Development and validation of a laboratory instrument for measuring visual fatigue variations

Visual fatigue could decrease precision and increase human error, hence declining productivity. Development of ergonomic laboratory instruments for diagnosing, evaluating, and monitoring visual fatigue could help productivity enhance in different occupations. This study aims to develop and validate laboratory instrument of visual fatigue (VFM-90.1). Method & Materials: VFM-90.1 was designed and programmed based on registering changes in Flicker value. Then a cross sectional study was done to validate instrument, enrolling 248 users of video display terminals (VDT) and using visual fatigue questionnaire of VDT users. For measuring error of the instrument, an oscilloscope was use as the initial standard and for analyzing the data simultaneously gathered through the questionnaires and the instrument, spss11.5 was employed, subsequently, sensitivity-specificity values calculated and receiver operating characteristic (ROC) curve and areas of visual fatigue, obtained. VFM-90.1 had resolution of 0.1 Hz and the average error of 0.8%. The maximum changes in flicker value and questionnaire score (prior to and after intervention) was calculated respectively as (-4.1) Hz and 5.83 (in 0-10 scale). The correlation between instrument results and the questionnaire was (-0.87) and cutoff points at (-0.5), (-2.2), and (-3.4) were defined as non, low, and moderate visual fatigue areas, respectively. The values less than (-3.4) were assigned to indicate severe visual fatigue area. VFM-90.1 has scientifically adequate precision and authenticity and could be used as an initial standard instrument in ergonomic laboratories regarding easy application in scientific research and clear evaluation and interpretation of the data on visual fatigue obtained from this instrument. So, an effective measure could be taken to enhance ergonomic and occupational health.