Basics Of Retinal Image Quality · • Airy’s Disk – contains the central maximum Diffraction - Circular Aperture • Diffraction pattern Aerial View 3D View Airy’s Disk Pedrotti

$Page 1: Basics Of Retinal Image Quality · • Airy’s Disk – contains the central maximum Diffraction - Circular Aperture • Diffraction pattern Aerial View 3D View Airy’s Disk Pedrotti$
Core 2016 Lecture II Dr. Applegate

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A Free sample background from www.pptbackgrounds.fsnet.co.uk

Slide 2

Basics Of Retinal Image

Quality

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Slide 3

The optics of the eye are the first stage of vision.

It is an extremely important stage but not

the only stage.

© RAA

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Slide 4

The optical quality of the retinal image is defined by

pupil size and:

Diffraction

Scatter

Chromatic Aberration

Wave aberration© RAA

© 2001 By Default!


Slide 5

Diffraction

“Any deviation of light rays from a rectilinear path which cannot be interpreted as reflection or refraction.”

Sommerfeld, ~ 1894

http://www.lrz.de/~Sommerfeld/Bilder/as97_01.gif

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Slide 6

Wavefronts connect points having the same phase.

Figure 5-1 from MacRae, Krueger and Applegate, Customized Corneal Ablation: The Quest for Super Vision, Slack, Inc. 2001.

© RAA


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Slide 7

To understand diffraction, it is necessary to understand the behavior of a wavefront

as it passes through an aperture or by edge.

© RAA

This eye can see the light.

© RAA

This eye cannot see the light.

© RAA

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Slide 10

But, the light can be dimly seen.

Light is apparently bent by the aperture.

How can this be explained?

© RAA

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Slide 11

How can we explain diffraction?

Use Huygen’s Principle to explain how light bends around edges– Each point on wavefront acts as a new source of light– These new “sources” emit spherical wavefronts

• same velocity and frequency as original wavefront– These new spherical wavefronts create a secondary

wavefront– Wavefront moves forward & process repeats

Christiaan Huygens

http://ressources2.techno.free.fr/informatique/sites/inventions/inventions.html

Huygens postulated that every point on a wavefront was the

source of asecondarywavefront.

© RAA


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For an unbounded system (no pupil), interference effects cause the light to

propagate only in the original direction.

However, for a bounded wavefront (with pupil), the effects do not cancel.

© RAA

unbounded bounded

Pupil

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Slide 14

© RAA

Light from the wavelets can reach the eye even though a straight line from the eye to the point source does not pass through the aperture.

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Slide 15

A special and particularly interesting case of Fresnel diffraction, called

Fraunhofer diffraction, occurs in the focal plane of an aberration-free or

nearly aberration-free imaging system.

The Fraunhofer diffraction pattern of an axial point source defines the

appearance of the point source in the

image plane.© RAA

Airy disc

Fraunhofer diffraction defines

the diffraction limited point spread

function (PSF).

© RAA

Diffraction - Circular Aperture

• Most relevant and important aperture shape– Shape of most lenses & apertures (like the pupil!)

• For the eye - diffraction pattern is the image of a distant point source on the retina– Also called Point Spread Function (PSF)

• Diffraction pattern (NO aberrations) consists of– central bright spot (central maximum)

• Contains majority of light (~84%)

– dimmer rings surrounding central maximum

• Airy’s Disk – contains the central maximum

Diffraction - Circular Aperture• Diffraction pattern

Aerial View 3D View

Airy’s Disk

Hecht. Optics. 2nd Ed. Addison-Wesley; 1987.Pedrotti & Pedrotti. Introduction to Optics. 2nd Ed. Prentice Hall; 1993.


4

Airy’s Disk

• How large is Airy’s Disk?

Sir George Biddel Airy: Inventor of spectacles for astigmatism

r sin 1.22d

θ = angle between peak & first minimum (in °)

λ = wavelength (in m)

d = diameter of circular aperture (in m)

dr

D

θ

Slide courtesy of Jason Porter © 2001 By Default!


Slide 20

The diameter of the Airy disc varies with pupil diameter.

The radius of the Airy disc increases as pupil size decreases

by the following formula.

© RAA

an

fr

'

'22.1

© 2001 By Default!


Slide 21

As the radius of the Airy disk decreases the higher the

fidelity of the retinal image. Said differently, in a perfect optical system the larger the pupil, the better the image.

© RAA

5 arc min.

