**1. Introduction**

Dry eye disease is a common disease caused by numerous factors including ocular surface problems, environmental factors such as humidity and wind, and systemic conditions. In addition, a variety of systemic medications can also induce dry eye disease [1–4]. Although it is widely recognized as an ocular surface disease, associated systemic conditions are not negligible, as they can negatively impact ocular health. Such systemic conditions include rheumatoid arthritis, vitamin A deficiency, bone marrow transplantation and postmenopausal estrogen therapy. Besides these causal relationships, epidemiological studies have also reported the association of dry eye disease with systemic diseases, including ischemic heart disease and hyperlipidemia. Depression, antidepressant use and insomnia are also reported to be associated with dry eye disease. Schein et al. reported that elderly individuals with systemic comorbidities are likely to have symptoms of dry eye disease [5]. These findings from statistical approaches and epidemiological studies should be carefully interpreted, as dry eye disease is a common disease and the elderly tend to be a ffected by multiple comorbidities.

Previous studies have demonstrated aging as the most clearly documented risk factor for dry eye disease [6]. Accordingly, the prevalence of this disease is increasing particularly in modern age societies like Japan. However, most previous studies reporting on the prevalence of dry eye disease and systemic comorbidities [4,7,8] have been based on epidemiological questionnaires. Therefore, the relationship between ocular parameters and systemic comorbidities has not been well investigated. For example, a previous study by Wang et al. revealed that a number of systemic diseases correlate with dry eye disease, but since the authors did not include any ocular examination, the relationship of specific dry eye parameters to these other conditions was not determined [9]. Therefore, we investigated the association between dry eye disease and systemic comorbidities, as part of the clinic-based Dry Eye Cross-Sectional Study (DECS-J) in Japan.

#### **2. Materials and Methods**
