Reading and Myopia: Contrast Polarity Matters

Abstract

In myopia the eye grows too long, generating poorly focused retinal images when people try to look at a distance. Myopia is tightly linked to the educational status and is on the rise worldwide. It is still not clear which kind of visual experience stimulates eye growth in children and students when they study. We propose a new and perhaps unexpected reason. Work in animal models has shown that selective activation of ON or OFF pathways has also selective effects on eye growth. This is likely to be true also in humans. Using custom-developed software to process video frames of the visual environment in realtime we quantified relative ON and OFF stimulus strengths. We found that ON and OFF inputs were largely balanced in natural environments. However, black text on white paper heavily overstimulated retinal OFF pathways. Conversely, white text on black paper overstimulated ON pathways. Using optical coherence tomography (OCT) in young human subjects, we found that the choroid, the heavily perfused layer behind the retina in the eye, becomes about 16 µm thinner in only one hour when subjects read black text on white background but about 10 µm thicker when they read white text from black background. Studies both in animal models and in humans have shown that thinner choroids are associated with myopia development and thicker choroids with myopia inhibition. Therefore, reading white text from a black screen or tablet may be a way to inhibit myopia, while conventional black text on white background may stimulate myopia.

Probing the Potency of Artificial Dynamic ON or OFF Stimuli to Inhibit Myopia Development

“…Furthermore, the direction of changes in choroidal thickness matched previous findings with text of different contrast polarities, assumed to stimulate either ON or OFF pathways. 21 Our study has also shown that ON stimulation increases retinal DA release. Because DA has been implemented in the visual control of axial eye growth and myopia, the changes in DA may be involved in the changes in choroidal thickness.…”

“…Subfoveal choroidal area was imaged with SD-OCT (HRAþOCT Spectralis), as previously described. 21 Focus was adjusted for each subject depending on their spherical equivalent refractions. Because the choroid-sclera border was not well defined in some subjects, we used the EDI (enhanced depth imaging) mode of our OCT machine to improve visualization of the choroidal limits.…”

“…Measurements of subfoveal choroidal area and subfoveal thickness were manually performed by carefully locating the margins of the choroid in the original images, using the public software package ImageJ (http://imagej.nih.gov/ij/; provided in the public domain by the National Institutes of Health, Bethesda, MD, USA), as previously described. 21 Because the images were slightly different due to eye movements during the measurements, a line was drawn perpendicular to the retinal surface from the floor of the foveal pit to the sclera. From there, an area of 260 pixels to the left and to the right of the image was analyzed.…”

“…Aleman et al 21 found that reading white text that stimulates the ON pathway increases choroidal thickness by 10 lm after 60 minutes, whereas reading black text decreased choroidal thickness by 16 lm. The magnitudes of these effects are similar to those in studies with lenses in adults and children, as well as after application of high-dose atropine (reviewed in Aleman et al 21 ). The dynamic ON or OFF stimulus was apparently less effective than reading text with different contrast polarities.…”

“…19,20 Recently, we found in young human subjects that 60 minutes of reading bright text on dark background made the choroid thicker, whereas the opposite happened when reading conventional text. 21 Using Cþþ software for realtime analysis of the visual world in terms of ON and OFF stimulus strengths (developed in our laboratory and available for downloading 21 ), it was found that black text on white background predominantly stimulates the OFF pathway, whereas white text on black background stimulates the ON pathway. Accordingly, we proposed that reading bright text on a dark background may have an inhibitory effect on myopia development, whereas the conventional text may stimulate myopia.…”