by Dan Roberts
Ophthalmic nearsightedness (myopia) results from an abnormal elongation of the eyeball during the growing years. This extra “axial length” causes objects at a distance to appear out of focus, which can usually be corrected with prescription glasses. The physical aspects of extreme nearsightedness (hypermyopia), however, can lead to a type of uncorrectable vision impairment called degenerative myopia. This occurs when the cell tissue at the back of the eye is stretched and thinned so severely by the elongation that it degenerates by either tearing or separating from its nutrition supply.
Understanding and preventing myopia have been hot topics lately, with the most recent study finding an association between years of schooling and degree of vision loss. Past research has implicated genetics, exposure to the outdoors and daylight, and prolonged near vision work such as reading. All of these may contribute to ophthalmic myopia, but we must avoid mental myopia in our interpretation of the reports. In particular, we must recognize that an associative relationship is not necessarily a causal relationship.
We read that the degree of myopia is associated with the number of years in school.(1) We read that using daylight spectrum indoor lamps may help prevent myopia, an assumption derived from reports that children who spend much of their time outdoors are less likely to be nearsighted than those who don’t.(2) We even read that reading itself may cause myopia.(3)
Geneticists place a substantial amount of the blame for the condition on inheritance.(4) Could it be that people who inherit myopia tend to favor academic activities like reading over activities requiring distance vision? Maybe playing outdoors slows the development of myopia, not because of the light spectrum, but because it encourages the eye to evolve distance vision. Such caveats are sometimes placed at the end of research reports where they don’t receive a lot of attention. And a paper titled “Higher Education Linked to Myopia” is more likely to make headlines than “Myopes Read A Lot”.
We should be quizzical. We learned so much when we were young, because “Youth” begins with “Why”. We should remember that and to ask “Why?” before accepting what we read at face value. To do less would be myopic in more ways than one.
1 Nearsightedness Linked to More Schooling. Robert Preidt (HealthDay News online, June 27, 2014)
2 Outdoor Activity during Class Recess Reduces Myopia Onset and Progression in School Children. Pei-Chang Wu, MD, PhD, et al (Ophthalmology, Volume 120, Issue 5 , Pages 1080-1085, May 2013)
3 Nature and nurture: the complex genetics of myopia and refractive error
(R Wojciechowski. Clinical Genetics, Volume 79, Issue 4, pages 301–320, April 2011. First published online: 13 DEC 2010; DOI: 10.1111/j.1399-0004.2010.01592.x
4 Genome-Wide Analysis Points to Roles for Extracellular Matrix Remodeling, the Visual Cycle, and Neuronal Development in Myopia.
Amy K. Kiefer, et al (PLOS Genetics, February 28, 2013DOI: 10.1371/journal.pgen.1003299)