Could reading, an activity often praised and encouraged by parents and teachers, possibly have an unexpected downside? Perhaps, and under certain conditions, reading causes myopia suggests a study.
The study published recently in the Journal of Vision shows that reading affects the eyesight of children and teenagers. This is because they spend more time reading while their eyes are still developing.
Myopia and reading
The study was conducted by Sabina Poudel, Hamed Rahimi-Nasrabadi, and their collaborators in the laboratory of Dr Jose Manuel Alonso at the State University of New York (SUNY) College of Optometry, United States.
“Our study aimed to understand the visual stimulation parameters that cause myopia [short-sightedness],” says Dr Alonso. The researchers measured the changes in brightness, eye and head movements, pupil changes, and the number of blinks while reading and walking.
When we read, our eyes exhibit minimal changes in these parameters and therefore reduce the stimulation of ON pathways (eye pathways responding to the onset of light), the study showed.
Role of brightness and contrast
ON pathways are best stimulated by bright scenes with high contrast, frequent eye movements, blinks, and scene changes, according to the study. For example, engaging in outdoor activities like walking or basketball, with a bright blue sky as the background provides optimal visual stimulation. These factors enhance the activation of ON pathways and provide clear vision.
Conversely, factors such as low light, low contrast, and lack of self-motion are less effective at activating the ON pathways. Inadequate activation eventually leads to the development of myopia or other visual disorders.
“The results from our study and other unpublished work from my lab strongly support the hypothesis that myopia develops because ON visual pathways are not properly stimulated,” Dr Alonso told Happiest Health. Individuals with genetic defects that fully inactivate ON visual pathways develop severe myopia.
Eye growth
Stimulation of the ON pathway can act as a signal to stop the growth of the eye. The eye stops growing when the response of the ON pathway (response to light) is as strong as that of the OFF pathway (response to darkness). However, to activate the ON pathway, the images that are processed in the retina must be sharp, clear, and change at a high frequency.
When we read for long periods, the stimulation of the ON pathway is reduced. So, the eye may continue growing and be unable to obtain a balance between ON and OFF pathways. This results in blurry vision at a distance.
Experts say that reading is associated with a higher risk of myopia while walking is associated with a lower risk of the condition.
The study further shows that engaging in outdoor activities such as walking or playing that involves looking at distant objects stimulates the ON pathways. This stimulation prevents excessive eye growth and reduces the risk of myopia. It eventually helps maintain a clear vision for distant objects.
Optimising visual environments
ON pathways are present in the eyes of all animals. Different animals adjust their ON pathways based on specific environmental factors. Primates and birds of prey excel in detailed vision, activated by bright light and high-resolution images moving slowly across their field of vision. For example, a bird of prey can spot its target from a mile away in the sky.
However, the ON pathways in animals with poor vision, like nocturnal rodents, are activated by dim light and low-resolution images moving quickly across their field of vision. An example is a scurrying mouse visualising the walls of a narrow cave. The activation of ON pathways helps animals adjust their eye size to their surroundings.
Key to reduce the risk of myopia
The research suggests that myopia may be prevented by exposing the eye to active visual navigation outdoors and scenes that are bright, have high contrast, and are continuously changing.
When reading, the risk of developing myopia may be reduced by increasing scene brightness (like avoiding dim lights), contrast (such as avoiding books with poor print quality), scene changes (like taking eye breaks and making the eye gaze on stimuli with high contrast), and self-motion (such as taking body breaks to move around).
“If our hypothesis and conclusions are correct, our work could lead to new approaches to the management of myopia by changing the ‘visual diet’ that our eyes have to process,” says Dr Alonso.
Note – Though reading is referred to as one of the causes of developing myopia, further research is needed to validate the findings of this research.
Read more about the holistic approaches for management of myopia here.
