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!