Buildings, Lighting, and the Myopia Epidemic

Myopia, also known as nearsightedness, is an eye disease that most often begins in early childhood and progresses through late adolescence. It was once relatively rare, but within a few generations it has grown in prevalence (Morgan et al. 2018; Williams et al. 2015), and is now a global epidemic of astonishing proportions (WHO 2016). Holden et al. (2016) predict that 50% of the world’s population will be afflicted by 2050, up from 34% today and 23% in 2000. A severe form of myopia (high myopia) is associated with increased risk of vision loss through glaucoma and retinal detachment (Williams and Hammond 2019). Current myopia interventions emphasize clinical treatments rather than prevention and focus on medications and refractive correction (Cooper and Tkatchenko 2018). Uncorrected refractive error has been estimated to cost more than $200 billion annually in global GDP (Naidoo et al. 2019). Many factors have been considered in myopia causation. Studies of genetic predisposition showed that the effect of any individual gene is small (Morgan and Rose 2019) and could not explain accelerating prevalence of the disease. This has refocused the myopia field on the question of whether changes in the human living environment are causing myopia. This thought progression is logical, not only because genetics are an inadequate explanation, but also because eye growth and focal length optimization are lightdependent. In the category of environmental influences, it has been proposed that excessive focus on nearfield visual tasks (Morgan et al. 2021; Wildsoet et al. 2019), circadian rhythm disruption (Chakraborty et al. 2018; Stone et al. 2013), and geographical and seasonal factors that influence light exposure (Cui et al. 2013) might be causative. However, in addition, and germane to this discussion, epidemiological studies have repeatedly shown that time spent outdoors is associated with myopia reduction (Sherwin et al. 2012; Xiong et al. 2017), while time spent indoors is a risk factor (Morgan et al. 2021). What is it about the outside lighting environment that can protect against myopia? Recent basic science discoveries have helped to crystalize a hypothesis. The light sensing proteins of animals are called opsins (Shichida and Matsuyama 2009). The human eye contains at least six opsins, four of which are involved in our visual function through rod and cone photoreceptors. The remaining two are the socalled nonvisual opsins, melanopsin (OPN4) and neuropsin (OPN5). Preclinical studies have implicated all six opsins in the regulation of eye growth and optimization of focal length (Brown et al. 2022). Melanopsin has a peak light sensitivity around 480 nm, a sky-blue color. This opsin has a role in systemic circadian function, but also regulates eye growth and focal length through its retinal expression (Chakraborty et al. 2022). Neuropsin is of special interest for this discussion because it has a peak sensitivity at 380 nm, a violet wavelength that is at the edge of visual perception for most adults. As with melanopsin, preclinical studies of the violet light-OPN5 response have shown that it regulates eye growth and focal length (Jiang et al. 2021). More specifically, when OPN5 is stimulated by violet light, myopic elongation of the eye is suppressed (Jiang et al. 2021). These basic science findings are complemented by studies performed in humans: Torii et al. (2017a) found that myopic children with corrective lenses that transmitted violet light had less myopic progression than those with lenses that blocked violet light. Likewise, in myopic adults, Torii et al. (2017b) found that wearing lenses with more violet light transmittance was associated with less myopic progression. When combined, these studies have led to the hypothesis that the myopia boom (Dolgin 2015) may be caused by a modern lifestyle that results in insufficient exposure to the violet light that stimulates OPN5 (Jiang et al. 2021). LEUKOS 2023, VOL. 19, NO. 1, 1–3 https://doi.org/10.1080/15502724.2022.2141503