A shout out to COVD members Jeffrey Cooper and Erica Schulman! Drs. Cooper, Schulman and Jamal just published a review of the development and treatment of myopia. This evidence-based review of over 200 articles has really got me thinking about the options in treating myopia (nearsightedness).
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.
Consideration of this body of evidence has resulted in renewed interest in the clinical use of orthokeratology – Ortho-K (aka corneal reshaping therapy or CRT) to reduce myopia progression. In addition to putting a clear and focused image on the fovea, orthokeratology fitted contact lenses flatten the central cornea which results in a steepening of the peripheral cornea. The end result is a reduction in the peripheral defocus on the retina, and therefore a reduction in the drive toward elongation of the eyeball.
After reviewing all the studies investigating Ortho-K and the progression of myopia conducted in the last 12 years, the authors conclude: “Ortho-K results in an approximately 40% reduction in the progression of myopia. Its advantages are that it both eliminates the need for daytime contact lens wear and reduces the progression of myopia. Its disadvantages include cost, risk of infection, discomfort, problems with insertion and removal, and reduced visual acuity as compared to glasses or daily wear contact lenses. In addition it is difficult to determine which subjects will demonstrate slowing of their myopia and by how much.”
Once again, the science is catching up to clinical practice. Many developmental optometrists have been aggressively using Ortho-K as one of the possible treatments to slow the progression of myopia. Renewed interest in the role of peripheral retina in the progression of myopia will lead to more research and more research will lead to better clinical guidelines in the use of Ortho-K. Developmental optometrists are sure to be at the forefront when putting the evidence into clinical practice.
Read more about Ortho-K here.