Read the following article and answer the question. Article: Up to 90% of school leavers in major Asian cities are suffering from myopia ---short-sightedness, a study suggests. Researchers say the "extraordinary rise" in the problem is being caused by students working very hard in school and missing out on outdoor light. Eye experts say that you are short-sighted if your vision is blurred beyond 2m. It is often caused by an elongation of the eyeball that happens when people are young. According to the research, the problem is being caused by a combination of factors - a commitment to education and lack of outdoor light. Professor Morgan who led this study argues that many children in South East Asia spend long hours studying at school and doing their homework. This in itself puts pressure on the eyes, but exposure to between two and three hours of daylight helps maintain healthy eyes. Cultural factors also seem to play a part. Across many parts of South East Asia, children often have a lunchtime nap. According to Professor Morgan they are missing out on natural light to prevent short-sightedness. A big concern is the numbers of the students suffering from "high" myopia. One in five of these students could experience severe visual impairment and even blindness. These people are at considerable risk--sometimes people are not told about it and are just given more powerful glasses--they need to be warned about the risk and given some self-testing measures so they can get to an ophthalmologist and get some help. For decades, researchers believed there was a strong genetic component to the condition. But this study strongly suggests an alternative view. "Any type of simple genetic explanation just doesn't fit with that speed of change; gene pools just don't change in two generations. Whether it's a purely environmental effect or an environmental effect playing a sensitive genome, it really doesn't matter, the thing that's changed is not the gene pool---it's the environment." Question: As is mentioned above, which factor mainly results in students' myopia in South East Asia? Answer:
Answer:
The shortage of outdoor light.