Shifting from a rectangular frame to a round frame, or vice versa, or from a larger frame to a smaller one, such a circumstance is called the headache from glasses frames. Your eyes may need some time to adapt to the new frame. Even if the new frame does not affect your vision, it will take several days for them to adjust their perception of your face. If you buy a frame with incorrect size, you need to adjust the frame so that you can wear it in a more comfortable way.
Eye fatigue tends to cause headaches. Moreover, eye fatigue is usually not accompanied by nausea or vomit. After long time of reading or sitting in front of the computer, crystalline lens have to adjust (adapt) frequently for seeing clearly. After a few hours, the eye fatigue will occur, leading to headache. In this case, you should take off your glasses, close your eyes for a rest or look into the distance. Ensure the blood of your eyes to be smoothly flowing.
If you buy new glasses with lens material different from old one, new lenses such as polarization, photochromism or blue blocking lens technology may take some time to adapt for new lens adopting polaroid, phototropy or blue blocking lens technologies.
In case of dye eye syndrome, your eyes may not adapt to the new prescription glasses and is likely to cause a headache. Dry eyes will make you more sensitive to light, causing you to squint, while continuous squinting may lead to muscle tension headache. As a rule, when you feel tired with your eyes, you must take care to have a rest. The best way to rest and adjust is to gaze into the distance, look out of the window, go to the balcony to overlook the distant sight, and view green plants, which is very helpful for relieving the eye fatigue and making an adjustment.