Handout 6

Question 1

Aberrations of the eye are taken into account in clinic for

Answer 1

Keratorefractive procedures, corneal grafts, keratoconus

Question 2

Aberrations of the eye can be measured with

Answer 2

Wavefront sensors

Question 3

Paraxial ray

Answer 3

A ray which makes a small angle to the optic axis of the system and lies close to the axis throughout the system

Question 4

Paraxial approximation

Answer 4

Incident rays are close to the optical axis yielding point images for point objects

Question 5

Is paraxial approximation tru

Answer 5

Not always

Question 6

Marginal ray

Answer 6

A ray peripheral to the optic axis and is bent more than axial or paraxial rays

Question 7

When paraxial optics dont apply 2 aberrations will occur called

Answer 7

Monochromatic and chromatic

Question 8

Monochromatic aberrations aka __. Include : (5)

Answer 8

Seidel 
Spherical
 coma 
oblique ast. 
Curvature of field 
Distortion

Question 9

spherical aberrations, when a pencil of light is refracted by a large-aperture optical system, different zones of the aperture have different focal lengths

Answer 9

Peripheral/marginal rays are focused differently than centra/ paraxial rays which affects sharpness

Question 10

Large aperture aberrations are mitigated by

Answer 10

The pupil because of its small size only accepts paraxial rays

Question 11

Spherical aberrations are considered in what lenses

Answer 11

High powered and convex lenses -> correct with aspheric

Question 12

Spherical aberrations can be negative

Answer 12

Peripheral rays refracted less than central (peripheral hyperopia).

Question 13

Spherical aberrations can be negative

Answer 13

• Peripheral rays have a shorter focal length/ are refracted more than central rays (peripheral myopia)
• More common than negative

Question 14

Hen oblique/ off axis rays are refracted by a large aperture optical system at different points than those incident on or near the optical axis produces a

Answer 14

Coma (comet)
Affects the sharpness of image points
-rarely a problem
-significant aberration of the eye itself in keratoconus and can increase after refractive surgery

Question 15

Factors than can control coma

Answer 15

Aperture size
Lens form
Angle of obliquity

Question 16

Increase in pupil size leads to

Answer 16

A decrease in image quality owing to increased aberration

-in high powered lenses, it is best to use aspheric lenses

Question 17

Whats an aspheric lens

Answer 17

Rotationally symmetric surface whose radius of curvature varies with position from lens center -> changes constantly across lens surface

Question 18

Modifies lens surfaces without changing lens power

Answer 18

Aspheric lenses

Question 19

Occurs when light passes obliquely through a spherical surface to form an interval of sturm rather than a point focus

Answer 19

Oblique astigmatism

Question 20

Oblique astigmatism aka ___ forms an __ instead of ___.

Answer 20

Radial astigmatism/marginal astigmatism

Interval of strum rather than a point focus

Question 21

Relation of oblique astigmatism and pupil/aperture size

Answer 21

Not dependent on each other

Question 22

All of I together form paranoid all surfaces

Answer 22

Teacup (tangential) and saucer (sagittal) surface. Tan is always steeper

Question 23

Curvature of field AKA

Answer 23

curvature of image aka power error

-ophthalmic lenses form curved not plane images

Question 24

A true Petzval surface can only exist when

Answer 24

Oblique astigmatism has been eliminated

Question 25

What keeps curvature of field to a minimum

Answer 25

Optimum base curvature

Question 26

Distortion occurs when

Answer 26

Magnification of an extended image varies with the distance of the corresponding object from the optical axis (pincushion and barrel)

Question 27

Distortion tends to

Answer 27

Falsify positions of objects and cause vertical lines to wave as the line of sight intersects different zones of the lens

Question 28

Distortion is mainly a problem for what lenses lenses

Answer 28

High power

Question 29

Pincushion disorder occurs with __ and __ are more magnified

Answer 29

Plus

Corners are more magnified

Question 30

Barrel distortion occurs with ___ and

Answer 30

Minus

-the corners receive less magnification than the middle

Question 31

What are orthoscopic lenses

Answer 31

Barrel distortion of one lens is counteracted by the pincushion distortion of the other lens
-used for optical devices

Question 32

Chromatic abbe ration affects image focus when

Answer 32

Polychromatic light goes through a lens

Question 33

Longitudinal (axial chromatic aberration

Answer 33

On axis aberration that occurs when different wavelengths of light are focused at different distances from the lens

Question 34

The eye has ~+1.50 D

Answer 34

Longitudinal aberration

Question 35

LCA

Answer 35

Diopters/abbe

Question 36

Test that takes advantage of LCA of the eye

Answer 36

Bichrome

Question 37

In bicrome test when red and green charts appear equally distinct it means

Answer 37

Eye is in for us for the yellow portion of the spectrum

Question 38

Transverse (lateral=) chromatic aberration

Answer 38

Occurs because equivalent focal length of a lens is different for components of light having different refractive indices

Question 39

When there’s TCA the wearer will see

Answer 39

Color fringes around objects, its more important for spectacles than LCA

Question 40

Chromatic aberration cannot be eliminated in an optical element made of a single material it requires

Answer 40

Achromatic systems

Question 41

How do Achromatic systems work

Answer 41

The focal lengths are the same for fraun C and F lines = dispersion will be zero

Question 42

A prism is considered achromatic if

Answer 42

It produces deviation withou dispersion -placing 2 prisms of different material in direct contact with bases in opposite directions