faith, service, innovation, truth, education evaluation of

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


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


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


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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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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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


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


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

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