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Eyes are the window to the soul

Although the origin cannot be confirmed, the saying ‘the eyes are the window to the soul’ is thought to trace back to the Book of Matthew in the Bible or to Cicero (106–143 BC). Supporting that saying, the article by Crewe et al. in this issue of Clinical and Experimental Ophthalmology reveals a strong association between depression and quality of life in people with severe vision impairment. This study and a growing body of research on the impact of vision impairment on quality of life and disability-adjusted life years reveal the importance of vision to quality of life. Depression is known to have affects on systemic health and is associated with increased mortality. The article by Crewe et al. demonstrates effect modification (to use an epidemiological term) in the relationship of depression and quality of life in people with severe vision impairment. It is worth considering these components separately. Depression rates vary greatly between countries, in part due to differences in assessment and definition, and in part due to cultural and perhaps genetic differences. A review of population-based depression rates reveals a greater than 10-fold variation, from 3.6% in China to 20.5% in Australia. In the USA, depression rates fell from 2004 to 2008, but the rates are higher in younger cohorts. Rates and causes of vision impairment also vary globally, in part due to measurement differences and in part due to access to health care services and differing environmental causes of vision impairment. Population-based studies show vision impairment ranging from 1.98% in the USA to 11.8% in Rotterdam. Vision impairment is expected to increase globally with increasing life expectancy and decreasing fertility rates because the major causes of vision impairment are age-related. How do rates of depression and vision impairment compare globally? A simple correlation of populationbased rates of vision impairment versus population-based rates of depression in six countries reveals a strong, although statistically insignificant correlation due to the small number of data points (Fig. 1, correlation = 0.65, P = 0.16, SPSS© version 15.0, Chicago, IL, USA). Although these data are subject to the ecological fallacy where individual-level associations cannot necessarily be inferred from group-level data as demonstrated in Figure 1, they do suggest an association between vision impairment and depression at the population level. The article by Crewe et al. clearly demonstrates the strong association between depression and quality of life for people with severe vision impairment. Perhaps eye care professionals should routinely screen and refer for depression and mental health professionals should screen and refer their patients for vision disorders that might be treatable. By attending to depression in people with vision impairment, it may be possible to improve their quality of life. This has profound clinical and public health implications.