Lowenstein-multifocal lenses Flashcards
what are all fused bifocals made of
glass
a fused bifocal is made by adding..
a glass of higher index
what index does glass exist as
1.5-1.8
what are round seg lenses limited to
22 and 24 mm
flat top segments are designated by the diameter of the circle that the seg would represent if it were complete, it sizes…
25, 28, 35, 45 mm
all plastic bifocal lenses are ______, but not all ______ lenses are plastic
one piece
what are the 2 glass one piece bifocals
ultex and exclusive
one piece bifocals are mostly made w/ a seg that has more ___________ than the main lens
plus base curve
what does an ultex consist of
very large blank w/ the base curve on the back
in which one case is the ultex design useful
produces a large round top segment w/ a very long distance from the top of the seg to the seg optical center
-this can produce a large base down prism in the seg that is not present in the dist portion of the lens
what is an executive bifocal
a one piece bifocal w/ the segment stretching across the entire lower half of the lens
where is the base curve and add in the exectuive
what about cyl
base curve is on the upper half of the lens and the add is ground onto the surface on the lower half of the lens
-cyl is ground onto the back surface and then the back surface will have 2 diff centers and radii (like all bifocals where the seg is on the front)
what is a one piece round seg bifocal
-what is the add provided by
lens made of a single plastic w the same index throughout
-add is provided by the increased radius of curvature in the seg area
how is a one piece flat top made
lens made of a single plastic w the same index throughout but w/ the top of the circle cut off
for a pt requiring an add greater than +1.75, there is often a region btwn _________________ where vision is blurred
50-100cm
-esp noticable when using a desk top computer
