

The curved surface of the contact lens acts as a mirror. Two images of the projected target are formed: a surface image and cleaner aerial image. The distance between focusing these two images gives the radius of curvature of the contact lens

Question 17

Describe the procedure to use a radiuscope to measure radius of curvature (6)

Answer 17

Centre the beam on the CL
Focus target image on lens surface (surface image)
Set internal scale to zero
Obtain aerial focus (aerial image) by moving microscope up
Read radius of curvature off the internal scale
Use an average of 3 readings

Question 18

When using a radiuscope to measure radius of curvature, in what size steps should you work in?

Answer 18

work in 0.5mm steps

Question 19

How accurate is the internal scale at measuring radius of curvature in radiuscopy?

Answer 19

within 0.01-0.02mm

Question 20

How does radiuscopy differ for toric lenses? Explain

Answer 20

Toric lenses have two radii of curvature, meaning that not all spokes of the aerial image will come into focus together. This means that 2 radings willn eed to be taken

Question 21

How does radiuscopy differ for a warped lens?

Answer 21

aerial image is not focusable

Question 22

What is the main problem with doing radiuscopy on SCLs?

Answer 22

Only a small amount of incident light is reflected back, therefore you need a very high intensity illumination system

Question 23

Describe how the template method for measuring radius of curvature is carried out (4)

Answer 23

Lens placed concave down on a template of known radius
If the two surfaces are not aligned, a bubble forms
The position of the bubble indicates if too flat or too steep
Can then place lens into an adjacent radius template until no bubble

Question 24

How accurate is the template method for measuring radius of curvature?

Answer 24

Very approximate (accuracy +/- 0.30mm)

Question 25

In what type of CLs is BPR measured?

Answer 25

RGPs

Question 26

In what type of CLs is FOZR measured?

Answer 26

RGPs

Question 27

Describe how a spherometer works (5)

Answer 27

Lens mounted and centred with convex surface upward in saline Viewed at 15x magnification Probe advanced until contact is observed Amount by which it needs to be advanced gives measure of sagittal depth (or "sag") BOZR is then calculated from the "sag"

Question 28

How does the radiuscope procedure differ when verifying BPR instead of BOZR?

Answer 28

Mount is tilted so the light falls on teh peripheral curve

Question 29

When would verification of BPR with a radiuscope be difficult? (2)

Answer 29

if narrow band width (<0.7mm) or blended peripherally

Question 30

Why is verification of BPR with a radiuscope not performed for SCLs? (1)

Answer 30

there is no visible junction for SCLs

Question 31

How does the radiuscopy procedure differ when verifying FOZR instead of BOZR? (2)

Answer 31

A special FOZR mount is used (i.e. convex surface UP) | The aerial image is obtained by moving the microscope DOWN (i.e. the image is below the lens rather than above it)

Question 32

How can we verify BOZD and BPZD in RGPs? (2)

Answer 32

Measuring magnifier | Projection magnifier

Question 33

What is a measuring magnifier?

Answer 33

magnifying lens with adjustable eyepiece focussed onto a clear platform with a graticule scale

Question 34

What is a projection magnifier? (2)

Answer 34

lens placed on stage in path of light beam. | shadow projected onto screen which has a mm grid scale.

Question 35

What 3 tools can we use to verify TD in RGPs?

Answer 35

Measuring magnifier Projection magnifier V-gauge

Question 36

What 3 tools can we use to verify TD in SCLs?

Answer 36

Measuring magnifier Projection magnifier Optimec device

Question 37

How does a V-gauge work? (3)

Answer 37

``` CL placed in wide end of gauge Slips down by gravity until it stops (do not push) Total diameter (TD) reads directly off the scale ```

Question 38

What is the tolerance for the V-gauge?

Answer 38

+/- 0.05mm

Question 39

What tool can we use to verify BVP? How easy is this in SCLs?

Answer 39

Projection vertometer. Difficult for SCLs

Question 40

What tools can we use to verify CT (centre thickness)? (4)0

Answer 40

``` Thickness gauge Pacymetry, A scan Electrical micrometer Radiuscope (also OCT, which is being developed for verification) ```

Question 41

How commonly do we verify water content?

Answer 41

uncommonly

Question 42

What tool would we use to verify water content?

Answer 42

Atago soft contact lens hand refractometer

Question 43

Outline the procedure for verifying water content (in SCLs)? (6)

Answer 43

Place lens on prism face Close plate and apply gentle pressure to obtain firm contact between lens and prism Point in direction of bright light source Observe scale through eyepiece Division of field into light and dark fields %H2O reads directly off the scale

Question 44

How can you verify surface quality of CLs? (4)

Answer 44

Slit lamp Radiuscope or keratometer Projection magnifier Hand magnifier

Question 45

How can you verify edge quality of CLs? (5)

Answer 45

``` Feel Slit lamp Simple inspection Projection magnifier Hand magnifier ```

Question 46

How do you calculate 1st BPR?

Answer 46

1st BPR = BOZR + 1st PCR

Question 47

How do you calculate 1st BPZD?

Answer 47

1st BPZD = BOZD + (1st PCW)x2

Question 48

How do you calculate 2nd BPR?

Answer 48

2nd BPR = 1st BPR + 2nd PCR

Question 49

How do you calculate 2nd BPZD?

Answer 49

2nd BPZD = 1st BPZD + (2nd PCW)x2

Question 50

Outline the 5 steps in contact lens practice

Answer 50

``` Full eye test CL fitting CL delivery/teach CL aftercare CL refitting? ```