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

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

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

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

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 Text @16.7 cms Accommodative stress ±1.50D flipper Up gaze 20cm above

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

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

Study1: Blink Rate & Discomfort 11/6/2018

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

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

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

Study2: EMG Results

Study2: Blink Results 11/6/2018

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

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

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