reshaping (orthokeratology) has proven successful among adolescents
as a visual aid in school, for sports and recreation and, perhaps
its most exciting prospect, for myopia control.
from the University of Houston College of Optometry and the
Institute for Eye Research in Sydney, Australia, indicates that
foveal imagery doesn't necessarily play the dominant role in axial
development. It may be the images that focus on the peripheral
retina that control the ultimate growth of the eye. This work
suggests that we may control myopia in young children by creating
optical aberrations that manipulate the peripheral optics of the
Myopia Control in Action
years ago patient CF, a -3.25D 9-year-old with progressive myopia
since age 6, was placed into CRT (Paragon Vision Sciences) lenses
for overnight ortho-k. At his last examination, his VA without
correction was 20/20 OU. Of greatest interest was that he has
required no change in the base curve radius of his lenses, implying
that his axial length hasn't increased.
this is a single case report, recent controlled studies by Cho and
Walline have demonstrated a trend toward myopia control in some
children wearing ortho-k lenses.
How it Works
mechanism for this effect appears related to the post-ortho-k
corneal shape. Figure 1 shows CF's right eye with a prefitting
corneal shape factor of +0.41 across the center 6mm of the cornea.
Post-ortho-k the cornea assumes a shape factor of -0.43, indicating
that the cornea is flatter in the center and gradually steepens
across the pupil.
Figure 1. Corneal topography
pre- and post-CRT.
well documented that myopic eyes (corrected with either spectacles
or contact lenses) exhibit significant
hyperopic defocus in the area of the peripheral retina. In this
situation the central rays of light come to focus on the fovea while
the peripheral rays of light fall posterior to the retina, allowing
the eye to grow more myopic (Figure 2). Conversely, the oblate
optics of a post-ortho-k cornea generate a negative curvature of
field in which the peripheral rays of light are focused anterior to
the retina, creating the environment for a myopia control effect
Figure 2. Myopic eyes
corrected with glasses or CL's exhibit a hyperopic
defocus and a positive curvature of field.
Figure 3. The post-ortho-k
optics create a negative curvature of field and myopic