Dear Doctor Cordain:
We are reviewing the subject of etiology of myopia, since we are planning a large epidemiological study in Colombia to be performed next year, including 5340 adults (2670 in cities and 2670 from rural areas) and we found your very interesting articles.
Have you published any additional work on the matter after the ones published in 2002 and 2003 (An evolutionary analysis of the aetiology and pathogenesis of juvenile-onset myopia. Cordain L, Eaton SB, Brand Miller J, Lindeberg S, Jensen C.Acta Ophthalmol Scand. 2002 Apr;80(2):125-35. Review.
Hyperinsulinemic diseases of civilization: more than just Syndrome X.Cordain L, Eades MR, Eades MD.Comp Biochem Physiol A Mol Integr Physiol. 2003 Sep;136(1):95-112. Review).
Where else can we find material on that issue?
We would like to have your advice: We are planning to measure insuline. What else do you think could be measured in this group of patients?
Thanks for all your support.
Dr. Cordain’s Response:
Good to hear from you and good luck with your large epidemiological study on myopia. I have not published any additional papers on myopia since those two papers, however a number of studies since then have implicated insulin resistance in the development of myopia:
1. Penha AM, Burkhardt E, Schaeffel F, Feldkaemper MP. Effects of intravitreal insulin and insulin signaling cascade inhibitors on emmetropization in the chick. Mol Vis. 2012;18:2608-22.
2. Ritchey ER, Zelinka CP, Tang J, Liu J, Fischer AJ. The combination of IGF1 and FGF2 and the induction of excessive ocular growth and extreme myopia. Exp Eye Res. 2012 Jun;99:1-16.
3. Zhu X, Wallman J. Opposite effects of glucagon and insulin on compensation for spectacle lenses in chicks. Invest Ophthalmol Vis Sci. 2009 Jan;50(1):24-36.
4. Feldkaemper MP, Neacsu I, Schaeffel F. Insulin acts as a powerful stimulator of axial myopia in chicks. Invest Ophthalmol Vis Sci. 2009 Jan;50(1):13-23.
5. Zhuang W, Yang P, Li Z, Sheng X, Zhao J, Li S, Yang X, Xiang W, Rong W, Liu Y, Zhang F. Association of insulin-like growth factor-1 polymorphisms with high myopia in the Chinese population. Mol Vis. 2012;18:634-44
6. Penha AM, Schaeffel F, Feldkaemper M. Insulin, insulin-like growth factor-1, insulin receptor, and insulin-like growth factor-1 receptor expression in the chick eye and their regulation with imposed myopic or hyperopic defocus. Mol Vis. 2011;17:1436-48.
7. Jacobsen N, Jensen H, Lund-Andersen H, Goldschmidt E. Is poor glycaemic control in diabetic patients a risk factor of myopia? Acta Ophthalmol. 2008 Aug;86(5):510-4
If possible, I suggest that you examine and refract indigenous, non-westernized (or minimally westernized) Indians as these groups have been previously demonstrated to have a low prevalence of myopia:
8. Jiménez JR, Bermúdez J, Rubiño M, Gómez L, Anera RG. Prevalence of myopia in an adult population of two different ethnic groups in the Ecuadorian Amazon. Jpn J Ophthalmol. 2004 Mar-Apr;48(2):163-5.
9. Thorn F, Cruz AA, Machado AJ, Carvalho RA. Refractive status of indigenous people in the northwestern Amazon region of Brazil. Optom Vis Sci. 2005 Apr;82(4):267-72
I believe that dietary induced insulin resistance brought on by the ubiquitous high glycemic load carbohydrates in the typical western diet contributes to the development of myopia along with the excessive near work of reading. Although no epidemiological studies have specifically examined myopia prevalence in illiterate and literate populations, it is almost certain that the prevalence of myopia would be less in the illiterate population. It would be even more revealing to examine the dietary glycemic load in each of these populations relative to myopia prevalence. If possible you should try to examine blood parameters that are gauges of long term glucose and insulin control such as hemoglobin A1C. Fasting insulin is a crude marker of insulin resistance, but is better than nothing and is considerably less expensive than other laboratory measurements of insulin homeostasis which would be prohibitively expensive for your study. Other physical markers which are easy to measure and which are markers of insulin resistance or consumption of high glycemic load carbohydrates are: BMI, number of dental caries, and presence of acne, skin tags, and acanthosis nigricans.