The most common eyeglass prescriptions consist of one number, which can be positive or negative. Negative numbers indicate that a prescription is correcting myopia commonly known as nearsightedness. The more negative the number, the more nearsighted you are. If the number is positive, they are meant to correct hyperopia, or farsightedness. The larger the number is, the more farsighted you are.
Individuals with astigmatism, a condition where light does not focus properly due to the fact that your cornea is not round, will have three numbers on their prescription, written in the form, spherical x cylinder x axis. The spherical number simply referred to the amount of near or farsighted you are, what your prescription would be without your astigmatism. The second number in the cylinder position is either negative or positive and tells the eye doctor what level of astigmatism you have and how your cornea is misshapen. The axis builds on this number, telling us in degrees where the misshapen cornea is in your eye.