This may be due to a decreased rate of blinking as you concentrate on reading or working on the computer. When you blink less, less tears are pumped out of the tear drainage system, leading to a welling of the tears. Also, if you have an unstable tear film in conjunction with a decreased rate of blinking, this could lead to reflex tearing. Patients who experience this often have evaporative dry eye, which could be diagnosed with some additional testing.