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Visual Stimulus Delivery with the Adaptive Optics Scanning Laser Ophthalmoscope Austin Roorda, PhD University of California, Berkeley Real-time confocal imaging with AO In an SLO, AO improves: throughput resolution contrast Romero, Donnelly, Hebert, Queener, Venkateswaran, Campbell 1.5 deg (~ 450 microns) Nerve fibers Vessels Cones Confocal imaging allows for imaging of independent retinal layers. AO may help to reveal mechanisms for glaucoma. Vilupuru, Rangaswamy, Frishman, Harwerth Dynamic imaging allows for direct visualization of blood flow in the smallest capillaries. Martin but AOSLO is for more than imaging Raster Modulation Past Research • Simultaneous imaging and stimulus presentation with an SLO was proposed since the time of its invention (Webb, Hughes, Pomerantzeff, Applied Optics, 1980) • More recent use of adaptive optics (Liang and Williams, JOSA, 1997) has enabled stimulus viewing with unprecedented resolution. • In this talk, we combine AO with stimulus delivery in an SLO AOSLO Laser Delivery/ Modulation Light Detection Wavefront Compensation Raster Scanning Eye Wavefront Measurement Adaptive Optics AO OFF AO ON AOSLO Scan Specifications • Laser beam is scanned in a raster fashion by • Vertical scan mirror operating @ 30 Hz • Horizontal scan mirror performing a sinusoidal scan @ 16 KHz • Each frame is defined by 480 horizontal lines • Each line is digitized @ 20 MHz sampling rate to create 512 pixels / line • For a 1 degree vertical field size, the pixel resolution is 8 arc seconds, which is higher than the cutoff frequency of the eye Raster Modulation TTL synchronization signal E E image stored in PC buffer waveform generator board line-by-line modulation signals acousto-optic modulator in AOSLO light delivery path raster pattern written to retina First Results In the AOSLO, the delivered stimulus is recorded as part of the image, so its exact location can be determined AO Stimulus Delivery Applications ÿ Visual performance after AO-correction ÿ Siddharth Poonja, Luis Henry • Psychophysics (Apparent Motion) • ‘True’ Micro-perimetry • Retinal micro-surgery? Visual Performance: Conditions 5 arc minutes (~25 microns) 20/10 letter 6mm AO corrected Visual Performance: Conditions PSFs 6mm pupil uncorrected expect large PSF & wave aberration 6mm pupil corrected with AO expect a compact PSF & near perfectly flat wave 3mm pupil corrected with AO expect larger PSF (less compact than condition two) & near perfectly flat wave Visual Performance: Methods • Four Alternate Forced-Choice Tumbling E or ‘illiterate E’ test • Stimulus presented is the letter ‘E’ in four different orientations on the raster • VA is the smallest letter size for which the orientation can be correctly identified (72.4% correct based on Weibull fit) Visual Performance Results: Typical Subject Psychometric Functions 100 90 % correct 80 6mm AO 70 60 3mm AO 50 6mm no AO 40 30 20 10 0 20/5 E 20/7.5 20/10 20/12.5 20/15 Letter Size 20/17.5 20/20 E Visual Performance Results: All Subjects Visual Acuity E 20/6.6 20/8 20/10 6mm AO 3mm AO 20/13.3 6mm no AO 20/20 E 20/40 SP JEF LAH AR Subject ASV S Summary of Visual Performance Results • The minimum resolvable angle improved 32% on average for 6 mm uncorrected pupils vs. 6 mm AOcorrected pupils (p<0.01) • The improvement in resolution between 3 mm AOcorrected and 6 mm AO-corrected pupils was not significant (10% average change, p=0.09) •Is the brain not equipped to deal with sharp images? •Are the cones not dense enough to sample the sharp image? AO Stimulus Delivery Applications • Visual performance after AO-correction ÿ Psychophysics (Apparent Motion) ÿ Scott Stevenson, Avesh Raghunandan, Siddharth Poonja, Jeremie Frazier • ‘True’ Micro-perimetry • Retinal micro-surgery? AO Psychophysics Module: Apparent Motion Referenced Motion AOSLO Image AOSLO Image Subject’s View Subject’s View 3‘ 19 arc minute Unreferenced Motion Dt AO Psychophysics Module: Apparent Motion referenced motion Frame 1 Frame 2 When the bar moves down in the frame, but upward with respect top the retina, what will the subject say, up or down? AO Psychophysics Module: Apparent Motion unreferenced motion When the bar has moved downward in world coordinates… …but has moved upward on the retina... what will the subject say? Up or Down? Apparent Motion Results Referenced Motion Un-referenced Motion Bar motion in world Bar motion on retina The eye’s judgement of motion compensates for errors due to small eye movements, even when there is no frame of reference. There are non-visual cues that the eye can use to correct for jitter. AO Stimulus Delivery Applications • Visual performance after AO-correction • Psychophysics ÿ ‘True’ Micro-perimetry ÿ Krishnakumar Venkateswaran, Azadeh Razmandeh, Siddharth Poonja • Retinal micro-surgery? ‘True’ Microperimetry Patient responses to flashed stimuli can be used to identify small retinal blind spots AOSLO raster animation demonstrating the opto-kinetic reflex National Science Foundation - Center for Adaptive Optics National Institutes of Health - Bioengineering Research Partnership