Optical Knowledge

Question 1

What is focal length?

Answer 1

The distance from a lens where rays of light are said to converge.

Question 2

Where is the focal length on a minus lens?

Answer 2

Behind or to the left of the lens.

Question 3

Where is the focal length on a plus lens?

Answer 3

In front or to the right of the lens.

Question 4

Are objects minimized or magnified by minus lenses?

Answer 4

They are minimized. The objects in the distance go with the movement of the lens.

Question 5

Are lenses magnified or minimized by a plus lens?

Answer 5

They are magnified.

Question 6

What is the constant for focal length or lens power?

Answer 6

1 meter or equivalent

Question 7

What are the equivalents of 1 meter?

Answer 7

1000 mm, 100 cm, or 40 inches

Question 8

How do you use focal length to get Diopter Power?

Answer 8

Divide focal length into the constant to get Diopter Power

Question 9

How do you get focal lentgth when given diopter power?

Answer 9

Divide diopter power into the constant to get Focal Length

Question 10

What is the resolving power of an emmetropic eye?

Answer 10

Resolving power of 1

Question 11

What does emmetropia mean?

Answer 11

Equal

Question 12

What does ammetropia mean?

Answer 12

Needs correction

Question 13

What is the 5 minute angle?

Answer 13

It is independent of distance of the object from the eye.

Question 14

What is exopthalmos?

Answer 14

Pushing forward of the eye/Graves condition

Question 15

What is the 5 minute angle of an emmetropoic eye?

Answer 15

5 minute angle at 20’

Question 16

What is the resolving power of a 20/40 eye?

Answer 16

Reolving powrer of .5

Question 17

How much larger do letters have to be for a 20/40 eye to reolve at 20’?

Answer 17

Letters have to be 2X as large

Question 18

When is there a 10 minute angle?

Answer 18

For a 20/40 eye

Question 19

How do you figure resolving power?

Answer 19

Take VA (20/60) and divide
Resolving power for 20/60 is .3333

Question 20

How do you determine the angle?

Answer 20

Take VA: 20/60 How many more times is 60 than 20? 3 So 5 times 3 = 15 minute angle

Question 21

What part of the prism gives you the image?

Answer 21

the apex

Question 22

Where are the rays directed in a prism?

Answer 22

To the base

Question 23

What does a prism do?

Answer 23

Bends light, changes the postition of an object, corrects muscle imbalances

Question 24

What is Prenctice’s Rule?

Answer 24

P x d (in cm) = Prism amount
P= Lens power in diopters
d= Decentration in .cm

Question 25

What is a tropia?

Answer 25

an obvious deviation (no depth perception)

Question 26

What is a phoria?

Answer 26

Sometimes there's a deviation

Question 27

What is an orthoptist?

Answer 27

a person who studies eye muscles

Question 28

What is an ocularist?

Answer 28

someone who makes artificial eyes

Question 29

Where is the apex of a prism placed?

Answer 29

Over the weak muscle

Question 30

Where is the base of a prism placed?

Answer 30

Opposite the deviating muscle

Question 31

What is the vertical tolerance for prism?

Answer 31

1/3 or .333

Question 32

How do you determine how much the lens is decentered?

Answer 32

Amount of prism / Diopter Power= d (in cm)

Question 33

Where is the optical center located in a flat top bifocal?

Answer 33

5 mm below top

Question 34

Where is the optical center located in a round bifocal?

Answer 34

In the center

Question 35

Where is the optical center located in an executive bifocal?

Answer 35

At the top

Question 36

How do you determine the index of refraction?

Answer 36

Speed of light in air/speed of light in optical medium=index of refraction of the lens

Question 37

What is the speed of light in air?

Answer 37

186,000 miles per second

Question 38

Regarding the power cross, how do you determine the sphere in + cylinder?

Answer 38

the sphere is always the lowest + or the most -

Question 39

How do you determine the sphere for minus cylinder?

Answer 39

the sphere is lowest - or most +

Question 40

Is high Abbe Value a good thing?

Answer 40

Yes

Question 41

``` List the following Abbe values: Glass CR 39 Hi Index 1.67 Hi Index 1.74 Polycarbonate ```

Answer 41

``` 70 40 36 34 30 ```

Question 42

Where do light rays focus on an emmetrope?

Answer 42

they come to a single point focus on the retina

Question 43

What is accomadative hyperopia?

Answer 43

person has enough accommation to overcome their refractive error

Question 44

What is manifest hyperopia?

Answer 44

part of the R.E. is taken care of by accommadation, but part is taken care of by lens

Question 45

What absolute hyperopia?

Answer 45

all of the R.E. is taken care of by the lens

Question 46

Name the 5 types of astigmatism.

Answer 46

Simple myopic, simple hyperopic, compound myopic, compound hyperopic, and mixed

Question 47

What is an isometropia?

Answer 47

a person with an equal Rx

Question 48

What is anisometropia?

Answer 48

Unequal amoundt: OD: -3.00, OS: -8.00

Question 49

Where is traditional slab-off placed?

Answer 49

ON the front surface of the lens

Question 50

Where is reverse slab placed?

Answer 50

Back surface of the lens

Question 51

Why is slab-off used?

Answer 51

Done for vertical imbalance; traditional slab done on highest minus

Question 52

What is diopter power of the emmetropic eye?

Answer 52

Eye=60 D (Cornea=43 D and lens=16-20 D)

Question 53

What are the indices of refraction for the following? | CR 39, Crown Glass, Tools, Cornea, Crystalline Lens, Polycarbonate

Answer 53

1.49, 1.523, 1.53, 1.37, 1.42, 1.61

Question 54

What three materials all have the same index of refraction? What is it?

Answer 54

Aqueous, Vitreous, Water = 1.33

Question 55

What is the index of refraction of air?

Answer 55

1.00

Question 56

What is Jaeger print used for?

Answer 56

Near vision