A comparison of accommodation and ocular discomfort change according to display size of smart devices

To evaluate the change of accommodation and ocular discomfort according to the display size, using quantitative measurements of accommodation and ocular discomfort through subjective and objective metrics. Forty six subjects without any ophthalmic disease history were asked to watch the documentary movie, using two different sizes of smart devices; smartphones and tablets. Before and after using devices, the near point accommodation (NPA) and the near point convergence (NPC) were measured, and objective accommodation was measured using an auto refractometer/keratometer. The subjective ocular discomfort was assessed through a survey. Both devices showed a decrease in post-use NPA and NPC, and the change after use of the smartphone was significantly severe, 1.8 and 2.5 folds respectively, compared to tablet (p = 0.044, p = 0.033, respectively). Neither smartphone nor tablet showed significant changes in the accommodative response induced by dynamic accommodative stimulus of auto refractometer/keratometer (p = 0.240 and p = 0.199, respectively). Subjects showed a more severe increase in ocular discomfort after using smartphones (p = 0.035) and reported feeling tired even with shorter use times (p = 0.012). Both devices showed significant decreases in NPA and NPC, and the larger changes were seen when using the small display smartphone. Even within 20minutes of using, subjects start to feel ocular discomfort, and it was more severe and faster after smartphones than tablets. Therefore, the smaller the display size, the greater the adverse impact on eyes, and thus, appropriate display size will need to be selected depending on the time and purpose of use.