The Box System Flashcards
(27 cards)
what are other terms used to describe the longest horizontal length?
“eyesize” when referring to the frame and “lens size” when referring to a lens
the A measurement is the
longest horizontal length
“eyesize” or “lens size”
the longest vertical height of the frame is called the ___ measurement
B
the C measurement is the:
horizontal midline
the C line intersects:
the midpoint of the B measurement
definition of the geometric center of the lens
is the point on the horizontal midline that is halfway between the two vertical lines bordering the lens
what is the effective diameter (ED)?
the distance from the geometric center to the furthest point on the frame, multiplied by 2
the effective diameter (ED) can be the same as the ___ measurement in some frames
A
ED is usually a ____ measurement
diagonal
bridge size is also called
DBL
the DBL is defined as the
the distance between the inside nasal eye wire grooves across the bridge area at the narrowest point
what is a concern of printed DBLs?
some frame manufacturers will state bridge sizes that do not match the DBL
what is the frame PD?
the distance between geometric centers (frame center distance)
what is another way to calculate the frame PD using other measurements?
A + DBL = Frame PD (FPD)
what can the difference between the horizontal and vertical frame measurements tell you about the shape of the frame?
the larger the difference, the more rectangular the shape
a high plus lens will be thicker where?
thicker on top and bottom
a high minus lens will be thicker where?
thicker on the sides
frame markings with __- ___- ___ indicate what measurements?
eyesize - bridge width - temple length
how must you change the OC for degrees of panoscoptic tilt?
lower OC 1 mm for every 2 degrees of tilt
BD prism causes eye to turn ___
up
BU prism causes eye to turn ___
down
prism in 1 eye requires unequal set heights, how many mm per prism diopter is needed?
0.29 mm per prism diopter
the segment top is always displaced from its original location in the direction of the ___ of the vertical prism
apex
minimum blank size (MBS) is based on:
- patient’s PD
- frame PD
- decentration
- ED
