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Beyond the letter chart:New clinical applications of
Hyperacuity
Paul H Artes,
Dalhousie University
2008
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How can psychophysics catch up
with advances in imaging?
sections through a healthy fovea, Spectralis OCT
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How can psychophysics catch up
with advances in imaging?
sdOCT: axial resolution: 5 microns
transverse resolution: 15 microns
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How can psychophysics catch up
with advances in imaging?
Hyperacuity psychophysics:
0.16 microns
sdOCT: axial resolution: 5 microns
transverse resolution: 15 microns
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How can psychophysics catch up
with advances in imaging?
sdOCT: axial resolution: 5 microns
transverse resolution: 15 microns
30 - 100Hyperacuity psychophysics:0.16 microns
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Visual Acuity
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Visual Acuity
By convention, 6/6 = 1 min or 60 sec
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Visual Acuity
Physiological limit set
by receptor spacing, ~30 (6/3)
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4.67 in = 12 degrees
6/12 letter = 10 min = 1/6 degree
4.67/72 = 0.065 in
6/60 letter = 50 min = 5/6 degree
4.67/14.4 =
Visual Acuity
6/12
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4.67 in = 12 degrees
6/12 letter = 10 min = 1/6 degree
4.67/72 = 0.065 in
6/60 letter = 50 min = 5/6 degree
4.67/14.4 =
Visual Acuity
6/60 6/12
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Hyperacuities
Visual tasks with thresholds much smaller
than foveal receptor spacing. Westheimer, 1981
30 60
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Hyperacuities
Visual tasks with thresholds much smaller
than foveal receptor spacing. Westheimer, 1981
30 60Hyperacuity:
as low as 5
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Classic Hyperacuities
chevronvernier bisection
5
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robust to blur and loss of contrast
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Radial Deformation Acuity
VR 98
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Radial Deformation Acuity
VR 98
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Radial Deformation Acuity
Mean radius (eg. 0.5 or 1 degree)Amplitude of sinusoidal deformation (in %)
RDA thresholds as low as 0.3%, or 3seconds of arc,
>10 times better than best possible
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4th derivative ofGaussian(resistant to optical
blur)
Radial Deformation Acuity
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4.67 in = 12 degrees
6/12 letter = 10 min = 1/6 degree
4.67/72 = 0.065 in
6/60 letter = 50 min = 5/6 degree
4.67/14.4 =
Radial Deformation Acuity
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4.67 in = 12 degrees
6/12 letter = 10 min = 1/6 degree
4.67/72 = 0.065 in
6/60 letter = 50 min = 5/6 degree
4.67/14.4 =
Radial Deformation Acuity
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4.67 in = 12 degrees
6/12 letter = 10 min = 1/6 degree
4.67/72 = 0.065 in
6/60 letter = 50 min = 5/6 degree
4.67/14.4 =
Radial Deformation Acuity
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RDA in Macular Disease
IOVS 2002
OVS 2003
Eyes with early AMD but good VA showed
large RDA deficits.
No relation with VA and Contrast Sensitivity.
No age-related decline in RDA.
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A test for foveal distortion?
Marc Amsler, 1949
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A test for foveal distortion?
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A test for foveal distortion?
5-alternative forced-choice
odd-one-out paradigm
(controls criterion effects)
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Early data: young volunteers*
-3.5 -3.0 -2.5 -2.0
0.0
0.2
0.4
0.6
0.8
1.0
-2.97
proportions
een
66666
5/6
4/64/6
2/62/5
1/4
log Radial Deformation (%)
0.1%, or 3.9
* Nayha Patel, undergraduate final year project, University of Manchester, UK
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Ongoing project: AMD*
* Nigel Rawlings, Resident in Ophthalmology and Visual Sciences, Dalhousie U.
Hypotheses
RDA charts correlate closely with early irregularity
of foveal receptor layers revealed by spectraldomain OCT & autofluorescence imaging.
High repeatability of RDA may provide more
powerful signals forearlychange in AMD, a usefulproperty for clinical trials of new therapies andpreventive strategies.
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Thank you!
