Asthenopia has been associated with reading under visually stressful conditions. However, it is not known whether increased cognitive load contributes to asthenopic symptoms. The purpose of this study was to evaluate the contribution of increased cognitive load (with or without visual stress inducing conditions) to asthenopic symptoms associated with prolonged near work.
Thirty-three visually normal subjects, aged 18 to 30 years, participated in the study. Subjects read texts or watched videos under different visual stress and cognitive loads. Visual stress conditions were good visual quality, low contrast, and induced refractive error. The cognitive load levels were watching video, reading fairy tales, and reading technical articles. As an additional task, subjects also listened to technical articles. At the end of each condition, subjects rated the magnitude of any asthenopic symptoms, visual discomfort, and cognitive discomfort they experienced during the task. Electromyography potentials recorded from the lower orbicularis oculi muscle were used to obtain blink rate.
Subjects reported greater internal symptoms for the refractive error condition coupled with higher cognitive load compared to good visual and low contrast conditions (p < 0.01). For the low contrast condition coupled with higher cognitive load, greater external symptoms were reported compared to good visual and refractive error conditions (p < 0.05). However, asthenopic symptoms were not reported for cognitively demanding tasks when the visual condition was good. Blink rates were not significantly different between the good visual and low contrast conditions within each cognitive load level. For the cognitively difficult reading conditions, blink rate was significantly decreased for the low contrast and good visual conditions compared to the refractive error condition.
An interaction between cognitive and visual demands was observed. Greater cognitive loads accentuate the same differentiated symptoms normally caused by visual stressors.