Mechanisms of myopia
Leigh Spielberg
Published: Sunday, September 23, 2018
“A poor image on the retina elongates the eye,” said Frank Schaeffel, University of Tübingen, Germany. “Surprisingly, an intact optic nerve is not needed, at least in animal models, and there is thus local, retinal control of eye growth.”
Dr Schaeffel addressed delegates at an ESCRS clinical research symposium on Saturday morning in Vienna. His presentation was entitled Biological Mechanisms of Myopia.
“Shifting the focal plane induces compensatory eye growth in a closed-loop feedback system,” he said. This manifests rapidly, in the form of choroidal thickness changes within hours of defocus, as well as in the long term, as expressed by axial lengthening due to scleral changes.
“In fact, retinal glucagon amacrine cells recognise defocus within a few minutes, as indicated by the expression of ZENK protein,” said Dr Schaeffel.
But what are the clinical applications?
“Inhibition of myopia is probably not an issue of accommodation, but rather local myopic defocus, which causes local inhibition of eye growth,” he said. “This effect also shows up in the foveal refraction.”
Undercorrection has been proposed to limit myopic progression. However, “The point about undercorrection is that the data are extremely variable regarding whether it inhibits myopia or not,” clarified Dr Schaeffel. “Perhaps better are multifocal lenses which generate a simultaneous secondary focal plane in front of the retina, as the fovea always drives accommodation, but the peripheral retina drives eye growth.”