Subjective Image Quality Metrics fromThe Wave Aberration

David R. WilliamsWilliam G. Allyn Professor of Medical Optics

Center For Visual ScienceUniversity of Rochester

Commercial Relationship:Bausch and Lomb

Funding:Bausch and Lomb

NSF Science and TechnologyCenter for Adaptive Optics

Collaborators:Univ of Rochester:Li ChenNathan DobleHeidi Hofer

Ian Cox, Bausch and LombRay Applegate, University of HoustonLarry Thibos, Indiana University

Scott MacRaeJason PorterBen SingerRemy Tumbar

How Bad Is This Wave Aberration?

Goal:

To compute a number that captures the subjective effect of the eye’s wave aberration.

Uses:

Assessing severity of the wave aberrationCalculating the best correction

How Bad Is This Wave Aberration?

RMS Wavefront Error = 0.87 µm

Some Aberrations Interact Strongly in Image Blur

Spherical Aberration

rms = 0.16 µm

Defocus andSpherical Aberration

rms = 0.52 µmDefocus

rms = 0.5 µm

Zernike Modes

trefoil coma coma trefoil

quadrafoil secondary spherical secondary quadrafoil

secondary secondarysecondary secondary

defocusastigmatism astigmatism

astigmatism astigmatism

trefoiltrefoil comacoma

Z20Z 2

-2 Z22

Z 3-1 Z3

1Z 3-3 Z3

3

Z40 Z4

2Z 4-2 Z4

4Z 4-4

Z51Z 5

-1 Z53Z 5

-3 Z55Z 5

-5

Higher OrderAberrations

2nd

radialorder

Lower OrderAberrations

3rd

4th

5th

pentafoilpentafoil

Zernike Modes

trefoil coma coma trefoil

quadrafoil secondary spherical secondary quadrafoil

secondary secondarysecondary secondary

defocusastigmatism astigmatism

astigmatism astigmatism

trefoiltrefoil comacoma

Z20Z 2

-2 Z22

Z 3-1 Z3

1Z 3-3 Z3

3

Z40 Z4

2Z 4-2 Z4

4Z 4-4

Z51Z 5

-1 Z53Z 5

-3 Z55Z 5

-5

Higher OrderAberrations

2nd

radialorder

Lower OrderAberrations

3rd

4th

5th

pentafoilpentafoil

Zernike Modes

trefoil coma coma trefoil

quadrafoil secondary spherical secondary quadrafoil

secondary secondarysecondary secondary

defocusastigmatism astigmatism

astigmatism astigmatism

trefoiltrefoil comacoma

Z20Z 2

-2 Z22

Z 3-1 Z3

1Z 3-3 Z3

3

Z40 Z4

2Z 4-2 Z4

4Z 4-4

Z51Z 5

-1 Z53Z 5

-3 Z55Z 5

-5

Higher OrderAberrations

2nd

radialorder

Lower Order Aberrations

3rd

4th

5th

pentafoilpentafoil

Zernike Modes

trefoil coma coma trefoil

quadrafoil secondary spherical secondary quadrafoil

secondary secondarysecondary secondary

defocusastigmatism astigmatism

astigmatism astigmatism

trefoiltrefoil comacoma

Z20Z 2

-2 Z22

Z 3-1 Z3

1Z 3-3 Z3

3

Z40 Z4

2Z 4-2 Z4

4Z 4-4

Z51Z 5

-1 Z53Z 5

-3 Z55Z 5

-5

Higher OrderAberrations

2nd

radialorder

Lower OrderAberrations

3rd

4th

5th

pentafoilpentafoil

There are strong interactions between Zernike Modes.

Therefore,Decomposing the wave aberration

into Zernike modes is not the best way to evaluate the subjective impact of

the wave aberration

How Bad is This Wave Aberration?

Point Spread FunctionWave Aberration

Use Retinal Image Quality, Not the Wave Aberration

Aberrations in Lens and Cornea Distort Wave front

Principle of Adaptive Optics

Deformable MirrorCorrects Wave front

Sharp Image in Camera

Wave front SensorMeasures Wave front

Adaptive Optics Sharpens the Eye’s Point Spread Function

QuickTime™ and aGraphics decompressor

are needed to see this picture.

Adaptive Optics Can Create Wave Aberrations (Subject: ND�)

Wave Aberration After AO correction With coma added

Convoluted retinal image

Wave aberrations from Lasik postOp patient

Wave aberrations created by adaptive optics (With real eye, JP)

Blur Matching

• Lots of Sharp Edges• Edges At All Orientations• Seen Through Adaptive

Optics

Binary Noise Stimulus

550 nm, 1 deg, 6 mm pupil

The subject adjusted the amplitude of defocus so that thesubjective blur matched that of the patient wave aberration.

Blur Matching of Patient Wave Aberrations

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Patient wave aberration Stimulus

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Zernike mode Zernike mode

Am

plitu

de(µ

m)

Def

ocus

(D)

Defocus

Blur Matching Controls for Neural Differences between

Patients

Using Multiple Subjects Controls for Neural Adaptation

Acuity does not always capture the subjective quality of vision

Equal Acuity But Different Subjective Image Quality

Compare Subject Matches with Matches Made Using Three Different Metrics

Wavefront RMSStrehl Ratio

Neural Sharpness

Wave Aberration RMS

Big RMS Small RMS

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

0

1

2

3

Am

plitu

de (µ

m)

Aperture(mm)

Big RMS

Small RMS

R2 = 0.4627

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

RMS Metric

Met

ric

mat

ches

(D)

Subject Matches (D)

Strehl Ratio of Point Spread Function

Diffraction-limited PSF(Perfect Eye)

Heye

Actual PSF(Aberrated Eye)

Strehl Ratio = H eye

H dl

C. of Austin Roorda

Hdl

Strehl Ratio Metric

R2 = 0.4902

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Met

ric

mat

ches

(D)

Subject Matches (D)

A Simple, Biologically-Plausible Metricfor Subjective Image Quality

( ) SubjectiveImage

Quality Point Spread

FunctionGaussian Neural Blur

σ = 0.8’

Σ x =

Neural Sharpness Metric

R2 = 0.703

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Met

ric

mat

ches

(D)

Experiment (D)

Wavefront RMS Neural Sharpness

R2 = 0.703

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Met

ric

mat

ches

(D)R2 = 0.4627

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Met

ric

Mat

ches

(D)

Subject Matches (D)

Collaboration to Identify the Optimum Image Quality Metric

Ray Applegate, University of Houston:Effectiveness of Image Quality Metrics in PredictingVisual Acuity with Convolution Simulations

David Williams, University of RochesterEffectiveness of Image Metrics in predictingSubjective Image Quality with Adaptive Optics

Larry Thibos, Indiana University:Effectiveness of Image Quality Metricsin Predicting Visual Acuity in the Population

defocus

met

ric v

alue

maximum

Optimizing refraction with an image quality metric

error

subjective

search in 3-D space

Guirao and Williams (2003)

Conclusions• Generating blur with adaptive optics leads

to a robust metric for correcting vision.

• It is hard to estimate subjective blur from the wave aberration.Zernike Decomposition doesn’t helpmuch.

• The point spread function combined with a biologicallyplausible model of neural bluris better.

• Standards for optimizing correction from wavefrontare in the works