This paper demonstrates fatigue assessment based on eye blinks that are detected by dye-sensitized photovoltaic cells. In particular, the sensors were attached to the temple of eyeglasses and positioned at the lateral side of the eye. They are wearable, did not majorly disturb the user’s eyesight, and detected the position of the eyelid or the eye state. The optimal location of the sensor was experimentally investigated by evaluating the detection accuracy of blinks. We conducted fatigue assessment experiments using the developed wearable system, or smart glasses. Several parameters, including the frequency, duration, and velocity of eye blinks, were extracted as fatigue indices. Successful fatigue assessment by the proposed system will be of great benefit for maximizing performance and maintenance of physical/mental health.

Death from overwork and severe accidents caused by mental fatigue and sleepiness are becoming one of the more pressing social problems of developed countries. Such mental fatigue and sleepiness often comes from declines and/or changes in wakefulness in our daily life. Recently, numerous researchers have focused on possible ways of utilising physiological signals to deduce alertness; however, the characteristic behaviours that can be used to deduce wakefulness are difficult to measure. To better understand the indices of change in wakefulness states, the authors fabricated a micro-optical sensor system that can measure physiological signals from eye and eyelid conditions without imposing stress on the user. Using the newly fabricated micro-optical sensor system, they have found and reproduced characteristic blink behaviours that are indicative of changes in a person's wakefulness. Herein, new indices are proposed that have potential for use in fatigue evaluation tests. The experimental results demonstrate that the sensor system can detect declines in and/or changes in wakefulness that indicate mental fatigue and sleepiness.

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Inverting glasses invert the wearer's visual field in the vertical or horizontal direction using total internal reflection by triangular prisms. Inverting glasses are powerful tools for investigating neural adaptation and are widely used in the fields of psychology and brain science. However, conventional inverting glasses are not equipped with a detection system for eye movement or the line-of-sight of the wearer during experiments. Inverting glasses were developed that can be mounted with a see-through eye detection system, which consists of micropatterned dye-sensitised photovoltaic cells that determine the position of the pupil by detecting light reflected from the black and white parts of the eye. The detector does not require an external camera and is thus lightweight and has low-power consumption, which is advantageous for mounting on the inverting glasses. Using the developed inverting glasses, which swap the left and right visual fields, they conducted tracking and pointing tasks while measuring eye movement. Gaze learning curves were obtained from the experiments for the first time, which they believe will provide new and useful information to the study of neural adaptation.