Prism in Multifocals Flashcards
horizontal distance from geometrical center to seg OC
total inset
prism considerations must be made for patients with anisometropia because it may result in _
anisophoria - unequal prismatic effects from looking away from OCs of ansiometropic lenses
to compute net horizontal prism, _ the prism powers
add
patients who have problems with convergence need extra _ prism at near
BI
to obtain horizontal prism: _ seg inset
increase
Where is unequal prism more troublesome, in the horizontal or vertical direction?
Vertical
VPI becomes more problematic when patient becomes _
presbyopic (looking down more often)
to compute net vertical prism, _ the individual prism powers
subtract
_D of anisometropia in vertical meridian is generally tolerable, consider correcting for _D
1.50 D
2 to 3 D
assuming add power is the same for both eyes, VPI only depends on _
distance rx
general rule: place OC _ mm below vertical center of frame in near vision glasses
5
to decrease VPI, it may be possible to _ the distance OC
so the patient looks less far from OC, but it induces prism in the distance portion
drop
to decrease VPI, it may be possible to _ the seg height
raise
fresnel press-on prisms fot on the _ part of a multifocal
lower part of the back surface of a multifocal
c=Z/Padd
calculate required distance between seg centers to correct VPI
