9 - Oblique Prisms Flashcards

1
Q

What is Oblique prism?

A

When there are prisms in two different directions horizontal and vertical.

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2
Q

Practice finding the compound prism from a V+H Prism

A
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3
Q

Practice resolving prism from compounded to H+V Prism

A
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4
Q

What are the steps to obliquely Crossed Prism

A

1 - Take each obliq prism - resolve into H + V Prism
2 - Add H components from the 2 prisms into 1
3 - Add V components from the 2 prisms into 1
4 - Combine resultant V+H components into a new, single prism

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5
Q

Practice examples of resolving obliquely crossed prism

A
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6
Q

What is a rotary (Risley’s Prism) prism?

A

Combination of two prims

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7
Q

What happens when the bases are next to each other in a rotary prism?

A

Add the Base prism together.

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8
Q

What happens when the bases are opposite to each other in a rotary prism?

A

The prismatic effect will cancel each other out.

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9
Q

What is the distance from the front surface of the cornea to the center of rotation?

A

13.50mm
see figure 15.27 page 303 SOD

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10
Q

What is the effective power of the prism?

A
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11
Q

What is Prentice’s Rule? 2

A

Prism Power is the amount light is displaced in CM at a distance 1m away from the lens/prism.
The displacement in cm over the distance in m.

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12
Q

What do the letters represent in the Effective Power Formula? Pe = P/ 1-(s/l)

A

Pe= Effective Prism
P=
s=
l=

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13
Q

What do the letters reporesent in the Prentice’s Formula?

A

c= decentration in cm
F= focal length in D (Power)

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14
Q

Decentering = lens moving
Looking away from OC = Eye Moving

A
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15
Q

How much prism is present when looking through the optical centre?

A

No prism is induced and the object is not displaced from its actual location.

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16
Q

What is the rules for decentering the lens of a Minus Prescription?

A

Up - Base Down
Down - Base Up
In - Base Out
Out - Base In

17
Q

What is the rules for decentering the lens of a Plus Prescription?

A

Up - Base Up
Down - Base Down
In - Base In
Out - Base Out

18
Q

When resolving what formulas do we use?

A

V/H = Psin0
V/H = Pcos0
P = Prism Power
0 = Base orientation

19
Q

What do we need to be careful of with these formualas? Psin0 Pcos0

A

They can each be used for horizontal and vertical components so take into account the angle given to see what is likely to be the horizontal and vertical.