Download Visual Stimulus Delivery with the Adaptive Optics Scanning Laser

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