1 mm 2 mm 3mm 4 mm

5 mm 6 mm 7 mm 8 mm

Diffraction PSFs for pupil diameters 1 - 8

© RAA

© 2001 By Default!


Slide 23

Any scene is a collection of points. The image of a scene is

represented by the point spread function of every point in the

scene. So what we learn about a point image can be used to

simulate the image of an object.

© RAA

© 2001 By Default!


Slide 24

Defocus = 0 D; RMS WFE = 0 mAiry disc diameter = 2.8 m

Pupil Diameter = 8.00 mm

20/12

20/20

20/40

5 arc min.

PSF

© RAA


5

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Slide 25


20/12

20/20

20/40


5 arc min.

© RAA

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Slide 26


20/12

20/20

20/40


5 arc min.

© RAA

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Slide 27


20/12

20/20

20/40


5 arc min.

© RAA

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Slide 28


20/12

20/20

20/40


5 arc min.

© RAA

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Slide 29


20/12

20/20

20/40


5 arc min.

© RAA

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Slide 30

Clinical Implications of Diffraction Include:

Diffraction fundamentally defines the upper limits of retinal image quality.

Diffraction effects increase as pupil size decreases making the quality of the retinal image poorer and poorer.

© RAA


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© 2001 By Default!


Slide 31


pupil size and:

Diffraction

Scatter



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Slide 32

Pupil

Back-scattered

Forward-scattered

© RAA

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Slide 33

Type of scatter depends on particle size

Rayleigh scatter For small particles (<< wavelength of light)

– Scatter is wavelength-dependent– Short wavelengths are scattered more than longer

wavelengths– Tends to have uniform scattering in all directions

Tyndall (Mie) scatter Applies to larger particles (> wavelength of light)

– Scatter all visible wavelengths equally– Forward scattering dominates– Since all λ’s scattered the same, causes object to look

white (or some saturation of white)

4

1Scatter

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Slide 34

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Slide 35 © 2001 By Default!


Slide 36

20/25 VA

Slitlamp Cross-section -

CataractRetro-Illumination -

Cataract© RAA


7

Tom van den Berg Tom van den Berg

Tom van den Berg

Ciliary corona

Actual subjective appearance of straylight: a pattern of very fine streaks, not at all like the circularly uniform (Airy disc-

like) scattering pattern of particles of approximate wavelength size

Tom van den Berg

© 2001 By Default!


Slide 41


pupil size and:

Diffraction

Scatter



The speed of light in in the eye varies with the wavelength of light. The

shorter the wavelength the slower the speed of light. Since the index of

refraction is the ratio of the speed of light in a vacuum to the speed of light

in the new medium, the index of refraction is greater for short

wavelengths than it is for longerwavelengths.

© RAA


8

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Slide 43

As light enters the eye, the higher the refractive index the greater the angle of refraction

as dictated by Snell’s law.

© RAA

'sin'sin inin

i

'in 'n

The speed of light in a material is dependent on refractive index

• Most materials exhibit dispersion, or a change in the index of refraction with wavelength

• What does dispersion imply about the following properties for different wavelengths in a material:– Velocity

n

high

lowshort long

Positive chromaticaberration

velocity c(speedoflight)

n

Shorter wavelengths: higher nslower velocity Slide courtesy of Jason Porter



• What does dispersion imply about the following properties for different wavelengths in a material:– Velocity– Angle of refraction

n

high

lowshort long


n*sini n' *sini'i

nn'

i'Shorter wavelengths: higher n’

smaller i’ – greater refractionSlide courtesy of Jason Porter



• What does dispersion imply about the following properties for different wavelengths in a material:– Velocity– Angle of refraction– Power of a surface

n

high

lowshort long


F n' nr

i

n n'Shorter wavelengths: higher n’higher power

Slide courtesy of Jason Porter

© RAA

Longitudinal (Axial) Chromatic Aberration

© 2001 By Default!


Slide 48

1D

The difference in longitudinal chromatic aberration between 486 and 656 nm is just over 1 D.

Adapted from Bennet & Rabbetts, 1989© RAA


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Transverse Chromatic Aberration

© 2001 By Default!


Slide 50


pupil size and:

Diffraction

Scatter



Simple Myopia© RAA

Simple Myopia with Optical Correction

© RAA

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Slide 53

In reality it is not so simple.

© RAA © RAA


10

© RAA

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Slide 56

The eye has higher order wave aberrations that become increasingly manifest as the pupil diameter increases.

