The Consumer Experience: A Clinical Perspective of The Safety Concerns in 3D Displays Jeffery K Hovis, OD, PhD, FAAO School of Optometry University 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 lenses Tend to be smaller images Asynchrony 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 common No mucoid discharge No 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 glasses Make 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 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 sec Thresholds for moderate and small sized objects 6 arc sec crossed (in front) 15 arc sec uncrossed (behind) Double vision/suppression occurs when the disparity exceeds arc sec for small and moderate sizes 4500 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 Months From Birch et al 1996 Better than 60 arc sec based on VEP No stereopsis based on VEP 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 viewing May be slower to perceive depth initially If there is an underlying binocular vision problem focusing problem uncorrected refractive error that hasnt 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

Schors 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? 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 Comfort Zone Uncrossed Disparity Limit (Divergence) Crossed Disparity Limit (Convergence) 2050 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 sec Strabismus (eye turn and/or lazy eye) Because presenting large disparities Could cause headaches and double vision during and afterwards Suppress 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 Insufficiency 2.25% to 8.3% children and adults (have stereo) Convergence Excess Trouble with displays within 1 m ~1.5% - 5.9% (have stereo & dont have)

Binocular Vision Problems More likely to have problems with displays further than 1 metre away Divergence Insufficiency <2% (have stereo & dont have) Divergence Excess 2%-7.5% (have stereo & dont have)

Accommodation Problems Frequencies arent as certain, but Accommodative Infacility Trouble with both distances 1.5% of the young adults and children Accommodative insufficiency Trouble with displays within 1 m 2.5% 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 dont 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 common Limits 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 programs If Disparities are near the limits for single vision for the average person then more complaints Thanks for the new business!