The cylinder power is astigmatism and is likely mostly determined by genetics. There is really nothing you can do to alter it unless you have surgery or do Ortho K treatments (which I don't recommend - another subject.) Sometmes, very intense frequent reading like for law school or post-graduate education can stimulate your eyes to get a little more nearsighted and it is also important to wear only the prescription power that you really need and no more. Keep a watch on your astigmatism numbers to make sure they don't continue to change a lot. Keratoconus is a condition where cornea becomes weaker and unstable and you can get very severe astigmatism. If numbers got a whole lot worse in the future it would be important to rule that out - but again you would likely have much worse astigmatism than you have now. Your mom and dad (genetics) are mostly responsible for your current prescription.
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