© RAA

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Slide 57

1mm 2mm 3mm 4mm

Diffraction-Limited System

Normal Eye with

Typical Aberrations

5mm 6mm 7mm 8mm© RAA

Diffraction-Limited System

Normal Eye with

Typical Aberrations

© 2001 By Default!


Slide 58

For many clinical eyes (ie. keratoconics), it is important to

correct the higher order aberrations.

For the normal eye, the gains obtained by correcting higher

order aberrations are primarily for large pupil sizes and diminish as

the pupil size gets small.

© RAA

© 2001 By Default!


Slide 59

In the past, a patient’s eye which could not be corrected

with conventional sphero-cylindrical corrections, was

often dismissed with a diagnosis of irregular astigmatism.

We are now in a position to attempt to correct these eyes.

© RAA

Larry Thibos has written a basic level article on wavefront sensing

and its advantages

• http://journals.lww.com/optvissci/Fulltext/2013/09000/The_2012_Charles_Prentice_Medal_Lecture__.4.aspx

• http://links.lww.com/OPX/A134


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© 2001 By Default!


Slide 61

Wavefront

Wavefront error.

The specification of wavefront error.

RMS WFE– By mode, age, pupil diameter

Visual image quality metrics derived from WFE

© RAA

With this overview in mind let’s exam:

© 2001 By Default!


Slide 62

To understand the need for the measurement of

wavefront error in the correction of refractive

errors, it is helpful to change our thinking from rays of

light to waves of light.

© RAA

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Slide 63

Rays

© RAA

Wavefronts

Focus

Wavefront After Refraction

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Slide 64

Wavefront

Wavefront error.




© RAA


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Slide 65

Ideal Aberrated

Rays

© RAA

Waves and Rays

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Slide 66

© RAA

Wavefront error is the difference

between the ideal wavefront and

the actual wavefront.


12

perfectretinal

image ofobject point

P

Unaberrated Eye focused for distance

Key points:

• All rays from P intersect at common point P on the retina.

• The optical distance from object P to image P is the same for all rays.

• Wavefront converging on retina is spherical.

Rays from distant object point, P.

Slide courtesy Larry Thibos

Aberrated eye

Key points:

• Rays do NOT intersect at the same retinal location.

• The optical distance from object to retina is NOT the same for all rays. OPD = Optical Path Difference

• Wavefront is NOT spherical.

Pflawedretinalimage

Rays from distant point source, P. P

Slide courtesy Larry Thibos

Plane wave

Spherical wave Aberrated wave

Ideal, Perfect Eye Normal, Aberrated Eye

Wavefront error is the difference between the ideal wavefront and the actual wavefront.

Slide courtesy of Jason Porter © 2001 By Default!


Slide 70

Wavefront

Wavefront error.




© RAA


© 2001 By Default!


Slide 71

A particularly useful (but not the only) representation of ocular

aberration is to fit the error between the actual wavefront and the ideal

wavefront in three dimensions with a Zernike expansion.

Fitting the error data with a Zernike expansion parcels the error into

unique building blocks.© RAA

-4 -3 -2 -1 0 1 2 3 4

0

1

2

3

4

nm

n

mZ

© RAA

2

0Z


13

-1 0 1

0

1n

m

The 0 and 1st radial orders of the Zernike expansion are generally ignored when measuring the monochromatic optical aberrations of the fixating eye. The reason is simple, neither affect the image quality of the fixating eye. The 0 radial order simply adds a constant to all locations and the 1st radial order are prism terms affecting the position but not the optical quality of the image.

0

0Z

1

-1Z 1

1Z

Z

© RAA

-2 -1 0 1 2

0

1

2

n m

Zn

m

The 2nd radial order in the Zernike expansion the traditional ophthalmic prescription.

reflect the spherical (defocus) error. and together reflect the cylindrical error.1

2Z 1

2Z

02Z

2

-2Z 2

0Z 2

2Z

© RAA

-4 -3 -2 -1 0 1 2 3 4

0

1

2

3

4

nm

n

m

Zernike Expansion modes in the 3rd order and higher are collectively called the higher order aberrations.

Z

© RAA

0

3 4 5

6 7 8 9

10 11 12 13 14

1 2

© RAA

2

3

DefocusAstigmatism Astigmatism

VerticalComa

HorizontalComa

SphericalAberration

Trefoil Trefoil

Tetrafoil Secondary Astigmatism

Secondary Astigmatism

Tetrafoil

4

-4 -3 -2 -1 0 1 2 3 4n

m

nm

Z

© RAA

Each mode’s magnitude (weight) is defined by a coefficient C having the same sub-

script and superscript as the Zernike mode.

