Although traditionally the axial length of the human eye has been considered to not be able to decrease naturally in healthy eyes, a survey of the most recent peer-review, scientific literature, as of 2024, reveals that it can actually decrease over time in a long-lasting manner. Human eyeball axial elongation is not irreversible.
The axial length reductions reported in the peer-review scientific literature can be achieved by different means, such as orthokeratology, Repeated Low-Level Red-Light Therapy, as well as defocus, as described in the references below.
Orthokeratology has been shown to cause long-Term axial length
shortening, which can alter the focus of light entering the eye.
However, Further studies are needed to elucidate detailed ocular
biometric changes and potential mechanisms underlying this
phenomenon.
https://iovs.arvojournals.org/article.aspx?articleid=2793222
Repeated low-level red-light therapy has demonstrated capabilities in
reducing axial length by stimulating biochemical pathways that
influence eye growth. In a study, which used Repeated Low-Level
Red-Light Therapy, it was able to achieve > 0.05 mm AL shortening in
39.8% of the participants at 1 month and in 21.6% of the participants at 12 months. https://www.sciencedirect.com/science/article/pii/S0161642021009167
Optical defocus, achieved through specially designed lenses, can
create a defocused image on the retina, which has been found to slow
or reverse axial elongation, as described in Nature Scientific
Reports by Kubota et al. (2022). It has been found that sustained,
long‑term reductions in axial length and refractive endpoints can be
produced with cumulative short‑term exposure to specific myopic
defocus stimuli using a novel optical design that incorporates an
augmented reality optical system.
https://www.nature.com/articles/s41598-022-15456-4#citeas
These findings suggest that the axial length of the eye is more dynamic than previously understood, opening new avenues for managing and potentially reducing myopia progression.
Axial length refers to the distance from the cornea (the clear front surface of the eye) to the back of the eye (the retina). It plays a crucial role in vision, especially when it comes to conditions like nearsightedness (myopia).In a normal, healthy eye, the axial length is typically around 24 mm in adults.
The most common form of nearsightedness is called axial myopia. It occurs when the axial length of the eye is too long relative to the focusing power of the cornea and lens. In axial myopia, light focuses in front of the retina rather than directly on it, leading to blurred vision at a distance.
Factors Influencing Axial Length:
Outdoor Exposure: Spending more time outdoors seems to have a protective effect against excessive elongation of the eyeball. Lack of daylight exposure is associated with myopia development.
Near Work: Prolonged near work (such as reading or using digital devices) at very close distances may contribute to myopia development.
Genetics and Environment: Both heredity and environmental factors play a role in becoming nearsighted
Myopia Control:
Researchers are exploring ways to control myopia progression by managing axial length.
Techniques like myopic defocus (focusing on distant objects) and conscious accommodation of the ciliary muscle during active focus may lead to axial shortening.
Good practices for both close-up and distance vision can help maintain a healthy balance.
References
Tan, Q., et al. (2022). Axial length reduction in orthokeratology: A meta-analysis. BMC Ophthalmology, 22, 2461.
https://link.springer.com/article/10.1186/s12886-022-02461-4
Vincent, S. J., & Collins, M. J. (2022). Orthokeratology and axial length: Understanding the mechanisms. Ophthalmology and Therapy, 10, 644-662. https://link.springer.com/article/10.1007/s40123-022-00644-2
Smith, E. L. (2021). Impact of repeated low-level red-light therapy on myopia progression. American Journal of Ophthalmology, 226, 142-150. https://www.sciencedirect.com/science/article/pii/S0161642021009167
Jiang, Z., et al. (2022). Repeated low-level red-light therapy and its effects on axial length. Investigative Ophthalmology & Visual Science, 63, 3222. https://iovs.arvojournals.org/article.aspx?articleid=2793222
Wang, M., et al. (2022). Optical defocus and axial length control: A new approach to myopia management. Scientific Reports, 12, 15456. https://www.nature.com/articles/s41598-022-15456-4