A Test-Bed for Vision Science Based on Adaptive Optics

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 enabledetailed 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 0.8 Rms wavefront error (µm) 0.6 0.4 0.2 0 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 Coma Spherical Aberration Defocus 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 Wavefront sensor Conventional Phoropter 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. Hamamatsu optically addressed nematic liquid crystalspatial light modulator - operational principles LCD LC LCD ( phase intensity ( phase map ( desired phase map Optically Optically written intensity map written here) here) electrically Spatial Imaging Imaging Backlighting written here) Light Lens Lens Laser Diode Modulator apprx. 30mw Aberated Process Beam C orrected Process Beam Imaging Optic Read Beam Write Beam

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

9. The SLM response is slightly uneven over the face of the device. 1 2 1 3 9 6 5 4 7 9 8 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.)

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

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

12. The LC-SLM is perfect for phase wrapping, effectively increasing stroke. Incoming light looks like this for all 3 cases below. l h(x) 0 h(x) l/2 l/4 0 0 Reflected light, for 3 different phase lags.

13. 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!

14. 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)

15. 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 0 300*(256/150) f(x) 150*(256/150) 0 f(x) 256 0 f(x) 150 0

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

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

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

19. Prototype adaptive phoropter using liquid crystal spatial light modulator

20. Prototype adaptive phoropter using liquid crystal spatial light modulator

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

22. 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

23. 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.