Four different magnitudes of secondary astigmatism.

4-2C 4

-2Z

4

-2C = 0.3μ 4

-2C = 0.2μ 4

-2C = 0.1μ 4

-2C = 0.05μ

© RAA


14

+ +

+ + +

+ + + +

=

Weighted Zernike modes through the 4th radial order in this PRK eye for a 6mm pupil are added together linearly to form the representation

of the total wavefront error.© RAA

2

3


SphericalAberration

Trefoil Trefoil



Tetrafoil

4

-3 -2 0-1-4 1 2 3 4Angular Frequency

Sine Cosine

VerticalComa

HorizontalComa

© RAA

+

To determine the magnitude and orientation of any given aberration that has an angular frequency other than zero, the sine and cosine modes for the aberration of interest are added. For example, vertical coma (sine mode) and horizontal coma (cosine mode) can be added together to establish the total magnitude and orientation of coma.

=

3

-1Z

Vertical Coma Horizontal Coma

© RAA

C3

-1

3

1ZC3

1

Total Coma

+ +

+ + +

+ + + +

=

2

3

4

n m 0 1 2 3 4-3 -2 -1-4

Sine Cosine

Thus, astigmatism modes can be added together, trefoil modes can be added together, coma modes can be added together, tetrafoil

modes can be added together, secondary astigmatism modes can be added together, etc.

© RAA

+

=++

+++

Defocus Astigmatism Trefoil Coma

Tetrafoil SecondaryAstigmatism

SphericalAberration

TotalAberration

It can easily be seen that this post PRK eye aberrations are primarily dominated by coma, spherical aberration, secondary astigmatism,

trefoil and a smaller amounts of defocus, astigmatism, and tetrafoil.

© RAA

© 2001 By Default!


Slide 84

How are aberrations distributed in the population?

and

What is the best way to display ocular aberrations in a meaningful

way?


15

Smirnov HS (1961). Measurement of the wave aberration in the human eye. Biophys6:52-66

“The method applied in the present work of determining the wave aberration is quite laborious; although the measurements can be taken in 1‐2 hours, the calculations take 10‐12 hours… Therefore, it is unlikely that such detailed measurements will ever be adopted by practitioner‐ophthalmologists.”

Slide courtesy of Jason Porter

Howland HC and Howland B (1977). A subjective method for the measurement of monochromatic aberrations of the eye. J Opt Soc Am, 67:1508-1518

55 eyes from 33 subjects

Howland & HowlandSmirnov

The means of almost all Zernike modes are approximately zero and have a

large intersubject variability

Mean of 109 subjects5.7 mm pupil

Mic

ron

s o

f A

ber

rati

on

Zernike Mode

-2

0

2

4

6

8

Z20 Z 2

-2 Z22 Z 3

-1Z31 Z 3

-3 Z33 Z4

0 Z42 Z 4

-2 Z44 Z 4

-4 Z51 Z 5

-1Z53Z 5

-3 Z55 Z 5

-5

Z 3-1 Z3

1 Z 3-3 Z3

3 Z40 Z4

2 Z 4-2 Z4

4 Z 4-4 Z5

1 Z 5-1 Z5

3 Z 5-3 Z5

5-0.3

-0.2

-0.1

0

0.1

0.2

0.3

Z 5-5

Spherical aberration

Porter et al., JOSA A (2001)

© 2001 By Default!


Slide 88

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27

Co

eff

icie

nt

Va

lue

in m

icro

met

ers

All Patients

7mm pupil

3rd 4th 5th 6th

TINCO Study Patients age > 20 < 82; N = 113

© 2001 By Default!


Slide 89

The reason that the average coefficient value approaches zero

is that for most modes of the Zernike expansion there are some eyes where the coefficient has a

negative sign and in others it has a positive sign.

© 2001 By Default!


Slide 90

This similar to saying that the following group of individuals on average have no refractive error.

Subject # Correction Subject # Correction

1 -2 6 2

2 -10 7 10

3 -5 8 5

4 -6 9 6

5 -15 10 15

Ave. = 0


16

© 2001 By Default!


Slide 91

Wavefront

Wavefront error.




© RAA


© 2001 By Default!


