Reading, despite its cognitive benefits, has been shown to increase the risk of myopia (nearsightedness) for reasons that are not yet fully understood. Inversely, the risk of myopia decreases with time spent engaging in outdoor activity. A new paper published recently in the Journal of Vision looks at the differences in visual stimulation between reading and walking and its implications in the development of myopia.
In the study, researchers led by the University of New York (SUNY) demonstrate that the images formed by our eyes during reading lack the diversity of contrasts, luminance transients, visual motion and visual change needed to activate major visual pathways signaling light stimuli, generally known as ON pathways (responsive to ‘light on’). The study compared the eye visual input and visuomotor activity generated by humans performing two visual tasks that are associated with different risk of myopia progression, reading (high risk) and walking (low risk). The results indicate that multiple factors including low light, low contrast, and the lack of self-motion make reading less effective at driving ON pathways than walking. Based on these results, the paper proposes a mechanism of myopia development that requires ON pathways to be strongly activated along the day to properly adjust eye growth. Under this mechanism, sustained reading for prolonged periods of time reduces the activation of ON pathways making the eye grow beyond its focus plane and blurring vision at far distance.
ON pathways are extremely well-preserved during evolution and are present in all animal eyes that can generate images, from flies to humans. These pathways are also carefully calibrated across species to be maximally activated by different visual environments. For example, in animals with high visual acuity such as primates and birds of prey, ON pathways are best stimulated by bright high-resolution images moving slowly within central vision (e.g. images in the eye of a bird seeing a prey one mile away from the sky). Conversely, in animals with low visual acuity such as nocturnal rodents, ON pathways are best stimulated by dim low-resolution images moving at fast speeds (e.g. images in the eye of a mouse seeing the walls of a narrow cave a few inches away while running). The visual activation of ON pathways provides an ideal signal to adjust the eye size based on the spatiotemporal properties of each visual environment. If the mechanism proposed by the authors is correct, their work could open new lines of myopia prevention and treatment based on visual diets that boost ON pathway activation.
Read the full news release from SUNY College of Optometry.
Source: SUNY College of Optometry