the consumer experience: a clinical perspective of the safety concerns in 3d displays jeffery k...
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The Consumer Experience:A Clinical Perspective of The Safety Concerns in 3D Displays
Jeffery K Hovis, OD, PhD, FAAOSchool of OptometryUniversity of Waterloo
A “real” safety concern
Photo Epilepsy Photosensitive epilepsy – seizures induced by
flashing lights Rare - approximately 1 in 4000 Most are sensitive to lights flashing near 16 Hz with frequencies
higher than 40 Hz less likely to cause a seizure Although rare in the general population
About 5% of epileptic subjects have a clear history of seizures evoked by visual stimuli encountered in daily life
Stimuli Include: Televisions Computer Monitors Faulty Fluorescent Lighting Traveling along tree lined streets in the daytime Fans
Photo Epilepsy
Concerns with 3D displays?Less than with 2D displays because 3D are
Usually Dimmer -polaroid lensesTend to be smaller imagesAsynchrony between eyes – worse if in-phase to each
eye
Although less of a concern than regular monitors, could be the stimulus for the first seizure
Red Eye: Conjunctivitis Inflammation of the outermost layers
of the eye and inner surface of the eyelids Symptoms: Red Eye, Irritation,
Watering, Mucuoid Discharge
Bacterial Infections: rarely threaten vision and are likely to be self-limiting Natural washing of tears and antibodies/antigens in the
tears further limit infections
Conjunctivitis: Viral
Viral infections are more commonNo mucoid dischargeNo treatment- self limiting
However natural defenses against viruses are not as effective so the outbreaks can spread more easily and there is one viral infection that is of concern
Conjunctivitis: Viral
Epidemic keratoconjunctivitis (EKC) is highly contagious and remains viable on inorganic surfaces for up to 35 days
“Outbreak of epidemic keratoconjunctivitis caused by adenovirus in medical residents”
[Molecular Vision 2009] In most countries EKC outbreaks must be reported
Conjunctivitis: EKC
Symptoms include pink eye", foreign body
sensations, pain, decrease in vision associated with malaise is frequently observed in one eye or both eyes
Pain and reduction in vision due to corneal infiltrates
Conjunctivitis
Outbreak of EKC is a concern because decreased vision (usually not permanent) and pain
Recommendations: Sanitizers, soap or alcohol wipes are the best way to
disinfect 3D glassesMake sure the material of the 3D glasses can
withstand the chemicals
Depth Perception Overview Depth Perception is the weighted summation of all
monocular and binocular depth information in display Actually not very good at judging absolute distances in
depth, but very good at relative distances Majority of depth clues are good at providing information
about relative distances, but not absolute distances
Depth Perception Overview Binocular Clues include
Eye Position- Angle of Convergence
LE
RE
LE
RE
Stereopsis – binocular disparity/retinal disparity Angles measured in arc sec
(1/3600 of a degree) Linear Separation for a fixed
disparity angle will vary with viewing distance
Stereopsis: In the population
97% of adults have stereo acuity of 120 arc sec 80% of adults have stereo acuity of 30 arc secThresholds for moderate and small sized objects
6 arc sec crossed (in front)15 arc sec uncrossed (behind)Double vision/suppression occurs when the disparity
exceeds2000-3000 arc sec for small and moderate sizes4500 arc sec for larger objects
Stereopsis: In the population
Stereopsis begins to form at 6 mons and is adult-like by 5-7 years threshold improving from 60 arc sec to 20 arc sec
MonthsFrom Birch et al 1996
Better than 60 arc sec based on VEP
No stereopsisbased on VEP
2010520
100
500
Age (years)
Ste
reop
sis
Thre
shol
ds (s
ec a
rc)
Leat et al 2001
Frisby Test (real depth)Randot Test (Polaroid)
So at what age?Depends if child can understand the task
eg Position and angle for optimum viewingMay be slower to perceive depth initially
If there is an underlying binocular vision problemfocusing problemuncorrected refractive error
that hasn’t been addressed, then could complain or just give up
Convergence-Accommodation Association
Convergence (Vergence): eye movements to keep image fixated on each
eye as the object moves closer or further away Accommodation:
increase in the power of the eye in order to focus on near objects
Schor’s Model of Accommodation and Vergence
AC/A
CA/C
Convergence-Accommodation Dissociation
Is there a Dissociation? Could be
An object moves closer Monocular clues are consistent with change in
depth Make anticipatory accommodation-convergence eye
movements Blur – stops accommodation, but disparity remains
Process disparities either for the “near object” or screen Blur through convergence accommodation link Takes some time and effort to reach steady-state
assuming you can make the correct vergence eye movements
Convergence-Accommodation Dissociation
So much blur is introduced through convergence?
Fixation Distance (Display)
1m
0.30.50.6 0.9
Noticeable BlurTroublesome Blur
Clear
24.0 >24.0
Depth of Focusfor 1MeterViewing Distance - 5 X LargerTarget (7.5 mmLetter)
*.01 mfor 100 sec
*.04 mfor 400 sec
*.01 mfor 100 sec
*.03 mf
0.1 Dioptre/2000 arc sec ~5,300 arc sec disparity at the clear limits
But still have to process the disparity
Another way to look at it
Vergence Angle (pd)
-15 -10 -5 0 5 10 15 20 25 30
Acc
omod
atio
n (D
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
BOBI
Deman
d
Comfort Zone
Uncrossed Disparity Limit (Divergence)
Crossed Disparity Limit (Convergence)
2050 arc sec
6100 arc sec
6100 arc sec
12,000 arc sec
Double the comfort limits for the disparities which produce either double vision or blurred vision(slow and steady changes)
Binocular Vision Problems
3% of the young adult population have stereothresholds worse than 120 arc secStrabismus (eye turn and/or lazy eye)
Because presenting large disparitiesCould cause headaches and double vision during and
afterwardsSuppress only regions of the deviating eye
Monocular (injury or large uncorrected refractive error in one eye )
Binocular Vision Problems
More likely to have problems with displays within 1 metre
Convergence Insufficiency2.25% to 8.3% children and adults (have stereo)
Convergence ExcessTrouble with displays within 1 m~1.5% - 5.9% (have stereo & don’t have)
Binocular Vision Problems
More likely to have problems with displays further than 1 metre awayDivergence Insufficiency
<2% (have stereo & don’t have)Divergence Excess
2%-7.5% (have stereo & don’t have)
Accommodation Problems
Frequencies aren’t as certain, butAccommodative Infacility
Trouble with both distances1.5% of the young adults and children
Accommodative insufficiencyTrouble with displays within 1 m2.5% of the young adults (under 40yrs) and children
SO Somewhere around 15% to 20% of patients with normal
stereopsis could have problems with the 3D displays Symptoms vary, but
Headaches Eyestrain Tiredness Double vision Dizziness
Visual training programs/spectacles can help Another 3% may not bother with 3D displays because
they don’t have any stereopsis or experience problems More difficult to improve through training
So
• If disparities are always near the limit of the “average” person for double vision, then reports of eyestrain and headaches will be commonLimits vary with size and duration
Conclusions Seizures are no more of a concern than with regular 2D
displays (may be less so) Spreading of eye infections, particularly viral are a
concern Age depends if the child understands how to use it Approximately 20% of the “normal” young adult
population may have eyestrain/headaches with extended viewing (>15 min) at either distance Most of these problems can be lessened with visual training
programsIf Disparities are near the limits for single vision for the
average person then more complaints Thanks for the new business!