We know that circadian rhythms regulate our sleep and alertness, blood pressure and heart rate, hormone secretion and more. As reported last week by Dr. Ranjay Chakraborty in the ophthalmic journal, mivision, evidence is now linking circadian rhythms with eye growth and refractive error developments (refractive errors usually mean you need glasses to correct them).
Armed with this growing knowledge, researchers are hoping to determine new approaches to improve refractive errors, such as myopia, which commonly develop in children.
What are circadian rhythms?
Circadian rhythms are physical, mental, and behavioural changes that follow a daily cycle. They respond primarily to light and darkness in a person's (or animal’s or plant’s) environment. Sleeping at night and being awake during the day is an example of a light-related circadian rhythm. Circadian rhythms are found in most living things, including people, animals, plants, and many tiny microbes.
Myopia and the myopia epidemic
Myopia, or short-sightedness as it is commonly known, is an eye condition where you do not see distant objects clearly. Myopia is a very common condition that usually begins in school-age children and can continue to progress until the eye stops growing. Adults can also develop myopia.
The prevalence of myopia is increasing worldwide. In some regions of Asia, its prevalence reaches 70–80 per cent of young adults, with reports as high as 96 per cent. In Australia, it currently affects around one third of the population.
In early 2016, it was announced that half the world’s population will be short-sighted by 2050 with many at risk of blindness. The global study, published by the Brien Holden Vision Institute, forecasts that 10 per cent of the world’s population will be at risk of blindness by 2050 if steps aren’t taken to stop myopia turning into high myopia (requiring glasses with a prescription of minus 5 or stronger).
Myopia, especially in its extreme degrees, is increasingly recognised as a major and alarming public health problem around the world.
Circadian rhythms and myopia
Knowledge of a possible link between circadian rhythms and myopia has largely come from decades of studies with animals. Research has shown that disrupting the daily light/dark cycle by altering the duration and/or intensity of light may lead to significant changes in normal eye growth of chickens and primates, possibly due to alterations in circadian rhythms.
Recent studies have also confirmed the positive effects of outdoor light exposure on both onset and progression of myopia in children.
A small number of recent clinical studies have directly looked into certain aspects of circadian rhythm disruption and myopia. Some have reported poor and delayed sleep in people with myopia compared with non-myopic individuals.
The common use of artificial lighting in our modern world has markedly affected how our biological systems interact with light. This, combined with increased 'screen time' has become a recognised concern in several health fields.
Besides effects on sleep and mood, circadian disruptions in contemporary societies are increasingly believed to contribute to certain cancers, neurological diseases, obesity and diabetes. So while the impact of circadian disruption hasn't been studied extensively, it's an exciting area of research which suggests we should stay tuned.