The goal of the study authors was to describe the time course of changes in both peripheral refraction and corneal topography in myopic adults wearing myopic orthokeratology (OK) lenses. That means that the researchers wanted to to see how the surface of the cornea - the clear dome that covers the colored part of the eye - changed over time and whether the focusing power of a subject's peripheral vision changed overtime when overnight orthokeratology lens retainers were worn.
The study design was simple. Nineteen patients were fitted with ortho-k lenses and the researchers measured their peripheral focusing power and the contours of the surface of the cornea after 1, 4, 7 and 14 nights of ortho-k retainer lens wear.
The study reached the following conclusions:
Orthokeratology caused significant changes in both peripheral refraction and corneal topography. The greatest change in refraction and corneal refractive power across the horizontal corneal meridian occurred during the first night of OK lens wear. Subsequent changes in both peripheral refraction and corneal topography were less dramatic, in the same manner as reported changes in apical radius and central refraction after OK. This study confirms that with OK treatment, the peripheral retina experiences myopic defocus, which is conjectured to underlie the observed slowing of myopia progression.The study adds to our understanding of the mechanism by which orthokeratology slows myopia progression. The culprit in myopia is thought to be focusing power in an eye's peripheral vision. This study explains how orthokeratology causes positive changes in this part of the eye that result in a slowing of myopia progression
The role of the peripheral retinal in causing myopia progression may be difficult for the lay person to understand. One of the best explanations that we have read comes from the College of Optometrists in Vision Development blog post, "Its All About the Blur":
New theories on the development of myopia are evaluating the role of peripheral retina. When lenses are prescribed for any type of refractive error (myopia, hyperopia, astigmatism), those lenses put a clear and focused image on the fovea, which is essentially the “bullseye” on the retina. Whenever we want to see something clearly, we aim our eyes so the image falls on the fovea. The lenses allow us to see clearly precisely because the image is focused on the fovea. But those lenses (especially spectacles) have a different curvature than the retina. The result is a slight defocus on the peripheral retina. The further away from the central retina you are, the greater the amount of defocus. This is not something noticeable by the average patient, because the amount of blur is small, and because we don’t notice blur as well in the periphery. But it seems that our retinas DO notice, because there is significant evidence that this peripheral defocus drives the eye to elongate, and that elongation results in myopia.
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