COVID-19 and myopia.

At the time of writing, it seems as if there is no end in sight to the ongoing COVID19 pandemic. The Omicron variant is the latest form of the virus, and seems unlikely to be the last one. Once again, public health discussions are being held around the world regarding the need for lockdowns, mask mandates, booster vaccinations, social distancing and remote working and/or education. One thing that has become apparent since the first recognition of the SARSCoV2 virus in late 2019 is a dramatic increase in the prevalence of myopia, particularly in studies emerging from China. 3 For example, Wang et al. observed a significant increase in myopia progression in children between 6 and 9 years of age in the year 2020, although it should be noted that their data comprised noncycloplegic refractions without concurrent axial length measurements. However, other investigations have also reported significant increases in myopia under cycloplegia, generally accompanied by increased viewing of electronic screens and reduced time spent outdoors. Indeed, an editorial by Klaver et al. referred to 2020 as the year of “Quarantine Myopia”. Sadly, it seems likely that this increase in refractive development will continue through 2021 and beyond. The key question is what is the underlying cause of this marked jump in myopia progression. The dramatic increase in screen time associated with home schooling and remote working is an obvious suspect. For instance, Ma et al. reported a huge increase in the amount of time spent looking at displays, with an average of 0.67 and 5.24 h of screen time per day in October 2019 (prelockdown) and May 2020 (postlockdown), respectively. The use of digital devices and especially smartphones, which are typically held at close viewing distances, is frequently linked with refractive error development. However, the myopia epidemic taking place around the world, but most especially in East Asia has been ongoing since the 1950s. Having a personal computer outside the workplace was rare before the mid1980s, and the first smartphone did not become available to the public until 2007; more than half a century after the “myopia boom” first began. Therefore, while it is easy to link viewing digital screens with myopia development, the data supporting such an association are limited. Another possibility is that the observed change is an accommodative aftereffect, resulting from a failure to relax the accommodative response completely following sustained periods of nearwork. This maintained response could result from the prolonged viewing of screens or other near targets, restricted conditions that do not allow distance fixation or both. For instance, a study performed in Turkey found less myopia progression in children who lived in “detached houses” versus “apartment blocks”. While these terms were not specifically defined, an inability to view targets at optical infinity will inhibit the complete relaxation of accommodation. This could occur for residents of small apartments or congested urban environments where windows may only provide a view of an adjacent building, rather than allowing fixation into the far distance. As an example of the effects of confined living conditions, the classic study by Kinney et al. noted small but statistically significant differences in binocular distance visual acuity and the amplitude of accommodation in naval submariners when compared with a control group of National Guardsmen, suggesting that the restricted environment found on a submarine could lead to accommodative aftereffects. Whether such changes lead to permanent axial changes in the eye is an entirely different question which must be considered unproven at the present time. Alternatively, the increase in myopia could result from reduced exposure to sunlight during pandemic lockdowns. Depending on the local laws, in some cases individuals were only allowed outside their place of residence for very limited periods of time per day, or could only travel a short distance away from their home. It has been well established that exposure to sunlight reduces myopia progression, and therefore the restricted time spent outdoors could have been responsible for the increased refractive development during lockdown, rather than the effects of additional nearwork or lack of adequate distance fixation. The spectral composition of the encountered illumination, whether ambient indoor lighting or that emitted from digital displays, may also play a role in the development of myopia. Chromaticity signals may be important for normal eye growth, which may at least partly explain why outdoor activity has a protective effect against myopia. Both ambient light emitting diode (LED) illumination and digital screens emit a high proportion of wavelengths at the blue end of the visible spectrum, and these wavelengths have been associated with axial growth. For example, tree shrews tended to become more myopic when raised in blue light, while exposure to red LEDs inhibited axial eye growth. However, these effects of ambient chromaticity on refractive development vary significantly across Published online: 11 January 2022