A device comprising: an image capturing unit configured to capture an image of eyes of a user who is watching three-dimensional, 3D, video; and a processor configured to: obtain an eye feature of the user from the captured image of the eyes of the user, determine a current degree of eyestrain of the user based on the obtained eye feature, adjust (S1030, S1040, S1050) a parallax parameter of a current frame of the 3D video within a parallax parameter threshold when the parallax parameter of the 3D video is equal to or greater than the parallax parameter threshold and the current degree of eyestrain of the user is equal to or greater than an eyestrain threshold, determine when a difference between parallax parameters of a current frame and a previous frame of the 3D video is equal to or greater than a parallax change threshold, wherein the parallax change threshold is dynamically determined according to the current degree of eyestrain of the user, and adjust the parallax parameter of the current frame of the 3D video such that the difference is within the parallax change threshold, when the difference between parallax parameters of the current frame and the previous frame of the 3D video is equal to or greater than the parallax change threshold. an image capturing unit configured to capture an image of eyes of a user who is watching three-dimensional, 3D, video; and a processor configured to: obtain an eye feature of the user from the captured image of the eyes of the user, determine a current degree of eyestrain of the user based on the obtained eye feature, adjust (S1030, S1040, S1050) a parallax parameter of a current frame of the 3D video within a parallax parameter threshold when the parallax parameter of the 3D video is equal to or greater than the parallax parameter threshold and the current degree of eyestrain of the user is equal to or greater than an eyestrain threshold, determine when a difference between parallax parameters of a current frame and a previous frame of the 3D video is equal to or greater than a parallax change threshold, wherein the parallax change threshold is dynamically determined according to the current degree of eyestrain of the user, and adjust the parallax parameter of the current frame of the 3D video such that the difference is within the parallax change threshold, when the difference between parallax parameters of the current frame and the previous frame of the 3D video is equal to or greater than the parallax change threshold. obtain an eye feature of the user from the captured image of the eyes of the user, determine a current degree of eyestrain of the user based on the obtained eye feature, adjust (S1030, S1040, S1050) a parallax parameter of a current frame of the 3D video within a parallax parameter threshold when the parallax parameter of the 3D video is equal to or greater than the parallax parameter threshold and the current degree of eyestrain of the user is equal to or greater than an eyestrain threshold, determine when a difference between parallax parameters of a current frame and a previous frame of the 3D video is equal to or greater than a parallax change threshold, wherein the parallax change threshold is dynamically determined according to the current degree of eyestrain of the user, and adjust the parallax parameter of the current frame of the 3D video such that the difference is within the parallax change threshold, when the difference between parallax parameters of the current frame and the previous frame of the 3D video is equal to or greater than the parallax change threshold.