Slide 92

On the other hand if we had looked at magnitudes we would have

found the average magnitude of the refractive error to be 7.60 D not

zero.

© 2001 By Default!


Slide 93

0

0.1

0.2

0.3

0.4

0.5

0.6

C6 C7 C8 C9C10

C11C12

C13C14

C15C16

C17C18

C19C20

C21C22

C23C24

C25C26

C27

Mag

nit

ud

e W

avef

ron

t E

rro

rin

mic

rom

eter

s

All Patients

7mm pupil

TINCO Study Patients age > 20 < 82; N = 113

3rd 4th 5th 6th

© 2001 By Default!


Slide 94

Magnitude of the wavefront error for any Zernike mode is

equivalent to the RMS wavefront error for that mode.

)(2 CabsCtermanyforerrorwavefrontRMS

© 2001 By Default!


Slide 95

RMS wavefront error is equivalent to the standard

deviation of the wavefront error over the pupil.

2

3


SphericalAberration

Trefoil Trefoil



Tetrafoil

4


Sine Cosine

VerticalComa

HorizontalComa

© RAA


17

© 2001 By Default!


Slide 97

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

C6 C7 C8 C9 C10 C11 C12 C13 C14

Co

eff

icie

nt

Va

lue

in m

icro

met

ers

3rd 4th

TICO Study Patients age > 20 < 82; N = 113

Coma

TrefoilS

ph

. Ab

2nd Astig.

Tetrafoil

© 2001 By Default!


Slide 98

RMS error trefoil =

RMS error coma =

RMS error tetrafoil =

RMS error 2nd astig. =

213

213 )()( CC

233

233 )()( CC

244

244 )()( CC

224

224 )()( CC

© 2001 By Default!


Slide 99

TICO Study Patients age > 20 < 82; N = 113

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

RM

S E

rro

rin

mic

rom

eter

s

Trefoil Coma Tetrafoil 2nd Astig Sph Ab

7mm pupil

© 2001 By Default!


Slide 100

While RMS plots of each type of aberration tell us how much and

which aberrations are contributing to the typical aberration structure,

such plots do not tell us the orientation of the aberration, or

how aberrations interact to increase or decrease visual

performance.

© 2001 By Default!


Slide 101

Aberrations for any given person vary as a function of several

factors including:

Age

Pupil diameter

Tear quality between blinks

Accommodation

Optical disease and conditions that affect ocular optical quality (CLs, refractive surgery, IOLs, etc.)

© 2001 By Default!


Slide 102

The most common metric of wavefront aberration is total high order RMS wavefront error. RMS

wavefront error is equivalent to the standard deviation of the high order wavefront over the pupil

aperture.

.....)()()()()( 244

233

213

213

233

CCCCCRMS


18

© 2001 By Default!


Slide 103

High order RMS aberration as a function of pupil size and age

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

3mm 4mm 5mm 6mm

RM

S W

avef

ron

t E

rro

rin

mic

rom

ete

rs

20<40

40<60

60<80

© 2006 Applegate

Applegate, RA, Donnelly, WJ III, Marsack, JD, Pesudovs, K, The 3-D relationship between high order RMS wavefront error, pupil diameter, and aging, J Opt Soc Am-A, 24:578-587, 2007.

© 2006 Applegate


Figure 3A.

© 2006 Applegate


Figure 3A.

Applegate, RA, Donnelly, WJ III, Marsack, JD, Pesudovs, K, The 3-D relationship between high order RMS wavefront error, pupil diameter, and aging, J Opt Soc Am-A, 24:578-587, 2007. Applegate, RA, Donnelly, WJ III, Marsack, JD, Pesudovs, K, The 3-D relationship between high order

RMS wavefront error, pupil diameter, and aging, J Opt Soc Am-A, 24:578-587, 2007.


19

© 2001 By Default!


Slide 109

For any given Zernike aberration visual performance

decreases as the RMS WFE increases.

For the optometrists amongst you the following simulations illustrate why

dioptric error can be very misleading

© 2001 By Default!


Slide 110

The following simulations fix the dioptric error of the eye at

0.25 D. Notice in these simulations that as pupil size

decreases so does RMS wavefront error despite the fact

that the dioptric defocus remains constant.

© RAA

© 2001 By Default!


Slide 111

Pupil Diameter = 2.00mm

Defocus = 0.25DRMS wave aberration = 0.036 µm

20/12

20/20

20/40

© RAA

© 2001 By Default!


