1. Relationship Between Visual Stress & Generalized Body Stress
Niru K Nahar
Sowjanya Gowrisankaran John R Hayes James E Sheedy

2. Objectives To Study the Effects of Long Term Reading
Under different Visual & Cognitive loads
On ocular symptoms, muscular tension & sympathetic nervous system activity
Can Cognitive stress
Increase sympathetic activity?
Increase muscle (Trapezius, Frontalis, Jaw, etc.) activity?
12/7/2018

3. High Level Visual Stress: 15min Trials
RE & GL, reduce image quality and benefit from eyelid squint, caused
Increased EMG power &blink rate
Eyelid squint response
LC & SF, reduce image quality but do not benefit from eyelid squint, resulted in
Increased EMG power
No changes in aperture size
Reduced blink rate (for LC)
Accommodative & Convergence Stress did not cause changes in EMG power, aperture size or blink rate
Contraction of orbicularis Oculi
A part of Asthenopia Mechanism
Related to Compromised Image Quality
Condition
EMG Power
Aperture Size
Blink Rate
Discomfort
Perceived Duration
Non-Stress (NS)
0.137(  )
0.016 (  )
0.913(  )
10.90 3.66
0.490(  )
Up Gaze (UG)
0.001(  )
<0.001 (  )
0.157(  )
40.85  1.866
0.016(  )
Group 3
Accommodation (AC)
0.088(  )
0.059 (  )
0.084(  )
38.95  1.640
0.107(  )
Convergence Stress (CO)
0.390(  )
0.061 (  )
0.911(  )
50.55  1.966
0.041(  )
Group 2
Low Contrast (LC)
0.007(  )
0.130 (  )
0.035(  )
63.65  1.863
0.002(  )
Small Font (SF)
0.034(  )
0.061(  )
0.231(  )
49.85 1.984
Group 1
Glare (GL)
<0.001(  )
<0.001(  )
0.010(  )
45.70  1.914
0.056(  )
Refractive Error (RE)
0.005(  )
86.45  1.451
0.066(  )
Summary from previous study

4. Lower Level Visual Stress: 5mins Trials
Squint-beneficial conditions are operated by a local mechanism involving
Contraction of the orbicularis
Increase in reflex blinking
Stress conditions that do not benefit from squint
Do not engage the orbicularis
Decreases blink rate, possibly through central inhibition of spontaneous blinking
Blink rate maybe a more sensitive measure for non-squint-beneficial conditions
EMG with longer trial durations should be tested for more conclusive results
Condition
Comfort
EMG BR
Not Improved by Squint
Font Size  ns
Font Type
Low Con.
Improved by Squint
Glare 
Ref. Err.
Not Improved by Squint
Improved by Squint
Font Size (pt)
Font Type
Contrast
(%)
Ref Error (D)
Glare 12
V‡ 12 CT† 40
0.50 cyl 25 10
V 12 non-CT 20
1.00 cyl 50 8
TNR* 12 CT
1.50 cyl 75 7
TNR 12 non-CT 5
2.00 cyl
100
2.50 cyl

