A man in northwest China went blind temporarily after playing games on his phone in the dark.
The man surnamed Wang, from Xian, Shaanxi province, said he lost his sight as he played on his phone in bed after turning the lights out.
On Tuesday, a doctor said Wang suffered an eye stroke - also known as a retinal artery occlusion - caused by a clot or narrowing of the blood vessels in the retina, which sends signals to the brain.
He said this can lead to permanent blindness if not treated quickly.
Wang said that he often played games on his phone after he went to bed, but the habit annoyed his wife.
"I was using my right eye to look at my phone, and I could see some words but not others," he said.
The doctor, Lei Tao, said he saw "around 20 patients a month" who suffered the same loss of vision after using their phones too much, and many of them were young people.
"Blockage of the arteries in the retina is sudden, serious and the primary manifestation of eye disease that leads to blindness, we commonly call it an 'eye stroke'," Lei said.
"The occurrence rate is getting higher each year, and there is a trend of younger victims. The rate of [permanent] blindness is also high, which can seriously affect the patient's quality of life and contribution to society."
Lei said that overuse of electronic items could lead to sudden vision loss.
"Using phones and electronic items is a big part of life for young people, which puts excessive strain on their vision. This can trigger eye stroke," he said.
"Preventive strategies are very important. Work and rest in a regular pattern, avoid staying up late at night and looking at phones, televisions and computers for a long time - these will all make a difference."