Human optical axial length changes in response to defocus

Human optical axial length changes in response to defocus
Scott A Read (PhD)
Michael J Collins (PhD)
Beata Sander (MD)
Contact Lens and Visual Optics Laboratory
School of Optometry
Queensland University of Technology
Brisbane, Queensland, Australia
2010

There have been numerous studies showing that myopia can be induced in chicks and monkeys, and that plus lenses (myopic defocus) can diminish induced myopia in animals. (studies by Schaeffel, Wallman and Wildsoet).  This study shows that in the human eye is also affected by minus (hyperopic defocus) and plus (myopic defocus) lenses, at least in the short term. The strength of the lenses used was -3 or +3, for a period of 60 minutes.

From the text:
"In conclusion, we have demonstrated for the first time that imposing a short period of defocus on the human visual system leads to significant changes in axial length.  These changes are bi-directional in nature, consistent with previous findings in experimental animals, and suggest that the human visual system is capable of detecting the sign of defocus and altering axial length accordingly in order to move the position of the retina
towards the image plane.  Whilst further research is required to more comprehensively describe the characteristic features of the response of the human visual system to defocus, these findings of short term ocular change associated with defocus may have significant implications for human refractive error development."

http://www.iovs.org/content/early/2010/06/30/iovs.10-5457.full.pdf