Trifocals Flashcards
(12 cards)
What are the advantages of trifocals?
Good for vari non-tol pxs
Pxs with <3D AoA
Wide FOV in segments
What are the disadvantages of trifocals?
Two points of jump and reflection
Don’t look good cosmetically
Inter seg is higher than near seg in a bif
Reading seg is lower than in a bif (allows room for inter seg)
What is the formula for IP/RP ratio?
IP/RP ratio = (int add/near add)x100
What is the IP/RP ratio?
How much of the reading add is needed for intermediate vision (i.e. what proportion of the near add is the inter add)
What is the IP/RP ratio usually?
50-60%
What measurements do you need for trifocals?
Binoc PD (D&N for inset)
Heights to lower limbus (near seg)
Heights 3-4mm above lower limbus (inter seg)
What is the minimum seg depth for trifocals?
20mm
What are the types of trifocal segs?
Flat (D)
Round
Double D
E-type
What flat segs are available?
S728
S835
S1435
What R segs are available?
R722
R728
R12C
What DD seg is available?
DD28
What is the depth of the inter seg in an E-type trifocal?
7mm