5. Condition Studied Visual Stress Cognitive Stress None Watching Video
Low
Easy Reading
High
Technical Text
Audio (ad)
High Contrast 11pt Verdana
Good Quality (gv)
Under Optimal Visual Condition (ge)
Under Optimal Visual Condition (gd)
Refractive Error (1.0D)
With Refractive Error (rv)
With Refractive Error (re)
With Refractive Error (rd)
Low Contrast (7%)
Of Degraded Image (lv)
Of Degraded Text (le)
Of Degraded Text (ld)
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6. Method 35 subjects 18-35 years old Inclusion criterion
20/20 aided or unaided visual acuity in each eye
No significant ocular pathologies
Text and Video selection
Reading from LCD Monitor
Viewing distance 60cm
Subject’s head supported by a chin & forehead rest
Contrast: 7% contrast text
Refractive error: –1.00 D astigmatism
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7. Method………… Two Visits 5 hours each
30min trials
5min break
Two 3min Controls before each session
Control1 Picture with highest contrast, no ref error
Control2 Picture + Audio
1min Picture Control before each condition
Experimental Setup includes……
Electromyography (EMG)
ISCAN
Video Recorder
Questionnaire
Symptoms
Discomfort
Text & Video
Pulse meter
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8. ElectroMyoGraphy Electrode Locations
Electrode size and intra-electrode separation
Facial  4mm, 1cm
Trapezious  10mm, 2.5cm
Orbicularis Oculi
4 pairs on lower
2 pairs on upper
Corrugators 2pairs
Frontalis 2 pairs
Trapezius  2pairs
Reference Electrodes
1 Facial Muscle
1 Trapezoidal Muscle
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9. Outcome Measures EMG Power: Blink Free EMG traces analyzed in 2 ways
For first & last 5mins
For whole 30mins duration
Blink Rate
Measured from EMG data
Aperture Size
Measured from Video Recordings using an onscreen ruler
Data analyzed in 3 time segments: 5mins, 15mins & 30mins
Pupil Diameter
Measured from ISCAN data
Pulse rate
Measured during the last minute of each trial
Symptoms
Measured off the questionnaire
Discomfort
Measured off the rating scales
None Moderate OK Quite Very
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10. EMG Results Emg measures were log transformed
Mixed model analysis was used for conditions with controls as covariates
Overall main effects
0.75 OO (p<0.001)
1.75 OO (p<0.001)
Corrugator (p=0.02)
Frontalis (p=0.002)
Blink rate (p<0.001)
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11. Blink Rate Results
No significant difference in blink rate between conditions
Trend in blink rates across different levels of cognitive loads
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12. Aperture Size Results
Mean aperture size for the first 5mins, 15mins and 30mins were not statistically significantly different
Visual stress component had a significant impact on aperture size (p<.001)
Induced refractive error conditions had a significantly smaller aperture size than the good vision (p=.009) and low contrast (p<.001)
Neither main effect of cognitive stress (p=.59) nor cognitive stress by visual stress interaction (p=.16) were significant
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13. Pupil Diameter Results
Clearly Cognitive Stress is a function of pupil diameter
Visual stress has an effect, but not nearly as dramatic
This results are being revisited!

14. Pulse Rate Result
No statistically significant differences in pulse rate between the conditions
Trend of increased in pulse rate with increased cognitive difficulty
Trend of increasing pulse rate appears to be steeper for the low contrast condition compared to the refractive error condition
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15. Symptom Results Symptom groups
Internal  ache, muscle stress inside & around eye
External  burning, irritation and dryness
Refractive error conditions scores high for internal symptoms (p<0.002)
Low contrast conditions high score of external symptoms (p<0.009)
Ocular
Internal factor
External factor
Muscle stress-inside
Muscle stress-around
Ache
Burning
Irritation
Dryness
Internal & external groups reconfirmed previously reported results
Central
Factor 1
Factor 2
Forehead stress
Head ache
Back ache
Shoulder ache
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16. Discomfort Score Visual Difficulty Cognitive Difficulty
Total Discomfort
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17. Summary of Results Outcome Measures Visual Stress (Refractive Error)
(Low Contrast)
Cognitive Stress
Orbicularis EMG
 P<0.001 NS
Aperture size
 P<0.001
Blink Rate
NS (trend )
NS (trend )
Frontalis EMG
 Significant
Pulse Rate
Symptoms
Internal, P<0.001
External, P<0.001
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18. Conclusions
Both Visual & Cognitive Load of a Near Task Determines Severity & type of Asthenopic symptoms
Visual Stress Inducing Conditions Triggers Both Localized & Generalized Physiologic Responses
It is possible that the tasks (especially cognitively demanding) if done under conditions of poor visual ergonomics could result in generalized stress responses which might lead to potential musculoskeletal disorders
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19. Acknowledgements
Study Supported by Microsoft Corporation Advanced Reading Technologies Group
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