Axial length

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Axial length of the eyeball is the distance from the lens to the retina. Axial elongation is the scientifically accurate reason why most myopes have myopia, as other causes are rare.

Biology

It would require precision engineering to be able to grow an eye that was perfectly emmetropic at birth. Instead, it is of approximate dimensions, and feedback during postnatal development tunes the axial length to match the focusing system. Two mechanisms are available: changing the thickness of the choroid, and changing the length of the eyeball itself. [1]

How it can be reduced

Myopic defocus, as well as conscious accommodation of the ciliary muscle during active focus, can cause axial shortening. Having good close-up and distance vision practices helps.

How it can be increased

Main article: Axial elongation

Hyperopic defocus, excessive myopic defocus, form deprivation, and accommodation strain can all cause axial elongation. In particular, using distances glasses for close-up is a very common cause of it.

Controversy

Hyperopes tend not to report back with any progress toward 20/20 vision. An implication is that EndMyopia techniques may not work for far-sighted people. This may indicate that we aren't changing axial length with EndMyopia techniques. Another theory is that EndMyopia might work by flattening the lens. It's easier to flatten a lens than to squeeze it, so this would explain why EndMyopia doesn't seem to attract people with hyperopic vision. Probably related, see also Dr. Carr.

Further Reading

References

  1. Wallman J, Winawer J (2004). "Homeostasis of eye growth and the question of myopia". Neuron. 43 (4): 447–68. doi:10.1016/j.neuron.2004.08.008. PMID 15312645.