8 - Multifocal Lenses - Exam 2 Flashcards
Where is the seg width measured?
Across the widest portion of the segment
How are seg depth and seg height different?
Seg depth is the longest vertical dimension of the segment itself
Seg height is dependent on the frame
What is the seg drop?
Distance from DRP to top of seg
What is inset?
Horizontal distance from the geometrical center of the frame to correspond with patient PD
What is seg inset?
Amount past the inset the seg must be decentered for its optical center to correspond with the near PD
What is the total inset?
Inset + seg inset
What are the 4 main ways multifocal lenses are usually constructed?
- Fused (only glass, has no ledge)
- One piece (plastic, has ledge)
- Cemented lenses (specialized round segs)
- Franklin construction (two sections glued together)
What are 7 types of bifocal lenses?
- Flat top (called “D” segs, D28 most common)
- Round seg (therapeutic for children, good cosmesis)
- Blended seg (boundary unnoticeable, but blurry)
- Ribbon seg (round seg with top and bottom gone)
- Curve top seg (distinct point on the corners)
- Executive (maximum reading zone)
- Ultex (large diameter round seg)
What percentage of the near add is the typical intermediate add?
50%
How are the dimensions of a trifocal specified?
The depth of the intermediate portion, followed by an “x” and then the seg with
example: 7 x 28
What are 3 types of trifocals?
- Flat top (similar to bifocal, with an intermediate zone)
- Executive (intermediate and near span the lens)
- E/D (executive intermediate, flat top near)
What should the seg line coincide with when fitting flat top bifocals?
The lower lid
What should the uppermost seg line coincide with when fitting trifocals?
The bottom of the pupil
If a patient has a very “chin up” posture, how should their seg height be adjusted?
Fit slightly lower than usual
If a patient has a very slouched posture, how should their seg height be adjusted?
Fit slightly higher than usual
