Beschreibung:
AbstractTo transmit the visual information detected by 125 Million photoreceptors in the retina through the optic nerve, with only about 1 Million ganglion cell axons, the retina has to compress information down to about 1 percent. Aside of receptor pooling, a major trick is to form receptive fields with ON/OFF structure which compare brightness in the center with the brightness in the periphery and reduce the information to spatial–temporal differences, while absolute luminances largely ignored. Two major types are found: ON center, which are activated by light in the center and inhibited by light in the periphery and OFF center with the inverse response patterns. Such receptive fields are perfectly suited to detect defocus which represents low pass filtering of the spatial frequencies in the image. It was found in animal models that suppression of ON pathways is generally related to more axial eye growth and can enhance deprivation myopia while suppression of OFF has little or an inverted effect. Analysing the ON and OFF input strength in our visual environment, we found that reading text with conventional contrast overstimulates OFF channels while reading with inverted contrast strongly stimulates ON channels. After reading for one hour, we found that the choroid becomes thinner with conventional text, but thicker with contrast‐inverted text. Since there is considerable published evidence that choroidal thickening is a precursor of myopia inhibition, reading text with inverted contrast may be beneficial against myopia progression. We have also tested different text sizes. The effect was not observed with a letter height of 0.25 deg (like on a smart phone) but prominent at 0.5 deg (like in a book). Interestingly, choroidal thickening was induced both in emmetropic and myopic subjects, suggesting that the approach should also work in myopes. We have previously found that myopic subjects show a reduced choroidal response, compared to emmetropes, when positive defocus was imposed for 30 min. The functional deficit in the myopic retina appears limited to the detection of defocus while the activity of ON and OFF pathways is not affected. A major question for future research is whether and how ON/OFF processing may be linked to the detection of the sign of defocus by the retina.Research supported by IOB.No proprietary interest.