In spite of the clarification of some significant physiological factors of visual fatigue caused by VDT work, pupillary reflexes have not been studied as to how they are affected after prolonged visual work. This study examined visual function changes objectively in terms of pupillary reflexes and lens accommodative responses after a 4-hr VDT operation task. The relationship between the two functions was also examined.Two measurements in this paper revealed the physiological function changes due to VDT operation. The subjects involved were five students with an average age of 22.6 years.First, near-reflex measurement ascertained decreases in amplitude and the velocity of accommodation function after the visual task. Second, light-reflex measurement revealed a delay of the reflex, an increase in the amplitude of the reflex, and a decrease in pupil size after the visual task. A weak correlation between the decrease in pupil size and accommodation function was found. The occurrence of visual fatigue due to 4-hr VDT operation was also confirmed by CFF measurements and reported subjective visual symptoms in this experiment.

This study ascertained that CRTs using a positive display polarity (dark characters on bright background) are ergonomically more appropriate for VDT operators than ones using a negative display polarity (bright characters on dark background), using both physiological and psychological indices. Differences of pupil size and subjective evaluation of visual comfort while undertaking visual tasks were examined for six experimental conditions (two CRT display types in three different illuminated levels). Pupil diameter was not affected greatly when working with the positive display for different illumination levels. The positive display also caused smaller differences in pupil diameter when viewing visual targets, namely CRT display, script, and keyboard, for all lighting conditions. The majority of the subjects also appreciated working with the positive CRT display at a regular office illumination level.

In order to meet the goal of user comfort of information displays, visual problems of video display terminal (VDT) work were studied through the analysis of visual functions in two experiments. Eye movement analysis, in Experiment 1, revealed that VDT operators had to move their eyes 2.5 times faster than traditional clerical workers. Lens accommodation, pupil size, and subjective visual comfort were investigated in Experiment 2. A significant correlation was found between the velocity of lens accommodation and the subjective visual comfort while viewing seven different displays (r = .809). A positive-type cathode-ray tube (CRT), which has dark characters on a light background, was ascertained to be the most appropriate display type, while working with a liquid crystal display (LCD) was considered to be the least visually comfortable, with the lowest accommodative velocity.

BackgroundThe rise in global temperature is well documented. Changes in temperature lead to increases in heat exposure, which may impact health ranging from mild heat rashes to deadly heat stroke. Heat exposure can also aggravate several chronic diseases including cardiovascular and respiratory disease.ObjectiveThis study examined the relationship between climate condition and health status and productivity in two main categories of the occupational setting – where one setting involves heat generated from the industry and the other with heat in a natural setting.DesignThis cross-sectional study included four industrial sites (pottery industry, power plant, knife industry, and construction site) and one agricultural site in the Pathumthani and Ayutthaya provinces. Exposure data were comprised of meteorological data and heat exposure including relative humidity (RH) measured by Wet Bulb Globe Temperature (WBGT) monitor. Heat index was calculated to measure the effects of heat exposure on the study population, which consisted of 21 workers at five worksites; a questionnaire was also used to collect data on workers.ResultsAmong the five workplaces, the outdoor WBGT was found to be highest at 34.6°C during 12:00 and 1:00 PM at the agricultural site. It was found that four out of five study sites had heat indices in the ‘extreme caution,’ where heat cramp and exhaustion may be possible and one site showed a value of 41°C that falls into the category of ‘danger,’ where sunstroke and heat exhaustion are likely and prolonged exposure may lead to heatstroke. Productivity as perceived by the workers revealed that only the construction and pottery industry workers had a loss of productivity ranged from 10 to 60 %.ConclusionsClimate conditions in Thailand potentially affect both the health and productivity in occupational settings.

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