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