Scott C. WilksCharles A. Thompson, Scot S. Olivier, Brian J. Bauman,

Lawrence Flath, and Robert SawvelAdaptive Optics Group

Lawrence Livermore National Laboratoryand

John S. Werner and Thomas BarnesCenter for Neuroscience

University of California, Davis 95616

This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory

under Contract No. W-7405-Eng-48.

A Test-Bed for Vision Science Based on Adaptive Optics

normal normal visionvision

supernormal vision

• New advances in ophthalmology may enable correction of high-order aberrations in the eye.– Advances in laser eye surgery, contact and interocular

lenses.

• Improved aberration correction could provide supernormal vision - better than 20/10 visual acuity, more than a factor of 3 increase in contrast sensitivity.

• Psycho-physical effects of aberration-free eyesight on visual performance are not known.

• We are using unique LLNL expertise in adaptive optics to enable detailed scientific studies of the visual performance benefits of improved aberration correction for the general population.

Diffraction-Limited Adaptive Optics and the Limits of Human Visual Acuity

• Normal human visual acuity is 20/20 on the Snellen scale after correction for defocus and astigmatism.

• The physiology of the average human eye can support better than20/10 visual acuity if higher-order aberrations are corrected.

normalvision

Super-normalvision

EyeImperfectCornea and Lens

Wavefront of distorted image

Wavefront of perfect image

• New advances in laser refractive surgery and contact lenses may enable correction of high-order aberrations.

Psf of 6.8 mmPupil w/ AO on/off

New advances in ophthalmology may enable SUPERNORMAL VISION

Zernike ModesDefocus

AstigmatismComa Spherical Aberration

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Z2,0 Z2,-2 Z2,2 Z3,-1 Z3,1 Z3,-3 Z3,3 Z4,0 Z4,2 Z4,-2 Z4,4 Z4,-4 Z5,1 Z5,-1 Z5,3 Z5,-3 Z5,5 Z5,-5

Rm

s w

avef

ront

err

or (

µm

)

Mean of 63 eyes5.7 mm pupil*

Uncorrected high order aberrations:LASIK, custom-made contact lenses

Regular eyewear

*J. Porter, private communication

Types of aberrations in population

Conventional Phoropter Wavefront sensor

• Ultimately, a clinical ophthalmic adaptive optics system could be used to replace the phoropter in order to allow optometrists to assess high-order aberrations in the eye while the patient directly observes the visual benefit of correction.

– Permanent correction of high-order aberrations could then be accomplished with custom laser eye surgery or contact lenses.

Liquid crystal corrector

High-resolution adaptive phoropter combines ophthalmic wavefront sensor with liquid crystal

wavefront corrector

Aberration-free vision

EDiffraction-limitedimage on retina:resolution only limitedby pupil size

Photoreceptors sampleimage 1-to-1:

optical resolution matchesretinal resolution

20/8 “supernormal” vision!

Can we really see the “E”?

Perfect lens

Eye

Eye chart

AberatedProcess

Beam

C orrectedProcess

Beam

SpatialLight

Modulator

LCD( desired phaseintensity map

electricallywritten here) Backlighting

Laser Diodeapprx. 30mw

Write Beam

Read Beam

ImagingLens

ImagingLens

ImagingOptic

LCD( phase intensity

map Opticallywritten here)

LC( phase map

Optically writtenhere)

Hamamatsu optically addressed nematic liquid crystalspatial light modulator - operational principles

SLM stroke vs Voltage shows us where to operate device, to maximize stroke.

SLM Stroke: Voltage, frequency space

0

200

400

600

800

1000

1200

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Voltage (Volts)

Stroke (nm)

450 Hz500 Hz550 Hz600 Hz650 Hz

The SLM response is slightly uneven over the face of the device.

We really only care about the PV that gives us the phasewe want to wrap at. This means we want to wrap on aSurface, and not just at a pixel value (say 150.)

Plot of the response of the SLM (Stroke) versus grey value (0-256) for our optimal values, 600 Hz, 3.6 Volts.

We write a pattern to the SLM, correcting for the abberations inhernet in the device.

Peak to Valley of ~ 400 nm (surface)

0

hx

0

The LC-SLM is perfect for phase wrapping, effectively increasing stroke.

0

hx

Incoming lightlooks like thisfor all 3 casesbelow.

Reflected light, for 3 different phase lags.

By wrapping at PV approximately 150, we can take out the0.7 micron abberation, using only 0.3 microns of stroke!

We can apply phase wrapping on the flat file.

Phase wrapping the flat file.

0 < PV < 254

0 < PV < 150(corresponding to ½ waveOf 630 nm light in WYKO)

both give this flatness of reflecting surface:

Either this:

or this, written to SLM…

Computationally, what does phase wrapping look like?

function wrap_phase_new, input

;This function wraps values > 150

; scale numbers up, so we wrap at 150, not 256

in=input*(256.0/150.0)

output = byte(in)

output = output*(150.0/256.0)

return,output

end

0

300x

0

300*(256/150)

x150*(256/150)

0

x256

0

x150

150

Phase wrapping a gaussian.

0 < PV < 150(corresponding to ½ waveOf 630 nm light in WYKO)

0 < PV < 254

PV = 254 PV = 300 Slice across center

Phase wrap the 633 nm, but not the 785nm.

Write pattern to SLM785 nmFar field spot

633 nmFar field spot

Grey bars havePixel Value = 150

633 light sees “flat” surface, while 785 sees a grating.

Now, phase wrap the 785 nm, but not the 633 nm.

Write pattern to SLM

785 nmFar field spot

633 nmFar field spot

633 light sees “flat” surface, while 785 sees a grating.

White bars havePixel Value = 254

Prototype adaptive phoropter using liquid crystal spatial light modulator

Prototype adaptive phoropter using liquid crystal spatial light modulator

Far field off SLM no aperture, in testbed.

reference

SLM unpowered

SLM with flat file

Dalsa CA-D6256x256, 8 bit Camera

Adaptive Optics Associates200mm pitch, 5mm f.l. Lenslet Array

Matrox PulsarFrame Grabber / VGA (SLM) Driver

Dell PC

Software

Current Status:•All pieces have been procured•Dalsa and Pulsar have been successfully run with Dell PC.•Software modifications in progress

Hamamatsu SLM

Control Hardware Integration Effort

Summary: There are many technical challenges in using SLM’s for Vision Correction.

• Hamamatsu LC SLM– We found a voltage-frequency combination that maximizes stroke.

– Stroke is still limited stroke < 1m: Solution? Use phase wrapping.

– SLM has much finer resolution than wavefront sensor – thus, using smaller aperture still gives high resolution, as well as flatter SLM.

– Chromatic dispersion (different response at different wavelengths) is consistent with advertised values: 2 color solution.

• Phase Wrapping– Principles of phase wrapping shown to work (2 color experiment.)

– Two color correction (close loop at one color, correct at another) will be our next test.