Standards And Measurements Flashcards
50-18-140
Eye-bridge-temple
Range of eye size
40-62
Range of bridge size
14-24
Range of temple measurements
120-150mm
Why are eyesize, bridge and temple listed o na frame and not any other measurements?
These are important for frame fit and selection. These are set and you cannot change these
Boxing system
Worldwide standardization of measurements of frames to determine frame size
A measurement
Horizontal width of the lens
Between the two vertical lines of the box to the edges of the lenses
Use the edge furthest to the temple and furthest to the nasal
B measurement
Vertical height of the lens
Greatest depth of lens (furthest top and bottom of the lens)
Datum line
Line right across the middle, vertical center of the frame
Geometric center
Half of the B and half of the A
The center of the lens
DBC
Distance between centers
-frame Pd
Horizontal centers b/w right and left openings
DBL
Distance between lenses
Shortest distance between the nasal edges of each lens
ED
Effective diameter
- 2x the longest radium from their geometric center of the lens to the furthest edge
- longest distance across the lens (not official)
- important for cutout
OTL
Length of temple
-distance between the middle of the screw barrel to the back edge of the temple, just the length of the temple
Optical center
Point on lens where the light ways pass undeviated. No unintentional prism induced into it
Optical center, pupil center, and MRP in ideal world
Should be the same, but never are
Pupil center
Same as the optical center when no pantoscopic tilt
For every 2 degrees of pantoscopic tilt, you should do what to the optical center
Lower it 1 degree
The positioning of the lens for edging, such that as lens optical center is positioned appropriately
Centration
MRP major reference point
Same thing as optical center when there is no Rxed prism
The displacement, usually horizaontl, of the optical center of a spectacle lens from the geometric center
Decentration
If frame PD > patient PD
Decentration In
If the patient PD > frame PD
Decentration out
Distance from pupil center to the other, set at infinity
Pupillary distance
How can you measure PD
Monocular and binocular
Far PD
Set it at infinity
Near PD
Converging eyes PD
PTs PD is split 34/32, Rx +2.50OU
If the frame size is 44-14-140, how much should each lens be decanters relative to the geometric center?
44+14=58
58/2=29 each side
34-29 is 5 on the right out
32-29 on the right out
Rule of thumb for near and far PD
Move in each 2mm, but not 100%
-5.00 Ds 1prismD in in OU
What is the amount of decentration necessary to have the prescribed prismatic effect?
Prentice rule
Prism= (decentration(mm) x Power)/10
1= (D.C. X -5.00)/10
D.C.=-2mm in
When looking for decentration, what rule do you use
Prentice rule
Prism power=(dc(mm)xPower)/10
Seg height
Ther vertical distance between the bottom edge of the lens and the top of the segment
The vertical distance between the datum line and the top of the bifocal or trifocals
Seg drop
The distance the center of the near segment is moved laterally from the OC
Seg inset
Typical segment heights
- bifocal
- trifocals
- progressive
Bifocal seg height
Top of lower lid
Trifocals seg heights
Lower lid margin
Progressive seg height
Pupil center
Progressive PD
Monocular PD
A formula used to determine the smallest possible lens black for a given frame and PD combination
Minimum blank size (MBS)
MBS=(DBC-PD) + ED
A= 52mm DBL=18mm PD=63mm ED=58mm Find MBS
52+18=70
MBS=(70-63)+58
65
If you get the MBS too thin, what is the problem
No room for error. Can add 2-4mm to it
The final step in the manufacturing of eyewear
The inspection process
A system of standard and tolerances used to verify eyewear
Inspection process
What benefit is the inspection process
Accountability
Standard system across optical dispensaries
Protest the patient
ANSI Z87.1
OSHA and educational eye and face protection that some people will need for their occupation
What is ANSI for
Optical and cosmetic ophthalmic. Allow for tolerances
How to calculate power in oblique meridians
Sph power + (the cyl power)(sin2theta)
Power=S+Csin2theta
The differential vertical prismatic effect between the two eyes
Vertical imbalance
Can be induced by the right or left lenses of unequal powers when the wearer lowers his or her eyes to view through the near addition
Vertical imbalance
Surfacing of a portion of a lens to as to add a second optical center
Slab off
Used to alleviate vertical imlabance at near
Used to creat vertical prism in the lower portion of the lens
Slab off creating vertical prism
Base up prism, so base down is removed
Vertical imbalance equation
Lens power@90 X distance from OC/10
Calculate the imbalance
OD -2.00 +2.25 add
OS +1.00 +2.25 add
Near power 10mm below OC
2BD
1BU
Vertical imbalance of 3D
The distance from the back surface of a spectacle lens to the apex of the cornea
Vertex distance
When the vertex distance changes
The back vertex needs changed, important for exams for Rxing for glasses and CL
Moving away from the eye, ______the effective plus power
Increases
-10 to -8 as getting further away from face
Equation for vertex distance
New power= (old power)/(1 + change x old power)
Change=change in vertex power
Minus=reduction
Plus=increase
In meters
