A recent study published in BMC Ophthalmology evaluated myopia risk factors, including the association between night-time reading habits under low illumination in children.
Give me some background.
While a family history of myopia is a well-known risk factor for early-onset myopia, environmental factors may play a determinant role in the development of myopia.
In fact: A growing body of literature has also highlighted the impact of environmental illumination on myopia:
- In one study, 5-year-old children had less hyperopic reserve when exposed to low-illuminated school environments
- A study in China showed that increasing illumination from 200 to 500 lux in classrooms decreased myopia progression in children
In addition: Going to bed late has been associated with myopia progression, but this study did not explore children’s reading habits while going to sleep or their bedroom illumination.
- Consequently: Researchers sought to understand the association between myopia and children’s habits at night when going to bed—with a focus on evaluating whether reading with low illumination is a risk factor for myopia.
Now, talk about the study.
Investigators analyzed data from a cross-sectional survey conducted in Argentina as part of the Myopia Awareness Campaign in June 2024; included were a total of 1,298 children (mean age 10.69 years, 51.5% males) aged 7 to 15 years.
The data was collected using a 23-question Google Form that asked about:
- Self-reported myopia
- Reading habits
- Illumination levels
- Type of housing
- Outdoor time
- Parental high myopia
Findings?
The prevalence of self-reported myopia in children was 23.7%.
Significant risk factors for myopia included:
- Parental high myopia (OR: 2.88, 95% CI: 2.07-4.00)
- High-intensity reading (OR: 1.69, 95% CI: 1.12-2.55)
- Living in a house without a garden (OR: 1.49, 95% CI: 1.12-2.00)
- Older age (odds ratio [OR]: 1.15, 95% confidence interval [CI]: 1.08-1.23)
- Less outdoor time (OR: 0.98, 95% CI: 0.97-0.999)
What about reading at night in the dark?
Almost half (49.5%) of children read at night in bed before sleeping, with 12.5% reading with lights off (i.e., only the light of the device) and 30.4% reading with one or two lights on.
While the initial unadjusted analysis suggested that reading at night in the dark was associated with myopia, the association lost significance after adjusting for age.
- Meaning: The observed relationship between myopia and reading in the dark may be confounded by age, with older children—who are more likely to be myopic—also being more inclined to read in the dark.
Expert opinion?
To start: Illumination is crucial for how the retina perceives the balance between ON and OFF contrast.
“This light adaptation of the retina could affect emmetropization, as it seems that under low illumination in mesopic conditions, the retina does not perceive accurately the ON contrast that stops the eye from growing,” the study authors highlighted.
Anything else?
Previous studies have demonstrated that bright light prevents experimental myopia progression when applied in the last hours of the day—but not in the morning or midday—and that myopic defocus is more effective in the afternoon than in the morning.
Meaning: It is probable that what children do in the last 2 hours before sleep could be related to myopia onset and progression.
- Why: The retinochoroidal signal for ocular growth may be present during the whole day, but as the eye grows more during the night, the signal sent in the last hours of the day may be more important for ocular growth than that from the morning.
Interesting … any limitations to this research?
A few. These included:
- Questionnaires are subject to recall bias
- The study recruited a convenience sample that was not necessarily representative of the population
- Myopia was self-reported by parents of school-aged children
Take home.
These findings highlight the role of genetic and environmental factors and lifestyle choices in myopia development, such as
- Parental high myopia
- High-intensity reading
- Living in a house without a garden
- Older age
- Less outdoor time
Although reading at night in the dark appeared as a potential risk factor, further research is required to elucidate its role in myopia development and progression.
Further: The existence of accessible outdoor areas may increase the time children spend outdoors—helping to mitigate myopia incidence.
Lastly, what are the next steps?
The authors concluded that future prospective studies using refractive error measurements with cycloplegic refraction to assess the possible risk factor of reading at night with low illumination are necessary to further clarify if this is a new risk factor for myopia.