Prolonged smartphone use could result in an acute eye condition in which one of the pupils turns inward, causing double vision and making the person appear cross-eyed, doctors in Japan have pointed out.
The condition, known as acute esotropia, has recently been seen frequently among children, who were rarely diagnosed with it in the past. People with this condition can see things normally with one eye, but when they use both eyes they get double vision.
Two years ago, a 16-year-old high school student in Saitama Prefecture, north of Tokyo, realized that something was wrong with her eyes.
"Your right eye has turned inward," the girl's 46-year-old mother told her. The girl had experienced double vision in the past, so didn't pay much attention to it, and simply continued to see her local eye doctor. But in December last year, when she was examined by associate professor Takashi Negishi at Juntendo University Hospital, he pointed out that she might have acute esotropia.
The girl, it emerged, had gotten a smartphone when she was in her sixth year of elementary school, and had watched videos on it for three to four hours a day. Negishi speculated that looking at her smartphone too much had resulted in the condition.
In the past, acute esotropia was generally caused by abnormalities in the brain and stress. There is no conclusive proof of any causal relationship with digital equipment. But Hirohito Iimori, a doctor at Hamamatsu University Hospital in the central Japan prefecture of Shizuoka, commented, "When a person looks at an object up close, their eyes turn inward to focus on it. The screens of digital equipment are small, so people often bring them close to their faces, and if they stare at them for a long time, it's possible that it may become difficult for the eye to return to its original position."
When a person contracts acute esotropia, they start to see things in double. When a child has this condition in the lower years of elementary school, it could negatively affect the development of their binocular vision -- by which they use the differences in the vision of each eye to perceive distance and three-dimensional objects. Iimori points out, "When children are young, even if they have symptoms, they often don't complain about them."
Smartphones are believed to play a part in the increased prevalence of esotropia among young people. According to the Ministry of Internal Affairs and Communications Institute for Information and Communications Policy, smartphone use among young people has been increasing year by year. In fiscal 2018, average weekday use of smartphones among teens was two hours and 25 minutes, while on weekends it was four hours a day.
There is some data to back up doctors' concerns. When a research team including members of Hamamatsu University Hospital conducted a survey of ophthalmologists, 158 of them, or over 40 percent of the 371 that responded, said that last year they had seen patients between the ages of 5 and 35 who had acute esotropia. A total of 122 of the eye doctors had experienced seeing patients whose use of smartphones and other digital equipment was thought to be related to their conditions.
"Previously, there had only been a few patients a year, but now this figure has increased to around 10," Iimori said, expressing his surprise.
It has also been pointed out that there are others who are close to being diagnosed with acute esotropia. Negishi comments, "With people who have poor binocular vision and say, for example, that they have trouble seeing things come out of the screen in 3D movies, it is possible that they have a weakness in adjusting the position of their eyes, and that smartphone use could make them susceptible to esotropia."
Treatment of acute esotropia involves using glasses with prisms that refract light to correct the image, and surgery to change the position and length of the muscles that move the eyes. There is also a method of treatment in which Botox is injected into the muscles that move the eye to temporarily paralyze them and keep the eye in the correct position. In March this year, the aforementioned girl from Saitama Prefecture received this treatment. However, differences are seen between individuals, and Negishi pointed out, "There are cases in which the person doesn't recover even if they receive an injection and surgery."
The Japanese Association for Strabismus and Amblyopia launched an investigation this autumn on the connection between esotropia and the use of digital equipment. The survey will target 200 people between the ages of 5 and 35, and restrict their use of digital equipment and examine whether this alleviates their symptoms.
(Japanese original by Yuki Ogawa, Lifestyle and Medical News Department)