The influence of the environment and lifestyle on myopia

Abstract

Background: Myopia, commonly known as near-sightedness, has emerged as a global epidemic, impacting almost one in three individuals across the world. The increasing prevalence of myopia during early childhood has heightened the risk of developing high myopia and related sight-threatening eye conditions in adulthood. This surge in myopia rates, occurring within a relatively stable genetic framework, underscores the profound influence of environmental and lifestyle factors on this condition. In this comprehensive narrative review, we shed light on both established and potential environmental and lifestyle contributors that affect the development and progression of myopia.

Main body: Epidemiological and interventional research has consistently revealed a compelling connection between increased outdoor time and a decreased risk of myopia in children. This protective effect may primarily be attributed to exposure to the characteristics of natural light (i.e., sunlight) and the release of retinal dopamine. Conversely, irrespective of outdoor time, excessive engagement in near work can further worsen the onset of myopia. While the exact mechanisms behind this exacerbation are not fully comprehended, it appears to involve shifts in relative peripheral refraction, the overstimulation of accommodation, or a complex interplay of these factors, leading to issues like retinal image defocus, blur, and chromatic aberration. Other potential factors like the spatial frequency of the visual environment, circadian rhythm, sleep, nutrition, smoking, socio-economic status, and education have debatable independent influences on myopia development.

Conclusion: The environment exerts a significant influence on the development and progression of myopia. Improving the modifiable key environmental predictors like time spent outdoors and engagement in near work can prevent or slow the progression of myopia. The intricate connections between lifestyle and environmental factors often obscure research findings, making it challenging to disentangle their individual effects. This complexity underscores the necessity for prospective studies that employ objective assessments, such as quantifying light exposure and near work, among others. These studies are crucial for gaining a more comprehensive understanding of how various environmental factors can be modified to prevent or slow the progression of myopia.

Keywords: Emmetropization; Environment; Epidemiology; Etiology; Genetics; Light; Myopia; Outdoor time; Progression; Risk factors.

Fig. 1

Schematic of emmetropia and axial myopia. A In an emmetropic eye, parallel rays of a distant object are focused on the retina. B When an eye is tasked to focus on a near object, without accomodation, the image of the object is focused behind the retina. C Accommodation can bring forward the image to focus on the retina. D In axial myopia, the eye's axial length has grown longer than the dioptric focus of the eye. Light rays are therefore focused in front of the retina resulting in the blurred vision of a distant object. E Myopia can be optically corrected using a concave lens (spectacles or contact lenses) which diverges the light rays and moves the image into focus on the retina

Fig. 2

Spectral power distribution of light in different environments, both outdoors (O) and indoors (I)

Fig. 3

A direct comparison of the levels and spectra of light measured indoors and outdoors. A Light levels outdoors are significantly higher than light levels indoors. B The light spectrum outdoors remains fairly unaltered when measured in different locations. Conversely, light levels outdoors can decrease by ~1 log unit between an open field and a denser building area or even indoors looking out from a window. Conversely, light levels can drop by more than 10 log units in a room equipped with artificial lighting. C The spectral power distribution of the average measurements outdoors (±SEM) compared to indoor scenarios. D, E, and F Normalized spectral power distribution of light outdoors compared to light indoors. While the spectrum remains fairly similar between 400 and 650 nm, windows block a considerable amount of ultra-violet (<400 nm) and near-infrared or infrared light (>650 nm) (D). Similar differences are observed between traditional indoor LED lighting (CCT: 4000 K) in addition to reduced composition in wavelengths between 400–440 nm and 480–560 nm (E). Similar observations can be made when comparing artificial lighting to sunlight seen through a window (F)