For years, the sharp rise in myopia – or nearsightedness – has been attributed primarily to the increasing use of screens, especially among children and young adults. However, new research from scientists at the SUNY College of Optometry suggests that the explanation may be more nuanced. A study to be publishedin Cell Reports suggests that myopia is influenced less by screens themselves and more by a common indoor behavior: prolonged focusing on close objects in low light, causing less light to reach the retina.
Short-Sightedness on the Rise Worldwide
“Myopia has reached near epidemic proportions worldwide, yet we still don’t fully understand why,” said Jose-Manuel Alonso, MD, PhD, SUNY Distinguished Professor and lead author of the study. “Our findings suggest that a common underlying factor may be how much light hits the retina during prolonged close work, especially indoors.”
Nearsightedness (myopia ) causes distant objects to appear blurry and is becoming increasingly common worldwide. It now affects nearly 50 percent of young adults in the United States and Europe, and nearly 90 percent in parts of East Asia. Although genetic factors influence the risk, the rapid increase within a few generations strongly suggests environmental influences.
Children of short-sighted parents do indeed have a higher risk of developing myopia themselves. However, genetics alone cannot explain the rapid increase within a few generations – a development that genetic changes simply could not bring about so quickly. This points strongly to environmental influences.
The most important environmental factors include a lack of daylight and time spent outdoors. Research shows that children who spend a lot of time outdoors have a significantly lower risk of developing myopia. Light stimulates the release of dopamine in the retina, a hormone that regulates the length growth of the eyeball. Excessive length growth leads to short-sightedness. Intensive close-up vision, such as reading, working on the computer or using smartphones and tablets, is also associated with an increase in myopia. Focusing on close objects for hours on end can increase the risk, particularly in children and adolescents whose eyes are still growing.
Other possible factors are lack of sleep, an unbalanced diet and urban living conditions. A densely built-up environment with few green spaces and constant screen use contribute to children and young people getting less natural light stimuli, which are important for healthy eye development. Overall, it is clear that myopia is not just a question of heredity, but is also strongly influenced by modern lifestyle habits.
A New Theory About Light on the Retina and the Focus of the Eye
In laboratory studies, myopia in animal models can be induced by visual deprivation or the use of negative lenses, although these two methods are thought to affect different neural pathways. Clinicians also slow the progression of myopia through various strategies that likely work through separate biological mechanisms (multifocal lenses, ocular atropine, contrast reduction, encouraging time outdoors, and others). Researchers at the College of Optometry at the State University of New York (SUNY) now hypothesize that there may be a single neural explanation that links these different methods of triggering and controlling myopia.
This new hypothesis attempts to resolve a long-standing question in vision science: Why do factors as diverse as close work and dim indoor lighting to treatments like atropine drops, multifocal lenses and increased time outdoors all seem to have an impact on myopia progression?
“In bright outdoor light, the pupil constricts to protect the eye while still allowing enough light to reach the retina,” explained Urusha Maharjan, a doctoral student in optometry at SUNY who conducted the study. “When people focus on close objects indoors, such as phones, tablets or books, the pupil can also constrict, but not because of brightness, but to make the image sharper. In low light, this combination can significantly reduce the illumination of the retina.”
According to this proposed mechanism, myopia can develop when insufficient light reaches the retina during sustained close work in dimly lit environments. If lighting is too dim and the pupil constricts excessively at short visual distances, retinal activity may not be strong enough to support normal visual development. In contrast, bright lighting allows the pupil to constrict in response to brightness rather than focus distance, which contributes to healthier retinal stimulation.
How Accommodation and Minus Lenses Play a Role
Accommodation refers to the eye‘s ability to change the refractive power of the lens to see objects in focus at different distances. Specifically, the following happens: When you look at a close object, the ciliary muscle tenses and the lens becomes thicker and more curved, allowing light to fall correctly on the retina. If you look at a distant object, the muscle relaxes, the lens becomes flatter and the focus is on more distant points.
In children and adolescents whose eyes are still growing, permanent accommodation can be problematic for close-up activities such as reading, writing, cell phone or computer use. The prolonged tension of the ciliary muscle changes the signals that the eye receives for the length growth of the eyeball. In the long term, this can contribute to the eyeball developing longer than normal, which means that the focal length for distant objects no longer fits and short-sightedness develops or worsens.
Interestingly, accommodation also interacts with retinal illumination. When focusing on close objects, the pupil constricts slightly (a natural reflex known as the near reaction), allowing less light to reach the retina. If this accommodation is maintained over longer periods of time or increased by strongly corrective minus lenses, the retina is less stimulated in the long term, which can further promote myopia.
The study also found that minus lenses reduce retinal illumination by constricting the pupil through accommodation (i.e. an accommodative increase in the lens power of the eye when focusing on images at short distances). This constriction increases when the visual distance is shortened or when minus lenses are worn that are too strong. It becomes even more pronounced when accommodation is maintained over a longer period of time (e.g. several tens of minutes) and increases further once the eye has already become short-sighted. The researchers also observed additional disturbances in eye movement during accommodation and a reduced effectiveness of the eye blink in triggering pupil constriction in myopic eyes.
Implications for the Prevention and Treatment of Myopia
If confirmed, this proposed mechanism could significantly change the way scientists and clinicians view the progression of myopia. The theory suggests that safe exposure to bright light while limiting accommodative pupil constriction may help control myopia. This reduction in constriction can be achieved by lowering the accommodative demand with lenses (multifocal or contrast reducing), directly blocking the muscles responsible for pupil constriction (atropine drops) or spending time outdoors without the need for accommodation (gazing into the distance).
Importantly, the researchers believe that any treatment method may be less effective if people continue to focus on close objects indoors in low light for long periods of time.
“This is not a definitive answer,” Alonso emphasized. “But the study offers a testable hypothesis that redefines the interactions between visual habits, lighting and eye focus. It is a hypothesis based on measurable physiology and brings together many existing findings. More research is needed, but it gives us a new way of thinking about prevention and treatment.”