If you feel your eyes strain and headaches, especially after reading or other long turn visual tasks, you are likely to suffer astigmatism. And squinting also is also a very common symptom of astigmatism. You'd better visit an eye doctor and get your eyes checked. Usually, astigmatism can be detected during a routine eye exam with the same instruments and techniques that used for the detection of nearsightedness and farsightedness. Eye doctor can estimate the amount of astigmatism by shining a light into your eye while manually introducing a series of lenses between the light and your eye.
You can have an astigmatism test online. Find the the online astigmatism test and then sit about 14 inches away from your computer screen. Next, cover one eye and look at the test with the uncovered eye to see whether you get blurry lines. If you find the lines seem to be different thicknesses, you may get astigmatism in the uncovered eye. If the lines appear to be clearly visible and uniform, you may not have astigmatism. Then change eyes and see whether you have got astigmatism in the other eyes. Normally people get astigmatism in only one eye.