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I read with interest the article by Jonas et al 1. The main purpose of the authors was to explore associations between a disc size change and other morphological parameters. Indeed, many non-ophthalmic and game-changing parameters are associated with disc size change and other morphological parameters, such as the serum lipids 2 dietary factors (such as lutein, zeaxanthin, and omega-3 fatty acids) 2-4, medications (such as lipid-lowering agents) 2, genetic susceptibility, body mass index, age and sex 3, among which only age and sex are addressed in their retrospective analysis.
According to the authors, decrease in the ophthalmoscopic disc size in the myopic eyes during the 10-year follow up, is likely related to a shift of the Bruch’s membrane opening as the inner of the three optic nerve head canal layers into the direction of the fovea. While their interpretations can be partly true, their attributed mechanism is subject to many biases.
Firstly, changes in ophthalmoscopical optic disc size and Bruch’s membrane are a function of macular pigment optical density 5-7, which in turn is a function of dietary carotenoid intake 8;9. Tong et al 10 have shown before that macular pigment optical density (MPOD) is inversely associated with axial length in Chinese subjects with myopia, suggesting that carotenoid intake, particularly lutein, is associated to axial length as well. Another study with a smaller sample size (45 eyes of 32 patients) with a different mean a...
Firstly, changes in ophthalmoscopical optic disc size and Bruch’s membrane are a function of macular pigment optical density 5-7, which in turn is a function of dietary carotenoid intake 8;9. Tong et al 10 have shown before that macular pigment optical density (MPOD) is inversely associated with axial length in Chinese subjects with myopia, suggesting that carotenoid intake, particularly lutein, is associated to axial length as well. Another study with a smaller sample size (45 eyes of 32 patients) with a different mean age did not show the same association 5. A detailed explanation of the reasons justifying these differences is provided elsewhere 11.
Secondly, in many medical situations (such as obesity, diabetes, etc.), MOPD is reduced dramatically 12;13. Jonas et al 1 report that only 89 highly myoptic eyes (i.e., 43.6%) were re-examined after 10 years. Although the authors report that the age of cases in 2011 did not differ significantly from the age of their controls in the survey of 2011, no other dietary or medical information is provided in their study. Thus, it is very difficult to draw a firm conclusion.
One can certainly question whether there were any changes in carotenoid intakes and/or any medical situation during a decade-long longitudinal study. In support of this argument, MOPD is reported to significantly increase within 3 months in healthy Japanese individuals supplemented with daily 10 mg of orally administered lutein or zeaxanthin 14. Interestingly, in high myopia, it has been shown that even after a shorter period of lutein supplementation (20 to 40 days), MPOD began to rise uniformly at an average rate of 1.13+/-0.12 milliabsorbance units/day. During this same period, the serum lutein concentration increased tenfold, and then approached a steady state plateau. Most critically, the optical density curve eventually levelled off some 40 to 50 days after the participants discontinued the supplement. Thus, even a modest period of dietary carotenoid intake may produce a 30 to 40% reduction in blue light reaching the photoreceptors, Bruch's membrane, and the retinal pigment epithelium 6.
Substantial differences are reported in terms of dietary carotenoid/lutein intake among Chinese population 15;16. This issue may be even more pronounced in a small sample size a low rate of re-participation.
We agree that geometrical reasons may lead to a decrease in the size of the ophthalmoscopically visible optic disc. However, their presumed mechanism 17 may simply be partially a byproduct of MOPD changes over time.
1. Jonas JB, Zhang Q, Xu L et al. Change in the ophthalmoscopical optic disc size and shape in a 10-year follow-up: the Beijing Eye Study 2001-2011. Br.J Ophthalmol. 2021.
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