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Refers to: https://www.sciencedaily.com/releases/2016/02/160217113308.htm

Short answer: Myopia is becoming a bigger issue but situation’s nowhere as alarmist as these headlines suggest.Too bad, Science Daily sensationally highlighted these projected numbers without critically examining how they were generated.

The article refers to a prevalence study (1) done by the Brien Holden Vision Institute, an Australian non-profit NGO which has 60 peer-reviewed scientific papers currently listed on PubMed, i.e., by eye experts with a solid track record in the field. Unlike unnecessary sensationalizing by general news media, the study authors themselves are more cautious and transparent, and point out inherent weaknesses (my emphasis in italics) that ensue from extrapolating estimates of current global myopia numbers far into the future,

  • The first is the paucity of prevalence data in many countries and age groups, across representative geographic areas, racial groupings, and HDIs*. This problem was greater for high myopia than myopia. The further the primary data are extrapolated, the greater the uncertainty of the estimates becomes.
  • Second, many countries and age groups across representative geographic areas, racial groupings, and HDIs lacked data on the change in myopia, especially high myopia, over time. Local effects on changes in myopia over time are potentially lost when annual changes are extrapolated across regions.
  • Third, projecting on the basis of current information has the potential to miss varying changes over time.
  • Fourth, variations in the definition of myopia and high myopia in the evidence base made it necessary to adjust each prevalence we used to a standard definition, which increases uncertainty.
  • There are conflicting data on the effect of gender on myopia prevalence.
  • Also, we used a logarithmic decay function to estimate the future prevalence of myopia, and thus it is possible that future prevalence may have been overestimated, especially for regions where the current prevalences are moderate to low.

* HDI = human development index

That last bit, using logarithmic decay function is an especially critical weakness of this study. Log function is okay when applied to inherently log functions such as fluorescence or bacterial growth rates. Are populations rates of myopia or high myopia inherently log functions? Obviously not. This means to take this study’s extrapolated year 2050 myopia estimates with more than a grain of salt. OTOH, actual current-day data do clearly suggest myopia global prevalence is rising, albeit with huge differences between countries and regions.

Where did the authors get these global myopia numbers in the first place? Using two sets of search terms on PubMed, either myopia AND prevalence or refractive error AND prevalence, they found a total of 1656 and 2632 articles, respectively. From these they chose population-based surveys, a total of 145 studies. Problem starts already with the fact that only 59 of these defined and measured high myopia in addition to myopia. According to the authors themselves, critical distinction between myopia and high myopia is it’s the latter that increases risk of cataract, glaucoma, retinal detachment and myopic macular degeneration. Since high myopia equals more healthcare costs, its numbers are more critical and in this meta-analysis, those numbers came from a small proportion (59 of 145 or ~40%) of the total studies. Another reason to take the extrapolated numbers with a grain of salt.

That said, the study does highlight an interesting global difference in high myopia rates. Why are they apparently rising so much more across much of Asia (if interested, take a look at the tables listing country-wide prevalence in Appendix 2 of the study)? Authors suggest dramatic lifestyle changes in extremely short time-span, principally less time outdoors, more time on near-work activities, especially given high-pressure educational systems and excessive electronic device use. If environmental factors drive much of this myopia rise, fix would require little by way of advanced biomedical R&D, an expensive healthcare intervention. Rather, the fix would be more in the form of lifestyle change, ensuring kids and young adults spend more time outdoors as a matter of course.

Foot-note

1. Holden, Brien A., et al. “Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050.” Ophthalmology (2016). http://www.sciencedirect.com/sci…

https://www.quora.com/How-big-of-a-healthcare-problem-is-vision-impairment/answer/Tirumalai-Kamala

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