Optician Formulas, Abberations, and more....

Question 1

Focal length

Answer 1

Inverse of the power of a lens in meters.

example:
+2.00
becomes
1/2= .5 meter

Question 2

Vertex

Answer 2

Distance from lens to the front of the eye.

Question 3

Meridians

Answer 3

Imaginary lines that help describe the location of axis powers Of a lens with correction for astigmatism.

Question 4

Index of refraction

Answer 4

Amount a material is able to bend light. The higher a materials index, the more it bends light.

Question 5

Abbe value

Answer 5

Amount of chromatic abberration produced by a lens material

Question 6

Snell’s Law

Answer 6

The angle of refraction depends on the angle of incidence of

• light
• the indices of refraction between the two mediums

Question 7

Index of refraction

Answer 7

Describes the density of a material

Question 8

Law of refraction

Answer 8

Light bends toward the normal when it enters a medium more dense than the one it came from.

Question 9

Refraction

Answer 9

How light bends when passing through a medium.

Question 10

Vogel’s Formula

Answer 10

Formula to choose a base curve

Plus lens- Spherical Equivalent, add 6 Diopters

Minus lens- 1/2 Spherical Equivalent, Add 6 Diopters

Question 11

Spherical Equivalent

Answer 11

1. Take 1/2 of Cylinder
2. Add to Sphere

Always round up to nearest quarter Diopter

Question 12

Rules for Vogel’s Formula

Answer 12

Both lenses Plus- Choose steeper base curve

Both lenses Minus- Choose flatter base curve

One Plus, one Minus- Choose highest base curve of two lenses.

Question 13

Vogel’s formula- power becomes more minus. What happens?

Answer 13

Front surface gets flatter. Back surface has to become steeper to maintain same power.

Question 14

Vogel’s formula- Power becomes more Plus. What happens?

Answer 14

Front surface becomes more curved( steeper). Back surface has to become flatter to maintain same power.

Question 15

Transposition

Answer 15

Converting a prescription:

Minus to plus or Plus to minus

Question 16

How to transpose a prescription?

Answer 16

Add cylinder and sphere
Change cylinder sign to opposite sign
Change Axis by 90

Axis cannot be more than 180

Question 17

Chromatic Aberration

Answer 17

Caused by the refraction of different wavelengths and results in colored fringes around images.

Question 18

Spherical Aberration

Answer 18

Occurs when parallel light rays move along the optical axis.

Question 19

Chromatic Aberration

Answer 19

When lens does not focus all wavelengths of color to one point.

Question 20

Coma

Answer 20

Lens aberration- Occurs when parallel light rays through a lens focus in a ring-shaped pattern with a V-shaped or comet-like flare at one end of an image.

Question 21

Visable Spectrum

Answer 21

380 to 760 nm

measured in nanometers

Question 22

Cylinder power 30 degrees away from axis?

Answer 22

25%

Question 23

Cylinder power 60 degrees away from axis?

Answer 23

75%

Question 24

cylinder power at 45 degrees

Answer 24

50% of cylinder added to the sphere