Opinion: Tailoring the lighting environment for a healthier ocular growth

Abstract

Many of us take sharp vision for granted. Yet, for images to be perceived clearly, the developing eye undergoes emmetropization, a visually-guided process whereby ocular growth is controlled and harmonised with the focal power of the eye to minimise refractive error and maximise visual acuity. Flaws in emmetropization can lead to refractive errors and blurred vision. Myopia, or near-sightedness, is a refractive error characterised by the blurred vision of objects when viewed at a distance. It is commonly due to excessive ocular axial growth leading to images being focussed in front of the retina. Myopia is more than an inconvenience that can be corrected by spectacles or contact lenses, it’s a highly prevalent sightthreatening disease that is projected to affect 50% of the world population by 2050, becoming the leading cause of irreversible blindness. Genetics play a part, but cannot explain the rapid increase in global myopia prevalence over the recent decades. The visual environment affects emmetropization and myopia development. For instance, increased time outdoors has been shown to be protective against myopia in children. The exact mechanisms underlying the antimyopiagenic effect of time outdoors are not fully understood, but could be due to a variety of synergetic factors such as reduction in accommodative fatigue, increase in spatial frequency in outdoor sceneries, and changes in the intensity and spectral features of light/sunlight, which lack in artificial lighting. While epidemiological studies highlight associations between myopia prevention and high intensity light experienced outdoors, substantial evidence in various animal models support a protective role of high intensity light against experimental myopia, through increases in retinal dopamine and changes in other ocular neuromodulators. These findings prompted the development of outdoor programs for myopia prevention. Nevertheless, increasing time outdoors is challenging, particularly during school years, given the cultural commitment to educational success in many parts of the world. Passive exposure to higher levels of light indoors (e.g., ∼500 lx of fluorescent light in classrooms) was also successful in lowering myopia onset. Taken together these findings suggest that increasing the intensity of the lighting environment, even intermittently, may be effective in preventing or delaying the onset of myopia. Emmetropization is also dependent on the spectral content of the lighting environment, with protective effects against myopia attributable to either short or long wavelength visible light, depending on the animal model. Today, the optimal intensity and spectral composition of light for emmetropization remains unidentified in humans, yet epidemiological and experimental studies provide evidence to suggest that the tailoring of architectural lighting at homes or schools, in a synergetic manner with other environmental features, may one day offer a passive, cost-effective and safe way to prevent, delay or slow the development of myopia in children, curbing the progression of this sight-threatening disease.