Formulas and Optical Theory

Question 1

TP = sphere power + cylinder power x sin 2 (0)

Answer 1

Power in Oblique meridians

Question 2

N1 sin i = N2 sin r

Answer 2

Snells’ Law

Question 3

angle I =angle r

Answer 3

Law of reflection

Question 4

Prism (^)=(hxD) / 10

Answer 4

Prentice Rule

Question 5

D = 1/f

Answer 5

Focal length - Dioptic power

Question 6

De = D1 +D2

Answer 6

Nominal Power

Question 7

FPD = A +DBL

Answer 7

Frame PD

Question 8

Dec = (FPD - PPD) / 2

Answer 8

Binocular decentration

Question 9

Speed of light in air/ speed of light in medium.

Answer 9

Index of refraction

Question 10

MBS = ED + (2 X Dec)

Answer 10

Minimum blank size

Question 11

I need a lens with power +3.50D. If I use a lens blank with a front surface power of +8.00D, what back surface do I need?

Answer 11

De = D1 + D2 +3.50 = +8.00 + D2 D2 = -4.50

Question 12

I have a lens with a front surface of +9.25D and a back surface of -2.25D. What is the power of the lens?

Answer 12

De = D1 +D2 De = +9.25 + -2.25 De = +7.00

Question 13

I want my lens to have a power of -3.00D. What back surface do I need if the front surface is +8.00D?

Answer 13

De = D1 +D2 -3.00 = +8.00 +D2 D2= -11.00

Question 14

What is the difference between a high index lens and a aspheric lens?

Answer 14

High index refers to the material of the lens; Aspheric refers to the surface design of the lens

Question 15

What are the three things that can happen to a ray of light when it passes through a lens?

Answer 15

Absorbed, reflected, refracted

Question 16

What is the difference between a monocular distance PD and a binocular distance PD?

Answer 16

Monocular PD: each eye is measured separately from the center line of the face
Binocular PD: the measurement is taken from the center pupil to center pupil

Question 17

What role does the Food and Drug Administration play in the ophthalmic industry?

Answer 17

They are responsible for the lens safety aspect of the industry. Impact resistance is their main focus.

Question 18

According to the Systems text, eyewear can be divided in to what three categories?

Answer 18

Dress eye wear - Designed for everyday use.

Safety eyewear - Designed to meet higher standards of impact resistance since it will be worn in situations that could be potentially hazardous to the eyes.

Sports eyewear - Designed to protect the eyes or enhance the vision in specific sports situations. What is appropriate will vary dramatically depending upon the sport.

Question 19

What are the Rx’s in a plus cylinder form of the following optical crosses?

• 1.00 @095 -3.00 @ 175
  - 2.00 @005 +1.50 @ 085

Answer 19

-2.00 + 1.00 x 005 -3.00 + 4.50 x 175

Question 20

What is transposition?

Answer 20

Transposition is the changing of a prescription from a plus cylinder to a minus cylinder or the other way around. It does not affect the powers of the prescription.

Question 21

What is the dioptric power a lens with a focal length of _____?

1. ) 40 mm
2. ) -33 mm

Answer 21

1. ) D = 1/f D = 1 / .04 D = +2.50

2. ) D= 1/f D = 1 / .33 D = -3.00

Question 22

What is the focal length of a -2.00 D lens in meters?

Answer 22

F = 1D F = 1/-2 F = -0.50 meters

Question 23

What type of image is formed by a minus lens?

Answer 23

Virtual

Question 24

A plus lens does what to light rays that pass through it?

Answer 24

Makes them converge

Question 25

What does the term critical angle of a material mean?

Answer 25

The ray of light is striking the surface at an angle so that the ray is refracted along the surface of the lens.

Question 26

What is the lens power in the 90th meridian for this lens prescription: +3.00 +1.00 x 180 a. +1.00 b. +2.00 c. +3.00 d. +4.00

Answer 26

+4.00

Question 27

A minus lens with the optical center moved up created _____. a. base up prism b. base in prism c. base out prism d. base down prism

Answer 27

base down prism

Question 28

A base-up prism _____. a. bends light towards the base b. bends light rays away from the apex c. projects an image of the object downwards d. all of the above

Answer 28

all of the above

Question 29

The wavelengths of visible light range approximately from _____. a. 200 - 400 nanometers b. 300 - 600 nanometers c. 400 - 720 nanometers d. 500 - 800 nanometers

Answer 29

400 - 720 nanometers

Question 30

The wavelengths of light that are the most pleasing to the eye are _____. a. ultra-violet b. infra-red c. blue-green d. orange

Answer 30

blue-green

Question 31

The breakdown of light into its component colors is called _____. a. dispersion b. refraction c. reflection d. aberration

Answer 31

refraction

Question 32

The point on a lens which a ray of light will pass through without being deviated is called _____. a. apex b. base c. optical zone d. optical center

Answer 32

optical center

Question 33

The lower the abbe number, the _____. a. less the chromatic aberration b. more the chromatic aberration c. thicker the lens d. thinner the lens

Answer 33

more the chromatic aberration

Question 34

If a lens deviates a ray of light 4 cm at a distance of 2 meters, the lens is said to have power of _____ diopters? a. .25 b. .50 c. 1.00 d. 2.00

Answer 34

2.00

Question 35

The transposed Rx of +3.00 - 1.00 x 30 is _____. a. +3.00 +1.00 x120 b. +2.00 -1.00 x 30 c. +2.00 +1.00 x120 d. +2.00 -1.00 x 30

Answer 35

+2.00 +1.00 x 120

Question 36

Which lens has the characteristic of magnification? a. Minus spherical b. Plus spherical

Answer 36

Plus spherical

Question 37

Which lens has the characteristic of thin center/thick edge? a. Minus spherical b. Plus spherical

Answer 37

Minus spherical

Question 38

Which lens has the characteristic of diverging light rays? a. Minus spherical b. Plus spherical

Answer 38

Minus spherical

Question 39

Which lens has the characteristic of with motion? a. Minus spherical b. Plus spherical

Answer 39

Minus spherical

Question 40

The lens design in which the front base curve gradually flattens is called _____. a. aspherical b. spherical c. corrected curve d. meniscus

Answer 40

aspherical

Question 41

Plus lenses _____. a. are diverging lenses b. are thicker at the center than the edge c. minify image size d. show with motion

Answer 41

are thicker at the center then the edge