Prism

Question 1

Apical angle, refracting angle

Answer 1

The angle formed by the intersection of the two surfaces at the apex

Question 2

Angle of deviation

Answer 2

The angle the ray of light is bent after passing though the prism/ prism power, refracting power

Question 3

Flat prism

Answer 3

The 2 non parallel surfaces have plane sides that do not change the vergence of incident light

Question 4

Meniscus prism

Answer 4

The two non parallel surfaces are curved and often posses focal power in addition to prism power (used in glasses)

Question 5

A prism changes the direction of light without changing

Answer 5

It’s vergence

Question 6

The deviation of light with a prism causes

Answer 6

Light to bend towards the base

Image to bend towards the apex

Question 7

PD creates a deviation of ___ unit at a distance of 100 Units

Answer 7

1 unit

Question 8

1 PD causes deviation of ____ at a distance of 1m

Answer 8

1 cm

Question 9

When prism is introduced monocularly, the eye moves an amount equal to

Answer 9

The angle of deviation ( eyes turn towards the apex)

Question 10

Resultant prismatic effect

Answer 10

Net separation of the eyes, the extent of the disjunctive movement

Question 11

How can you use prism clinically

Answer 11

Therapeutically
Reduce PAL thickness
Exam room
Prescribed

Question 12

How is prism used therapeutically

Answer 12

Vision therapy under doctor supervision and weekly sessions, sometimes with home exercises

Question 13

How is prim used in vision therapy programs

Answer 13

Visually train eyes monocular or binocular. Image is moved to make eyes diverge/converge/ or make a version movement

Question 14

How is prism used to reduce PALS thickness

Answer 14

Equal amounts of vertical prism can reduce overall thickness and is called prism thinning (BU prism is removed)

Question 15

How is prism used in the exam room?

Answer 15

Cover test to quantify alignment( tropias/phorias)

Fusional ranges

Question 16

Why would prism be prescribed to a patient? For what disorders?

Answer 16

To correct or alleviate double vision or eyestrain. 
BV disorders (Convergence insufficient, tropias, CN palsy’s)
Vertical imbalance

Question 17

How does prism help in binocular vision disorders?

Answer 17

Prism can move images of the world in the direction of the misaligned eyes which helps the pts eyes to simultaneously view the image

Question 18

What is vertical imbalance

Answer 18

A differential vertical prismatic effect between the two eyes at a specific point on the lens
(Prentices rule)

Question 19

Anisometropia

Answer 19

Unequal refractive state between eyes can lead to vertical imbalance

Question 20

When does an anisometrope usually notice vertical imbalance?

Answer 20

When they lower their eyes to read through an add because our eyes have limits capability of vertical fusional movements

Question 21

Vertical imbalance can be a problem is recent onset/ and unilateral

Answer 21

Cataract surgery
Trauma
Retinal surgery
(Scleral buckle)

Question 22

What is the prescriber method for prism?

Answer 22

Horizontal/vertical prism is written with “ok to split”

Question 23

In what forms can prism be prescribed?

Answer 23

Ground, lens decentration, clip on, fresnel

Question 24

How is ground prism produced

Answer 24

By grinning a difference between edge thickness along the base apex line

Base apex line= meridian of prismatic effect
BO= line at 180