[1] Symptoms often occur after long-term use of computers, staring at phone screens, digital devices, reading, or other activities that involve extended visual tasks[2] which are broadly classified into external and internal symptom factors.
Closing the eyes for ten minutes and relaxing the muscles of the face and neck at least once an hour usually relieves the problem.
A page or photograph which shows the same image twice, but slightly displaced–from a printing mishap, a camera moving during the shot, etc.–can cause eye strain due to the brain misinterpreting the image fault as diplopia and reacting by adjusting the sideways movements of the two eyeballs, in an attempt to fuse the two images into one.
Eye strain can also happen when viewing a blurry image (including images deliberately partly blurred for censorship), due to the ciliary muscle tightening in an attempt to focus the blurring out.
Symptoms of eye strain can include:[4][5] One known method of relieving strain of the ocular muscles is taking periodic breaks by closing the eyes.