faith, service, innovation, truth, education evaluation of
TRANSCRIPT
Faith, Service, Innovation, Truth, Education
Evaluation of a New Test ofDistance Stereopsis
Jeff Rabin,1,2 Michael Castro,1 Daniel Ewing,1
Hayley George,1 Paul Lau,1 Shannon Leon,1
Andrew Yoder,1 John Gooch2 and Steve Wright2
1Univerity of the Incarnate Word Rosenberg School of Optometry
2US Air Force School of Aerospace Medicine
84th Annual AsMA Scientific Meeting
Faith, Service, Innovation, Truth, Education
84th Annual AsMA Scientific Meeting
Disclosure Information
Speaker: Jeff Rabin
I have no financial relationships to disclose.
I will not discuss off-label use and/or investigational use in my presentation.
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A common misconception is that depth perception requires two eyes.
That depth perception is strictly a binocular function.
But there are numerous monocular cues to depth.
Introduction
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Pictorial Cues – those which can be displayed on a two-dimensional picture or painting
Linearperspective
Texture
Monocular Depth Cues
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Trees are same size;Appear to grow larger because we expect them to be smaller on retina
A Size-Distance Illusion
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Pictorial Cues – those which can be displayed on a two-dimensional picture or painting
Shadow Interposition
(Minnie-Me)
www3.azwestern.edu
Monocular Depth Cues
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Accommodation – focusing for near As we focus & converge our eyes
for near the brain expects the object to move closer and the retinal image to increase.
Monocular Cues to Depth
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Motion Parallax As we move our head a more
distant object appears to move with the head
Closer object moves opposite the head
Monocular Cues to Depth
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Absolute Depth Judge distance to a single object. Encountered less frequently. We’re not very good at this. Does come up in aviation.
Relative vs. Absolute Depth
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Relative Depth Judge distance between objects Very common We are very good at this
Examples:Dentist judging depth of cavityEye doctor judging depth of corneal foreign body
Relative vs. Absolute Depth
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Stereopsis… Perception of relative depth
based on difference in horizontal extent of two images in two eyes from objects at different distances.
Stereopsis
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What is Stereopsis?
What? That makes my head hurt!
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What is Stereopsis?
Perceived depth between two objects Distance between objects in space Imaged on retina of each eye as a
horizontal line of stimulation Slight difference in length of the lines
of stimulation is used by the brain to perceive depth
Faith, Service, Innovation, Truth, Education
141414PD
d1 d2
d
a
b
a ab
b
What is Stereopsis?
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What is Stereopsis?
383838
PD
d1 d2
Stereo = angle a – angle btan(a) = PD/d1 and tan(b)= PD/d2
Thus Stereo = PD/d1 - PD/d2
Stereo = PD(d2 – d1)d2
Computation of Stereopsis
2
)(Stereo
d
dPD
d
a
b
a abb
Brain compares a to b length in right eye to a to b length in left eye to perceive depth between
points a and b in real space.
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Importance of Stereopsis
Stereopsis AKA Stereo-acuity Powerful cue to relative depth
Hyperacuity Stereo as fine as 3” of arc 10x smaller than cone cell 20x better than 20/20!
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Importance of Stereopsis
Stereopsis is most precise at near but decreases with square of distance, hence it is less important for depth at distance
In aviation and other settings devoid of depth cues, stereopsis is all important for accurate depth perception.
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Our purpose was to evaluate a new, computer-based test
of distance stereopsis to determine its potential for widespread application.
Purpose
Faith, Service, Innovation, Truth, Education
Stereopsis was tested with Innova Systems, Inc. computer-based distance stereo test (DST).
Uses red-green glasses to present separate images to each eye to stimulate stereopsis.
Method
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Subject uses remote control to select 1 of 4 circles which appears closer than the other 3.
Up-down staircase determines threshold.
Method
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Faith, Service, Innovation, Truth, Education
20 subjects were tested with the DST and the near Random DOT Stereopsis Test (NST) using a similar method in book format.
Method
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Faith, Service, Innovation, Truth, Education
Red-green glasses present slightly offset images to each eye (1 of 4 circles) to produce stereo. Remote used to select circle which appears closest..
Method
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Distance Stereo Test
Faith, Service, Innovation, Truth, Education
Polaroid glasses allow presentation of slightly
offset images to each eye (1 of 3 circles) to produce
stereo depth. Subject identifies the finest stereo
target she/he can see.
Method
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Near Stereo Test
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No difference between mean stereo thresholds achieved with distance and near stereo tests Distance stereo test = 15.7” Near stereo test = 15.9” t = 0.1, p > 0.9
Results
Faith, Service, Innovation, Truth, Education
No Difference Between Tests
0
5
10
15
20
Distance Near
Stereo Test
Stereo Threshold (sec of arc)
Mean values, n=20, p>0.9
15.7” 15.9”
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Using the DST (distance stereo test)10 of 20 subjects achieved
exceptional distance thresholds of 12” of arc or less.
Because the NST (near stereo test) does not measure stereo <12.5” of arc, direct comparison in all subjects was not possible.
Results
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The new distance stereo test (DST) provides stereo thresholds which equal or exceed those obtained with standard testing.
Conclusions
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Computer-based DST has potential for widespread application in clinical, military and occupational settings
As well as for vision screenings and pediatric use.
Conclusions
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DST automated scoring and recording can be combined with other new tests to better quantify visual performance.
Conclusions