Can the axial length of the human eye decrease?

Question

I understand that the axial length of the eyeball grows until you are around 20 years of age, which is why hypermetropia decreases with age but myopia doesn't. My question is: can the axial length of the eyeball decrease, and does it do so naturally?

I know that certain conditions can cause the axial length to decrease, such as very low pressure or disease, but my question is regarding a normal healthy eye.

• Weihua Meng, Jacqueline Butterworth, François Malecaze, Patrick Calvas; Axial Length of Myopia: A Review of Current Research. Ophthalmologica 1 March 2011; 225 (3): 127–134. https://doi.org/10.1159/000317072

This study by Meng et. al. (2011) says that with current research we KNOW that the axial length decreases with age this same point was also in a different study based on the idea of a an emmetropizing mechanism for the adult eye but many people have criticised this study and due to this apparently the studies findings should be taken with a grain of salt but if this is the case why is it that many articles do say that the axial length reduces with age is there another study that shows this?

• Scott A. Read, Michael J. Collins, Beata P. Sander; Human Optical Axial Length and Defocus. Invest. Ophthalmol. Vis. Sci. 2010;51(12):6262-6269. doi: https://doi.org/10.1167/iovs.10-5457.

This study by Read et. al. (2010) basically used lenses to create hyperopic and myopic defocus in participants and they measured the axial length of the eyeball after exposure to the blur. They found that the axial length did decrease in the case of myopic defocus and increased in the case of hyperopic defocus in order to create a clearer image by focusing the image on the retina. But if this article provides definitive proof that the eye does in fact change its axial length then why is that people still say it doesn't happen?

Also do we know which mechanisms allow the eye to determine whether it is myopic defocus or hyperopic defocus that is presented to the retina?

Lastly, if the eye's axial length is able to reduce wouldn't myopia have a cure or at least a method to reduce it based on the reduction of the axial length of the eyeball?

https://www.quora.com/How-can-the-axial-length-of-an-eye-decrease-as-they-say-that-it-does-with-ageing

Answer 1

Generally the axial length doesn't decrease: graph

Although there is discussion of various conditions where it has been observed to decrease, i.e. nanophthalmos, microphthalmos, and retinoblastoma... A review of current research is here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501611/ quote:

It is considered that the axial length reaches adult length by the age of 13 years, showing no further increase in length. Recent cross-sectional studies found that the axial length in older adults tended to be shorter, suggesting that it may decrease with aging. However, in a recent longitudinal study by He et al., slight increase of the axial length in adults (mean refractive error, −0.44 ± 2.21 diopters) was reported. Conversely, an increase in the axial length in adults with highly myopic eyes is common and has been previously shown in longitudinal studies [5–7]. However, to the best of our knowledge, there have been no studies directly comparing the increase in the axial length in adults with non-highly myopic eyes or highly myopic eyes. In addition, because previous studies on the axial length in highly myopic eyes have not compared between eyes with and without macular complications, their influence on the axial length remains unknown.

Can myopia be treated with a reduction in axial length? Presumably, yes it could, if opticians had figured a way to do it... Do you suggest that a drug or a medical intervention can flatten the entire eyeball a bit? perhaps a drug could but it would reduce the entire eyeball, you'd have to find a way to administer it. Apparently doctors haven't researched that option, but perhaps they will in future. Laser currently seems like a better way.

https://www.google.com/search?hl=en&biw=1706&bih=951&sxsrf=ALeKk01GuiHpl6-_fRp-Bg_UdsYOdqVzbg%3A1596509065944&ei=icsoX9aRObLMgweX6KboCQ&q=%22decrease+in+axial+length%22+of+optical

https://www.google.com/search?hl=en&biw=1706&bih=951&sxsrf=ALeKk03b75zOsA6CN_Ypqdv5v7hqfVWLbA%3A1596509091797&ei=o8soX8ySMIyqUP2dtvgI&q=%22reduction+in+axial+length%22+of+optical&oq=%22reduction+in+axial+length%22+of+optical

Answer 2

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