This article was originally published in a sponsored newsletter.

It is accepted that the primary cause of myopia is elongation of the eye, and eyes that are elongated may also have thinner choroidal layers.¹ It has been suggested that the choroid may be involved in eye growth regulation and that changes in choroidal thickness may be predictive of eye growth.² Changes in choroidal thickness enact changes in eye growth. Myopic defocus has been shown to cause choroidal thickening and slowing of eye growth whereas hyperopic defocus causes choroidal thinning, eye growth, and myopia.²

A few facts about the choroid:

1. The choroid is a vascular connective tissue layer of the eye between the sclera and retina.³
2. Functions of the choroid include providing nutrition and oxygen to the retina, thermoregulation, absorption of excess light, modulation of intraocular pressure, and drainage of aqueous humor.³
3. The choroid is a dynamic structure; fluctuations in the choroidal thickness move the retina backward and forward aligning photoreceptors with the plane of focus.³
4. Choroidal thickness is modulated in humans by both physiologic and visual cues, which include but are not limited to physical activity, time of day, caffeine intake, water intake, pregnancy, light intensity and wavelength, and defocus.⁴

A key idea that may impact the realm of myopia management is the notion of whether short-term choroidal thickness modulation can be used as a biomarker to determine whether a stimulus is protective against or inducing myopia.⁴Quantifying choroidal biometrics has yet to be standardized and is especially challenging when looking at small changes as described in human choroid changes in response to protective or myogenic factors.⁴

Reminder:

• Interventions involving myopic defocus and choroidal thinning include orthokeratology, most myopia control spectacles, and dual-focus contact lenses.^4,5 They reduce myopic progression by reducing eye elongation.
• Interventions that may involve choroidal thickness include atropine, environmental manipulations (i.e., increased time outdoors), and repeated low-level red light therapy (RLRL).^4,6

Light and choroidal thickness has been a recently trending conversation. A randomized controlled trial in China showed that RLRL slowed myopic progression.⁷Safety and the risk for rebound potential, however, have been questioned and further study is needed to adequately determine the best clinical protocols.⁸

1. Hansen MH, Kessel L, Li XQ, Skovgaard AM. Axial length change and its relationship with baseline choroidal thickness – a five-year longitudinal study in Danish adolescents: the CCC2000 eye study. BMC Ophthalmol. 2020 Apr 15;20:152.

2. Hung LF, Wallman J, Smith EL III. Vision-dependent changes in the choroidal thickness of macaque monkeys. Invest Ophthalmol Vis Sci. 2000 May;41:1259-1269.

3. Nickla DL, Wallman J. The multifunctional choroid. Prog Retin Eye Res. 2010 Mar;29:144-168.

4. Ostrin LA, Harb E, Nickla DL, et. al. IMI – The Dynamic Choroid: new Insights, Challenges, and Potential Significance for Human Myopia. Invest Ophthalmol Vis Sci. 2023 May 1;64:4.

5. Wildsoet CF, Chia A, Cho P, et al. IMI—Interventions Myopia Institute: Interventions for Controlling Myopia Onset and Progression Report. Invest Ophthalmol Vis Sci. 2019 Feb 28;60:M106-M131.

6. Zhou L, Xing C, Qiang W, Hua C, Tong L. Low-intensity, long-wavelength red light slows the progression of myopia in children: An Eastern China-based cohort. Ophthalmic Physiol Opt. 2022 Mar;42:335-344.

7. Jiang Y, Zhu Z, Tan X, et al. Effect of Repeated Low-Level Red-Light Therapy for Myopia Control in Children: A Multicenter Randomized Controlled Trial. Ophthalmology. 2022 May;129:509-519.

8. Tang J, Liao Y, Yan N, et al. Efficacy of Repeated Low-Level Red-Light Therapy for Slowing the Progression of Childhood Myopia: A Systematic Review and Meta-analysis. Am J Ophthalmol. 2023 Aug;252:153-163.