1. Niru K. Nahar Sowjanya Gowrisankaran James E. Sheedy
Blinking & Squinting when Reading: Trade-off Between Cognitive & Visual Stress
Niru K. Nahar Sowjanya Gowrisankaran James E. Sheedy

2. Purpose of The Study Blinks Squint
To determine Orbicularis Oculi (OO) Response to Visual Stress Inducing Conditions
To test EMG as an Objective Measure of Eyestrain
Blinks
Squint
EMG Traces of OO Contraction while Reading

3. Methods Two Studies Subject position fixed by a chin & forehead rest
Study1: High level Visual stress for long term (15mins or until tolerable!)
Reading from Printed Pages
Viewing distance 60cm
Study2:Lower level Visual Stress for short term (5mins)
Reading from LCD Monitor
Viewing distance 55cm
Subject position fixed by a chin & forehead rest
Surface EMG response of the Orbicularis Oculi
Recorded with electrodes (1 pair of 4mm)
Located 1.25cm below the lower right eyelid
ISCAN video camera recorded palpebral fissure height
Conditions were presented in Latin Square order

4. Methods….. Study1 20 subjects (18–36 years) with 20/20 vision Baseline
Silent picture viewing for 5mins
Non-stress condition (10pt Verdana) for 15mins
Study2
31 subjects (ages 18 & above) with 20/20 vision
Controls
Verdana CT, 12 pt, highest contrast, no glare or refractive error
Presented 6 times at equal time spacing
27 trials: 5mins reading for each trial

5. Study1: Conditions Studied
Inducing Conditions
Group 1
Group 2
Group 3
Refractive error (+2.00/-4.00x180 OU
Glare
7000 fl
Low contrast 3.5% contrast
Small font
5pt Verdana
Convergence Stress
cms
Accommodative stress ±1.50D flipper
Up gaze 20cm above

6. Study1: Measures
Analysis done from measurements of middle portion of pages
Outcome Measures
EMG power  3 sec blink free traces analyzed
Aperture size  Measured from video
Blink rate Counted from the video images
Discomfort score  Measured off the rating scale
None Moderate OK Quite Very

7. Study1: EMG Power & Aperture Size
11/6/2018

8. Study1: Blink Rate & Discomfort
11/6/2018

9. Study1: Categorization of Visual Stress Conditions
Group1: Refractive Error &Glare
Increased EMG & Reduced Aperture Size
Visual benefits of squinting
Clear image in the presence of optically induced blur
Reduced sensitivity to glare
Aperture and field stop effect of the eyelids
Group2: Low Contrast & Small Font
Increased EMG and No Change in Aperture Size
Possible explanations for increased OOEMG for Group2…
Generalized Body Stress
Visual Stress due to Reduced Visual Acuity and Contrast Reserves
Group3: Accommodation & Convergence
No Change in EMG or Aperture Size
No engagement of orbicularis oculi for Group3 visual stress conditions
11/6/2018

10. Study1: Results Summary
Orbicularis Oculi muscle responds to conditions that result in 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(  )
11/6/2018

11. Study2: Conditions Studied
Stress Conditions
Not Improved
by Squint
Font Size
VCT7
VCT8
VCT10
VCT12
Font Type
TNR12CT
TNR12nonCT
V12CT
V12nonCT
Contrast 5%
10%
20%
40%
Improved by Squint
Ref. Error
Cyls 0.5
Cyls 1.0
Cyls 1.5
Cyls 2.0
Cyls 2.5
Glare
25%
50%
75%
100%
11/6/2018

12. Study2: EMG Results

13. Study2: Blink Results
11/6/2018

14. Study2: Results Summary
Stress Conditions
Comfort Rating
EMG
Blink Rate
Not Improved by Squint
Small Font Size (FS)
p<0.001
NS, p<0.70
p=0.026
Font Type (FT)
 Font Type, P<0.03
 Color Type, p<0.001
NS, Font Type, p<0.47
NS, Color Type, p<0.051
NS, Font Type, p<0.97
NS, Color Type, p<0.30
Low Contrast (LC)
 p<0.001
NS, p=0.93
 p=0.013
Improved by Squint
Glare (G)
 p=0.001
 p=0.002
Refractive Error (RE)
 p<0.001

15. Conclusions
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
Decrease blink rate  possibly through central inhibition of Spontaneous blinking
EMG Response Sensitive Objective Measure for Squint-Beneficial Conditions
Blink Rate may be a more sensitive objective measure for Non-Squint-Beneficial Conditions
What’s Next?
Find Relationship between Visual & Cognitive System
Study with Longer duration (>15mins)
EMG Study for
Different positions of Orbicularis
Other facial muscles
Tapezious Muscles
Explore Cognitive responses due to eye strains

16. Acknowledgements
Studies Supported by Microsoft Corporation Advanced Reading Technologies Group
11/6/2018