While most myopia management interventions exploit the use of peripheral defocus to influence the increase in axial length (AL) that leads to myopia, another hypothesis has been proposed which, instead, exploits the contrast of images upon the retina.
A long-held view from animal studies states that reduced contrast is a signal for myopia development at lower light levels.1 Better understanding of the genetics of myopia has, however, suggested this is not the case. Mutations in the long-wavelength (L) or middle-wavelength (M) cone opsin genes leads to a dramatic reduction in functional opsin in affected cones, causing abnormally high perceived retinal contrast which seems to cause high myopia. This observation suggests that abnormal contrast signalling between neighbouring full and empty cones may stimulate axial elongation.2 So, the contrast hypothesis goes, perhaps our high contrast modern visual environment projects high contrast images on the retina, which may be a signal for axial elongation and myopia.3 And, if this is the case, then a corrective spectacle lens that slightly reduces contrast signalling in the retina might slow myopia progression.
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