Unit 6+7: Dispensing And Fabrication

Question 1

How to find binocular pupillary distance decentration

Answer 1

Distance between centres= (lens size+bridge size)

Decentration per lens= DBC - PD (all divided by 2)


Question 2

How to find monocular pupillary distance decentration

Answer 2

DBC (lens+bridge)/2 -monocular PD

Question 3

How to find vertical decentration

Answer 3

OC height - (lens height/2)

Question 4

How to find minimum blank size

Answer 4

ED(diagonal)+2x(per lens decentration) +2mm (for bevel)

Question 5

What is an aberration

Answer 5

Whenever a correctly powered lens delivers less than a perfect image

Question 6

Two subtypes of chromatic aberration

Answer 6

-Longitudinal (axial)
-Lateral


Question 7

What does a high abbe value in a lens mean

Answer 7

The less chromatic aberration is present in the lens
(High abbe value is better)

Question 8

What has a higher Abbe value? CR 39, polycarbonate, or trivex

Answer 8

Cr-39: 58 (high)
Trivex: 43-45 (mid)
Polycarbonate: 30 (bad)

Question 9

Types of monochromatic aberrations

Answer 9

-Spherical aberration
-Coma
-Oblique astigmatism
-Curvature of field
-Distortion

Question 10

UVA radiation exists at this wave length

Answer 10

315-380nm

Question 11

UVB radiation exists at this wave length

Answer 11

290-315nm

Question 12

UVC radiation exists at this wavelength

Answer 12

200-290nm

Question 13

Compensated lens power equation

Answer 13

New= (current power)/1-(vertex change)(current power)

=D/1-dD

Question 14

Effective lens power equation

Answer 14

Same as compensated power equation but with a plus

Question 15

How does a plus lens need to be corrected when the vertex is moved away from the eye

Answer 15

Need a weaker lens

Question 16

How does a minus lens with a vertex moved away from the eye need to be corrected

Answer 16

Needs a stronger lens

Question 17

If you’re moving the lens away from the eye what does this add?

Answer 17

More minus power

Question 18

Basic impact materials have a minimum thickness of this

Answer 18

3mm

Question 19

High impact materials have a minimum thickness of this

Answer 19

2mm

Question 20

Anti-reflection coatings do this to high impact materials

Answer 20

Greatly reduce the impact resistance

Question 21

When working on a patterned edger how do you change which lens is being cut

Answer 21

Flip over the pattern

Question 22

What do you do if a lens is edged too small

Answer 22

Remake the lens

Question 23

Why is it important for the base curve of a lens to be close to the wrap of the frame

Answer 23

If they aren’t a close match the frame shape is changed

Question 24

If no optical centre height is specified where should it be placed vertically

Answer 24

At datum or half the B measurement

Question 25

What kind of lens doesn’t have a bevel

Answer 25

Nylon cord frames or rimless frames

Question 26

Compensated lens power is:

Answer 26

What new prescription we need to order from the lab

Question 27

Effective lens power is:

Answer 27

What prescription the patient is seeing (maybe not the actual perscription)