Shut schools, closed parks and cancelled playdates meant many parents plonked their child in front of the TV during the world's various lockdowns.
While it may sound like a relatively harmless way to pass the time, medics from the Chinese University of Hong Kong have warned that too much screen time amid the coronavirus outbreak may have triggered a surge in short-sightedness.
The team analysed more than 1,700 children aged six to eight. Of these, 709 were recruited at the start of the pandemic, while the remaining children were already being monitored pre-pandemic.
Results – published in the British Journal of Ophthalmology – suggest just under a third (28%) of six-year-olds alone developed short-sightedness during the pandemic, versus less than one in five (17%) pre-coronavirus.
This corresponded with an increase in screen time from an average of 2.5 hours to seven hours a day.
Left untreated, short-sightedness is "a major cause of visual disability among children", and may predispose them to complications that "increase the risk of irreversible vision loss later in life".
The coronavirus was formally identified on 31 December, 2019. By the following September, more than 180 countries had closed their schools and colleges, affecting 1 billion students.
Short-sightedness – known medically as myopia – occurs when the eye changes shape, causing light rays to bend incorrectly. Images are therefore focused in front of, rather than on the surface of, the retina.
Myopia has previously been linked to working in front of a screen and spending little time outdoors.
To learn more, the Chinese University scientists analysed participants of the ongoing Hong Kong Children Eye Study.
Of the participants, 709 were recruited in December, 2019, or January, 2020, before being followed for around eight months. The remaining 1,084 children had been monitored for about three years pre-pandemic.
The scientists assessed the children's vision, while questionnaires provided details on their lifestyle.
In Hong Kong, one of the world's most densely populated cities, the "overwhelming majority" of residents live in "high-rises and small apartments, where outdoor spaces such as backyards, gardens and outdoor playgrounds are hard to come by".
Children in Hong Kong and the rest of the world also "required [the] use of digital platforms to continue learning" after school gates closed.
In the seven months between January and August 2020, just under one in five (19%) of the children in the "pandemic group" developed short-sightedness.
This is less than the 36% who were already enduring the eye condition pre-pandemic, but the latter cases arose over a period of more than three years.
Six-year-olds were found to be the worst affected. Among the participants aged seven or eight, 27% and 26% are thought to have developed short-sightedness amid the pandemic, respectively. This is compared to 16% and 15% before the outbreak.
As well as corresponding with an increase in screen time, the time the children spent outdoors also fell from an average of 75 minutes to just 24 minutes a day.
Watch: Remote learning affecting children's eyesight
The scientists have stressed their study was observational, and therefore does not prove cause and effect. Questionnaires also rely on the participants recalling their behaviour, which may be inaccurate.
In addition, the results may not apply in other parts of the world, with coronavirus restrictions varying.
"It should be noted this was carried out in an urbanised East Asian population, among whom myopia levels are generally higher than in groups of European ancestry," said Professor Oliver Braddick, from the University of Oxford.
"It remains unclear whether there is any genetic component to this difference or whether it is a result of cultural factors."
Nevertheless, the Chinese University scientists wrote: "Despite all these insurmountable study limitations, our initial results still show an alarming myopia progression that warrants appropriate remedial action.
"[They] serve to warn eye care professionals – and also policy makers, educators and parents – that collective efforts are needed to prevent childhood myopia, a potential public health crisis as a result of COVID-19 [the disease caused by the coronavirus]."
Although the pandemic "will not last forever", the scientists worry "the increasing adoption of and reliance on digital devices, as well as behavioural changes resulting from extended home confinement, may have long-lasting effects on myopia progression".