Integration of Defocus by Dual Power Fresnel Lenses Inhibits Myopia in the Mammalian Eye

Integration of Defocus by Dual Power Fresnel Lenses Inhibits Myopia in the Mammalian Eye.Invest Ophthalmol Vis Sci. 2014 Jan 7McFadden SA, Tse DY, Bowrey HE, Leotta AJ, Lam CS, Wildsoet CF, To CH.

This study found that in guinea pigs, myopia can be induced and then reduced by using plus lenses and dual focus fresnel lenses.  In this study, like in many other animal studies, this reduction of myopia through the use of plus lenses seems to be fairly effective, but it's on induced myopia, so it might not be as effective in human myopia, which is not induced.  The question that remains for me is, what are the triggers that begin the process of developing myopia?  Since there appears to be a very strong genetic component to human myopia, and many have proposed that genetic predispositions are triggered by environmental factors, what are the triggers?  And in the cases where these genetic predispositions exist, can environmental changes (like more sunlight as is suggested in many studies, or plus lenses, for example) be as effective as in the cases of induced myopia?

Link: http://www.ncbi.nlm.nih.gov/pubmed/24398103

Peripheral defocus link

Below is a link to a website (myopiaprevention.org) that offers information on myopia.  The link opens a page on the site that lists articles on peripheral defocus.  Peripheral defocus in myopia is interesting, because it has been shown to impact the development and progression of myopia in some animal studies.  Myopic defocus at the periphery appears to slow the progression of myopia, and single vision glasses and lenses work in the opposite way: they make the peripheral vision more hyperopic, and may therefore encourage myopia progression.  This argument has been made for a long time (that minus glasses might worsen myopia)  but the exact mechanism by which single vision glasses or contact lens wear might affect the development of myopia is unknown; peripheral refraction possible plays a role.  Radial refractive glasses like Myovision (Zeiss) and dual focus contact lenses are designed to address this issue.

http://www.myopiaprevention.org/references_peripheral_defocus.html

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.
Benavente-Perez A, Nour A, Troilo D.
SUNY College of Optometry, New York, New York.
Invest Ophthalmol Vis Sci. 2012 Sep 21;53(10):6479-87.

In this study dual focus contact lenses used on ten marmosets were shown to alter refraction and eye length in a period of 10-12 weeks.  The length of their eyes was compared to those of marmosets who wore contact lenses without prescription and others who wore contact lenses with +5 or -5.  The marmosets with the dual focus lenses had smaller eyes than the ones who wore -5 lenses, slowing down their myopia progression.

From the abstract:
"Conclusions. Imposing hyperopic and myopic defocus simultaneously using concentric contact lenses resulted in relatively smaller and less myopic eyes, despite treated eyes being exposed to a greater percentage of negative defocus. Exposing the retina to combined dioptric powers with multifocal lenses that include positive defocus might be an effective treatment to control myopia development or progression."

Link to the abstract:

http://www.ncbi.nlm.nih.gov/pubmed/22918633