Unit 6+7: Dispensing And Fabrication Flashcards
How to find binocular pupillary distance decentration
Distance between centres= (lens size+bridge size)
Decentration per lens= DBC - PD (all divided by 2)

How to find monocular pupillary distance decentration
DBC (lens+bridge)/2 -monocular PD
How to find vertical decentration
OC height - (lens height/2)
How to find minimum blank size
ED(diagonal)+2x(per lens decentration) +2mm (for bevel)
What is an aberration
Whenever a correctly powered lens delivers less than a perfect image
Two subtypes of chromatic aberration
-Longitudinal (axial)
-Lateral

What does a high abbe value in a lens mean
The less chromatic aberration is present in the lens
(High abbe value is better)
What has a higher Abbe value? CR 39, polycarbonate, or trivex
Cr-39: 58 (high)
Trivex: 43-45 (mid)
Polycarbonate: 30 (bad)
Types of monochromatic aberrations
-Spherical aberration
-Coma
-Oblique astigmatism
-Curvature of field
-Distortion
UVA radiation exists at this wave length
315-380nm
UVB radiation exists at this wave length
290-315nm
UVC radiation exists at this wavelength
200-290nm
Compensated lens power equation
New= (current power)/1-(vertex change)(current power)
=D/1-dD
Effective lens power equation
Same as compensated power equation but with a plus
How does a plus lens need to be corrected when the vertex is moved away from the eye
Need a weaker lens
How does a minus lens with a vertex moved away from the eye need to be corrected
Needs a stronger lens
If you’re moving the lens away from the eye what does this add?
More minus power
Basic impact materials have a minimum thickness of this
3mm
High impact materials have a minimum thickness of this
2mm
Anti-reflection coatings do this to high impact materials
Greatly reduce the impact resistance
When working on a patterned edger how do you change which lens is being cut
Flip over the pattern
What do you do if a lens is edged too small
Remake the lens
Why is it important for the base curve of a lens to be close to the wrap of the frame
If they aren’t a close match the frame shape is changed
If no optical centre height is specified where should it be placed vertically
At datum or half the B measurement
What kind of lens doesn’t have a bevel
Nylon cord frames or rimless frames
Compensated lens power is:
What new prescription we need to order from the lab
Effective lens power is:
What prescription the patient is seeing (maybe not the actual perscription)
