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prism peter Flashcards

(50 cards)

1
Q

What does a relieving prism do?

A

Displaces the image toward the direction the eye turns

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2
Q

Prism Base

A

A prism is placed before the eye with reference to the base

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3
Q

3 Effect of a prism on light

A

Displacement, Dispersion, Deviation

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4
Q

Effects of prism on light

A

Prism will have no focal length and light will deviate toward the base

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5
Q

The_____ the prism the ______ the light will _____ and the _____ the image will be ______

A

Stronger, more, Deviate, More, Displaced

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6
Q

Strabismus (heterotropia)

A

When one eye is not aligned with the other eye to look in a different direction

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7
Q

What is Adverse Prism?

A

Stimulate an eye muscle to work harder, designed to strengthen weak muscles

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8
Q

Who came up with Fresnel Prism

A

French physicist, Augusti Jean Fresnel

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9
Q

What is Dissociating Prism

A

Affect temporary interference with a fusion of both eyes, use of risley prisms in phoropter

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10
Q

Base
Compounding Situations

A

Base up and Base down
Base in and Base in
Base out and Base out

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11
Q

What is the Prismatic effect?

A

visual discomfort when optical centers are not situated over the pupils

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12
Q

What is Excessive Base down?

A

Makes people and vertical objects seem taller than they are

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13
Q

Excessive Base Up

A

Makes people and vertical objects seem shorter than they are

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14
Q

4 different prism power units

A

Deviating Angle, Prism Diopter, Centrad, Apical

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15
Q

What is the Rule of Thumb for 45° off axis?

A

50% of cylinder power

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16
Q

What unit is used to measure prism power in optics?

A

Prism diopter (∆)

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17
Q

What is the apex of a prism?

A

The edge where two prism surfaces meet

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18
Q

What is the patient’s reaction to excessive prism?

A

Discomfort, dizziness, and spatial distortion

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19
Q

What is one drawback of Fresnel prisms?

A

Reduced visual contrast

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20
Q

What happens with excessive BD prism?

A

Objects appear concave; patient feels like standing in a bowl

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21
Q

Base
Cancelling situations

A

Base up and base up
Base down and base down
Base in and base out

22
Q

What does a 1 prism diopter do to light?

A

Deviates light 1 cm at 1 meter distance

23
Q

What is the formula for decentration from prism power?

A

Dec = 10 × ∆ / D

24
Q

Why add 2mm in MBS calculation?

A

To compensate for edge chipping or defects

25
How is total prism effect calculated in compound situations?
Add both prisms together
26
What base direction is used for esotropia correction?
Base in (apex in)
27
How can you detect vertical imbalance?
Using lensometer and patient reading complaints
28
What happens with excessive BU prism?
Objects appear convex; patient feels like on a mound
29
What happens if dotted PD does not match patient PD?
Visual lines do not pass through optical centers
30
What are the four prism power units?
Apical angle, Deviating angle, Prism Diopter, Centrad
31
What is exotropia?
Outward turning of the eye
32
What is the optical center in a minus lens?
Located at the apex
33
What is a centrad?
A unit measuring displacement on an arc 1 meter from the prism
34
What is the ANSI Z80 standard unit for prism?
Prism Diopter
35
What causes vertical prism imbalance?
Looking above or below the optical center of the lens
36
What is Prentice's Formula?
∆ = D × decentration (in mm) / 10
37
How is total prism effect calculated in canceling situations?
Subtract smaller prism from the larger
38
How does a prism deviate light?
Toward the base
39
What are Risley prisms used for?
Applying a dissociating prism in a phoropter
40
What is the goal of prescribing prism?
To align visual axes and reduce strain
41
What base direction is used for exotropia correction?
Base In (apex out)
42
What is the effect of base out prism?
Objects shift toward the apex; horizontal tilt in view
43
How is distance between lenses measured?
DBL – shortest distance between nasal edges
44
What happens when lenses are decentered outward in minus lenses?
Base In prism is induced
45
What causes horizontal prism imbalance?
Incorrect decentration
46
What is the base direction for decentering plus lens outward?
Base Out
47
What is prismatic deviation?
The angle the light ray is bent from its original path
48
What is the standard distance for prism measurement?
1 meter
49
What is a Fresnel prism?
A wafer-thin press-on prism used for temporary correction
50
How does a stronger prism affect light?
It bends light more and increases image displacement