Multifocal Lenses Flashcards
widest section of the segment area prior to edging, often part is cut off
seg width
seg depth vs seg height
depth is in uncut blank
height is in lens cut to fit frame
vertical distance from DRP to top of seg
seg drop
distance that the lens must be decentered from GC to correspond with OC
inset
amount the seg must be further decentered to correspond with the near PD
seg inset
total inset=
inset+seg inset
multifocal construction where no ledge or change of curvature on the front surface can be felt, it’s only available with glass (2 materials), having a higher index than the carrier lens
fused
multifocal construction where only one material is used, power change occurs due to change in surface curvature, you can feel the segment, all plastic-like materials are made of this design
one piece
multifocal construction where custom small segments are glued onto the carrier lens, usually a round small segment
cemented lens
multifocal construction where two sections are glued together as upper and lower type, near OC can be displaced from distance OC
franklin construction
franklin construction is only used for creating _
horizontal prism in the near portion
most commonly used non-PAL type of multifocal
D segments with OC 5 mm below seg
D-_ is most common
What is the range?
seg drops range from?
28
25-45
2mm to 7mm
round segs vary in size: _
main advantage:
a main use:
seg drop:
22mm to 40 mm (smaller available for occupational)
very unnoticeable
therapeutic lens for children
4 mm to 9mm
a _ is a round seg that tapers off into the distance portion
blur zone:
blended seg
2-3mm
difference between B and R ribbon segments?
OC is at center of B, OC can be moved up and down for R
ribbon segs are used for what occupations?
bricklayers and heavy equipment operators
B ribbon segs allow for _
distance vision below the segment
curve top segs (like D) sizes vary:
OC is _mm below top
22-28mm
4.5mm
executive lens is similar to franklin, but only one-piece and distance and near OCs are _
coincident
main advantage of executive lens
maximum reading zone
disadvantages of executive? ledge increases as _ increases thickness is dependent on _ _ than D-segs large ED should be avoided
add power
near power
thicker/heavier
ultex: round seg with _ diameter
where is near OC?
very large
bottom of blank, may be cut off with edging
trifocals are typically _% of add power
trifocals are not available with near add powers of less than _
50
+1.50
7x28 trifocal means:
7mm height, 28mm width
flat top trifocal is typically a _
executive trifocal spans _
D-seg
width of lens
E/D trifocal is _
used for which type of work?
executive intermediate, D-25 near
office desk work, largest intermediate possible
occupational segs are double round _ _ or _mm
seg separations are _mm
are dissimilar adds available?
22, 25, 28
14
yes
a quadrafocal is a double round occupational lens with a _
trifocal on bottom seg
golfer’s classic:
_mm round seg
_ add
_ seg drop
15mm
low
10mm
High DefAmberd High Contrast Orange
28mm wide _
_mm seg drop
good for who?
flat top
7
outdoor enthusiasts
in flat top bifocal, seg line should coincide with _
lower lid
when fitting trifocals, top of intermediate zone should coincide with _
bottom of the pupil
if a patient is erect with head up, fit _
lower
if a patient is slouched with chin down, fit _
higher (already looking down)
height:
tall patients?
short patients?
lower segs - need to turn eyes downward more
don’t raise for short patients
fit round segs slightly _
higher (1mm) because top of seg is useless
blended bifocals should be fit 1mm _, be aware of blur zone
higher
for high powered distance rxs, fit BF a little _
and put OC a little _
higher
higher
if seg is too high, _ vertex distance
if seg is too low, _ vertex distance
decrease
increase
to compensate for seg height difference due to different size frames
1) determine difference in A dimension
2) divide by 2
3) add to measured seg height
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