by Tiffany Yanese Park
There is no denying that the ways children use their eyes have shifted significantly in the recent decades. There appears to be a parallel with these behaviors to the rising numbers of children affected by myopia. An abundance of concern circle around screen time specifically. These discussions boil down to the significance of
- the viewing distance: is there a difference between watching or reading something up close versus far away?
- the duration: how long is the child focusing?
To understand the context of the consequences of near work on the eye, the workings of the eye’s accommodative system should be reviewed. For a distant target to be perceived as clear, it must be exactly focused onto the retina. When the viewing distance shortens, the natural lens of the eye typically preserves this focus by flexing or relaxing. If the focus is inaccurate or latent, the image will not land on the retina, resulting in blur. Imprecise focus, or accommodative lag, is not a characteristic exclusive to children with myopia, so its significance is debatable (1-3). However, there appears to be a link between sustained near work and accommodative retention, leading to latent or transient myopia (4). Successive cycles of near work induced transient myopia can create a net defocus and presumably stimulate axial elongation (5). This has been demonstrated in children with emmetropia and hyperopia, but most prominently in those with myopia (6,7). Children’s prolonged near work continues to be a topic of critical examination and is implicated as a contributor to myopia progression (8).
How close is too close?
We know that children’s eyes usually have an impressive ability to accommodate as compared to those of adults. The average amplitude of accommodation for a child is about 14 diopters (9), meaning children can hold things about 3 inches from their eyes and could potentially still see it crispy clear! That is awfully close and not typical for most children, however parents have become increasingly worried about close reading and watching distances for their children. Multiple studies have pinpointed working distances shorter than 20 to 30 centimeters as an increased risk for myopia (10-14). For context, that is nearly equivalent to the dimensions of a piece of paper! But screen time cannot be singled out to be criticized. Whether the viewing target is a coloring book, a novel or a phone, it is the working distance that seems be problematic, which connects the involvement of the accommodative system (13, 15-19). A parent’s intuition for a child to scoot back is valid!
Interestingly, the studies that included television watching had a less definitive correlation to myopia. Some showed no relationship or an inverse relationship between the activity and myopia (15,16,20-22). Children may be overjoyed to know this at first glance, but most authors admit there is unlikely a true protective effect of watching television. Rather, the complex accommodative system is not stimulated or there is a substitution effect of less time spent using their eyes at closer working distances. Before handing the remote back to their children, parents should instead consider heading outdoors (hyperlink to “What Makes The Great Outdoors Great? Peering More Into Select Environmental Risk Factors For Myopia”).
How much time is too long?
The intensity of near work has been another area of high concern. Not only is viewing distance a pertinent factor in near work behaviors, but also the time spent. Total weekly use of 3 to 4 hours (23, 24) and a range of 20 minutes to one hour of continuous near work have been associated with myopia (23, 25). Those findings may cause dismay, because frankly some children can easily exceed those time limits in a single day. Parents can have reassurance that time outdoors can dampen this repercussion of near work (25-27). With the future of virtual schooling uncertain, it is even more imperative that parents be mindful of the extracurricular ways children are using their eyes. Recommendations have been made that children take a break every 30 minutes to be outdoors (13, 26), as continuous time spent with near work may have an even stronger effect than cumulative time (11, 13).
Children’s vision demands inherently change with age, as they go through higher school grades and have less time or interest to play outside (24). With all of this in mind, parents should be aware of how certain aspects of near work habits such as working distance and duration influence their child’s eyes. The simplified “20-20” adage propagated by the eye care community seems to have some bearing: after 20 minutes, look 20 feet away. Making deliberate daily modifications can chip away at a child’s risk of myopia and its progression.
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