Objective Measurements of Levels of Visual Stress Niru K. Nahar 1, Sowjanya Gowrisankaran 2, James E. Sheedy 3 1 Dept. of Electrical and Computer Engineering, 2 College of Optometry, The Ohio State University, Columbus, OH College of Optometry| Pacific University | [2043 College Way] | [Forest Grove] | [97116] | Oregon OBJECTIVES  To determine Orbicularis Oculi Response to Visual Stress Inducing Conditions  To test EMG as an Objective Measure of Eyestrain CONCLUSIONS RECENT PUBLICATIONS ON THE TOPIC CONTACT INFORMATION Study1  Group1: Refractive Error (RE) & Glare (GL), which reduce image quality and benefit from eyelid squint, caused  Increased EMG power  Eyelid squint response  Increased blink rate  Group2: Low Contrast (LC) & Small Font (SF), which 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)  Group3: Accommodative & Convergence Stress did not cause changes in EMG power, aperture size or blink rate.  Results suggest that contraction of the orbicularis oculi is a part of the asthenopia mechanism related to compromised image quality Study2  Results suggest that the 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.  EMG response is a sensitive objective measure for the squint-beneficial conditions.  Blink rate may be a more sensitive objective measure for the non-squint-beneficial conditions  EMG with longer trial durations should be tested for more conclusive results.  Sowjanya GowrIsankaran, James E. Sheedy, John R. Hayes, “Eyelid Squint Response to Asthenopia-Inducing Conditions”, Vol. 84, No. 7, pp.611–619, Optometry and Vision Science  Niru K Nahar, James E. Sheedy, John R. Hayes, and Yu-Chi Tai, “Objective Measurements of Lower-Level Visual Stress”, Vol. 84, No. 7, pp. 620–629 Optometry and Vision Science Principal Investigator Jim Sheedy, OD, PhD College of Optometry Pacific University, OR97116 Phone: METHODS Two Studies were done with a set-up  Reading from LCD Monitor  Viewing distance 55cm  Subject position fixed by a chin & forehead rest  Surface EMG response of the orbicularis oculi was recorded with (1 pair of 3mm) electrodes located 1.25cm below the lower right eyelid. Sampling frequency  1kHz  ISCAN video camera recorded palpebral fissure height  Conditions were presented in Latin Square order Study1 (15mins Reading)  20 subjects (18–36 years) with 20/20 vision  Baseline: silent picture viewing for 5 mins & non-stress condition for 15mins  Stress Inducing Conditions:  Glare  Refractive Error (OU: +2.00/-4.00x180)  Low Contrast (3.5%)  Small font 60cms)  Up Gaze (20cm above straight gaze)  Accommodative Stress (±1.50DS)  Convergence Stress 16.7cms) Study2 (Shorter 5mins Reading)  31 subjects (ages 18 & above) with 20/20 vision  Controls  Verdana CT, 12 pt, highest contrast, no glare, no ref. error (RE)  Presented 6 times at equal time spacing within the testing session  27 trials: 5 minutes reading for each trial ACKNOWLEDGEMENTS These Studies were Supported by a Grant from Microsoft Corporation, Advanced Reading Technologies Group Study 2 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% RESULTS: Study1 with High Level Visual Stress  Duration 15mins RESULTS: Study2 with Lower Level Visual Stress  Duration 5mins EMG Power: Measured from 3sec Blink Free Traces Aperture Size: Measured from the Video Blink Rate: Calculated from the Video Discomfort Level : From Subjects assessment Inducing Conditions Group 1 Group 2Group 3 Refractive error Glare Low contrast Small font Convergence stress Accommodative stress Up gaze ConditionEMG PowerAperture SizeBlink RateDiscomfortPerceived Duration Non-Stress (NS) 0.137(  )0.016 (  )0.913(  )10.90  (  ) Up Gaze (UG) 0.001(  )<0.001 (  )0.157(  )40.85  (  ) Group 3 Accommodation (AC) 0.088(  )0.059 (  )0.084(  )38.95  (  ) Convergence Stress (CO) 0.390(  )0.061 (  )0.911(  )50.55  (  ) Group 2 Low Contrast (LC) 0.007(  )0.130 (  )0.035(  )63.65  (  ) Small Font (SF) 0.034(  )0.061(  )0.231(  )49.85  (  ) Group 1 Glare (GL) <0.001(  )<0.001(  )0.010(  )45.70  (  ) Refractive Error (RE) <0.001(  )<0.001(  )0.005(  )86.45  (  )