0.75 cm Inferior OO 0.75 cm Superior OO 1.75 cm Inferior OO 0.75 cm Inferior OO Corrugator 1.75 cm Inferior OO 0.75 cm Superior OO Corrugator Frontalis Ground for all facial muscle signals Ground for all trapezoidal muscle signals Relationship between vision stress and generalized body stress Niru K. Nahar 1, Sowjanya Gowrisankaran 2, John R. Hays 3, 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 OBJECTIVE  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) activity? METHODS  37 subjects (18-35yrs)  Control conditions: Two 3mins controls before each visit  Control 1  Viewing a picture with highest contrast, no ref error  Control 2  Listening to technical text Audio while viewing picture  1min Picture Control before each 30mins condition to assess fatigue  Stress Conditions: A matrix of 10 visually & cognitively stressful conditions  At the end of each reading session subject rated the severity of symptoms experienced on a visual analog scale  Equally spaced markers on the visual analog scale were  Not at all, moderate, Ok, quite, very  Symptoms tested  burning, irritation, dryness, tired eyes, ache, muscle stress around and inside the eye.  Measurements Used  Electromyography (EMG) Electrode Locations o 4 pairs on lower Orbicularis o 2 pairs on upper Orbicularis o 2 pairs on Corrugators o 2 pairs on Frontalis o 2 pairs on Trapezius  ISCAN  Video Recorder  Pulse meter  Questionnaire  Outcome Measures  Symptoms  Discomfort  EMG power  Blink Rate  Aperture Size  Pupil Diameter  Pulse Rate Visual StressCognitive Stress None Watching Video Low Easy Reading High Technical Text NoneAudio (ad) Low High Contrast 11pt Verdana Good Quality (gv)Under Optimal Visual Condition (ge) Under Optimal Visual Condition (gd) High Refractive Error (1.0D) With Refractive Error (rv) With Refractive Error (re) With Refractive Error (rd) High Low Contrast (7%) Of Degraded Image (lv) Of Degraded TextOf Degraded Text (ld)  Mean aperture size for the first 5mins (8.85mm), 15mins (8.74mm) and 30mins (8.80mm were not statistically significantly different.  Visual stresses had significant impact on aperture size (p<.001)  Mean aperture size for induced refractive error conditions had a significantly smaller aperture size than the GV (p=.009) & LC (p<.001)  Neither main effect of cognitive stress (p=.59) nor cognitive stress by visual stress interaction (p=.16) were significant. APERTURE SIZE RESULTS  Measured from Video Recording  No significant difference in blink rate between conditions  Trend in blink rates across different levels of cognitive loads BLINK RATE RESULTS  Measured from EMG Data Outcome Measures Visual Stress (Ref error) Visual stress (Low contrast) Cognitive stress Orbicularis EMG P<0.001  NSNS Aperture size P<0.001  NSNS Blink Rate NS (trend  ) NS (trend  ) Frontalis EMG NS P<0.001  Significant  Pulse Rate NSNS NS (trend  ) Symptoms Internal, P<0.001 External, P<0.001 NS (trend  )   Clearly cognitive stress is a function of pupil diameter  Visual stress has an effect, but not nearly as dramatic. PUPIL DIAMETER RESULTS  Measured from ISCAN data  Overall condition main effect was significant for  0.75cm & 1.75cm below lower lid margin (p<.001) & (p<.001) respectively  corrugator (p=.02), frontalis (p=.002) & blink rate (p<.001)  Main effects for EMG measures from beneath the eyebrow (p=.17), trapezius (p=.29), and pulse rate (p=.22) were not significant.  No statistically significant differences in pulse rate between the conditions  There is a trend of increase in pulse rate with an increase in cognitive difficulty  The trend of increasing pulse rate appears to be steeper for the low contrast condition compared to the refractive error condition. EMG and PULSE RATE RESULTS Internal factorExternal factor Muscle stress-inside the eye Muscle stress-around the eye Ache Burning Irritation Dryness Condition 1Condition 2p-values GvRd GeRv< GeRe GeRd< GeLd GdRd LvRd LvLd Condition 1Condition 2p-values AdLd GeLe GeLd GdLd LvLd This study was supported by a grant from Microsoft Corporation ACKNOWLEDGEMENTS  Both V  Both Visual & Cognitive load of a near task determines the severity and type of asthenopic symptoms experienced by the subjects.  2 types of physiologic responses: localized & generalized, specific to types of visual stress inducing conditions.  It is possible that the tasks (especially cognitively demanding tasks) if done under conditions of poor visual ergonomics could result in generalized stress responses which might lead to potential musculoskeletal disorders. CONCLUSIONS SYMPTOMS AND DISCOMFORT RESULTS  Internal symptom group  ache, muscle stress inside & around eye  External symptom group  burning, irritation and dryness  Reff. rrror conditions high score of internal symptoms (p<0.002)  Low contrast conditions high score of external symptoms (p<0.009)  Internal & external groups reconfirmed previously reported results  For same level of visual difficulty, subjects perceived cognitively difficult task to be more visually challenging (p<0.037)  Perceived total discomfort increased with an increase in cognitive load for the same visual stress level External factor across conditions Internal factor across conditions