In the news: Myopia: Too Much Near Work, Too Little Time Outdoors? Meta-analysis: Fish Consumption & AMD Risk

Myopia: Role of Close Work, Time Outdoors?

According to an article published last year in the journal Nature, there has been a dramatic increase in myopia worldwide. Myopia now affects about 50% of young adults in the US and Europe – double the prevalence of a half-century ago (1). The predominate theories as to why this ‘epidemic’ is occurring center around the possibility of too much sustained near work or insufficient outdoor bright light exposure.

A recent systematic review (2) evaluated myopia in East Asian and Southeast Asian young adults. The authors conclude that increased myopia is now largely associated with environmental factors rather than genetic background and that recent trials suggest the onset of myopia may be reduced by increasing time children spend outdoors.

How outdoor time might be protective isn’t well understood. One theory is that sunlight exposure triggers the release of dopamine in the retina, which blocks elongation of the eye during development. Another potential explanation involves sunlight stimulating vitamin D production. It’s thought that vitamin D influences ocular growth through interactions with vitamin A. Finally, others postulate that more time outside might simply mean less time engaged in sustained near tasks.

Results from the just published 3-year follow-up of The Beijing Myopia Progression Study (3) challenge the idea that outdoor time is protective. This cohort study, which analyzed the refractive error and daily activity data of 222 urban students, reports no significant association between outdoor activity and myopic refractive change.
 
After stratifying the students’ activity hours (assessed via a daily questionnaire) into quartiles, students with a greater near workload at baseline exhibited a greater myopic refractive change and had a higher risk of developing myopia. While this finding suggests that greater near work activity is a myopic trigger, more research is needed to learn whether sunlight and outdoor time are also contributing factors.

Fish Intake Linked to Lower AMD Risk

Because the association between fish consumption and risk of AMD is still unclear, a research team from the Ophthalmology Departments of several university-affiliated Chinese hospitals collaborated to conduct a meta-analysis (4) of select observational studies.

The authors report finding a linear (dose response) association between the amount of fish consumed (0-5 servings weekly) and AMD risk (p = 0.001). As little as one serving weekly was linked to an 11% risk reduction (RR = 0.89, 95% CI, 0.83–0.96).

The analysis identified prospective cohort studies that reported relative risks (RRs) and 95% confidence intervals (CIs) for the link between fish consumption and risk of AMD. A total of 8 cohort studies of high methodological quality were included, involving nearly 129,000 participants and 4202 cases of AMD.

The main finding was a risk reduction of 24% when any AMD was considered (RR = 0.76, 95% CI, 0.65-0.90). Subgroup analyses by AMD stage showed that fish consumption reduced the risk of both early and late AMD by 17% and 24% respectively. (For early AMD, RR = 0.83, 95% CI, 0.72–0.96; for late AMD, RR = 0.76, 95% CI, 0.60–0.97).

Stratified analyses by the type of fish consumed indicated that dark meat fish intake was associated with a reduction in risk of 32% (RR = 0.68, 95% CI, 0.46-0.99). Tuna fish consumption, in particular, was associated with a 42% risk reduction (RR = 0.58, 95% CI, 0.47-0.71). Darker fleshed fish generally have higher omega-3 fatty acid content than leaner fish species with lighter colored flesh.

References

1. Dolgin E. The myopia boom. Nature 519:276-78, 2015.
2. Morgan IG et al. Epidemic of pathologic myopia: What can laboratory studies and epidemiology tell us? Retina. Epub ahead of print Sept. 8, 2016.
3. Lin Z, et al. The influence of near work on myopic refractive change in urban students in Beijing: a 3-year follow up report. Graefes Arch Clin Exp Ophthalmol. 254:2247-55, 2016.
4. Zhu W, et al. Fish consumption and age-related macular degeneration incidence: A meta-analysis and systematic review of prospective cohort studies. Nutrients. 8:743-56, 2016.