lec 13: monocular aberration

Question 1

What kind of optical defects do eyes have?

Answer 1

1. Sphere and cylinder refractive error
2. Chromatic aberrations (LCA & TCA)
3. monochromatic aberration (zernike forms)
4. Diffraction

Question 2

are chromatic and monochromatic aberrations easily correctable?

Answer 2

no

Question 3

seidel aberration

Answer 3

off axis astigmatism, curvature of field, distortion

Question 4

zernike describes what?

Answer 4

wavefront aberrations

Question 5

is focal point a single point in real eye?

Answer 5

no! its aberrated

Question 6

Impact of higher-order aberrations on light entering the eye

Answer 6

causes multiple focal points

Question 7

Impact of higher-order aberrations on light exiting the eye is what?

Answer 7

the same as that entering

in real eye, wavefront is spherical but after light leaves it, its not planar anymore

Question 8

zernike low order aberrations

Answer 8

1 and 2 order

Question 9

zernike high order aberrations

Answer 9

3,4,5 order

Question 10

zenike polynomials

Answer 10



set of basic shapes that are used to fit the wavefront

Question 11

in clinic what are we measuring for zernike polynomials?

Answer 11

second order (sphere and cylinder)

Question 12

do optometrists correct high order aberrations?

Answer 12

no

Question 13

first order of zernike polynomials

Answer 13

prism (not important to us)

Question 14

how do we write zernike polynomials?

Answer 14

Z (m/n)

Question 15

Each individual aberration will have a unique impact on what?

Answer 15

on retinal image quality

Question 16

whats the dominant optical aberration?

Answer 16

2nd order

Question 17

relationship of zernike order to aberration of the optics

Answer 17

inverse relationship

2nd order has more of an effect on eye’s optics compared to 5th order

Question 18

terms are not similar in any way, so the weighting of one term does
not depend on whether or not other terms are being fit

Answer 18

orthogonal

Question 19

the RMS (root-mean-square) wave aberration can be simply calculated as the vector of all or a subset of coefficients

Answer 19

normalized

Question 20

Zernike shapes are very similar to typical aberrations found in the eye (ie principal components)

Answer 20

efficient

Question 21

properties of zernike polynomials

Answer 21

orthogonal
normalized
efficient

Question 22

Recent data confirm that correcting HOAs (monochromatic aberrations) can dramatically improve what?

Answer 22

monochromatic VA, but need an AO mirror.

Question 23

20/10 is not possible with normal levels of monochromatic aberrations (t/f)

Answer 23

true (optics always have aberration)

Question 24

By correcting aberrations, can clinician see finer detail in the fundus image?

Answer 24

cannot see capillaries or individual cells

Question 25

principle of adaptive optics

Answer 25

deformable mirror corrects wavefront

Question 26

does AO improve cone image?

Answer 26

yes

Question 27

increase defocus, astigmatism, and spherical aberration, will decrease what?

Answer 27

optics ((lower zernikes) defocus, astigmatism, and spherical aberration have the most effect compared to other zernikes)

Question 28

lower zernikes affect optics more than higher zernikes (t/f)

Answer 28

t

Question 29

spherical aberration (zernike number)

Answer 29

12, (z4,0)

Question 30

present in all spherical optical surfaces/lenses) is variation in focus (power) as a function of ray height from pupil center.

Answer 30

spherical aberration

Question 31

Spherical aberration in diopters, LSA, equals what?

Answer 31

difference in vergence between peripheral rays (y2) and paraxial (central) rays (y1) in image space.

Question 32

Spherical aberration is considered _______ if peripheral rays focus in front of paraxial rays.

Answer 32

positive

Question 33

Magnitude of spherical aberration is much larger in classical schematic eyes (with spherical surfaces) than in what?

Answer 33

real human eyes

Question 34

peripheral rays focus more (in front) than central rays (t/f)

Answer 34

t

Question 35

n variation in fish lens _______ its optical power and ________ spherical aberration

Answer 35

increases, reduces

Question 36

gradient refractive index does what to positive SA?

Answer 36

reduces

Question 37

n is high in center of lens, what does that do?

Answer 37

central light rays focus more (in front), reduces positive SA

Question 38

Isolated crystalline lens has more power near the optical axis than near the equator. This cause ______ spherical aberration (SA) of crystalline lens itself.

Answer 38

negative

Question 39

For crystalline lens, accommodation causes a larger increase in refractive power centrally than at the margins. Therefore, spherical aberration becomes_________ during accommodation.

Answer 39

even more negative

Question 40

Positive spherical aberration of _______ is balanced partially by negative aberration of lens.

Answer 40

cornea

Question 41

center of cornea is steep, while periphery is what?

Answer 41

flat

Question 42

Cornea is ____ curved at its periphery than at its center. | This asphericity reduces the amount of positive spherical aberration.

Answer 42

less

Question 43

Typical eye has _________ when relaxed, but _________ when accommodating.

Answer 43

positive SA, negative SA

Question 44

index of refraction of lens is _____ near its power surface than at its center. This gradient of index produces _______.

Answer 44

lower, negative SA

Question 45

effect of accommodation on spherical aberration

Answer 45

increase accommodation, decrease spherical aberration (becomes negative)

Question 46

SA is minimized by about ____ accommodation on average.

Answer 46

1.5 D

Question 47

This change in sign (when accommodating) is due what?

Answer 47

the change in balance between positive corneal aberration and negative lens aberration.

Question 48

3rd order aberrations can be used as sensitive method for diagnosing ___________.

Answer 48

keratoconus

Question 49

Zernike Spectrum for normal eyes without correction of lower order aberrations (sphere and astigmatism). Notice that 93% of RMS comes from ___________!

Answer 49

sphere and cylinder in uncorrected eyes

Question 50

How are aberrations measured subjectively?

Answer 50

! Vernier alignment ! Spatially resolved refractometer ! Subjective aberroscope

Question 51

How are aberrations measured objectively?

Answer 51

! Objective aberroscope ! Laser ray tracing (Aberrometer) ! Shack-Hartmann wavefront sensor

Question 52

Principles of the Shack-Hartmann Wavefront Sensor

Answer 52

Sub-divide the wavefront with micro-lenslets. | Local slope determines spot position on video sensor.

Question 53

what happens when wavefront is aberrated using the shack hartmann sensor?

Answer 53

will have new focal point from where it should be

Question 54

The local slope (or the first derivative) of the wavefront is determined at what?

Answer 54

lenslet location

Question 55

• The _______________ is determined by a least squares fitting of the slopes to the derivative of a polynomial selected to fit the wavefront

Answer 55

corresponding wavefront

Question 56

____________ is one of the most commonly used way to describe eye’s wavefront aberrations

Answer 56

zernike polynomial

Question 57

which instrument is likely to give the most info about the optics of the eye?

Answer 57

aberrometer

Question 58

in most eyes high order aberrations are large compared to low order aberration. (t/f)

Answer 58

false

Question 59

high order aberrations decline with radial order and vary significantly from person to person (t/f)

Answer 59

true

Question 60

secondary astigmatism is one of the 4th order aberrations

Answer 60

true

Question 61

12th mode in zernike polynomials is what?

Answer 61

spherical aberration