Retinal Image Quality

Question 1

Extent to which the copy matches the original

Answer 1

Fidelity

Question 2

What is fidelity always less than

Answer 2

1, the original object is gold standard

Question 3

Filters and fidelity

Answer 3

Can make the image look better despite infidelity

Question 4

Smaller pupil and image quality

Answer 4

Large DF

Quality cant be gerenalized, depends on what you want. There will be a clear background and image

Question 5

Large pupil and image quality

Answer 5

Small DOF

Blurry background and clear up close object

Question 6

The illuminance or luminance in the image of a point source of light

Answer 6

PSF

Question 7

What does PSF depend upon

Answer 7

Diffraction, defocus, aberrations, and scattered light

Question 8

In the absence of defocus, aberrations, and scatter, the PSF is called

Answer 8

Diffraction limited PSF

Question 9

What do defocus, aberrations, and scattered light do to PSF

Answer 9

Shorten and broaden it

Question 10

Aberrated PSF

Answer 10

For pupil diameter greater than 2mm, or in polychromatic light, aberrations tend to ‘spread out more’ relative to the diffraction limited PSF

Question 11

What does the FORM of the PSF depend on

Answer 11

Shape and diameter of the aperture stop

Question 12

Pupil size and best retinal image quality

Answer 12

3mm

Question 13

PSF metrics to quantify image quality

Answer 13

The rayleighs criterion
The half width
The strehl ratio

Question 14

This states the two point resolution limit occurs when the first minimum (the boundary of Airy’s disk) of one diffraction pattern coincides with the center maximum of the other diffraction limited pattern

Answer 14

Rayleighs criterion

Question 15

The diffraction pattern formed on a distant screen resulting from a uniformly illuminated circular aperture has a bright region in the center known as

Answer 15

Airys disk

Question 16

The central disk plus the surrounding series of concentric bright rings is called the

Answer 16

Airy pattern

Question 17

The width of PSF at half the peak height is called

Answer 17

The half width, or full width and half maximum

Question 18

What is the half width of the diffraction limited PSF

Answer 18

3.23

Question 19

The half width of the PSF and aberrations

Answer 19

The half width of the PSF increases with the introduction and increase of aberrations

Question 20

Half width and astigmatism/coma

Answer 20

When astigmatism and coma are Preston, the half width should be considered in two mutually perpendicular directions, where the width is minimum and maximum. These can be reduced to a single number by taking the arithmetic or geometric mean of the two widths

Question 21

This is a measure of the effect of aberrations on reducing the maximum or peak value of the PSF

Answer 21

Strehl ratio

Question 22

What is the equation for strehl ratio

Answer 22

PSF of image/PSF of diffraction limited

Question 23

What is the strehl ratio always equal to and why

Answer 23

Since the effect of aberrations is too spread out, the PSF decrease the maximum peak height, the strehl intensity ratio is ways less than or equal to one

Question 24

What happens to the strehl ratio when the aberrations are greater

Answer 24

The greater the aberrations, the lower the value of the strehl intensity ratio and the poorer the image quality

Question 25

What is considered a good, near to diffraction limited system strehl ratio

Answer 25

0.8

Question 26

The luminance or illuminance distribution in the image of a line source of light

Answer 26

Line spread function (LSF) Used for multifocal lenses

Question 27

Measuring the PSF (LSF) of the human eye

Answer 27

The light distribution of a point source at the retina cannot be measured directly, but the light passing back out of the eye (the Aerial or external image) is measureabel. Because the light is passed twice through the eyes optical system, this method is known as double pass method

Question 28

What are two important factors in understanding optical transfer function (OTF)

Answer 28

Resolution and contrast

Question 29

Systems ability to distinguish object detail

Answer 29

Resolution

Question 30

Defined as how faithfully the minimum and maximum intensity values are transferred from object to image plane

Answer 30

Contrast or modulation

Question 31

Do abberations affect resolution or contrast

Answer 31

Both

Question 32

How well intensity of image is transferred to image

Answer 32

Modulation or contrast

Question 33

Frequency and OTF (MTF)

Answer 33

The higher the frequency, the worse the resolution and at some point no resolution, decreased MTF (OTF)

Question 34

What does the optical transfer function include

Answer 34

The MTF and PTF

Question 35

What does OTF equal

Answer 35

MTF + PTF

Question 36

The amplitude A' of the image divided by the amplitude A of the object, and it is a function of spatial frequency

Answer 36

MTF MTF=A'/A=1

Question 37

What is MTF normalized to

Answer 37

Due to light aberrations, MTF is normalized to 1

Question 38

What is MTF a function of

Answer 38

Spatial resolution, which refers to the smallest line-park the system can resolve

Question 39

What is the anzi standard for IOL lens

Answer 39

.43

Question 40

For a lens, this is the measurement of its ability to transfer contrast at a particular resolution from the object to the image

Answer 40

MTF, this is way to incorporate resolution and contrast into a single specification

Question 41

What happens to MTF as line spacing decreases

Answer 41

As line spacing decreases on the target test, it becomes increasingly difficult for the lens to efficiently transfer this decrease in contrast, as a result, MTF decreases

Question 42

What is the spatial domain

Answer 42

PSF

Question 43

What is the object domain

Answer 43

Optical transfer function

Question 44

Defocus effect

Answer 44

Decrease in amplitude

Question 45

Astigmatism effect

Answer 45

Decrease in amplitude (defocus) on both meridians

Question 46

Spherical aberrations effect

Answer 46

Decrease in amplitude

Question 47

Coma and its effect

Answer 47

Decrease in amplitude no cause transverse phase shift on the image position (PTF)

Question 48

Distortion and its effect

Answer 48

Transverse shift of the image position (PTF)

Question 49

Field curvature and its effect

Answer 49

Decrease in amplitude (defocus) independent of meridian

Question 50

Those aberrations that produce a transverse shift produce what?

Answer 50

Coma and distortion: an effective phase shift in the image

Question 51

The phase shift across a range of spatial frequencies is called

Answer 51

The phase transfer function

Question 52

Phase change in on-axis

Answer 52

In an on-axis in a rotationally symmetrical optical system, there is no change in phase with spatial frequency -in these situations, OTF is identical to MTF and we can use the terms interchangeably OTF=MTF+PTF OTF=MTF

Question 53

Where in the eye is there no change in phase and the PTF=0

Answer 53

Central vision

Question 54

When does PTF become significant

Answer 54

If off axis - periphery - coma, produces TCA, phase shift increase

Question 55

MTF for higher levels of defocus

Answer 55

Decreases and eventually becomes negative

Question 56

What happens when the MTF is negative in defocus on the curve

Answer 56

The image pattern has reversed contrast compared with that of the object, this means that the brighter parts of the object become the darker parts of the image and vice versa

Question 57

The spatial frequency at which the modulation transfer function first goes to zero

Answer 57

Resolution limit | -grating not very visible here. No difference of black and white as it goes below zero, contrast reversed now

Question 58

Any resolution of higher frequency patterns than resolution limit is called

Answer 58

Spurious resolution

Question 59

Phenomenon in whihc the contrast of the image of a periodic grating first goes to zero or essentially zero as defocus levels is increases and then rises again at higher levels of defocus. Thus the grating may be visible at higher levels of defocus than that at which it first disappeared (went to zero)

Answer 59

Spurious resolution