Lesson 8 Flashcards
Helps reduce the chance of damaging delicate frames
Frame adjustment pliers
Holds lens and screw when bending temples or bridge area
Rimless mounting adjustment pliers
Designed to easily and safely remove compression mounted hardware
Compression hardware removal plier
Designed to trim of extra plastic blushing material before mounting
Sleeve trimming plier
Designed for easy assembly of single or double leg compression mounted frames
Compression plier
What is a thumbtack useful for when adjusting frames
- aligning the barrels of a spring-hinged temple
- removing bottom nylon cord from a semi-rimless frame
- removing top cord from semi rimless frame
- assembling a rimless compression mount frame
Lens bulge is the same as the _________
Sag of the front surface
Vertex depth is the same as the ______
Sag of the back surface
Calculating edge thickness for decerneted lens A=48mm DBL=16mm PD=25/25 N-1.6 CT=1mm Rx=-4.00D
48+16=64
Half of that is 32 (mono frame PD)
32-25=7mm decentration
48/2=24=24
24+7=31=h
- 4(31^2)/(2000(1.6-1)
3. 20mm+1=4.20mm
A lens clock calibrated for n=1.523 is placed on a surface with a refractive index of 1.8. If the clock reads +8.00, what is the true power of the surface
(1. 8-1/1.523-1)x8
- 12.24
When finding net prism what do you do
Take the difference
When asked to add the prism what do you do
Pythagorean theorem or add them together if they are the same
Prism thickness
(Zh)/(100(n-1))
Using thickness difference to determine prism power
Z=(100t(n-1))/h
Inducing a vertical prismatic effect in the lower half of one leans to correct vertical imbalance
Slab-off
Induces BU prism in the most minus lens in the vertical meridian in order to offset excessive base down prism induced by the opposite lens
Slab off
Provides BD prism so it is always used in the most plus lens int he vertical meridian in order to offset excessive BU prism induced by the opposite lens
Reverse slab off
When using slab off
Higher minus
Lowest plus
The minus lens
When using reverse slab
Lowest minus
Highest plus
The plus lens
When is slab off used the most
Lined bifocals
How can you correct vertical imbalance
- Slab off
- Dissimilar segs (place OC of the right and left segs at different positions)
- multiple specs
- contact lenses
- fresnel prism
The sudden displacement of an image at the bifocal line
Image jump
Calculating image jump
Independent of distance power and seg location, just depends on add power and shape of seg
Calculate image jump
- Rx: +2.00-1.25x180 +2.00D
- seg drop=4mm
- seg=flat top 28 (the seg OC is 5mm from the distance)
5mmx2.00/10=1D BD image jump
Calculate image jump
- 30mm round seg
- Rx: +2.00-1.00x180 +2.00D
30/2=15mm
15x2/10
3BD
Mag/min and plus lens
Plus lens creates magnification, a larger than normal retinal image
Minus lenses and mag/min
Create minification, smaller than normal retinal image
Lenses and mag
All lenses produce magnification
What happens to mag/min if you increase the power
It also increases
Greater vertex distance and mag
Increases it
Describes the ratio of image height to object height
Lateral magnification
Ratio of the angle subtended by the image produced by an optical system
Angular magnification
The ratio in image size for a spectacle lens corrected eye compared with the size of the image for the uncorrected eye, impacted by power of the lens and its shape
Spectacle magnification
SM=Ig/Io
Ig=retinal image size with glasses
Io=without glasses
What elements contribute to spectacle magnification
Power factor
Shape factor
A component of spectacle magnification that is determined by the back vertex power and the vertex distance of the lens
Power factor in spectacle magnification
1+dPv
Power factor for hyperope
Always >1
Power factor for mope
Always<1
A component of spectacle magnification that is determined by the base curve and the thickness of the lens
Shape factor
1+(t/n)P1
For a meniscus lens, the shape factor
Is always >1
To find spectacle magnification
Add shape factor and power factor
SM=Mp+Ms
Lens is thick and BC is steep, so increases one or the other will have a meaningful effect on shape factor
Hyperope
Lens is thin and BC is flat, so in order to have a meaningful effect not he shape factor, both lens thickness and drop surface power must be increases
Myope
Binocular condition in which the apparent sizes of the images seen with the two eyes is unequal
Aniseikonia
Lenses for aniseikonia
Lens design is not intended to remove magnification or exactly match magnification from each lens. It decreases the magnification difference so that binocular vision is restored
Called Iseikonic lenses
Variables that can be changed to reduce magnification
Base curve
Center thickness
Index refraction
Vertex distance
CANNOT CHANGE POWER
Left and right eyes produce equally sized images on the retina
Iseikonia
Iseikonic lenses
Custom designed lenses that use the optimal curvature, thickness, and index of a given prescription combination to balance the magnification
Occurs with specular, not diffuse, reflections
Polarization
The angle of incidence at which reflected light from a refracting surface is completely polarized
Brewsters angle
What are the 2 axis for polriazwtion
Absorption axis
Transmission axis
Where is a absorption axis in a polarixaed lens
Horizontal
Where is the transmission axis on polarized lenses
Vertically
A thin film made by taking polyvinyl acetate (PVA) film, stretching it to five times its normal length and dipping it in iodine. Polarization is caused by absorption of iodine between the chains of PVA molecules
Polaroids
When switching from front to back surface, why does the axis change and how much
Mirror image
What kind of refractive index is thinner in higher RX?
Higher
As RI increases, what happens to abbe
Decreases
