7 - Aspheric Lenses - Exam 2

Question 1

Spherical and toric lenses both have circular curvatures. How many circular curvatures does each style of lens have?

Answer 1

Spherical lenses have one circular curvature
-therefore one radius of curvature
Toric lenses have two perpendicular circular curvatures - therefore two radii of curvature

Question 2

Does an aspheric lens have a constant radius of curvature?

Answer 2

No

Question 3

What are 2 advantages of aspheric lenses?

Answer 3

1. May reduce off-axis aberrations

2. Reduce lens thickness

Question 4

What is 1 disadvantage of aspheric lenses?

Answer 4

More difficult to manufacture than spherical lenses

Question 5

What is the asphericity of a circle?

Answer 5

Q = 0

Question 6

How does an oblate ellipse compare to a circle?

Answer 6

Steeper - more curvature

Q > 0

Question 7

How does a prolate ellipse compare to a circle?

Answer 7

Flatter - less curvature

-1 < Q < 0

Question 8

What is the asphericity of a parabola?

Answer 8

Q = -1

Question 9

What is a 3D parabola called?

Answer 9

Paraboloid

Question 10

Do paraboloids have any spherical aberrations?

Answer 10

No

Question 11

What is the asphericity of a hyperbola?

Answer 11

Q < -1

Question 12

What is a 3D hyperbola called?

Answer 12

Hyperboloid

Question 13

In which meridian is the power drop off faster in an aspheric lens, sagittal or tangential?

Answer 13

Power drops off faster in tangential meridian

Question 14

What is the difference between a full aspheric lens and a nonfull aspheric lens?

Answer 14

Full - Asphericity starts at the vertex of the lens

Nonfull - has spherical and aspherical components

Question 15

What is the cap in a nonfull aspheric lens?

Answer 15

The central spherical area of the lens

Question 16

Is it possible for a lens that does not have a +6.00 BC fit into a frame designed for that base curve?

Answer 16

Yes

Aspheric lenses may approximate that shape without changing the optics of the lens

Question 17

When talking about PALs, which portion of the lens is typically spherical and which is typically aspheric?

Answer 17

Distance portion is usually spherical

Add portion is usually aspheric

Question 18

What is an atoric lens?

Answer 18

Similar to aspheric, but for spherocylindrical prescriptions

Question 19

What cylindrical power are atoric lenses recommended for?

Answer 19

> 2.00 D of astigmatism

Question 20

What is a finished single vision atoric lens composed of on each surface?

Answer 20

Spherical front surface

Atoric back surface

Question 21

What is a semi finished single vision atoric lens composed of on each surface?

Answer 21

Atoric front surface

Spherocylindrical back surface

Question 22

Can decentration be used to achieve prism in an aspheric lens?

Answer 22

No

However prism can be ground into the lens

Question 23

What are 4 ways of identifying aspheric lenses?

Answer 23

1. Use a lens clock
2. Use a grid pattern behind the lens
3. Note the lens surface curvature
4. Look for manufacturer markings

Question 24

What the DRP coincide with especially in the case of aspheric lenses?

Answer 24

The optical center

Question 25

What is the maximum amount of pantoscopic tilt for aspheric lenses?

Answer 25

10 degrees

counteracted by 5mm decentration

Question 26

What are 4 types of patients who would benefit from aspheric lenses?

Answer 26

1. High plus or high minus Rx
2. Anisometropic patients
3. Patients that want good cosmetics
4. Older patients - aspheric lenses are lighter