Red light and myopia

Myopia, also near nearsightedness because the afflicted individual sees near objects but has issues with far away objects, has been reviewed on Wikipedia. Wikipedia authors attribute the main factors as increased length of the eyeball and/or changes in the refractive index of the cornea. A few publications were found demonstrating that red light used to treat myopia also increases blood flow. This post expanded relaxation of smooth muscle controlling blood flow to other contractile cells that control the length of the eyeball. Click here for an image.

What is myopia?

Also according to Wiki authors, the prevalence of myopia in China is extremely high, at least 37% in some large Chinese cities and about a fifth of the human population of the world. Not surprisingly, most of the clinical studies come from China. Time spent outdoors and exercise are thought to lessen the likelihood of developing myopia according to Wikipedia authors. According to Wikipedia authors, the sclera is composed mainly of connective tissue. 

Contractile cells: choroid and retina, sclera [1, 2]

The Kur review does an excellent job covering mechanisms of controlling blood flow through the retina and the choroid. Many these are smooth muscle functions involving cGMP and myosin light chain. Smooth muscle actin binding proteins like calponin are also covered. Pericytes, cells with a contractile phenotype, regulate blood flow in the choroid capilaries. [1] Since this post is about myopia, we need to examine the role of contractile cells in the sclera in a tree screw model of myopia published in 2009. [2] The connective tissue in myopia exhibits increased extensibility. TGF-β production has been linked to production of the matrix protein collagen in the sclera. {2]

Thiol Nitrosylation in myopia [3]

This study is from China, of course. The authors acknowledged the role of nitrix oxide and soluble guanylyl clyase. Myopia was induced unilaterally with defocus lenses sutured in place. 

1. 15 mice (30 eyes), lens-induced 0-week group (take eyeballs at the age of 3 weeks)
2. 50 mice (50 left eyes), self-control eyes of the experimental group (take eyeballs at the age of 7 weeks)
3. 50 mice (50 right eyes), -10D lens-induced 4-week group (take eyeballs at the age of 7 weeks).

By four weeks Doppler flow was decreased and axial length were increased in Group 3. By the end of seven weeks the nNOS expression had not changed, however, the PSNO (nitrosylated protein) relative to beta actin was half that of the controls in Group 3. These authors only reported changes in the enzyme alpha enolase. 

Does red light affect blood flow and axial length in myopia?

This sort of becomes a philosopical question. If there is some red light induced release of SNO, is it going to relax blood vessel smooth muscle and myofiborblasts living in the sclera?

in adults [4]

Twice a day subjects wore glasses that delivered 650 ± 10 nm at an illuminance level of approximately 1600 lux through the pupil to the fundus. At the end of 28 weeks axial length had decreased from from 24.63 ± 1.04 mm to 24.57 ± 1.04 mm. Choroid thickness had increased.

in children [5]

he children used a commercial Chinese device that delivered 1,600 lux with a power of 0.16 mW through a 4-mm pupil and a wavelength of 650 ± 10 nm. The choroid blood flow was measured shortly after 3 minutes of low level red light therapy (LLRLT). Retinal fovea perfusion density (RFPD) was found to to increase close to 2%. Choroidal fovea blood flow (CFBF) was not changed. This study was one of the first to cover acute effects of LLRLT in children. There are many more studies not covered in this post.  

References

1. Kur J, Newman EA, Chan-Ling T. Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease. Prog Retin Eye Res. 2012 Sep;31(5):377-406. PMC free article
2. Jobling AI, Gentle A, Metlapally R, McGowan BJ, McBrien NA. Regulation of scleral cell contraction by transforming growth factor-beta and stress: competing roles in myopic eye growth. J Biol Chem. 2009 Jan 23;284(4):2072-9. free paper
3. Lu Y, Song W, Li Y, Xiao J, Du K, Fu Q, Zhang Y, Zhao L, Yin Y, Hu T, Wen D. Mechanisms of NO-Mediated Protein S-Nitrosylation in the Lens-Induced Myopia. Oxid Med Cell Longev. 2022 Nov 16;2022:8296043. doi: 10.1155/2022/8296043. PMC free article
4. Liu G, Li B, Rong H, Du B, Wang B, Hu J, Zhang B, Wei R. Axial Length Shortening and Choroid Thickening in Myopic Adults Treated with Repeated Low-Level Red Light. J Clin Med. 2022 Dec 17;11(24):7498. PMC free article
5. Yang W, Lin F, Li M, Wei R, Zhou J, Zhou X. Immediate Effect in the Retina and Choroid after 650 nm Low-Level Red Light Therapy in Children. Ophthalmic Res. 2023;66(1):312-318. free paper