Ophthalmic Prisms and Prismatic Effects
What is 2.50 base 320 in the 180 degree reference system for prisms?
2.50 prism diopters base 140 down **remember that for the 180 degree system you must specify up or down **slide 35
What is 3.0 prism diopters base 30 down in the 360 degree reference system for prisms?
3.0 prism diopters base 210 **slide 36
A 3.0 prism diopter base out for the LEFT eye is written as __________ using the 360 degree reference system for prisms.
3.00 prism diopters base 0 **slide 32
What is the formula for effective power of a prism in an oblique meridian?
Pa = Pcos(a) **a =alpha = angle between the unknown meridian and the BASE-APEX meridian. **Pa = the effective power of a prism at this new meridian
The effective power of prisms can be increased or decreased by OBJECT distance. If you ________ the object distance, you will have a DECREASE effectivity. A. increase B. decrease
B. decrease **slide 39
Which prisms are used to treat phorias? A. conjugate/yoked prisms B. disjunctive prisms
B. disjunctive prisms **both BI or both BO **slide 13
Which prisms are used to treat strabismus? A. conjugate/yoked prisms B. disjunctive prisms
B. disjunctive prisms **both BI or both BO **slide 13
When dealing with compounded prisms, the vector representation _____________ about which eye is in question A. tells you B. does not tell you
B. does not tell you **that is why you draw a picture with nose as a reference point **slide 22
Excessive base up prism may give the feeling that you are walking ________ A. uphill B. downhill
B. downhill
Prisms straighten a strabismic eye A. true B. false
B. false
In order to create a prismatic effect, prisms must be incorporated into spectacles A. true B. false
B. false **we can create prismatic effects by optical decentration
BI prism OD causes the image (and therefore the eye) to move in what direction? A. inward (towards nose) B. outward (towards right ear)
B. outward (towards left ear)
In a patient with a right homonymous hemianopsia, how should you place Fresnel prisms to help this patient? A. position the apex in the direction of the defect (base right) B. position the base in the direction of the defect (base right)
B. position the base in the direction of the defect (base right) **slide 50
When viewing a near object, the effective prism power is __________ A. increased B. reduced
B. reduced **slide 37
Excessive base down prism may cause vertical surface or people to look _______ A. shorter B. taller
B. taller
Fresnel prisms can help patients with nystagmus. With these patients, use ________ A. disjunctive Fresnel prisms B. yoked prisms
B. yoked prisms
What is the formula for the minimum angle of deviation found in prisms?
d = a(n-1) **this formula works for thin prisms (less than 10 degrees) **d = angle of deviation **a = apical angle **n = index of refraction
The light that enters a prism refracts towards the ________ of the prism while the image is moved to the ________. A. apex; base B. base; apex
B. base; apex
Prisms are normally prescribed _______ A. monocularly B. binocularly
B. binocularly
As far as visual acuity is concerned, Fresnel prisms ________ A. do not affect VA B. cause about one line loss in Snellen acuity
B. cause about one line loss in Snellen acuity
Excessive base down prism may cause the ground/floor to look ________ A. convex B. concave
B. concave
The definition of a prism diopter is the deviation of light by ______cm at a total distance of ______ cm
1 100
What is the effective power of a 5 prism diopter prism 60 degrees from its base-apex line? **use the formula: Pa = Pcos(a)
2.5 prism diopters **Pa = Pcos(a) **P(60) = 5cos(60) **slide 40
A 2.50 prism diopter base up for the LEFT eye is written as __________ using the 360 degree reference system for prisms.
2.50 prism diopters base 090 **in this case it doesn't make a difference if it is left or right eye **slide 32
A PLUS lens can be conceptualized as two prisms _______ A. base to base B. apex to apex
A. base to base
If you have a Fresnel prism that has the bases pointing towards the center, then this is a _______ prism A. base to base (plus) B. apex to apex (minus)
A. base to base (plus)
The 180 degree reference system for prisms is written as _______ (select all that apply) A. base up B. base down C. base in D. base out E. all of the above
A. base up B. base down **slide 33
Excessive prisms may _______ (select all that apply) A. cause objects to appear slanted B. cause diplopia C. may cause discomfort
A. cause objects to appear slanted B. cause diplopia C. may cause discomfort
Which prisms are used to treat visual field defects and scotomas? A. conjugate/yoked prisms B. disjunctive prisms
A. conjugate/yoked prisms **slide 13
Which prisms are used to treat visual neglect? A. conjugate/yoked prisms B. disjunctive prisms
A. conjugate/yoked prisms **slide 13
Excessive base up prism may cause the ground/floor to look ________ A. convex B. concave
A. convex
Which are disadvantages to Fresnel prisms? (select all that apply) A. cosmetically unappealing B. thin C. can be cut to any shape D. hard to keep ledges clean
A. cosmetically unappealing D. hard to keep ledges clean **choice B and C are advantages
The effective power of prisms can be increased or decreased by VERTEX distance. If you ________ the vertex distance, you will have a DECREASE effectivity. A. increase B. decrease
A. increase **slide 39
BO prism OS causes the image (and therefore the eye) to move in what direction? A. inward (towards nose) B. outward (towards left ear)
A. inward (towards nose)
Excessive base up prism may cause vertical surface or people to look _______ A. shorter B. taller
A. shorter
Fresnel prisms are typically applied ___________ A. to one eye B. to both eyes
A. to one eye
Fresnel prisms can be applied to diving masks A. true B. false
A. true
Excessive base down prism may give the feeling that you are walking ________ A. uphill B. downhill
A. uphill
When HIGH amounts of prisms are required ________ A. you can use Fresnel prisms B. you cannot use Fresnel prisms
A. you can use Fresnel prisms
A MINUS lens can be conceptualized as two prisms _______ A. base to base B. apex to apex
B. apex to apex
If a patient has a BLIND EYE that deviates out and you want to correct this eye to look cosmetically appealing, what prism position should you choose? A. base in B. base out
B. base out **if this was a functional eye then we would do base in, but in this case we want the image of the eye to appear straight (cosmetically pleasing), so we use base out.
What are the two formulas used to calculate prism diopters?
P = 100 (x/y) P = 100 (tan d)
These prisms are thin, lightweight, and can be cut to any shape. Secretary Clinton used this prism on her left eye.
Fresnel prisms **they are like stickers