Flashcards in 4 - Prisms Deck (10)

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1

##
Movements thru prisms

-light

-image

-eyes

###
Light -> base

Image + eyes -> apex

2

##
Deviation power (Z or Δ)

-equation

###
Δ =y/x

y: linear distance the beam is shifted in CENTIMETERS

x: distance between the prism and the wall in METERS

3

##
Prism power and apex angle

-equation

###
d = A(n-1)

Deviation angle in degrees = apex angle*(n-1)

Every 1 degree deviation = 1.75Δ prism

4

##
Prism and power thickness

-equation

###
Δ = 100*(g(n-1)) ÷ ℓ

PD = 100 * (diff in thickness bw apex and base(n-1)) ÷ apex to base length

g and ℓ must be in the same units

5

##
Prentice’s rule

-equation

###
Δ = dF

PD = distance from optical center in CENTIMETERS * lens power

6

##
Prentice’s rule

-4 uses

###
Decentration

Vertical imbalance (binocular)

Image jump

Total prismatic effect (monocular)

7

## Combining prisms problems

### Draw vectors and use pythagorean theory

8

## Correcting vertical imbalance

###
Slab off - use Base Up to the more Minus lens (BUM)

Dissimilar segs

Contact lenses

Multiple specs instead of multifocals

Fresnel prisms

9

##
Image jump

-what 2 things you need to know to solve

###
Add type

Add power

Then use Prentice’s rule where d is the sag drop for that type of BF (e.g. 5mm for FT-28, so use .5cm)

10