Optical Characteristics of Multifocal Lenses Flashcards
age based add power in 40s
about 1.00 to 1.75
age based add power in 50s
about 2.00 to 2.75
add based add power in 60s
about 3.00 (absolute add)
as the patients add power increases, the near working distance
decreases
in fused multifocals, what material is it made of and what index of refraction
glass only
-segment has higher index of refraction than distance carrier
all plastic lenses are made as what mutlifocals
one piece mutlifocals
how does seg differ in one piece multifocals
the change in power in set due to change in surface curvature of the lens
fused lens add power calculation
F(add)= (F1-F4) / {(n’ - n)/(n”-n’)]
F4 is also referred to as the
countersink (Fc) curve
the higher the index of refraction of the seg material, the ___ the add power that is produced
higher
countersink curve calculation
solving for F4 using Fc because Fc=F4
what sign is the countersink curve
(-)
Fc is negative number
which curves are the same in one piece lenses
front curve (F1) - back surface curve of set (F4)
exception to F1=F4 rule for one piece lenses is
Ultex
which curves are the same in Ultex?
back surface curve of carrier (F2) = front surface curve of seg (F3)