Slide 112


Defocus = 0.25DRMS wave aberration = 0.14 µm

20/12

20/20

20/40

© RAA

© 2001 By Default!


Slide 113


Defocus = 0.25D RMS wave aberration = 0.58 µm

20/12

20/20

20/40

© RAA

© 2001 By Default!


Slide 114

In this case, wavefront error tells us that the image is getting better or worse, dioptric error does not.

© RAA

0.58µm WFE 0.036µm WFE

8.0mm pupil 0.25D Myope 2.0mm pupil


20

© 2001 By Default!


Slide 115

Wavefront

Wavefront error.




© RAA

With this overview in mind let’s exam:Unfortunately changes in RMS WFE are not always well correlated to changes in

visual performance.

Applegate, RA, Sarver, EJ, Khemsara, V, Are All Aberrations Equal? Journal of Refractive Surgery, 18:S556‐S562, 2002.

2nd

3rd

4th

-4 -3 -2 -1 0 1 2 3 4

RMS = 0.25 μ over a 6mm pupil, Equiv. D = 0.19 D Letter size 20/40

Applegate, RA, Sarver, EJ, Khemsara, V, Are All Aberrations Equal? Journal of Refractive Surgery, 18:S556-S562, 2002. © RAA

Let

ters

rea

d o

n a

ber

rate

d c

har

t –

Let

ters

rea

d o

n u

nab

erra

ted

ch

art

-14

-12

-10

-8

-6

-4

-2

0

0 0.2 0.4 0.6 0.8 1

RMSUH © RAA

Applegate, RA, Sarver, EJ, Khemsara, V, Are All Aberrations Equal? Journal of Refractive Surgery, 18:S556-S562, 2002.

RMS = 0.25 μ6mm pupilEquiv. D = 0.19 D

Let

ters

rea

d o

n a

ber

rate

d c

har

t –

Let

ters

rea

d o

n u

nab

erra

ted

ch

art

UH WFC 2011

2

3


SphericalAberration

Trefoil Trefoil



Tetrafoil

4


Sine Cosine

VerticalComa

HorizontalComa

n

mZCn

m

Hig

her

Ord

erL

ow

er O

rder

Rad

ial

Ord

er

UH


21

-14

-12

-10

-8

-6

-4

-2

0

0 0.2 0.4 0.6 0.8 1

y = -12.684 + 20.513x R 2= 0.80928

Visual Strehl

Let

ters

rea

d o

n a

ber

rate

d c

har

t –

Let

ters

rea

d o

n u

nab

erra

ted

ch

art

UH

SD 1.083475

Minimum -2.50526

Maximum 1.924988

Interaction between aberrations can improve or reduce visual performance, Journal Cataract and Refractive Surgery, 29:1487‐1495, 2003.

Single valued metrics of optical quality derived from wave aberration predict visual performance, Journal of Vision, 4:322‐328. 2004

+ =

0.25 µ+

=22 15.02.0 Applegate, RA, Marsack, J., Ramos, R., Interaction Between Aberrations Can Improve or

Reduce Visual Performance, J Cataract and Refractive Surgery, 29:1487-1495, 2003

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logVSXlog

The Visual Strehl

UH

Six just noticeable differences in retinal image quality in one line of visual acuity: Towards quantification of ‘20/20 happy’ vs. ‘20/20 unhappy’, Journal of Cataract and Refractive Surgery, 37:1523–1529, 2011.


22

In this paper, Ravikumar et al reported the visual Strehl could distinctly quantify 6 just noticeable changes in blur prior to a 1 line

loss of logMAR acuity.

Given the task in a subjective refraction is to say which is better # 1 or #2, this results suggests that the visual Strehl can be used to objectively define the sphere cylinder and axis that best balances an individuals higher order aberrations.

Change in visual acuity is highly correlated with change in image quality metrics independent of wavefront error and/or pupil diameter, Journal of Vision, 12:1‐13, 2012.

Change in log VSX

-2.1-1.8-1.5-1.2-0.9-0.6-0.30.0

Cha

nge

in lo

gMA

R a

cuity

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Change in logMAR = - 0.453 * Change in log VSX -0.0877r2 = 0.87, p < 0.001

B

Th

at’s

it

for

tod

ay

Documents

Basics Of Retinal Image Quality · • Airy’s Disk – contains the central maximum Diffraction - Circular Aperture • Diffraction pattern Aerial View 3D View Airy’s Disk Pedrotti