In recent years, the number of patients with dry eye disease has rapidly increased. A major factor behind this is thought to be the increase in work that uses displays, such as personal computers and tablet terminals [1,2]. This change in lifestyle has led to increased stress for most members of society. A Japanese epidemiological survey of office workers confirmed dry eye in 65.5% of the participants. The majority are affected by dry eye with decreased tear stability without epithelial damage, called short tear breakup time dry eye [3].

Dry eye can be accompanied not only by ophthalmologic but also by psychosomatic symptoms. It is associated with psychiatric disorders such as depression, anxiety, and sleep disorders [[4], [5], [6], [7], [8]], suggesting that it may be a stress-related disease. Stress affects the autonomic nervous system. Lacrimal secretion is regulated by the activity of the autonomic nerves; when the sympathetic nervous system becomes dominant owing to stress, the secretion of tears controlled by the parasympathetic nervous system decreases [9]. Regarding the relationship between dry eye symptoms and the autonomic nervous system, we have previously shown that dry eye symptom intensity is associated with fluctuations in parasympathetic nerve activity in short tear breakup time dry eye, but not in aqueous tear-deficient dry eye [10]. Thus, we speculated that short tear breakup time dry eye was associated with increased mental stress, whereas aqueous tear-deficient dry eye was not.

Studies using functional magnetic resonance imaging (fMRI) in patients with dry eye revealed dysfunction of the frontal cortex, which is closely related to stress [[11], [12], [13], [14], [15], [16]]. Accordingly, we hypothesized that the dry eye state would sensitize the frontal cortex, resulting in the development of dry eye symptoms, especially in patients with short tear breakup time dry eye. Thus, in this study, we evaluated stress levels determined using frontal electroencephalogram (EEG) signals and investigated their relationship with symptoms in short tear breakup time dry eye and aqueous tear-deficient dry eye.