Time spent on digital devices is on the rise, and long-term screen exposure has been linked with visual issues such as eye strain, blurring, dry eye and ocular discomfort. A new study from South Korea suggests both smartphone and tablet use can also decrease near point accommodation and near point vergence, with the most dramatic effect occurring when individuals focus on the small display of a smartphone screen. Even within 20 minutes of use, the researchers reported their participants started to feel ocular discomfort, which was more severe and more quickly induced with smartphones than tablets.

A total of 46 participants who had no history of ophthalmic disease watched a movie on a smartphone and then a tablet. The investigative team measured the subjects’ near point accommodation and near point convergence before and after device use, in addition to objective accommodation with an auto refractometer/keratometer. Participants also answered a survey about their perceived ocular discomfort.

Participants showed a decrease in near point accommodation and near point convergence after watching the movie on both devices. However, the change in each measurement (1.8 and 2.5 times higher, respectively) was most prominent with the smartphone.

Neither device appeared to cause significant changes in the accommodative response induced by the dynamic accommodative stimulus of an auto refractometer/keratometer.

Based on the survey results, study subjects said they had greater ocular discomfort after using the smartphone and reported feeling tired even after shorter periods of time on the device.

“According to the results of this study, we suggest that the display size of smart devices can have different effects on the eye, so it should be adjusted according to the user’s accommodative functions and ocular discomfort when using smart devices,” the study authors wrote in their paper.