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