An excessive use of smartphones by teenagers may cause them to suffer from eye deviation, experts warned Tuesday, adding users must refrain from viewing displays for more than 30 minutes consecutively.

Chonnam National University Hospital said it has found the possible relationship between convergent strabismus, a symptom in which a patient's eye moves inward eventually to become "cross-eyed," and excessive use of smartphones based on its study on 12 patients aged seven to 16.

The convergent strabismus is more common among westerners, and usually appears before the age of five. Thus, it is rare for a South Korean youth to suffer from the condition.

The research team said the 12 patients' daily use of smartphones came to four to eight hours. The distance between their eyes and screens were also close at 20 to 30 centimeters.

Nine of the 12 patients, however, were cured from the disorder after ceasing to use smartphones for around two months, researchers said, adding the result proves the link between the condition and smartphone use.

The research team added users must refrain from looking at smartphone screens for more than 30 minutes at a time, and parents should take their children to see a physician if their eyes seem to be deviated. (Yonhap)