1. A Test-Bed for Vision Science Based on Adaptive Optics
Scott C. Wilks
Charles A. Thompson, Scot S. Olivier, Brian J. Bauman,
Lawrence Flath, and Robert Sawvel
Adaptive Optics Group
Lawrence Livermore National Laboratory
and
John S. Werner and Thomas Barnes
Center 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.

2. Diffraction-Limited Adaptive Optics and the Limits of Human Visual Acuity
normal
vision
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.

3. New advances in ophthalmology may enable SUPERNORMAL VISION
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 than
20/10 visual acuity if higher-order aberrations are corrected.
Psf of 6.8 mm
Pupil w/ AO on/off
Wavefront of
Wavefront of
distorted image
perfect image
Super-
normal
vision
normal
vision
Imperfect
Eye
Cornea and Lens
New advances in laser refractive surgery and contact
lenses may enable correction of high-order aberrations.

4. Types of aberrations in population
1.4
Mean of 63 eyes
5.7 mm pupil*
1.2 1
Rms wavefront error (µm)
0.8
0.6
0.4
0.2
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
Zernike Modes
Defocus
Coma
Spherical Aberration
Astigmatism
Regular
eyewear
Uncorrected high order aberrations:
LASIK, custom-made contact lenses
*J. Porter, private communication

5. High-resolution adaptive phoropter combines ophthalmic wavefront sensor with liquid crystal wavefront corrector
Conventional Phoropter
Wavefront sensor
Liquid crystal corrector
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.

6. Aberration-free vision
Eye E
Diffraction-limited
image on retina:
resolution only limited
by pupil size
Eye chart
Perfect lens
Photoreceptors sample
image 1-to-1:
optical resolution matches
retinal resolution
20/8 “supernormal” vision!
Can we really see the “E”?

7. Adaptive optics control wavefront phase to compensate for optical aberrations
corrector
Aberrated
wavefront
Corrected
wavefront
Wavefront
sensor
Wavefront
control
computer

8. Adaptive optics can provide unique diagnostic capability to study effects of vision correction
An adaptive optics
system can be used to sense and correct aberrations in a subject’s eye and allow detailed studies of visual performance under a variety of conditions.
Deformable Mirror
CCD
Hartmann-Shack
Wavefront Sensor
Laser Beacon
Optical aberrations
in subject’s eye
Telescope
computer
and light
source E AB
CFDG
Eye Chart
Adaptive optics is the only demonstrated method for effectively correcting high-order aberrations in the eye

9. Hamamatsu optically addressed nematic liquid crystal spatial light modulator - operational principles LC
LCD (
phase map (
phase intensity
LCD
Optically written
map Optically (
desired phase
here)
written here)
intensity map
Spatial
Imaging
Imaging
electrically
written here)
Backlighting
Modulator
Light
Lens
Lens
Laser Diode
Aberated
apprx. 30mw
Process
Beam C
orrected
Process
Beam
Imaging
Read Beam
Optic
Write Beam

10. Demonstration of high-resolution wavefront control using liquid crystal spatial light modulators
High-resolution liquid crystal
spatial light modulator
Yellow HeNe
Laser
Collimating
Optic
Kinematic Mounted
Mirror (19 actuator
DM or Flat ) T
elescope
Lens
Expanding Telescope
Reducing
Telescope
micro
scope
Objective
1K x 1K Farfield
Scoring Camera
Spatial
Light
Modulator
LCD
(desired phase
map electrically
written here)
Backlight
Diode
Write Beam
Imaging
Lenslet
Array
1K x 1K
Sensor
Kinematicly Mounted
(OALCSLM, Flat, or MEMS
Device can be installed)
1K x 1K Nearfield
Camera
Wavefront
Reference
Source
High-resolution
wavefront
control test-bed
schematic
HAMAMATSU LC SLM
High-resolution
wavefront sensor
High-resolution wavefront correction results
Reconstructed
aberrated wavefront
Aberrated far-field
image: Strehl  0.3
Corrected far-field
image: Strehl  0.7
40x50 Hartmann sensor image

11. SLM stroke vs Voltage shows us where to operate device, to maximize stroke.
450 Hz
500 Hz
550 Hz
600 Hz
650 Hz

12. The SLM response is slightly uneven over the face of the device.1 2 3 1 9 5 6 4 7 8 9
We really only care about the PV that gives us the phase
we want to wrap at. This means we want to wrap on a
Surface, and not just at a pixel value (say 150.)

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

14. Wavefront Aberrations of SLM
Note: We are currently working with Hamamatsu
to improve optical quality of the device.

15. We write a pattern to the SLM, correcting for the abberations inhernet in the device.
Peak to Valley of ~ 400 nm (surface)

16. Reflected light, for 3 different phase lags.
The LC-SLM is perfect for phase wrapping, effectively increasing stroke.
Incoming light
looks like this
for all 3 cases
below. l
h(x)
h(x)
l/4
l/2
Reflected light, for 3 different phase lags.

17. We can apply phase wrapping on the flat file.
By wrapping at PV approximately 150, we can take out the
0.7 micron abberation, using only 0.3 microns of stroke!

18. Phase wrapping the flat file.
Either this:
both give this flatness of reflecting surface:
0 < PV < 254
or this, written to SLM…
0 < PV < 150
(corresponding to ½ wave
Of 630 nm light in WYKO)

19. 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
300
f(x)
150
300*(256/150)
f(x)
150*(256/150)
f(x)
256
f(x)
150

20. Phase wrapping a gaussian.
PV = 254
PV = 300
Slice across center
0 < PV < 150
(corresponding to ½ wave
Of 630 nm light in WYKO)
0 < PV < 254

21. Phase wrap the 633 nm, but not the 785nm.
Far field spot
633 nm
Far field spot
Write pattern to SLM
Grey bars have
Pixel Value = 150
633 light sees “flat” surface, while 785 sees a grating.

22. Now, phase wrap the 785 nm, but not the 633 nm.
Far field spot
633 nm
Far field spot
Write pattern to SLM
White bars have
Pixel Value = 254
633 light sees “flat” surface, while 785 sees a grating.

23. Prototype adaptive phoropter using liquid crystal spatial light modulator

24. The Rubreye
Will be used as a model eye to
align, calibrate and perform initial tests
on the Adaptive Optics System.

25. Prototype adaptive phoropter using liquid crystal spatial light modulator

26. Far field off SLM no aperture, in testbed.
reference
SLM unpowered
SLM with flat file

27. Control Hardware Integration Effort
Dalsa CA-D6
256x256, 8 bit Camera
Hamamatsu SLM
Adaptive Optics Associates
200mm pitch, 5mm f.l. Lenslet Array
Matrox Pulsar
Frame Grabber / VGA (SLM) Driver
Current Status:
All pieces have been procured
Dalsa and Pulsar have been successfully run with Dell PC.
Software modifications in progress
Software
Dell PC

28. 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 < 1mm: 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.